| [GMCnet] Alignment question [message #163150] |
Fri, 16 March 2012 10:47  |
glwgmc
Messages: 1014
Registered: June 2004
Karma:
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Senior Member |
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Wish I could, Ken, but we just returned from a 3500 mile jaunt and have a 1000+ mile coming up when we go to Casa de Fruita for the GMCWS rally in April. One of these days I have to stay home and build some furniture to restock our gallery. We sold nearly out by the end of the Christmas season. Good "problem" to have but a time problem for me none the less..
I think the point to stress is that any time the GMC is jacked up for any reason it has to be driven a few miles to fully settle the suspension down to where it will be going down the road. Any jig that sits parallel with the wheel (yours, mine, etc.) will work just fine if the turn plates are low enough to allow the coach to be driven or pushed up on them. If the coach has to be jacked up to fit the turn plates under the wheels or for the mechanic to reach the adjuster cams, then all bets are off.
Once ride height is correct front and rear, then it is straight forward to measure camber, caster and toe on the front and camber on the four rears with any kind of digital angle finder that is accurate to around +- 0.1 degrees across the scale and which can be zeroed to the slope of the pad the GMC is parked on. Tell the audience to be careful of the ones that are only +- 0.1 degrees at zero and ninety degrees. Who knows what they are in between! Using either the Sears laser like you use or the gun sight lasers that I use it is easy to set the steering wheel to center, then set the front wheels to frame parallel using the tie rod end adjusters. Tell them to recheck toe to be sure it is still zero. Use the lasers to check frame parallelism on the rears. If they are not parallel then the arms need to be bent (if only one is off) or shimmed (if both are off the same amount) to get them parallel. Encourage the audience to set the rears to tire top in by one degree to kee
p the coach from over steering at the limit. I am not a fan of differential caster or camber to "correct" for crown in the road as not all roads have the same amount of crown and I think a differential may cause more issues than it is supposed to cure with our GMCs.
Hope this helps and wish I could be there to join in on the fun.
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
www.southernoregonguild.org
www.siskiyouguild.org
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Message: 17
Date: Thu, 15 Mar 2012 20:38:16 -0400
From: Ken Henderson <hend4800@bellsouth.net>
Subject: Re: [GMCnet] Alignment question
To: gmclist@temp.gmcnet.org
Message-ID:
<CANsh1i0o0tNMZFzgZLjKKi2J5_7Piyda2L4YqB7A9+Dp-2BoEg@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Hey, Jerry,
Are YOU coming to Shawnee? If so, I'll be glad to cede the floor to
you for the seminar. Maybe show my jigs as an alternative to yours to
achieve the same result. Of course, one hour won't be enough to go
into all the in's & out's like diagonal biases, ride height
variations, etc. My intention is to postulate most of that as
prerequisite and concentrate on pure alignment using our simple
equipment.
Ken H.
On Thu, Mar 15, 2012 at 2:49 PM, Gerald Work wrote:
> I'm sure you have already checked ride height, but also take a look at weight loading. ?A slight pull can sometimes be caused by a torsion bar loading imbalance offset by differential air in the rear bags. ?Start by checking the air pressure in each bag when your coach is at correct rear ride height. ?If they are not the same, then block the center of the rear at correct ride height, dump 15psi out of both bags and recheck front ride height. ?If that checks out ok then recheck tire pressure and even wear. ?Swap the front tires side to side and see if that helps. ?Start playing with differential camber only if all else checks out. ?Road crown is not consistent so it is hard to set the "right" amount of differential for that reason.
>
> Jerry
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Jerry & Sharon Work
78 Royale
Kerby, OR
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