Home » Public Forums » GMCnet » [GMCnet] Torque steer and tire wear
| [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:
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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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