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| [GMCnet] caster settings [message #138104] |
Mon, 08 August 2011 19:12  |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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I am not sure we can be off enough to make it worth the time to measure...
I did a brief survey of the GMCnet, and seems like most don't care.... or
worry about difference in caster;>)
here are some of the comments:
--------------------------
When taken to alignment shop the camber has been within 1-2* sometimes
closer. The caster has always been more on the drivers side??
Usually
2 1/2 on Pass side and
3 1/2 on drivers side.
--
C. Boyd
On Double Trouble which was a Transmode manufactured in November of 1974
the
most caster Tom Hampton could get with offset bushings was 1.9 degrees on
both sides. After John Sharpe and I installed Dave Lenzi's offset upper
control arms the alignment shop got 5 degrees. Double Trouble drives like
it's on rails!
Even caster is not difficult to determine. The digital level can be
zero'd at one 20* turn angle and then read at the opposite 20*
position. That reading multiplied by 1.4 should give the caster.
And, as you suggested, since we're really only interested in getting
as much as possible, that value isn't really important -- what we
really want is to the get the caster close to the same on both sides.
Considering that most of our driving is usually on nearly-flat
highways, I'm not even very concerned about setting a road-crown bias.kenh
,
I believe that is just a starting point. The key is to max out caster
while still maintaining zero camber. You may have some adjustment left in
the rearmost adjuster but zero camber is the limiting factor.stevef
All the cams appear to be at about the same position front and back.
Certainly not
what I would have expected. The printout from their machine is not handy
but I
think it was as close to 0,0 as expected and caster was 3.0 and 3.4 .
I think there is room for more caster... what say yea? bruceh
Besides, on the GMC, I'm not sure it even makes sense to waste time
measuring caster -- I've never heard of anyone with too much. :-)
Ken H.
Usually my attitude toward things isn't very popular, but my belief is that
if the toe
& caster is right & the caster is sufficient that the vehicle drives well,
is within
specs & don't wear out tires, it ain't broke
daveB
Last time I spoke to Dave he noted that he was of the opinion that current
generation radial tires like to run flat on the road hence his
recommendation of a 0° camber setting.
I know Dave is constantly changing the settings he runs to see how they
affect the handling of the GMC. Dave's recommends 5° Caster, 0° Camber, and
0 Toe in/out when you install a pair of his offset upper control arms.
I have never heard or read of anyone with concentric or offset upper control
arm bushing ever getting anywhere near 5° caster. So if 5° caster was the
number that was proclaimed we’d have heaps of people saying there was NO
WAY the alignment shop could get that much caster. By saying as much caster
as
you can get it solves that problem.
Here's the settings on Double Trouble AFTER John Sharpe and I installed a
set of Dave's offset upper control arms.
Left:
Camber: 0.1 degrees
Caster: 5.2 degrees
Toe: 0.0 inches
Front Axle 1
Right
Camber: -0.2 degrees
Caster: 4.8 degrees
Toe: 0.0 inches
rob
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
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Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] caster settings [message #138190 is a reply to message #138104] |
Tue, 09 August 2011 15:06  |
KB
Messages: 1262
Registered: September 2009
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Nice collectin' Gene. I've been wondering what's "typical". From what we've
learned, the coaches almost always have more caster on the left than the right
if everything is set the same. So one approach could be to set the cams as
we've already described, and drive it. If it pulls, adjust the left side rear cam
out a little bit to reduce caster, and move the left side front cam in the same
little bit to maintain 0 camber. Probably won't work with all coaches, but a good guess.
It'd be nice to know how far that "little bit" should be, though it probably varies.
And of course if the front end isn't good, frame is bent, etc, etc, all bets are off.
Karen
1973 23'
1975 26'
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] caster settings [message #138197 is a reply to message #138194] |
Tue, 09 August 2011 17:15 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Bruce,
I am NOT an alignment specialist, however, I LISTEN attentively to people
who do KNOW what they're talking about and as far as front end alignment
goes IMHO that is Bob Drewes and Dave Lenzi (listed alphabetically). Plus I
worked with Ken Henderson aligning the front end on his 23' ex-Birchaven and
he taught me a lot.
From them (and chatter on the GMC net) I have "heard" that early coaches (up
to and including 1976 (I'm not sure I that was the year or not) it was hard
to get much caster. The MM specifies 1 1/2° to 2 1/2°.
Double Trouble (1975 Avion) started life as a Transmode and was built in
October of 1974 (found that written in pencil under the carpet behind the
passenger seat). After installing offset bushings in the upper control arm
rear "legs" the max caster Tom Hampton could get was 1.9° on both sides.
Unfortunately I don't know what was possible before I installed offset
bushings.
After 1976 it was possible to get more caster and "word on the street" was
that GMC did "something" to the control arm mounting tabs.
As far as the settings being "all over the map" I had a chat with Alex Sirum
about GMC handling at a rally and he noted that he could never figure out
why they were so different. Some of the handled great others didn't. He
noted that there was one coach he worked on and no matter what he did to it
he COULD NOT get the thing to handle.
I think we are hung up on trying to set the ride height at the manual specs
because GMC specified a tolerance of +/- 1/4". As you noted I agree it is
important on the front end to get the drive axles in alignment to reduce
wear on the CV joints.
For the life of me I can't think of any other reason to set the rear end
lower than to increase the amount of caster that you can get. Maybe 0.3°
makes a difference? Maybe there were GMC's that you couldn't get the 1 1/2°
to 2 1/2° the MM specifies without dropping the rear end?
Thinking about it I don't know why if one could set their GMC up so the belt
line is dead level and get 5° of caster why it would not handle the same as
a GMC with a droopy butt set up at 5° of caster!
BTW if you want to put the ° symbol in a message you:
1) set Num Lock On
2) hold down the Alt key
3) type 0 1 7 6 on the numeric keypad
4) release the Alt key
5) ° will appear
I learned that trick here from Little Yimmy Melberg!
See I told you I listen and learn a lot here! ;-)
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: Bruce Hislop
I'm confused...
So we want as much caster as possible, upto 5*....
Yet the settings seem to be all over the map....
Yet we are hung up on exact ride height giving that saggy over-loaded
looking rear end to improve caster... by all of 0.3* ?
I agree that the front axles should be level for minimum wear on the CV
joints and minimum torque vectors (or whatever the technical term is)... but
I don't think 0.3* of caster is going to make that much difference.
--
Bruce
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] caster settings [message #138209 is a reply to message #138197] |
Tue, 09 August 2011 20:18 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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Senior Member |
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Rob, I wonder the same thing about level coach with proper caster. The droopy butt thing looks....... well, like ass. Anybody got an answer to Robs question????????
Sully
77 royale
Sent from my Verizon Wireless BlackBerry
-----Original Message-----
From: "Rob Mueller" <robmueller@iinet.net.au>
Sender: gmclist-bounces@temp.gmcnet.org
Date: Wed, 10 Aug 2011 08:15:25
To: <gmclist@temp.gmcnet.org>
Reply-To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] caster settings
Bruce,
I am NOT an alignment specialist, however, I LISTEN attentively to people
who do KNOW what they're talking about and as far as front end alignment
goes IMHO that is Bob Drewes and Dave Lenzi (listed alphabetically). Plus I
worked with Ken Henderson aligning the front end on his 23' ex-Birchaven and
he taught me a lot.
From them (and chatter on the GMC net) I have "heard" that early coaches (up
to and including 1976 (I'm not sure I that was the year or not) it was hard
to get much caster. The MM specifies 1 1/2° to 2 1/2°.
Double Trouble (1975 Avion) started life as a Transmode and was built in
October of 1974 (found that written in pencil under the carpet behind the
passenger seat). After installing offset bushings in the upper control arm
rear "legs" the max caster Tom Hampton could get was 1.9° on both sides.
Unfortunately I don't know what was possible before I installed offset
bushings.
After 1976 it was possible to get more caster and "word on the street" was
that GMC did "something" to the control arm mounting tabs.
As far as the settings being "all over the map" I had a chat with Alex Sirum
about GMC handling at a rally and he noted that he could never figure out
why they were so different. Some of the handled great others didn't. He
noted that there was one coach he worked on and no matter what he did to it
he COULD NOT get the thing to handle.
I think we are hung up on trying to set the ride height at the manual specs
because GMC specified a tolerance of +/- 1/4". As you noted I agree it is
important on the front end to get the drive axles in alignment to reduce
wear on the CV joints.
For the life of me I can't think of any other reason to set the rear end
lower than to increase the amount of caster that you can get. Maybe 0.3°
makes a difference? Maybe there were GMC's that you couldn't get the 1 1/2°
to 2 1/2° the MM specifies without dropping the rear end?
Thinking about it I don't know why if one could set their GMC up so the belt
line is dead level and get 5° of caster why it would not handle the same as
a GMC with a droopy butt set up at 5° of caster!
BTW if you want to put the ° symbol in a message you:
1) set Num Lock On
2) hold down the Alt key
3) type 0 1 7 6 on the numeric keypad
4) release the Alt key
5) ° will appear
I learned that trick here from Little Yimmy Melberg!
See I told you I listen and learn a lot here! ;-)
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: Bruce Hislop
I'm confused...
So we want as much caster as possible, upto 5*....
Yet the settings seem to be all over the map....
Yet we are hung up on exact ride height giving that saggy over-loaded
looking rear end to improve caster... by all of 0.3* ?
I agree that the front axles should be level for minimum wear on the CV
joints and minimum torque vectors (or whatever the technical term is)... but
I don't think 0.3* of caster is going to make that much difference.
--
Bruce
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] caster settings [message #138226 is a reply to message #138197] |
Wed, 10 August 2011 05:23 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Robert Mueller wrote on Tue, 09 August 2011 15:15 |
...
After 1976 it was possible to get more caster and "word on the street" was
that GMC did "something" to the control arm mounting tabs.
...
|
I think that makes sense...
I know my 1973 (with the front "close" to spec) drives much better with the rear a bit LOWER than spec. BUT my 1978 (with the front lower than spec) doesn't seem to change that much even with the rear a little HIGHER than the front.
I kind of like the look of the front being lower and the coach level but am a bit concerned with the CV joints angle. I have seen front wheel well "spats" that give a similar look with the correct ride height.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] caster settings [message #138229 is a reply to message #138226] |
Wed, 10 August 2011 06:17 |
Jim Bounds
Messages: 842
Registered: January 2004
Karma: 0
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Senior Member |
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I too agree that the coach looks less than cool with the back look like it's "packing". There is a perfect reason and it all ties together. The adjustible rear suspension was not just to level in a park, that would be a waste of energy and GM did not look at the GMC as a "camper". In "travel" mode, the suspension is set up for highway driving--- as much caster as reasonable (I have found over 3 deg. and the front end starts to float a bit and you loose feeling of the road, like a big ole Lincoln-- which I have 2) When you raise the rear end, your caster goes negative which makes it easier to turn tight corners, neg. caster is like turning the handle bars of your bike around, it has tight response but dives into a ditch if you are not with it and carefull. The same thing happens when you raise the rear of the coach. With less caster, the coach will turn tighter and the holding tank and bumper are within the civil enginners spec for the height of the
vehicle to the distance from the bumper to rear "axle" 9we don;t have one of those but still there are 2 rear wheels to fulcrum the coach from. There is a spec. for that, DOT sets it and our coach is fine--- in town--- looks better---- with the rear end up.
The rear up means you can turn tighter and the rear of the coach is safe, lower you are good to go on a highway with the best highway handling characteristics. If you drive your coach in travel in town, first it looks silly and like it's "packn" AND the rear of the coach is at risk. All factory settings make a vehicle body "level" to the ground, ours was made that way too. In town is when folks would be admiring the coach, it should be up in the back. On the highway it was determined you would be a blurrrr blowing by so folks would not look at it so critically whicle on the highway-- thus the ass is lowered. Kinda like those really ugly rear spoilers that pop up when your car is on the highway.
In "travel", caster over 3 deg. starts to make the coach hard to feel the road, that's not whats called "better". When totally rebuilding the front end, you can put an offset bushing in the rear position which will give you more caster, it's not a bad idea. The pass. side of the coach takes the curbs and is usually the side that is caster poor, the offset on each side assures you can reach 2.5-3 deg. of caster. It was not a mistake or change, it seems it's down to how many curbs the coach had hit over it's life.
It may have said it in the manual (remember, attorneys had their hand in that" but you should drive your coach in "raise" in town and only use "travel" on the highway. The coach looks better sporting around town and is safe then with the push of the "travel" button, you are ready to "travel" with increased caster.
As far as the rest of the specs (camber, toe) they all should be right on straight. Forget toeing it out because it is "front wheel drive" , that may be true on a tuner car but for us, you want the wheels straight up and facing forward-- the more you have that the less wear, the better driving you have.
I don;t want my coach to be seen butt down packing, it draws so much more attention and personally looks cooler level to the ground at least if not up in the back (what can I say, I had shackles on my first car!). Only use travel on the highway and bring the ass up before you hit the exit and you will get more attention-- try it.
I think the attorneys did not want you to know all this, if you drive the coach with the rear up on the highway, it will be on the squirley side-- some yahoo would leave it there-- forgot because of the beer-- would drive 90 mph cause he could-- would not be able to hold her straight and GM would be sued because bubba didn;t push "travel". No, they tell you to not drive over 15mph in raise-- what a waste! Jack-r-up in town, women will love you-- at least the car nuts will pay more attention, leave the ass low in town and you will be asked what the problem was or "do you need a new diaper"!
Hope this helps,
Jim Bounds
-----------------------
--- On Wed, 8/10/11, Mike Miller <m000035@gmail.com> wrote:
> From: Mike Miller <m000035@gmail.com>
> Subject: Re: [GMCnet] caster settings
> To: gmclist@temp.gmcnet.org
> Date: Wednesday, August 10, 2011, 6:23 AM
>
>
> Robert Mueller wrote on Tue, 09 August 2011 15:15
> > ...
> > After 1976 it was possible to get more caster and
> "word on the street" was
> > that GMC did "something" to the control arm mounting
> tabs.
> > ...
>
>
> I think that makes sense...
>
> I know my 1973 (with the front "close" to spec) drives much
> better with the rear a bit LOWER than spec. BUT my
> 1978 (with the front lower than spec) doesn't seem to change
> that much even with the rear a little HIGHER than the
> front.
>
> I kind of like the look of the front being lower and the
> coach level but am a bit concerned with the CV joints
> angle. I have seen front wheel well "spats" that give
> a similar look with the correct ride height.
>
> --
> Mike Miller -- Hillsboro, OR -- on the Black list
> (#1)'73 26' exPainted D. -- (#2)`78 23' Birchaven Rear Bath
> -- (#3)`77 23' Birchaven Side Bath
> http://m000035.blogspot.com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] caster settings [message #138800 is a reply to message #138194] |
Sat, 13 August 2011 00:03 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| RF_Burns wrote on Tue, 09 August 2011 15:32 |
I'm confused...
So we want as much caster as possible, upto 5*....
Yet the settings seem to be all over the map....
Yet we are hung up on exact ride height giving that saggy over-loaded looking rear end to improve caster... by all of 0.3* ?
I agree that the front axles should be level for minimum wear on the CV joints and minimum torque vectors (or whatever the technical term is)... but I don't think 0.3* of caster is going to make that much difference.
|
There ia a downside to increased caster and it involves pitman arm loads. It looks like so far no one has had an issue, but until 1973 on the radial tire equipped Monte Carlo, caster angles in excess of 3 degrees could snap a pitman arm under high impact loads such as potholes. High caster angles dramatically increase steering system loads and I would be somewhat cautious about this on the GMC. Once again, does anyone think that GM had no idea why they specked the caster angle that they did?
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] caster settings [message #138808 is a reply to message #138800] |
Sat, 13 August 2011 01:30 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Bob,
First of all I state unequivocally that I do NOT "think that GM (engineers)
had no idea why they specked the caster angle that they did." I am confident
they knew what they were doing.
However, I can assure you that Double Trouble went from a vehicle that was
difficult to control to a vehicle that is easy to control after I installed
Dave Lenzi's offset upper control arms allowing me to increase the positive
caster from 1.9° to 5°.
As I understand (and I may not) it when you turn a vehicle to the left or
right from straight ahead the greater the positive caster the greater amount
of force it takes because positive caster is trying to lift the vehicle.
This would increase loads on the steering system components. I can assure
you that if it can be shown that the additional 3° of caster has created an
unsafe vehicle the upper control arms will be removed post haste.
It is not clear to me how hitting a pot hole would create greater forces on
the pitman arm if one was going straight ahead.
Am I correct in assuming that higher caster angles would make the amount of
force transmitted to the pitman arm go up because the wheels would resist
being forced left or right when you hit a pothole?
If what I have related above is incorrect in any way, shape, or form PLEASE
correct me. Could you please provide some details as to how/why extra
positive caster causes higher loads on the steering system.
Regards,
Rob M.
-----Original Message-----
From: Bob de Kruyff
There is a downside to increased caster and it involves pitman arm loads. It
looks like so far no one has had an issue, but until 1973 on the radial tire
equipped Monte Carlo, caster angles in excess of 3 degrees could snap a
pitman arm under high impact loads such as potholes. High caster angles
dramatically increase steering system loads and I would be somewhat cautious
about this on the GMC. Once again, does anyone think that GM had no idea why
they specked the caster angle that they did?
--
Bob de Kruyff
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] caster settings [message #138837 is a reply to message #138808] |
Sat, 13 August 2011 08:52 |
Jim Bounds
Messages: 842
Registered: January 2004
Karma: 0
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Senior Member |
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Rob,
I would guess setting extreme specs migh increase stresses a bit but I would believe that if you could stay within a range that the stresses would not be a factor.
I have found caster over say 3.5 deg. cuases difficult steering in an oposite drirection from a neg. caster situation. Too light a wheel makes it difficult to "feel" the road. I think too much caster causes this so I usually lat a coach go with 2.5-3.5 deg. of caster in both wheels. Usually you can get this with a stock a arm and stock control arm bushings. You can put a pair of offset bushings in the rear position (1 on each side) and this will assure you will be able to reach 3.5 deg. easily.
Years of taking speed bumps, pot holes and curbs tends to distort the frame alignment a bit which will of course make it more difficult to reach good alignment specs. I think this is the wild card that makes every alignment a bit different and why sometimes some coaches simply will not set up well. It's that way in a car that gets hammered in an accident. My Dad would never buy a car with a front clip job-- said it will never be the same. We are seeing this in the coaches, loose frames, missing body pads, crushed hoses, rusted frames-- it all goes in to make the alignment specs easy or hard to reach. These are old machines so there is no telling the condition of each component and every component of the suspension and steering must be right or it seems nothing is working right. So setting up a suspension on a 30+ year old GMC can be a challenge, you have many things to consider.
Jim Bounds
---------------------
--- On Sat, 8/13/11, Rob Mueller <robmueller@iinet.net.au> wrote:
> From: Rob Mueller <robmueller@iinet.net.au>
> Subject: Re: [GMCnet] caster settings
> To: gmclist@temp.gmcnet.org
> Date: Saturday, August 13, 2011, 2:30 AM
> Bob,
>
> First of all I state unequivocally that I do NOT "think
> that GM (engineers)
> had no idea why they specked the caster angle that they
> did." I am confident
> they knew what they were doing.
>
> However, I can assure you that Double Trouble went from a
> vehicle that was
> difficult to control to a vehicle that is easy to control
> after I installed
> Dave Lenzi's offset upper control arms allowing me to
> increase the positive
> caster from 1.9° to 5°.
>
> As I understand (and I may not) it when you turn a vehicle
> to the left or
> right from straight ahead the greater the positive caster
> the greater amount
> of force it takes because positive caster is trying to lift
> the vehicle.
> This would increase loads on the steering system
> components. I can assure
> you that if it can be shown that the additional 3° of
> caster has created an
> unsafe vehicle the upper control arms will be removed post
> haste.
>
> It is not clear to me how hitting a pot hole would create
> greater forces on
> the pitman arm if one was going straight ahead.
>
> Am I correct in assuming that higher caster angles would
> make the amount of
> force transmitted to the pitman arm go up because the
> wheels would resist
> being forced left or right when you hit a pothole?
>
> If what I have related above is incorrect in any way,
> shape, or form PLEASE
> correct me. Could you please provide some details as to
> how/why extra
> positive caster causes higher loads on the steering
> system.
>
> Regards,
> Rob M.
>
> -----Original Message-----
> From: Bob de Kruyff
>
> There is a downside to increased caster and it involves
> pitman arm loads. It
> looks like so far no one has had an issue, but until 1973
> on the radial tire
> equipped Monte Carlo, caster angles in excess of 3 degrees
> could snap a
> pitman arm under high impact loads such as potholes. High
> caster angles
> dramatically increase steering system loads and I would be
> somewhat cautious
> about this on the GMC. Once again, does anyone think that
> GM had no idea why
> they specked the caster angle that they did?
> --
> Bob de Kruyff
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] caster settings [message #138852 is a reply to message #138837] |
Sat, 13 August 2011 09:52 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Jim,
During my first visit with Double Trouble to the Coop we installed rebuilt
lower control arms from Steve Ferguson, rebuilt hubs / knuckles, idler arm,
and relay lever from Dave Lenzi and MOOG offset bushings in the rear "legs"
of the upper control arms. Jason checked all the rest of the steering and
suspension and said it was OK. When we got done you did an alignment and it
drove fine. Unfortunately the printer on your alignment machine was having
problems so you took a picture of the screen showing the settings and
emailed it to me. Unfortunately I can't find that picture so I don't know
what you got in the way of caster / camber / toe in-out.
You noted that "things" would settle down and it would be a good idea to
align it again after "a few" miles. The next year when we got close to Tom
Hampton's shop I had a few things that needed doing and decided to take your
advice and have him re-align it. While were getting ready to do the
alignment Tom noticed that the steering box had developed a slight leak from
the seal below the spline at the top. He had me pull the box out and we
replaced the seal. While it was out we adjusted the steering box as per the
MM.
With zero camber the max caster Tom could get was 1.9 degrees on both sides.
Adjusting the steering did box make a difference as the amount of play in
the steering wheel dropped to 1/2 - 3/4 inches. Double Trouble drove a bit
better.
I heard via the GMC grapevine that Dave Lenzi was developing a set of offset
upper control arms that would allow one to obtain more caster. I was
returning to Sydney and decided to wait until the next visit before trying a
pair.
Later I heard that Tom Hampton fitted a pair of them to his coach and he
felt the increased caster made his coach easier to drive and a bit more
stable. I also spoke to Lanny Young and he noted the same thing. When I got
back to Humble John Sharpe had fitted a pair to his GMC and I drove it. It
handled WAY better than Double Trouble so I decided to go for a pair.
John and I installed a pair on Double Trouble and I had an alignment done at
Beasley Tire; a truck alignment facility in Humble, Texas. The machine he
used was a state of the art computerized alignment machine and technician
that did it had 14 years experience. He was VERY meticulous and you know for
ME to say that he damn sure must have been!
I wound up with the following settings:
Left:
Camber: 0.1 degrees
Caster: 5.2 degrees
Toe: 0.0 inches
Front Axle 1
Right
Camber: -0.2 degrees
Caster: 4.8 degrees
Toe: 0.0 inches
If I'm in the center lane on a freeway I can let go of the wheel and Double
Trouble goes straight ahead, if I'm in the left lane she drifts slowly to
the left and if I'm in the right lane she drifts slowly to the right. Don't
get me wrong, I still have to drive Double Trouble but the effort it takes
to keep her heading down the road straight is really low.
There seems to be an added benefit she's much more stable going down the
road. When I am passed by semi's from the rear I hardly get and "push" at
all and when I am passed by oncoming semi's the buffeting hardly seems to
affect Double Trouble at all.
My next step is to install a Quadra Bag rear suspension system to see how
much that improves Double Trouble's stability.
Tell you what, next time I visit the Coop Resort or we run into each other
at a rally you can drive Double Trouble and tell me what you think.
Regards,
Rob M.
Sydney, Australia
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Jim Bounds
Sent: Saturday, 13 August 2011 11:53 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] caster settings
Rob,
I would guess setting extreme specs migh increase stresses a bit but I would
believe that if you could stay within a range that the stresses would not be
a factor.
I have found caster over say 3.5 deg. cuases difficult steering in an
oposite drirection from a neg. caster situation. Too light a wheel makes it
difficult to "feel" the road. I think too much caster causes this so I
usually lat a coach go with 2.5-3.5 deg. of caster in both wheels. Usually
you can get this with a stock a arm and stock control arm bushings. You can
put a pair of offset bushings in the rear position (1 on each side) and this
will assure you will be able to reach 3.5 deg. easily.
Years of taking speed bumps, pot holes and curbs tends to distort the frame
alignment a bit which will of course make it more difficult to reach good
alignment specs. I think this is the wild card that makes every alignment a
bit different and why sometimes some coaches simply will not set up well.
It's that way in a car that gets hammered in an accident. My Dad would
never buy a car with a front clip job-- said it will never be the same. We
are seeing this in the coaches, loose frames, missing body pads, crushed
hoses, rusted frames-- it all goes in to make the alignment specs easy or
hard to reach. These are old machines so there is no telling the condition
of each component and every component of the suspension and steering must be
right or it seems nothing is working right. So setting up a suspension on a
30+ year old GMC can be a challenge, you have many things to consider.
Jim Bounds
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] caster settings [message #138890 is a reply to message #138837] |
Sat, 13 August 2011 13:56 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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Senior Member |
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Is there any frame data available with control points and their respective positions for the gmc frame? It might be interesting to see how much variance currently exists in the control arm mounting areas compared to original. If the frame has sagged toward the centerline with time and gravity accross the upper control arm mounting area it might make achieving correct camber with ideal caster more difficult. Then again, typical tolerances in the 70's was probably + or - 1/2" :) I am a bit curious. I have a laser vehicle measuring system and am willing to do some measuring but without original specs to compare to I would only be able to check for symmetry.
Sully
77 royale
Sent from my Verizon Wireless BlackBerry
-----Original Message-----
From: Jim Bounds <gmccoop@yahoo.com>
Sender: gmclist-bounces@temp.gmcnet.org
Date: Sat, 13 Aug 2011 06:52:37
To: <gmclist@temp.gmcnet.org>
Reply-To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] caster settings
Rob,
I would guess setting extreme specs migh increase stresses a bit but I would believe that if you could stay within a range that the stresses would not be a factor.
I have found caster over say 3.5 deg. cuases difficult steering in an oposite drirection from a neg. caster situation. Too light a wheel makes it difficult to "feel" the road. I think too much caster causes this so I usually lat a coach go with 2.5-3.5 deg. of caster in both wheels. Usually you can get this with a stock a arm and stock control arm bushings. You can put a pair of offset bushings in the rear position (1 on each side) and this will assure you will be able to reach 3.5 deg. easily.
Years of taking speed bumps, pot holes and curbs tends to distort the frame alignment a bit which will of course make it more difficult to reach good alignment specs. I think this is the wild card that makes every alignment a bit different and why sometimes some coaches simply will not set up well. It's that way in a car that gets hammered in an accident. My Dad would never buy a car with a front clip job-- said it will never be the same. We are seeing this in the coaches, loose frames, missing body pads, crushed hoses, rusted frames-- it all goes in to make the alignment specs easy or hard to reach. These are old machines so there is no telling the condition of each component and every component of the suspension and steering must be right or it seems nothing is working right. So setting up a suspension on a 30+ year old GMC can be a challenge, you have many things to consider.
Jim Bounds
---------------------
--- On Sat, 8/13/11, Rob Mueller <robmueller@iinet.net.au> wrote:
> From: Rob Mueller <robmueller@iinet.net.au>
> Subject: Re: [GMCnet] caster settings
> To: gmclist@temp.gmcnet.org
> Date: Saturday, August 13, 2011, 2:30 AM
> Bob,
>
> First of all I state unequivocally that I do NOT "think
> that GM (engineers)
> had no idea why they specked the caster angle that they
> did." I am confident
> they knew what they were doing.
>
> However, I can assure you that Double Trouble went from a
> vehicle that was
> difficult to control to a vehicle that is easy to control
> after I installed
> Dave Lenzi's offset upper control arms allowing me to
> increase the positive
> caster from 1.9° to 5°.
>
> As I understand (and I may not) it when you turn a vehicle
> to the left or
> right from straight ahead the greater the positive caster
> the greater amount
> of force it takes because positive caster is trying to lift
> the vehicle.
> This would increase loads on the steering system
> components. I can assure
> you that if it can be shown that the additional 3° of
> caster has created an
> unsafe vehicle the upper control arms will be removed post
> haste.
>
> It is not clear to me how hitting a pot hole would create
> greater forces on
> the pitman arm if one was going straight ahead.
>
> Am I correct in assuming that higher caster angles would
> make the amount of
> force transmitted to the pitman arm go up because the
> wheels would resist
> being forced left or right when you hit a pothole?
>
> If what I have related above is incorrect in any way,
> shape, or form PLEASE
> correct me. Could you please provide some details as to
> how/why extra
> positive caster causes higher loads on the steering
> system.
>
> Regards,
> Rob M.
>
> -----Original Message-----
> From: Bob de Kruyff
>
> There is a downside to increased caster and it involves
> pitman arm loads. It
> looks like so far no one has had an issue, but until 1973
> on the radial tire
> equipped Monte Carlo, caster angles in excess of 3 degrees
> could snap a
> pitman arm under high impact loads such as potholes. High
> caster angles
> dramatically increase steering system loads and I would be
> somewhat cautious
> about this on the GMC. Once again, does anyone think that
> GM had no idea why
> they specked the caster angle that they did?
> --
> Bob de Kruyff
>
>
>_______________________________________________
> GMCnet mailing list
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>
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] caster settings [message #138938 is a reply to message #138890] |
Sat, 13 August 2011 19:46 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
|
Senior Member |
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|
Sully,
Would that the data was available!
You would need the blueprints of the front frame to find this out and I've
been hanging around here for four years and NEVER seen any reference to
them.
However, the word on the street is that GMC did something in 1976 that
enabled coaches to get more caster. I am not sure if the year is correct. It
would be interesting if you could check a 1974 coach and a 1978 coach with
your laser measuring system and see what you find.
As far as the frame sagging I have seen several pairs of frame rails and
when you look down them like you look down a 4 x 2 (we don't call them 2 x
4's here in Australia) I couldn't see any bow. I realize that's a half-a$$ed
measurement but that's what I've noted.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of sgltrac@gmail.com
Sent: Sunday, 14 August 2011 4:56 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] caster settings
Is there any frame data available with control points and their respective
positions for the gmc frame? It might be interesting to see how much
variance currently exists in the control arm mounting areas compared to
original. If the frame has sagged toward the centerline with time and
gravity accross the upper control arm mounting area it might make achieving
correct camber with ideal caster more difficult. Then again, typical
tolerances in the 70's was probably + or - 1/2" :) I am a bit curious. I
have a laser vehicle measuring system and am willing to do some measuring
but without original specs to compare to I would only be able to check for
symmetry.
Sully
77 royale
Sent from my Verizon Wireless BlackBerry
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] caster settings [message #138941 is a reply to message #138938] |
Sat, 13 August 2011 19:58 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
|
Senior Member |
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Its a longshot but ill call chief next week and ask them if they have any data. Then ill probably listen to them laugh.
Sully
77 royale
Sent from my Verizon Wireless BlackBerry
-----Original Message-----
From: "Rob Mueller" <robmueller@iinet.net.au>
Sender: gmclist-bounces@temp.gmcnet.org
Date: Sun, 14 Aug 2011 10:46:27
To: <gmclist@temp.gmcnet.org>
Reply-To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] caster settings
Sully,
Would that the data was available!
You would need the blueprints of the front frame to find this out and I've
been hanging around here for four years and NEVER seen any reference to
them.
However, the word on the street is that GMC did something in 1976 that
enabled coaches to get more caster. I am not sure if the year is correct. It
would be interesting if you could check a 1974 coach and a 1978 coach with
your laser measuring system and see what you find.
As far as the frame sagging I have seen several pairs of frame rails and
when you look down them like you look down a 4 x 2 (we don't call them 2 x
4's here in Australia) I couldn't see any bow. I realize that's a half-a$$ed
measurement but that's what I've noted.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of sgltrac@gmail.com
Sent: Sunday, 14 August 2011 4:56 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] caster settings
Is there any frame data available with control points and their respective
positions for the gmc frame? It might be interesting to see how much
variance currently exists in the control arm mounting areas compared to
original. If the frame has sagged toward the centerline with time and
gravity accross the upper control arm mounting area it might make achieving
correct camber with ideal caster more difficult. Then again, typical
tolerances in the 70's was probably + or - 1/2" :) I am a bit curious. I
have a laser vehicle measuring system and am willing to do some measuring
but without original specs to compare to I would only be able to check for
symmetry.
Sully
77 royale
Sent from my Verizon Wireless BlackBerry
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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