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| [GMCnet] My new Manny 1 ton [message #240962] |
Sun, 23 February 2014 09:38  |
Sharon Work
Messages: 9
Registered: April 2012
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From my web site, jerrywork.com, or from the web sites of several of our clubs like GMCWS.ORG you can download a presentation I gave at GMCWS Casa de Fruita a couple of years ago that outlines why we now need alignment specs that are different from the GMC maintenance manual. Basically, radial ply tires behave very differently from bias ply tires and require different alignment specs. When GM began offering radial ply tires on our motorhomes around the middle of the production run, they continued to offer bias ply tires as well. While they did change the alignment specs when changing to radial ply tires on the Olds and Cad passenger cars, they did not do so for the motorhome. Because of the behavior of radial ply tires under speed, a radial ply tired car will benefit from greater caster than the same car shod with bias ply tires. But, there are definite limits. The greater the caster, the greater the load on the front end components for a given weight. For our coaches
running radial ply tires, 3 to 5 degrees of caster seems to be the sweet spot IF the ride height front and rear is correct. More than 5 and we are on the edge of over loading the front end components and over running the angle at which some of the front end components were designed to run. Less than 3 and we are on the edge of wandering. Camber for our coaches is also a balance where too much tilt in at the top is as bad on handling and tire wear as too much tilt out at the top. Zero (straight up and down) seems to be the best balance given that most of us now run radial ply tires. Toe in or out is largely a function of the condition of all the front end components. Again, zero seems to be a good balance for most coaches.
Since we all own and drive only one or two of these things it is natural to think that what works for our coach(s) is correct for all other coaches. As a result, there are many different opinions one will read on this forum. If you really want to deviate from the 3-5 degrees of caster, zero camber and zero toe, be sure to do the iterative process described in the presentation required to get your ride height at the factory spec front and rear first. Then set the 3-5, 0, 0 and drive your coach for a while. From there, do your own thing if you wish, but keep a close eye on tire wear front and rear.
Hope this helps.
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: 1
Date: Sun, 23 Feb 2014 14:49:42 +1100
From: "Robert Mueller" <robmueller@iinet.net.au>
Subject: Re: [GMCnet] My new Manny 1 ton
To: <gmclist@temp.gmcnet.org>
Message-ID: <AB9B81FE435846FF92698B4F4C860A5E@DellDesktop>
Content-Type: text/plain; charset="iso-8859-1"
Ken,
I have Dave Lenzi's offset upper control arms in Double Trouble and when I installed them he noted NOT to set the caster above 5?
because the outer CV joints were at or getting close to the max they could handle at 5? caster when you turn hard left or right.
It might be a good idea to check and see what you've got.
He also noted that 0? caster was what was desired because radial tires like to run flat against the road surface.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
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| Re: [GMCnet] My new Manny 1 ton [message #241021 is a reply to message #240962] |
Sun, 23 February 2014 16:24  |
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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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Jerry,
I'm a bit confused by this statement: "The greater the caster, the greater the load on the front end components for a given weight."
I don't think there's any additional load when you're going straight down the road, however, when you turn the load goes up because
the caster causes the front end to rise.
Your email has caused another synapse to fire and I remembered that DaveL noted that running caster above 5° caused the relief valve
in the power steering pump on his 8.1 Vortec to pop open and relieve.
IIRC the last alignment done on Double Trouble resulted in 4.9° of caster. I don't have any problems with the 455's power steering
pump, however, from time to time when I turn at full lock (can't remember if it's left or right) I can hear the CV joints
"complaining."
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Sharon Work
From my web site, jerrywork.com, or from the web sites of several of our clubs like GMCWS.ORG you can download a presentation I gave
at GMCWS Casa de Fruita a couple of years ago that outlines why we now need alignment specs that are different from the GMC
maintenance manual. Basically, radial ply tires behave very differently from bias ply tires and require different alignment specs.
When GM began offering radial ply tires on our motorhomes around the middle of the production run, they continued to offer bias ply
tires as well. While they did change the alignment specs when changing to radial ply tires on the Olds and Cad passenger cars, they
did not do so for the motorhome. Because of the behavior of radial ply tires under speed, a radial ply tired car will benefit from
greater caster than the same car shod with bias ply tires. But, there are definite limits. The greater the caster, the greater the
load on the front end components for a given weight. For our coaches
running radial ply tires, 3 to 5 degrees of caster seems to be the sweet spot IF the ride height front and rear is correct. More
than 5 and we are on the edge of over loading the front end components and over running the angle at which some of the front end
components were designed to run. Less than 3 and we are on the edge of wandering. Camber for our coaches is also a balance where
too much tilt in at the top is as bad on handling and tire wear as too much tilt out at the top. Zero (straight up and down) seems
to be the best balance given that most of us now run radial ply tires. Toe in or out is largely a function of the condition of all
the front end components. Again, zero seems to be a good balance for most coaches.
Since we all own and drive only one or two of these things it is natural to think that what works for our coach(s) is correct for
all other coaches. As a result, there are many different opinions one will read on this forum. If you really want to deviate from
the 3-5 degrees of caster, zero camber and zero toe, be sure to do the iterative process described in the presentation required to
get your ride height at the factory spec front and rear first. Then set the 3-5, 0, 0 and drive your coach for a while. From
there, do your own thing if you wish, but keep a close eye on tire wear front and rear.
Hope this helps.
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] My new Manny 1 ton [message #241054 is a reply to message #240962] |
Sun, 23 February 2014 20:34 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| Sharon Work wrote on Sun, 23 February 2014 08:38 |
From my web site, jerrywork.com, or from the web sites of several of our clubs like GMCWS.ORG you can download a presentation I gave at GMCWS Casa de Fruita a couple of years ago that outlines why we now need alignment specs that are different from the GMC maintenance manual. Basically, radial ply tires behave very differently from bias ply tires and require different alignment specs. When GM began offering radial ply tires on our motorhomes around the middle of the production run, they continued to offer bias ply tires as well. While they did change the alignment specs when changing to radial ply tires on the Olds and Cad passenger cars, they did not do so for the motorhome. Because of the behavior of radial ply tires under speed, a radial ply tired car will benefit from greater caster than the same car shod with bias ply tires. But, there are definite limits. The greater the caster, the greater the load on the front end components for a given weight. For our coaches
running radial ply tires, 3 to 5 degrees of caster seems to be the sweet spot IF the ride height front and rear is correct. More than 5 and we are on the edge of over loading the front end components and over running the angle at which some of the front end components were designed to run. Less than 3 and we are on the edge of wandering. Camber for our coaches is also a balance where too much tilt in at the top is as bad on handling and tire wear as too much tilt out at the top. Zero (straight up and down) seems to be the best balance given that most of us now run radial ply tires. Toe in or out is largely a function of the condition of all the front end components. Again, zero seems to be a good balance for most coaches.
Since we all own and drive only one or two of these things it is natural to think that what works for our coach(s) is correct for all other coaches. As a result, there are many different opinions one will read on this forum. If you really want to deviate from the 3-5 degrees of caster, zero camber and zero toe, be sure to do the iterative process described in the presentation required to get your ride height at the factory spec front and rear first. Then set the 3-5, 0, 0 and drive your coach for a while. From there, do your own thing if you wish, but keep a close eye on tire wear front and rear.
Hope this helps.
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
===========
Message: 1
Date: Sun, 23 Feb 2014 14:49:42 +1100
From: "Robert Mueller" <robmueller@iinet.net.au>
Subject: Re: [GMCnet] My new Manny 1 ton
To: <gmclist@temp.gmcnet.org>
Message-ID: <AB9B81FE435846FF92698B4F4C860A5E@DellDesktop>
Content-Type: text/plain; charset="iso-8859-1"
Ken,
I have Dave Lenzi's offset upper control arms in Double Trouble and when I installed them he noted NOT to set the caster above 5?
because the outer CV joints were at or getting close to the max they could handle at 5? caster when you turn hard left or right.
It might be a good idea to check and see what you've got.
He also noted that 0? caster was what was desired because radial tires like to run flat against the road surface.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
==============
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GM tire and wheel systems determined what tires where going to be used where. The 1973 monte Carlo was the first to use radial tires. It had a specific front frame section and 5 degrees of Caster. We built 200 non radial vehicles with different front frames. The steering gear and pitman arm loads were high and radials were not rolled out untill individual applications were validated. Tire and wheel systems moved the entire industry from dirt bag bias tires to premium radial tires.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] My new Manny 1 ton [message #241056 is a reply to message #241021] |
Sun, 23 February 2014 20:37 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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""Jerry,
I'm a bit confused by this statement: "The greater the caster, the greater the load on the front end components for a given weight."
I don't think there's any additional load when you're going straight down the road, however, when you turn the load goes up because
the caster causes the front end to rise.
Your email has caused another synapse to fire and I remembered that DaveL noted that running caster above 5° caused the relief valve
in the power steering pump on his 8.1 Vortec to pop open and relieve.
IIRC the last alignment done on Double Trouble resulted in 4.9° of caster. I don't have any problems with the 455's power steering
pump, however, from time to time when I turn at full lock (can't remember if it's left or right) I can hear the CV joints
"complaining."
Rob, the dynamic loads on the gear, pitman arm and tie rods are dramatically higher with increasing caster. The loads are capable of breaking a pitman arm with unpleasant results/
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] My new Manny 1 ton [message #241063 is a reply to message #241062] |
Sun, 23 February 2014 21:01 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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""He also noted that 0° caster was what was desired because radial tires like to run flat against the road surface.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426"'
No, when you hit a bump or pothole.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] My new Manny 1 ton [message #241067 is a reply to message #241063] |
Sun, 23 February 2014 21:14 |
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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,
I goofed when I wrote 0° caster I meant 0° CAMBER.
To make sure I've got it right; the higher the caster the higher the loads on steering components when the vehicle:
1) hits a bump
2) hits a pothole
3) turns left or right
Anything else?
What if. If you're going straight down a smooth road
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Bob de Kruyff
No, when you hit a bump or pothole.
--
Bob
_______________________________________________
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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