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| [GMCnet] Torque steer and tire wear [message #261954] |
Mon, 15 September 2014 10:37  |
glwgmc
Messages: 1014
Registered: June 2004
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I suggest a slight alteration to your recommendations, Rob. Too much static caster can put undo strain on the steering components. With a one ton front end and radial ply tires I suggest max static caster UP TO 5 DEGREES so long as it is even on both sides. Many GMCs are not capable of achieving 5 degrees on both sides so get as much as you can but no more than 5 degrees. 3 or 4 degrees of static caster will make most GMCs track straight at speed without too much load on the steering gear in low speed turns and that can only be achieved on most GMCs by using the offset bushings. Zero caster and zero toe seem to work best on most coaches so long as the front and rear wheels are all frame parallel with the steering box centered.
For those who might not be too familiar with this topic, the issue we are dealing with is our coaches were designed around bias ply tires which behave at speed very differently from the radial ply tires most all of us use these days. The bias ply tire contact patch moves back at speed resulting in an additional one or two degrees of caster while under way. The radial ply tire contact patch does not so we have to dial in more static caster to compensate. The factory started with 3 degrees of static caster and expected the bias ply tire behavior to add another one to two degrees at speed. They must have found something (too much steering gear wear?) as they changed that spec to 2 degrees in 74 and it stayed there all throughout the production run. Since they offered both bias ply and radial ply tires from the middle of the run on, the spec did not change.
Everything starts by setting ride height front and rear to the factory spec and driving the coach a few miles to settle the suspension. Do not jack it up after that. Do all your alignment measurements without jacking up the coach (difficult for many commercial alignment shops and not what they are used to doing). Tires and tire wear also seem to make a big difference on some coaches so always try moving them around side to side and front to rear if you still have pull or wander at speed after setting the caster, camber and toe as above. Do not use the factory spec if you are using radial ply tires. The factory spec is fine if you are still using bias ply tires (are any still even made in our load range?).
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
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Message: 13
Date: Mon, 15 Sep 2014 00:15:24 -0500
From: "Rob Mueller"
Subject: Re: [GMCnet] Torque Steer and Tire Wear
To:
Message-ID:
Content-Type: text/plain; charset="us-ascii"
Jeff.
In a nutshell you want the MAX amount of caster with zero degrees of camber and zero tow in/out.
Your coach is a 1973 and you probably won't be able to get more than 1 degree of caster. If you install offset bushings in the rear
arm of the upper control arm you'll gain another half a degree possibly a bit more.
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Torque steer and tire wear [message #262027 is a reply to message #261954] |
Tue, 16 September 2014 09:15  |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Jerry et al,
Disregard my comments regarding wheel alignment on this coach; I FORGOT it has a 1 Ton front end.
I would like to know if Matt or anybody else can get 3° caster as noted in the X-7425 manual on any GMC with an OEM front
suspension.
Double Trouble has Dave Lenzi's offset upper control arms and I run 5° caster / 0° camber / 0" toe.
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Work Jerry
Sent: Monday, September 15, 2014 10:38 AM
To: Gmc Forum
Subject: [GMCnet] Torque steer and tire wear
I suggest a slight alteration to your recommendations, Rob. Too much static caster can put undo strain on the steering components.
With a one ton front end and radial ply tires I suggest max static caster UP TO 5 DEGREES so long as it is even on both sides. Many
GMCs are not capable of achieving 5 degrees on both sides so get as much as you can but no more than 5 degrees. 3 or 4 degrees of
static caster will make most GMCs track straight at speed without too much load on the steering gear in low speed turns and that can
only be achieved on most GMCs by using the offset bushings. Zero caster and zero toe seem to work best on most coaches so long as
the front and rear wheels are all frame parallel with the steering box centered.
For those who might not be too familiar with this topic, the issue we are dealing with is our coaches were designed around bias ply
tires which behave at speed very differently from the radial ply tires most all of us use these days. The bias ply tire contact
patch moves back at speed resulting in an additional one or two degrees of caster while under way. The radial ply tire contact
patch does not so we have to dial in more static caster to compensate. The factory started with 3 degrees of static caster and
expected the bias ply tire behavior to add another one to two degrees at speed. They must have found something (too much steering
gear wear?) as they changed that spec to 2 degrees in 74 and it stayed there all throughout the production run. Since they offered
both bias ply and radial ply tires from the middle of the run on, the spec did not change.
Everything starts by setting ride height front and rear to the factory spec and driving the coach a few miles to settle the
suspension. Do not jack it up after that. Do all your alignment measurements without jacking up the coach (difficult for many
commercial alignment shops and not what they are used to doing). Tires and tire wear also seem to make a big difference on some
coaches so always try moving them around side to side and front to rear if you still have pull or wander at speed after setting the
caster, camber and toe as above. Do not use the factory spec if you are using radial ply tires. The factory spec is fine if you
are still using bias ply tires (are any still even made in our load range?).
Jerry
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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] Torque steer and tire wear [message #262030 is a reply to message #262027] |
Tue, 16 September 2014 09:29 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Rob, I do these oem front ends frequently and rarely do I find one that
does not have offset upper control arm bushings that you can obtain much
more than 2° Caster. But, there are exceptions. I also find the locating
perches that are welded to the frame rails are not all jigged to the same
position on the rails. Lots of weld spatter in there as well. When I do a 1
ton install, I run an angle grinder with a wire brush in there to make it
easier to adjust the snail cams. Just what I do, others might vary.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Sep 16, 2014 7:16 AM, "Rob Mueller" wrote:
> Jerry et al,
>
> Disregard my comments regarding wheel alignment on this coach; I FORGOT it
> has a 1 Ton front end.
>
> I would like to know if Matt or anybody else can get 3° caster as noted in
> the X-7425 manual on any GMC with an OEM front
> suspension.
>
> Double Trouble has Dave Lenzi's offset upper control arms and I run 5°
> caster / 0° camber / 0" toe.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> USAussie - Downunder
> USA '75 Avion - Double Trouble TZE365V100426
> AUS '75 Avion - The Blue Streak TZE365V100428
>
> -----Original Message-----
> From: gmclist-bounces@temp.gmcnet.org [mailto:
> gmclist-bounces@temp.gmcnet.org] On Behalf Of Work Jerry
> Sent: Monday, September 15, 2014 10:38 AM
> To: Gmc Forum
> Subject: [GMCnet] Torque steer and tire wear
>
> I suggest a slight alteration to your recommendations, Rob. Too much
> static caster can put undo strain on the steering components.
> With a one ton front end and radial ply tires I suggest max static caster
> UP TO 5 DEGREES so long as it is even on both sides. Many
> GMCs are not capable of achieving 5 degrees on both sides so get as much
> as you can but no more than 5 degrees. 3 or 4 degrees of
> static caster will make most GMCs track straight at speed without too much
> load on the steering gear in low speed turns and that can
> only be achieved on most GMCs by using the offset bushings. Zero caster
> and zero toe seem to work best on most coaches so long as
> the front and rear wheels are all frame parallel with the steering box
> centered.
>
> For those who might not be too familiar with this topic, the issue we are
> dealing with is our coaches were designed around bias ply
> tires which behave at speed very differently from the radial ply tires
> most all of us use these days. The bias ply tire contact
> patch moves back at speed resulting in an additional one or two degrees of
> caster while under way. The radial ply tire contact
> patch does not so we have to dial in more static caster to compensate.
> The factory started with 3 degrees of static caster and
> expected the bias ply tire behavior to add another one to two degrees at
> speed. They must have found something (too much steering
> gear wear?) as they changed that spec to 2 degrees in 74 and it stayed
> there all throughout the production run. Since they offered
> both bias ply and radial ply tires from the middle of the run on, the spec
> did not change.
>
> Everything starts by setting ride height front and rear to the factory
> spec and driving the coach a few miles to settle the
> suspension. Do not jack it up after that. Do all your alignment
> measurements without jacking up the coach (difficult for many
> commercial alignment shops and not what they are used to doing). Tires
> and tire wear also seem to make a big difference on some
> coaches so always try moving them around side to side and front to rear if
> you still have pull or wander at speed after setting the
> caster, camber and toe as above. Do not use the factory spec if you are
> using radial ply tires. The factory spec is fine if you
> are still using bias ply tires (are any still even made in our load
> range?).
>
> Jerry
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Torque steer and tire wear [message #262046 is a reply to message #262030] |
Tue, 16 September 2014 11:16 |
|
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Jim,
That is my experience with Double Trouble as well with offset upper bushings.
Subsequent to installing a set of Dave Lenzi's offset upper control arms I now run 5° without any problems for three tours / 15,000
miles.
OK, to save you harbingers of doom the time; "You'd better be careful your Pitman arm is going to break in half any minute!"
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
Sent: Tuesday, September 16, 2014 9:30 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Torque steer and tire wear
Rob, I do these oem front ends frequently and rarely do I find one that
does not have offset upper control arm bushings that you can obtain much
more than 2° Caster. But, there are exceptions. I also find the locating
perches that are welded to the frame rails are not all jigged to the same
position on the rails. Lots of weld spatter in there as well. When I do a 1
ton install, I run an angle grinder with a wire brush in there to make it
easier to adjust the snail cams. Just what I do, others might vary.
Jim Hupy
Salem, Or
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Unsubscribe or Change List Options:
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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] Torque steer and tire wear [message #262048 is a reply to message #262046] |
Tue, 16 September 2014 11:28 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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If you can even get 5° of caster, about the worst problems I have noticed
is a groan of protest from the power steering pump at parking speeds when
approaching full lock. But as always, your experience might vary somewhat.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Sep 16, 2014 9:16 AM, "Rob Mueller" wrote:
> Jim,
>
> That is my experience with Double Trouble as well with offset upper
> bushings.
>
> Subsequent to installing a set of Dave Lenzi's offset upper control arms I
> now run 5° without any problems for three tours / 15,000
> miles.
>
> OK, to save you harbingers of doom the time; "You'd better be careful your
> Pitman arm is going to break in half any minute!"
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> USAussie - Downunder
> USA '75 Avion - Double Trouble TZE365V100426
> AUS '75 Avion - The Blue Streak TZE365V100428
>
> -----Original Message-----
> From: gmclist-bounces@temp.gmcnet.org [mailto:
> gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
> Sent: Tuesday, September 16, 2014 9:30 AM
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] Torque steer and tire wear
>
> Rob, I do these oem front ends frequently and rarely do I find one that
> does not have offset upper control arm bushings that you can obtain much
> more than 2° Caster. But, there are exceptions. I also find the locating
> perches that are welded to the frame rails are not all jigged to the same
> position on the rails. Lots of weld spatter in there as well. When I do a 1
> ton install, I run an angle grinder with a wire brush in there to make it
> easier to adjust the snail cams. Just what I do, others might vary.
> Jim Hupy
> Salem, Or
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Torque steer and tire wear [message #262073 is a reply to message #262046] |
Tue, 16 September 2014 14:30 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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USAussie wrote on Tue, 16 September 2014 10:16Jim,
That is my experience with Double Trouble as well with offset upper bushings.
Subsequent to installing a set of Dave Lenzi's offset upper control arms I now run 5° without any problems for three tours / 15,000
miles.
OK, to save you harbingers of doom the time; "You'd better be careful your Pitman arm is going to break in half any minute!"
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
Sent: Tuesday, September 16, 2014 9:30 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Torque steer and tire wear
Rob, I do these oem front ends frequently and rarely do I find one that
does not have offset upper control arm bushings that you can obtain much
more than 2° Caster. But, there are exceptions. I also find the locating
perches that are welded to the frame rails are not all jigged to the same
position on the rails. Lots of weld spatter in there as well. When I do a 1
ton install, I run an angle grinder with a wire brush in there to make it
easier to adjust the snail cams. Just what I do, others might vary.
Jim Hupy
Salem, Or
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GMCnet mailing list
Unsubscribe or Change List Options:
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""OK, to save you harbingers of doom the time; "You'd better be careful your Pitman arm is going to break in half any minute!"
Regards,
Rob M.
The Pedantic Mechanic""
Haha--I'm going to say it anyway. The first GM car to go to 5 deg of caster was the 1973 Monte Carlo equipped with radials. During durability testing we did indeed snap several pitman arms. As a result, that model got specific steering gears and pitman arms. Pitman arm loads subsequently became a standard test on all new platforms. Modern design tools will hopefully prevent those problems in the future, but increased caster does indeed cause higher stress. Is the GMC an issue? I guess time will tell.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Torque steer and tire wear [message #262083 is a reply to message #262027] |
Tue, 16 September 2014 17:56 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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USAussie wrote on Tue, 16 September 2014 10:15Jerry et al,
Disregard my comments regarding wheel alignment on this coach; I FORGOT it has a 1 Ton front end.
I would like to know if Matt or anybody else can get 3° caster as noted in the X-7425 manual on any GMC with an OEM front
suspension.
Double Trouble has Dave Lenzi's offset upper control arms and I run 5° caster / 0° camber / 0" toe.
Regards,
Rob M.
Rob,
I will let you know in a couple of months. I'm going to try to borrow a friend's instrument and measure what my caster, caster and toe are before I take it apart for some serious preventive maintenance.
Matt - Leaving Devil's Tower
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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