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| [GMCnet] Alignment observations from SOOR [message #143575] |
Fri, 16 September 2011 12:07  |
glwgmc
Messages: 1014
Registered: June 2004
Karma:
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We are just back from a fun and informative un-official, non-rally, SOOR event. While we did not have enough coaches there to draw any kind of general conclusions for all 8,000 of our coaches, there were some interesting observations that may be helpful to others.
First, excluding mine, only one coach that came to the SOOR non-rally was at proper ride height when it arrived. All the rest were low in front, rear or both. Being low in front throws off camber, caster and toe all three unless the coach had been specifically aligned at that lower height.
One owner took the time to restore the proper ride height. When he did, he found the camber, caster and toe returned to the nearly correct settings. It took only a bit of toe adjustment to get it spot on. With the front end low all three alignment settings were off. At proper ride height the coach was already aligned correctly. I think we might all learn something from that observation.
With Manny's expert wrenching and unlimited energy level, two owners installed the new one ton V-II front end on their coaches. One was an early 73 and the other was a 29 foot stretch made from a later model. In both cases the install went smoothly. It takes about a day for two people to do it and a day and a half to two days for one person. In both cases the ride heigh adjustment as not touched during the install. Manny has a way of using a chain and leverage to get the new lower control arms on without backing off on the torsion bar adjusters.
On the 73 coach the post-kit ride heigh was about 2" too low in front likely due to the increased leverage resulting from the wheel spacers necessary to allow the 16" Alcoas to clear the much larger brake rotors and calipers. We started with the guess that ride height would change about 1/4" per full turn of the adjuster bolt. It took four tries of adjusting the rear with air, then adjusting the front torsion bars, then driving the coach to settle the suspension, to get the ride height correct. It looks like the effective change in ride height is more like 1/8" per turn. On the later model stretch coach it came out about an inch too low in front but still took four tries to get the ride heigh correct. In both cases it is clear that the torsion bars do not respond linearly to rotation of the adjuster bolt.
Best guess for subsequent coach owners who need to adjust the ride height is the adjustment will be between 1/8" and 1/4" change in ride height for each full turn of the adjuster bolt but that decreases as you make subsequent adjustments. Remember to adjust ONLY after removing the tension on the adjuster bolt and nut with a quality torsion bar unloader tool. We had three different unloader tools available there and only the factory original tool worked well for all the users. The other two sorta worked......
Both of the one ton installs found the camber and caster to be about correct once ride height was properly set when the rear upper A arm was pushed all the way back and the front arm was centered in the slot. On the 73 the owner did have to readjust the front upper A arm cam on one side by 1/8 turn to get camber and caster the same as the other side. In both cases toe did need to be adjusted to get to zero total toe with the steering box and wheel centered.
From my own experience and from what we learned here at SOOR I remain convinced that getting our coaches to proper ride height is the singularly most important thing you can do to improve the handling of your coach. Following that, mounting proper fabric side wall radial ply tires on radial rated rims and inflating the tires to the proper pressure for the weight carried is way more important for safe driving than anything else. If you have an ill handling coach, do these things first, before you start swapping components so you have a proper base line. Then set total toe to zero and see how your coach drives. If you still feel like you are all over the road, then you will know you have worn out A arm bushings, ball joints, tie rod ends, transfer lever pivots and/or steering components. But, once your coach is at the correct ride height and you have the right tires properly inflated (which will be about 60 to 65 psi front and 55 to 60 psi rear on most 26 footers) and you
set total toe to zero, you may be quite surprised at how well your coach drives right now.
On the SOOR coaches we checked we found several had at least one bent rear bogie arm even though tire wear did not seem excessive. Most had the proper rear camber.
The alignment kit worked well and the users reported no problems in getting accurate measurements or in understanding the step-by-step instructions. So, over the weekend I will publish release version 1.0 that you can download for free. It will be on the GMC page of my web site http://jerrywork.com and can be posted on any GMC related web site with proper attribution. It is a .pdf file that includes information on why even competent professional alignment shops may struggle to properly align our GMC motor coaches, what you need to check to see if the job was done correctly or not, step-by-step instructions on how to use the inexpensive alignment kit I developed, and instructions on how you can build one to donate to your GMC club if you prefer to build rather than buy. 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
Founder of the Southern Oregon Guild
www.southernoregonguild.org
Member of the Siskiyou Guild
www.siskiyouguild.org
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Jerry & Sharon Work
78 Royale
Kerby, OR
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