| [GMCnet] Wheel Spacers [message #170779] |
Thu, 24 May 2012 21:41  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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Very interesting observations. Chart two which shows up to 4 degrees of camber change on bounce is far more than I have been able to measure. Charts one and three which show the stock and 1 ton with relocated upper mounts seem to reflect a similar small camber change on bounce so that appears on the surface to be a good modification. I have no idea how it would effect the many other elements of front end geometry. One that is set by the ride height and location/effective length of the upper control arms and cannot be adjusted is anti-dive geometry that helps keep the front end from adopting an excessive nose down attitude under hard braking. I must be missing something on the two spindle height readings (9" stock and 11" 1 ton) as I can't see how that fan change if the tire and wheel diameter is constant. I also question the nine decimal points shown in measuring top ball joint to bottom ball joint height with a ruler. I suspect that one is a glitch in the spread sheet
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Time will tell but so far most who have installed the 1 ton and have set ride height to factory spec have experienced very positive driving improvements. A few have not and we don't know why or what may be different on their coaches. We have observed that many of the early coaches have welded on frame reinforcing near where the front end components mount that are not present on the later coaches.
Of greatest curiosity to me is that GM originally speced caster at rest at 3 degrees. By the 76 supplement they backed that off to two degrees, likely because of overloading the steering gear at speed when the bias ply tires contact patch moved back resulting in five to six degrees of effective caster. It stayed at two degrees at rest through the 78 supplement even though the tires changed to radials which do not exhibit the backward movement of the contact patch at speed. They also continued to offer bias ply tires as options clear through the end of production. Contrast that with the Toro specs which changed dramatically when they switched to radial ply tires. So, the car engineers had a green light to alter the front end geometry on a car that would continue in production while the coach engineers apparently did not get the same green light since coach production was already planned to be dropped.
Now 40 or so years later we are left to do a bit of experimenting on our own without the knowledge, design models or computing power to do it right. I applaud everyone who tries and reports their antidotal observations to the group. We just will have to sift out what really works from what only appears to work for a short time. Absent any other direct info, I find the 1 ton a most worthwhile upgrade so long as ride height is set to factory spec front and rear and so long as the alignment is done properly front and rear to result in three or four degrees of caster at rest, zero camber, zero toe, front and rear wheels frame parallel, no more than 1 to 2 degrees of tire top in camber on the rears to keep the rear end from coming around on a hard turn and the steering box centered when the front wheels are frame parallel. That seems to be the best combo at this point. But, and it is a big but, over 90% of the coaches we measured coming into the GMCWS rally at Casa de Fruita
last month were front ride heigh LOW, some significantly. That throws everything off so the antidotal observations coming from the drivers of those coaches may or may not be helpful in the long run.
Jerry
Jerry Work
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
glwork@mac.com
http://jerrywork.com
541-592-5360
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Message: 5
Date: Fri, 25 May 2012 09:40:35 +1000
From: "Rob Mueller" <robmueller@iinet.net.au>
Subject: Re: [GMCnet] Wheel Spacers
To: <gmclist@temp.gmcnet.org>
Message-ID: <C83D25D936A44C5FA55DA7A3C34FF2CC@DellDesktop>
Content-Type: text/plain; charset="us-ascii"
Jerry,
Interesting observations re the steering geometry, what do you think about the information Bill Wevers put together?
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Re: GMCMI Tech Session? [message #170050 is a reply to message #169677 ] Thu, 17 May 2012 21:09
This discussion got me wondering how the One Ton Mod affects the front suspension geometry. So I spent the last few days working on
an excel spreadsheet entering in the stock suspension numbers.
And then I plotted the Camber Change, Toe in change and front track change. The results can be seen here:
http://onetonsuspensionmods.shutterfly.com/pictures/9#11
I measured with a tape measure and got these numbers:
Lower Control Arm length = 14.75"
Upper " " = 9.75"
Stock spindle height = 9"
One Ton spindle height = 11" and various other dimensions.
See the images for the numbers I used.
What is interesting is how little toe change and track change there is with the stock suspension designed 50 years ago.
The one ton suspension seems to have a lot of camber and front track change.
I can send you the excel spreadsheet if you are interested.
Regards,
Bill
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Wheel Spacers [message #170785 is a reply to message #170779] |
Thu, 24 May 2012 22:32  |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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Anti dive is controlled by the "splay" or side view canting of the control arms.
The caster spec was driven by limitations of pitman arm loads
The rear camber needs to be at 0 degrees and has no effect on the rear end coming around
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Wheel Spacers [message #170789 is a reply to message #170785] |
Thu, 24 May 2012 22:58 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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BTW, just like the Fiero, I don't think the engineering team knew the GMC was cancelled untill all the work had already been done.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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