Home » Public Forums » GMCnet » [GMCnet] 1 ton alignment - lessons learned, part 2
| [GMCnet] 1 ton alignment - lessons learned, part 2 [message #137587] |
Fri, 05 August 2011 11:26  |
glwgmc
Messages: 1014
Registered: June 2004
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This is a continuation of my comments following the installation of the 1 ton front end and what I learned during and following that process about alignment and ride height on our coaches.
In my previous post I said I had the ride height spot on when we took the coach to the alignment shop. When they were finished the professional alignment shop indicated they lowered ride height a bit to "even things out". When we returned from our 750 mile trip I found the ride height low by two full inches on both sides. By the time I finished putting the ride height back where it should have been I had to turn both torsion bar adjuster bolts EIGHT FULL TURNS. So, what the alignment guy said was "a bit" turns out to have been a bunch!
The point here is not to denigrate the alignment guy (even though I would like to thump him on the head), the point is if this reputable alignment shop with a tech who said he had done lots of these GMC motorhomes ignored my instruction not to monkey with the ride height and chose instead to use his "experience" to lower it that much, then what is happening with all the other alignments being done on our coaches? Is it just luck of the draw that the ride height and alignment turns out to be correct after driving the coach enough to fully settle the suspension?
My surmise is that by raising the wheels off the ground to make his adjustments the coach did not settle down when he checked the measurements so he lowered the ride height to get it to come down on his rack. After several iterations of this the ride height wound up adjusted wildly low. By the time I drove the coach the suspension settled to the point that it became two inches too low throwing caster and camber out the window and negating the whole alignment process.
So, the real lesson I learned through all of this is the requirement to drive the coach further than you think you will need to in order to settle the new suspension components before measuring the result of any change you make to either ride height or alignment. That means you will either need (1) a very patient and accommodating alignment shop and lots of time, or (2) plan on doing the alignment and ride height adjustments yourself. I don't know of an option (3).
As to the question about the need for turntables and setting/measuring caster -
I think they are necessary as we cannot be sure that 35 plus years later the frame and A arm attachment points are where they started out at the factory nor can we be sure that the two offset bushings that we have to press into the rear upper A arm go in exactly in the same spot on both sides. So, while turning the rear upper A arm adjustment cams to pull that end of the A arm as far toward the center of the coach as possible will result in maximum caster, it will not necessarily result in maximum EVEN caster. To achieve that one needs turntables and a way to measure the number of degrees the camber changes when the wheels are turned 15 to 20 degrees (determined by the measuring device itself) inward and outward. That difference is the amount of caster.
In addition to maximum even caster on both sides we also need to set the initial camber with the wheels in the straight ahead position to zero by turning the front upper A arm adjustment cams. When either cam is turned, both camber with the wheels straight ahead and resulting caster are effected. Raising or lowering the ride height will also effect both caster and camber. And, any time the wheels are jacked up off the ground we need to drive the coach quite a bit to get the suspension to fully settle before checking our measurements.
It may be fine for some to simply set the tire pressure and ride height correctly, then turn the rear upper A arm adjuster to maximum caster, and then turn the wheels straight ahead to set camber to zero and toe to zero and call it good. But, from what I learned we can only call that our initial or base line setting. Once we drive the coach a number of miles to fully settle the new suspension components, the resulting ride height change alone might well throw caster and camber both way off from where we thought they were so it is necessary in my opinion to remeasure ride height, caster, camber and toe to confirm that they are where they should be. That can only be done accurately with turntables and a device designed to measure caster as well camber and toe with the wheels in the straight ahead position.
We cannot expect or assume that an alignment shop will get this right either. I doubt that my experience is a unique one. My guess is if we measure all of the coaches in our collective fleet we will find that a high percentage of them will be off quite a bit in ride height or caster or camber or toe or all four. Hence, my conclusion that each of our clubs need to assemble the simple kit of tools and a good set of instructions that will allow all our owners to check their coach themselves. This is important for safety and for long term drivability. 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
541-592-5360
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Jerry & Sharon Work
78 Royale
Kerby, OR
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[GMCnet] 1 ton alignment - lessons learned, part 2
By: glwgmc on Fri, 05 August 2011 11:26 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: Kosier on Fri, 05 August 2011 13:22 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: WD0AFQ on Fri, 05 August 2011 13:29 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: KB on Fri, 05 August 2011 14:04 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: KB on Fri, 05 August 2011 17:11 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: USAussie on Fri, 05 August 2011 19:19 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: Kosier on Fri, 05 August 2011 22:04 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: KB on Fri, 05 August 2011 22:15 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: KB on Fri, 05 August 2011 22:17 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: KB on Sat, 06 August 2011 13:04 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: KB on Sat, 06 August 2011 13:31 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: KB on Sat, 06 August 2011 13:41 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
By: KB on Sun, 07 August 2011 11:40 |
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Re: [GMCnet] 1 ton alignment - lessons learned, part 2
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