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| [GMCnet] More on torsion bars [message #157583] |
Sun, 22 January 2012 10:15  |
Gerald Work
Messages: 102
Registered: June 2010
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Hi Gene,
One item I would add to your list is that we know the rear ride height has a big effect on front ride height and therefore weight transfer and torsion bar loading. I have no evidence whether improperly set rear ride height plays a role in the torsion bar/pork chop issue or not, but I don't think it can be ignored as a potential causal factor.
Jerry Work
78 Royale on the road again,
900 miles and counting on this trip,
70,000 and counting since buying the coach 1/03
Sent from my iPad
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| Re: [GMCnet] More on torsion bars [message #157594 is a reply to message #157583] |
Sun, 22 January 2012 11:14  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Jerry, I try to visualize the GMC ride height in the following way. Draw
straight lines from the center of the frame slots in an X fashion front to
rear. Where the lines intersect, place an imaginary fulcrum (balance
point). Then imagine what effect the raising or lowering any one of the 4
corners will do to the other 3. If you lift the left rear, it has some
effect on all the others. Same can be said for all the others. That is why
when I do ride height, I always do the back of the coach first, and why I
prefer to use rigid jack stand like supports under the rear frame slots. I
can eliminate the effect that adjusting the front torsion bars will have on
the rear ride height. It just simplifies the thought process by eliminating
half of the variables. This just works for me, and might for others also.
You have done enough of this stuff, that I am probably preaching to the
choir here, but others who read this are in GREAT NEED of some less
complicated thinking when it comes to ride height. It is not just a static
adjustment. It affects dynamic loading on all the suspension and steering
components as well. Just a Sunday morning brain bubble rising to the
surface. Have fun in Quartzite. I wish I was there with you, but I have
GMCs that need my attention. (not mine).
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sun, Jan 22, 2012 at 8:15 AM, Gerald Work <glwork@me.com> wrote:
> Hi Gene,
>
> One item I would add to your list is that we know the rear ride height has
> a big effect on front ride height and therefore weight transfer and torsion
> bar loading. I have no evidence whether improperly set rear ride height
> plays a role in the torsion bar/pork chop issue or not, but I don't think
> it can be ignored as a potential causal factor.
>
> Jerry Work
> 78 Royale on the road again,
> 900 miles and counting on this trip,
> 70,000 and counting since buying the coach 1/03
>
> Sent from my iPad
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] More on torsion bars [message #157624 is a reply to message #157583] |
Sun, 22 January 2012 14:06 |
captjack
Messages: 271
Registered: February 2010
Location: Sebastopol, California
Karma: 1
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James,
I guess I don't understand your method. I tried to use it to adjust the front height by putting precisely measured blocks under the rear slots to insure their proper heights. Then I adjusted the front torsion bars. But, upon removing the blocks, returning the rear support to the bogies and starting to adjust the rear bags I found the front height way too high. A little thought, rather than blindly proceeding as I am sometimes want to do, caused me to realize that by supporting the coach well behind the bogie loading point I was increasing the load on the front end resulting in my misadjustment. So, could you tell me more about your method.
Thanks,
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
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| Re: [GMCnet] More on torsion bars [message #157627 is a reply to message #157624] |
Sun, 22 January 2012 14:52 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Jack, I will try to step by step it for you.
1. Verify that all tires are at the correct pressure. Very important.
2. Drive the coach for a few miles to warm up the suspension bags and
suspension bushings. When you approach your work area, drive straight in
and making sure the front wheels are pointing straight ahead, stop the
coach using as few brakes as possible.
3. Raise the rear of the coach an inch or two over ride height, place
the stands under the slots in the rear of the frame, and lower the coach
onto the stands using the suspension controls, or very slowly let the air
out of the schrader valves until the frame just touches the stands. (My
thinking here is to move the coach up and down as little as possible so as
not to disturb the front ride height.
4. Very carefully measure the front ride height. Write it down. I
usually start with the side that is the lowest, and in my experience,
unless some Knot headed alignment shop has been at work, the coaches are
almost always too low in front. Assume nothing. Check everything.
5. After the front ride heights have been documented, start adjusting
the torsion bar pork chop by the following method. Placing a floor jack of
the appropriate size under the engine cradle crossmember, not the radiator
support and raise the front end until the ride height is correct.
6. Place the torsion bar adjusting tool around the cross member that
contains the pork chop, and adjust it until the adjustment bolt loosens in
the dimple in the end of the porkchop.
DO NOT RAISE THE FRONT OF THE COACH WITH THE TORSION BAR UNLOADER TOOL! It
is not designed to do that, and DO NOT use an air impact wrench on it to
make the adjustment. BE SURE to lubricate the end of the tool as well as
the threads on the center bolt. Because I am kind of anal when it comes to
fasteners, at this time I usually remove the adjustment bolt completely
along with the nut. I generally throw both pieces in the glass beader and
remove all the rust and scale from both pieces. I then very completely
remove all glass bead residue from both pieces and use thread chaser dies
and taps to clean out and straighten out the threads. Screw in the bolt
into the nut and check the fit. If it is able to be turned, but does not
coast when an attempt to spin it is tried, it is probably ok to reuse. Too
loose, replace them both. These two pieces maintain your adjustment. If
they are bad, so is your adjustment.
7. Replace the bolt and nut and screw the bolt into the nut until the
rounded end of the bolt just comes snug into the dimple. Repeat the process
on the opposite side of the coach.
When both sides have been adjusted, remove the torsion bar unloader tool,
lower the coach jack, remove the stands in the rear and test drive the
coach for a couple of miles.
8. Return to the work area the same way I described earlier and reset
the rear ride height the same way as before and recheck your front ride
height. It will not be too high, more than likely will be a little bit low.
Readjust as before. You must drive the coach after the front end adjustment
is changed. Trust me on this, it is important.
Any other details, contact me off net because they will be lengthy and
subject to editing by the monitors of the net. I will be doing training
seminars at Casa de Fruta GMCWS Spring rally on this very thing, along with
Manny T, Gerry Work, Gary Bovee, and Armand and Frank Condos will have
scales there to weigh the coaches. If you are west of the Mississippi, plan
to attend if you can.
Jim Hupy GMCWS Tech VP
Salem, OR
78 GMC Royale 403
On Sun, Jan 22, 2012 at 12:06 PM, Jack Christensen <captjack@sonic.net>wrote:
>
>
> James,
> I guess I don't understand your method. I tried to use it to adjust the
> front height by putting precisely measured blocks under the rear slots to
> insure their proper heights. Then I adjusted the front torsion bars. But,
> upon removing the blocks, returning the rear support to the bogies and
> starting to adjust the rear bags I found the front height way too high. A
> little thought, rather than blindly proceeding as I am sometimes want to
> do, caused me to realize that by supporting the coach well behind the bogie
> loading point I was increasing the load on the front end resulting in my
> misadjustment. So, could you tell me more about your method.
> Thanks,
> --
> Jack Christensen - K6ROW,
> '76 Glenbrook/Clasco - "The Silver Bullet",
> '65 Clark Cortez,
> Sebastopol, CA
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] More on torsion bars [message #157652 is a reply to message #157627] |
Sun, 22 January 2012 17:08 |
captjack
Messages: 271
Registered: February 2010
Location: Sebastopol, California
Karma: 1
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Senior Member |
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Thanks Jim,
My failure was in your step 3. Rather than leave the weight on the bogies, I transferred it all to the blocks by deflating the bags and it went downhill from there.
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
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| Re: [GMCnet] More on torsion bars [message #157654 is a reply to message #157627] |
Sun, 22 January 2012 17:54 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Jim,
I'm afraid I don't follow the rationale nor the steps of your procedure.
Disregarding the absence of any adjustment of the rear ride heights (which
I assume you've already done or plan to do later) the hard fixing of the
rear heights seems to abrogate the "X" principle you presented earlier. If
the two aft points of the X are fixed, how can the forward ends move other
than together? Ignoring box/frame flexing, adjusting one front side should
be followed precisely by the other.
I'm a bit baffled by the front ride height adjustment procedure: Do you
jack under first one side and then the other, or under the center of the
cross member? With the rear heights fixed, I guess it doesn't much matter.
It's been a long day -- maybe I'm missing something? I suppose if you
adjust the rear ride height after the front, weight imbalances will be
corrected, I just have difficulty visualizing it "backward" and believe the
front heights will be disturbed.
Ken H.
On Sun, Jan 22, 2012 at 3:52 PM, James Hupy wrote:
> Jack, I will try to step by step it for you.
> 1. Verify that all tires are at the correct pressure. Very important.
> 2. Drive the coach for a few miles to warm up the suspension bags and
> suspension bushings. When you approach your work area, drive straight in
> and making sure the front wheels are pointing straight ahead, stop the
> coach using as few brakes as possible.
> 3. Raise the rear of the coach an inch or two over ride height, place
> the stands under the slots in the rear of the frame, and lower the coach
> onto the stands using the suspension controls, or very slowly let the air
> out of the schrader valves until the frame just touches the stands. (My
> thinking here is to move the coach up and down as little as possible so as
> not to disturb the front ride height.
> 4. Very carefully measure the front ride height. Write it down. I
> usually start with the side that is the lowest, and in my experience,
> unless some Knot headed alignment shop has been at work, the coaches are
> almost always too low in front. Assume nothing. Check everything.
> 5. After the front ride heights have been documented, start adjusting
> the torsion bar pork chop by the following method. Placing a floor jack of
> the appropriate size under the engine cradle crossmember, not the radiator
> support and raise the front end until the ride height is correct.
> 6. Place the torsion bar adjusting tool around the cross member that
> contains the pork chop, and adjust it until the adjustment bolt loosens in
> the dimple in the end of the porkchop.
> DO NOT RAISE THE FRONT OF THE COACH WITH THE TORSION BAR UNLOADER TOOL! It
> is not designed to do that, and DO NOT use an air impact wrench on it to
> make the adjustment. BE SURE to lubricate the end of the tool as well as
> the threads on the center bolt. Because I am kind of anal when it comes to
> fasteners, at this time I usually remove the adjustment bolt completely
> along with the nut. I generally throw both pieces in the glass beader and
> remove all the rust and scale from both pieces. I then very completely
> remove all glass bead residue from both pieces and use thread chaser dies
> and taps to clean out and straighten out the threads. Screw in the bolt
> into the nut and check the fit. If it is able to be turned, but does not
> coast when an attempt to spin it is tried, it is probably ok to reuse. Too
> loose, replace them both. These two pieces maintain your adjustment. If
> they are bad, so is your adjustment.
> 7. Replace the bolt and nut and screw the bolt into the nut until the
> rounded end of the bolt just comes snug into the dimple. Repeat the process
> on the opposite side of the coach.
> When both sides have been adjusted, remove the torsion bar unloader tool,
> lower the coach jack, remove the stands in the rear and test drive the
> coach for a couple of miles.
> 8. Return to the work area the same way I described earlier and reset
> the rear ride height the same way as before and recheck your front ride
> height. It will not be too high, more than likely will be a little bit low.
> Readjust as before. You must drive the coach after the front end adjustment
> is changed. Trust me on this, it is important.
>
...
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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] More on torsion bars [message #157697 is a reply to message #157627] |
Sun, 22 January 2012 23:32 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I disagree with your blocking the frame at the rear adjustment measurement holes. You have now changed the fulcrum and the weight changes accordingly on the fronts We did this once while the fronts were on the scales and found the weight increased significantly on the fronts when we blocked the rear anywhere behind the the spot between the bogies. When you block the rear you need the support the coach between the wheels in the area where the jack goes.
One other thing we discovered was a 1/4" difference on one side of the rear made a 100 pound difference on the opposite side front. This is why it is important to block the rears at an exact equal height when adjusting the fronts. This is more important than getting the pair of rear heights exactly correct when adjusting the fronts.
I think the problem people have with this concept is the torsion bars and air bags both flex to absorb the first amount of unequal side to side weight without moving the coach up or down. Only after some unknown amount of additional weight is absorbed does changing the adjustment actually move the coach up or down.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] More on torsion bars [message #157699 is a reply to message #157654] |
Sun, 22 January 2012 23:32 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Ken, I omitted some steps because I didn't want to have my post chopped, as
has happened to me before many times on complex, wordy responses. It was
incomplete on the rear ride height adjustments intentionally. I believe the
object of the discussion was torsion bar adjustments, not overall or rear
adjustments. I tried to only concentrate on the importance of having the
rear at ride height before any attempt is made to adjust the torsion bars.
That is why I render the rear rigid. The X illustration was for the purpose
of illustrating that adjusting one end or one side has an effect on the
opposite side or corner. It just makes the solution too complex if one
consideres what happens to the right rear when you adjust the left front,
and so on. The main theme that I want to emphatize is that the coach must
be driven after the front is adjusted before an accurate measurement can be
made. I have done this procedure enough times to know what works for me. I
believe that Jerry work will agree with the premise of driving the coach.
What I do with both rear heights immobile and raising the front in the
center with the jack is triangulate the frame. I do not mean to totaly
unload the suspension with the jack, only to raise it to ride height. This
is an empirical process. You rarely get it right by counting turns on a
bolt and nut. One must measure before raising the coach on the front, then
unload the torsion bar, make the adjustment, drive the coach and measure
again. Almost every coach that I have ever adjusted was low in the front
unless it had been recently messed with. It is just what I find, and Jerry
also has noted the same thing. Jim K also. I can only rely on my personal
experience. My way might not be the only way to do this. It agrees with the
factory manual for the most part. I am sorry if you find my proceedure
confusing. If you have a technique that works for you, by all means feel
free to do what you want. Two heads usually are better than one when
problem solving. I welcome your comments and imput.
Jim Hupy
Salem, OR
78 GMc Royale 403
On Sun, Jan 22, 2012 at 3:54 PM, Ken Henderson <hend4800@bellsouth.net>wrote:
> Jim,
>
> I'm afraid I don't follow the rationale nor the steps of your procedure.
>
> Disregarding the absence of any adjustment of the rear ride heights (which
> I assume you've already done or plan to do later) the hard fixing of the
> rear heights seems to abrogate the "X" principle you presented earlier. If
> the two aft points of the X are fixed, how can the forward ends move other
> than together? Ignoring box/frame flexing, adjusting one front side should
> be followed precisely by the other.
>
> I'm a bit baffled by the front ride height adjustment procedure: Do you
> jack under first one side and then the other, or under the center of the
> cross member? With the rear heights fixed, I guess it doesn't much matter.
>
> It's been a long day -- maybe I'm missing something? I suppose if you
> adjust the rear ride height after the front, weight imbalances will be
> corrected, I just have difficulty visualizing it "backward" and believe the
> front heights will be disturbed.
>
> Ken H.
>
> On Sun, Jan 22, 2012 at 3:52 PM, James Hupy wrote:
>
> > Jack, I will try to step by step it for you.
> > 1. Verify that all tires are at the correct pressure. Very important.
> > 2. Drive the coach for a few miles to warm up the suspension bags and
> > suspension bushings. When you approach your work area, drive straight in
> > and making sure the front wheels are pointing straight ahead, stop the
> > coach using as few brakes as possible.
> > 3. Raise the rear of the coach an inch or two over ride height, place
> > the stands under the slots in the rear of the frame, and lower the coach
> > onto the stands using the suspension controls, or very slowly let the air
> > out of the schrader valves until the frame just touches the stands. (My
> > thinking here is to move the coach up and down as little as possible so
> as
> > not to disturb the front ride height.
> > 4. Very carefully measure the front ride height. Write it down. I
> > usually start with the side that is the lowest, and in my experience,
> > unless some Knot headed alignment shop has been at work, the coaches are
> > almost always too low in front. Assume nothing. Check everything.
> > 5. After the front ride heights have been documented, start adjusting
> > the torsion bar pork chop by the following method. Placing a floor jack
> of
> > the appropriate size under the engine cradle crossmember, not the
> radiator
> > support and raise the front end until the ride height is correct.
> > 6. Place the torsion bar adjusting tool around the cross member that
> > contains the pork chop, and adjust it until the adjustment bolt loosens
> in
> > the dimple in the end of the porkchop.
> > DO NOT RAISE THE FRONT OF THE COACH WITH THE TORSION BAR UNLOADER TOOL!
> It
> > is not designed to do that, and DO NOT use an air impact wrench on it to
> > make the adjustment. BE SURE to lubricate the end of the tool as well as
> > the threads on the center bolt. Because I am kind of anal when it comes
> to
> > fasteners, at this time I usually remove the adjustment bolt completely
> > along with the nut. I generally throw both pieces in the glass beader and
> > remove all the rust and scale from both pieces. I then very completely
> > remove all glass bead residue from both pieces and use thread chaser dies
> > and taps to clean out and straighten out the threads. Screw in the bolt
> > into the nut and check the fit. If it is able to be turned, but does not
> > coast when an attempt to spin it is tried, it is probably ok to reuse.
> Too
> > loose, replace them both. These two pieces maintain your adjustment. If
> > they are bad, so is your adjustment.
> > 7. Replace the bolt and nut and screw the bolt into the nut until the
> > rounded end of the bolt just comes snug into the dimple. Repeat the
> process
> > on the opposite side of the coach.
> > When both sides have been adjusted, remove the torsion bar unloader tool,
> > lower the coach jack, remove the stands in the rear and test drive the
> > coach for a couple of miles.
> > 8. Return to the work area the same way I described earlier and reset
> > the rear ride height the same way as before and recheck your front ride
> > height. It will not be too high, more than likely will be a little bit
> low.
> > Readjust as before. You must drive the coach after the front end
> adjustment
> > is changed. Trust me on this, it is important.
> >
> ...
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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