Home » Public Forums » GMCnet » [GMCnet] torsion bar summary
| [GMCnet] torsion bar summary [message #157539] |
Sat, 21 January 2012 22:10  |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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The following is a summary of information on issues with the Torsion Bars
in the GMC.
1 all of the available data says the torsion bar problems appear to be on
the driver side TBs.
2 All of the occurrences have happened on OEM front ends
3 *none* of the occurrences happened on " spacer or one-ton" front ends
(not the problem)
4 Our favorite SOB (SteveF) feels the problems occur because of worn
bushings allowing movement of the torsion bar, in the suspension.
5 there is no indication of a "fatigued" torsion bar being the root cause
of the problems, or even exists ( one did break)
6 universally the "pork chop" bolts on the driver side are not long enough,
(showing the problem, or a weight difference on all GMCs)
7 Our favorite SOB, feels that if you change the bushings, you have to
reinforce the TB socket and the lower control arms
8 since our favorite SOB, no longer rebuilds lower control arms (is this
true?), these 40 year old systems are at risk
9 the *future* path to solve this problem is to install the "available"
one-ton front end with all of the above done , plus all new parts(bearings,
bushings,cv joints, seals, boots, etc)
so
I am open to any *data* that seems to counter these assertions,
looking for new directions ( I am willing to be wrong;>)
gene
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
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| Re: [GMCnet] torsion bar summary [message #157543 is a reply to message #157539] |
Sat, 21 January 2012 22:58  |
Kirk
Messages: 80
Registered: April 2008
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I concur Gene; however my pork chop adjusting bolt on the "passenger' side is bottomed out. I'll try the longer bolt but I think a different pork chop (probably both of them) is in my future.
Kirk & Eloise Yeager -
Motorcyclists/RVers/Dog Lovers -
77 Royale 455/TBI/3:55 -
49ers - N. Nevada -
NdnKirk at Gmail dot com
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| Re: [GMCnet] torsion bar summary [message #157554 is a reply to message #157549] |
Sun, 22 January 2012 02:03 |
pickle4k
Messages: 129
Registered: January 2011
Location: San Leandro
Karma: 0
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Gene,
My coach was leaning to the passenger side when I got it. The adjustment bolt is maxed out now and still the ride height is a little low. After the one-ton install the coach leaned again to the passenger side and needed to be adjusted again, even without disturbing the set of the bolt. I am waiting for the new MAX Suspension pork chop to be built and will install one on the passenger side to get the coach level and at proper height.
Regards,
Nick R. NorCal
76-23'Transmode-Norris
Rear Bath and
75-26' Avion
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| Re: [GMCnet] torsion bar summary [message #157561 is a reply to message #157539] |
Sun, 22 January 2012 07:11 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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Gene,
I am still in the business of rebuilding lower control arms. I have never
stopped rebuilding them. As the newer, improved ones appear at Applied,
they will cost less, and have one new additional reenforcement not seen
before on the left coast.
On Sat, Jan 21, 2012 at 9:10 PM, gene Fisher <mr.erfisher@gmail.com> wrote:
> The following is a summary of information on issues with the Torsion Bars
> in the GMC.
>
> 1 all of the available data says the torsion bar problems appear to be on
> the driver side TBs.
> 2 All of the occurrences have happened on OEM front ends
> 3 *none* of the occurrences happened on " spacer or one-ton" front ends
> (not the problem)
> 4 Our favorite SOB (SteveF) feels the problems occur because of worn
> bushings allowing movement of the torsion bar, in the suspension.
> 5 there is no indication of a "fatigued" torsion bar being the root cause
> of the problems, or even exists ( one did break)
> 6 universally the "pork chop" bolts on the driver side are not long enough,
> (showing the problem, or a weight difference on all GMCs)
> 7 Our favorite SOB, feels that if you change the bushings, you have to
> reinforce the TB socket and the lower control arms
> 8 since our favorite SOB, no longer rebuilds lower control arms (is this
> true?), these 40 year old systems are at risk
> 9 the *future* path to solve this problem is to install the "available"
> one-ton front end with all of the above done , plus all new parts(bearings,
> bushings,cv joints, seals, boots, etc)
>
> so
> I am open to any *data* that seems to counter these assertions,
>
> looking for new directions ( I am willing to be wrong;>)
> gene
>
>
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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--
Fathom the hypocrisy of a nation where every citizen must prove they have
health insurance......but not everyone has to prove they're a citizen.
Steve Ferguson
Sierra Vista, AZ
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| Re: [GMCnet] torsion bar summary [message #157568 is a reply to message #157539] |
Sun, 22 January 2012 09:10 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Gene,
There is a possible solution that you haven't addressed; probably because
it's not yet common knowledge. Metal has been cut on an adapter to allow
the 1-3/4" Chevy truck Torsion Bars to be used on the GMC. The design,
which has not yet been installed anywhere, will distribute the torsion load
over the OEM socket much better than the OEM TB does. It will probably
work even in a failed socket, and should eliminate the need for any
reinforcement of that area.
In addition, the use of the later, more readily available TB's, will also
allow one to choose from a wide range of TB strengths. The GMC torsion
bars are apparently rated at either 4000 ft-lb or 4200 ft-lb torque; Chevy
truck TB's are available in ~200 ft-lb increments from 4553 ft-lb to 9054
ft-lb ratings. Compensation for spacers will be much easier with those
available.
Re: SuspensionMaxx adjustable "pork chops": The originals are really not
suitable for use on the GMC. Those devices are similar to the OEM pork
chop, but are larger overall than those on the GMC, making it necessary to
either modify the #4 cross member, where the TB ends, or the "pork chop"
itself. Neither is a good idea. While the cross member does not transfer
much load into the chassis, it does react each side's torsion bar load
against that from the other side -- a LOT of force. Opening up the lower
side of the TB opening into the cross member may not result in serious
degradation of the member. Grinding or cutting the TOP of the cross
member, where the upper part of the "pork chop" rests, could be
catastrophic -- and quickly. Modifying the SuspensionMaxx "key", or
"torsion bar lever" (our "pork chop") should NOT be attempted. The
inventor/designer/manufacturer of that device is himself working on that
problem -- carefully and with knowledge of the stresses involved -- DON'T
try to second guess him. I'm in frequent contact with him and can assure
you that he will do it RIGHT.
Patience.
HTH,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Sat, Jan 21, 2012 at 11:10 PM, gene Fisher <mr.erfisher@gmail.com> wrote:
> The following is a summary of information on issues with the Torsion
> Bars in the GMC.
> ...
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] torsion bar summary [message #157572 is a reply to message #157568] |
Sun, 22 January 2012 09:32 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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Good
I hoped that something would come from the previous talks.
the information I collected, showed that the problems were endemic with
the OEM front end not spacers, etc
I hope this does not involve moving the cross member forward, because I
don't think most owners would be up to doing that (like me ;>)
good luck
now you need another GMC to test on....
gene
On Sun, Jan 22, 2012 at 7:10 AM, Ken Henderson <hend4800@bellsouth.net>wrote:
> Gene,
>
> There is a possible solution that you haven't addressed; probably because
> it's not yet common knowledge. Metal has been cut on an adapter to allow
> the 1-3/4" Chevy truck Torsion Bars to be used on the GMC. The design,
> which has not yet been installed anywhere, will distribute the torsion load
> over the OEM socket much better than the OEM TB does. It will probably
> work even in a failed socket, and should eliminate the need for any
> reinforcement of that area.
>
> In addition, the use of the later, more readily available TB's, will also
> allow one to choose from a wide range of TB strengths. The GMC torsion
> bars are apparently rated at either 4000 ft-lb or 4200 ft-lb torque; Chevy
> truck TB's are available in ~200 ft-lb increments from 4553 ft-lb to 9054
> ft-lb ratings. Compensation for spacers will be much easier with those
> available.
>
> Re: SuspensionMaxx adjustable "pork chops": The originals are really not
> suitable for use on the GMC. Those devices are similar to the OEM pork
> chop, but are larger overall than those on the GMC, making it necessary to
> either modify the #4 cross member, where the TB ends, or the "pork chop"
> itself. Neither is a good idea. While the cross member does not transfer
> much load into the chassis, it does react each side's torsion bar load
> against that from the other side -- a LOT of force. Opening up the lower
> side of the TB opening into the cross member may not result in serious
> degradation of the member. Grinding or cutting the TOP of the cross
> member, where the upper part of the "pork chop" rests, could be
> catastrophic -- and quickly. Modifying the SuspensionMaxx "key", or
> "torsion bar lever" (our "pork chop") should NOT be attempted. The
> inventor/designer/manufacturer of that device is himself working on that
> problem -- carefully and with knowledge of the stresses involved -- DON'T
> try to second guess him. I'm in frequent contact with him and can assure
> you that he will do it RIGHT.
>
> Patience.
>
> HTH,
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI+ & EBL
> www.gmcwipersetc.com
>
>
>
> On Sat, Jan 21, 2012 at 11:10 PM, gene Fisher <mr.erfisher@gmail.com>
> wrote:
>
> > The following is a summary of information on issues with the Torsion
> > Bars in the GMC.
> > ...
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
_______________________________________________
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Unsubscribe or Change List Options:
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| Re: [GMCnet] torsion bar summary [message #157573 is a reply to message #157566] |
Sun, 22 January 2012 09:43 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| mgrue wrote on Sun, 22 January 2012 08:55 |
This discussion prompts a question I hope someone can answer. How many pounds does it take to make one side squawt one inch? In other words how many pounds per inch is the spring rate on the front end.
Mark
|
It is my contention that the front leaning and running out of adjustment on the bolt is caused by:
1. Torsion bar twisted in the socket a-frame socket
2. Worn A-frame bushings.
3. Incorrect rear air bag adjustment. The only way you are going to find this is:
3a. with a set of scales or
3b. by blocking the rear. To do this find a flat concrete floor and put equal height blocks under the bogie support frame and deflate the bags until it is sitting on the blocks.
The blocks do not need to be exactly the same as the rear ride height but they should be close. The important thing is they need to be EQUAL in height. Once that is done then the rear air pressure and loading is not a factor affecting the front.
Now the front ride heights can be checked. I prefer to check the heights while sitting on a set of scales and adjusting the torsion bars to make the weights equal. Then I check the actual heights to see what they look like.
If you do not have access to scales then set them to the correct ride height but it is anyone's guess as to how much weight is actually on each wheel when you finish.
Once the above is set then air up the bags again. If you still have the lean after airing them up then your problem is with the rear inflation and not the front.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] torsion bar summary [message #157576 is a reply to message #157572] |
Sun, 22 January 2012 09:39 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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No, the adapter should not require any change to the location of the #4
cross member. The adapter itself should compensate for the 4-1/4"
difference in TB lengths.
I think I'll let someone else be the guinea pig on this one. :-)
Ken H.
On Sun, Jan 22, 2012 at 10:32 AM, gene Fisher <mr.erfisher@gmail.com> wrote:
> Good
>
> I hoped that something would come from the previous talks.
> the information I collected, showed that the problems were endemic with
> the OEM front end not spacers, etc
>
> I hope this does not involve moving the cross member forward, because I
> don't think most owners would be up to doing that (like me ;>)
>
> good luck
> now you need another GMC to test on....
>
> gene
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] torsion bar summary [message #157585 is a reply to message #157573] |
Sun, 22 January 2012 10:23 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
Ken,
I can see how you'd get correct ride heights with your method and scales.
Without them, how do you keep the two sides' loading equal? With the rear
heights fixed, adjusting either front side will bring the other to almost
the same height, frame/body twist being the only thing keeping them from
being the same.
I prefer to:
1. Remove the front wheels and jack under the center of the main (#2 /
front) cross member. Set the front ride heights so that their AVERAGE is
at spec.
2. Adjust the rear ride heights in "Travel/Auto". This allows the air
suspension to compensate for lateral weight differences, regardless of
their longitudinal location. The front ride heights should assume their
correct values when the rears are set. If they don't, obviously there's
twist in the body/frame -- a whole new problem.
3. Set the suspension to "Hold". The bags now contain fixed pressures
adequate to level the coach laterally.
4. Re-mount the front wheels and adjust the front ride heights. Any
discrepancy between them now MUST be due to TB adjustment differences.
Iteration between sides will be necessary. Scales could eliminate that
necessity.
JWID,
Ken H.
On Sun, Jan 22, 2012 at 10:44 AM, Ken Burton wrote:
It is my contention that the front leaning and running out of adjustment on
> the bolt is caused by:
>
> 1. Torsion bar twisted in the socket a-frame socket
>
> 2. Worn A-frame bushings.
>
> 3. Incorrect rear air bag adjustment. The only way you are going to find
> this is:
>
> 3a. with a set of scales or
>
> 3b. by blocking the rear. To do this find a flat concrete floor and put
> equal height blocks under the bogie support frame and deflate the bags
> until it is sitting on the blocks.
> The blocks do not need to be exactly the same as the rear ride height but
> they should be close. The important thing is they need to be EQUAL in
> height. Once that is done then the rear air pressure and loading is not a
> factor affecting the front.
>
> Now the front ride heights can be checked. I prefer to check the heights
> while sitting on a set of scales and adjusting the torsion bars to make the
> weights equal. Then I check the actual heights to see what they look like.
>
> If you do not have access to scales then set them to the correct ride
> height but it is anyone's guess as to how much weight is actually on each
> wheel when you finish.
>
> Once the above is set then air up the bags again. If you still have the
> lean after airing them up then your problem is with the rear inflation and
> not the front.
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] torsion bar summary [message #157618 is a reply to message #157567] |
Sun, 22 January 2012 12:59 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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I still play the guitar and am still living the good life.
Yes, If you want the coach to handle like new, make everything new and
don't try to shave a buck here or there. Once that is done, correctly set
the ride height and get the best wheel alignment possible.
If someone can adapt a later TB for use in the GMC, I would say go for
it. No matter what TB you use, the bottom line is you still have to do the
above.
I have given up on the new tubular lower control arms I was so hoping
would be available by now. The engineer who was designing the prototypes
pretty much went to all ahead STOP when I changed the design on him to
utilize the 1T knuckles and ball joint. He had made it far enough to solve
the TB socket issue and also found an easily replaceable ball joint that
had 30% more surface area. That makes two companies that have given up on
the project (or gone out of business) and cost Jim K. and I a lot of time,
money and parts.
As you say Gene, grumble, grumble, snort.........
On Sun, Jan 22, 2012 at 7:58 AM, gene Fisher <mr.erfisher@gmail.com> wrote:
> > Gene,
> > I am still in the business of rebuilding lower control arms. I have
> never
> > stopped rebuilding them. As the newer, improved ones appear at Applied,
> > they will cost less, and have one new additional reenforcement not seen
> > before on the left coast.
> >
>
> GOOD NEWS
> I thought you were playing the guitar, and living the good life.
>
> glad to have you here, any thoughts on torsion bars?
>
> gene
>
>
>
>
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Fathom the hypocrisy of a nation where every citizen must prove they have
health insurance......but not everyone has to prove they're a citizen.
Steve Ferguson
Sierra Vista, AZ
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| Re: [GMCnet] torsion bar summary [message #157675 is a reply to message #157561] |
Sun, 22 January 2012 20:47 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Steve,
Those of us on the far south coast would sure like to see what the additional reinforcement is so we can incorporate it!
Regards,
Rob M.
-----Original Message-----
From: Steven Ferguson
Gene,
I am still in the business of rebuilding lower control arms. I have never stopped rebuilding them. As the newer, improved ones
appear at Applied, they will cost less, and have one new additional reenforcement not seen before on the left coast.
Steve
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] torsion bar summary [message #157677 is a reply to message #157623] |
Sun, 22 January 2012 20:54 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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| Ken Henderson wrote on Sun, 22 January 2012 13:34 |
Dennis,
Thanks for that -- I'd somehow missed it.
I'm not convinced the buttresses are necessary. Their inclusion assumes
the existence of lateral forces that I can't envision occurring.
Ken H.
|
Well with a lot of my "engineering" I'm not always sure how to make things "just strong enuf" for the intended use. However I can usually ensure that what I do is more than strong enough for what I intend +++ a "bit more". That may be what was going on with the pictured a-arm mods. Hopefully the poster of those pics will comment.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] torsion bar summary [message #157701 is a reply to message #157585] |
Mon, 23 January 2012 00:10 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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[quote title=Ken Henderson wrote on Sun, 22 January 2012 10:23]Ken,
I can see how you'd get correct ride heights with your method and scales.
Without them, how do you keep the two sides' loading equal? With the rear
heights fixed, adjusting either front side will bring the other to almost
the same height, frame/body twist being the only thing keeping them from
being the same.
I prefer to:
1. Remove the front wheels and jack under the center of the main (#2 /
front) cross member. Set the front ride heights so that their AVERAGE is
at spec.
2. Adjust the rear ride heights in "Travel/Auto". This allows the air
suspension to compensate for lateral weight differences, regardless of
their longitudinal location. The front ride heights should assume their
correct values when the rears are set. If they don't, obviously there's
twist in the body/frame -- a whole new problem.
3. Set the suspension to "Hold". The bags now contain fixed pressures
adequate to level the coach laterally.
4. Re-mount the front wheels and adjust the front ride heights. Any
discrepancy between them now MUST be due to TB adjustment differences.
Iteration between sides will be necessary. Scales could eliminate that
necessity.
JWID,
Ken H.
I have read this 4 times and I'm not sure what you are doing by jacking up the front end and removing the wheels.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] torsion bar summary [message #157725 is a reply to message #157701] |
Mon, 23 January 2012 07:54 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
Just getting all bias from the front end out of the equation: Removing the
wheels allows the height to be set exactly without any lateral effect from
them. If the average of the sides' ride heights is on-spec, then when the
rear ride heights are set, the fronts should be also (except for any
permanent body/chassis twist). Then it's just a matter of setting the TB's
to achieve equal loading on them, the balance having been set in the rear.
Ken H.
On Mon, Jan 23, 2012 at 1:10 AM, Ken Burton wrote:
>
> I have read this 4 times and I'm not sure what you are doing by jacking up
> the front end and removing the wheels.
> --
>
_______________________________________________
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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