Karen,
Can you jack up the rear of the coach in the middle to see if the front wheels are loaded equally?
Regards,
Bill

bwevers wrote on Fri, 23 January 2015 10:56

Karen,
Can you jack up the rear of the coach in the middle to see if the front wheels are loaded equally?
Regards,
Bill

Don't think I understand how that would work. And is there a center jack point in back?
I thought it could only be lifted from the side frames at the bogies.

Might have to beg/borrow some scales, but then still wouldn't know how to fix an imbalance.
Is this something a good alignment shop could determine?

thanks,
Karen
1975 26'

Consider this method:
On a level, flat hard surface like concrete:
-raise the rear slightly and put jack stands or blocks under the bogies and then let the air out so the coach rear is resting on the blocks.
-Now the rear suspension is not pressing up with more force on one side than the other.
-Now check your front end, it should be level. If one side is higher then you know the torsion bars are out of balance.

Just my farm-boy mechanic way of seeing a solution for you.

First, let me say that I have had this discussion with both Alex Sirum and Colonel Ken. Both of them disagree with me, so you may see disagreement posted here. I firmly believe they are wrong but that is their right to disagree. There is seldom only one correct way to get something done.


Here is how I and a few others adjust both front and rear GMC weights and ride heights.

First let me say a few things. You are dealing with three items that are fluid. These items are the air bags in the rear, the torsion bars in the front and the frame of the coach. These items move and flex according to the amount of weight applied to them. So do not think in terms of the frame being a solid brick, or the bags and torsion bars as being solid items. All three of these items will absorb some of the applied weight BEFORE they start moving.

I also believe that balancing the rear weight of the coach on the rear trailer hitch is a dumb idea. That is around 8000 pounds on a hitch designed only to hold 500 pounds applied in the opposite direction. Has anyone really ever done this?

The objective of this exercise is to get the front and rear ride heights correct while keeping the side to side weights as balanced as possible. The two examples given previously in this thread were clearly not adjusted correctly.

The one example stated that the torsion bar on the left front was cranked almost all the way up while the right rear had 10 to 12 PSI more air pressure that the left. This is clearly an indication of maladjustment causing the coach weights to be heavy on opposite (diagonal) corners. While PSI is not a measurement of weight, PSI change or imbalance is a direct result of the system trying to counter for the additional weight being applied to that or the opposite corner of the coach.

So how do we adjust for this?

The rear of the coach adjustment is strictly a ride height adjustment. If there is additional weight applied to a rear corner of a coach the bag will compress and the leveling switches will add air to the bag correcting the height of that corner. The switches do not sense weight They sense only height.

I say that you need to set the rear ride height EXACTLY correct while ignoring any weight differences. I have a set of 2x4 blocks cut that we use to measure the rear height under the frame measurement holes. These slide under the frame at or near the measurement holes so you can quickly see how far you are off.

There is a dead band area in the leveling switches and there is a delay in adjustment sensing switch changes while driving. So I suggest that you adjust the rear switches to set the EXACT height and then go drive it. Come back, recheck the heights, and fine adjust the measurements as necessary. I also suggest that you later re-check the switches during or after a trip to see if they are still on the money. The adjustable links sold by Colonel Ken Henderson and Dave Lenzi make this a quick and easy adjustment to do on the road with only one open end wrench and the 2x4 blocks.

Once the rear is set correctly, I raise the coach slightly, slide the rear adjustment blocks under the frame and drop the coach until some of the coach weight of the coach is sitting on the blocks. What we are doing is trying to assure that the rear will not move as we make changes to the front torsion bar adjustments. Using my scales we have determined that a 1/4" difference in rear ride height adjustment will change the front weight imbalance by 125 pounds.

Now go to the front torsion bar adjustment. Unlike the rear bags which are solely adjusted by height sensing, the torsion bars are weight sensitive. They will flex as you change the applied weight to the wheel. As you adjust them they will first twist or untwist some before actually raising or lowering the coach. So raising and lowering is not a direct linear relationship. Meaning 6 turns will not always give you the same amount of lift or drop because some of the weight may transfer to the other side and torsion bar.

Once you have the ride height set you will find that the bars will be similar in the number of turns on the adjustment bolts. This is because you are only adjusting front heights while the flexing of the rear air bags is not happening and has no influence on the front. Also you are holding the flexing of the frame in it's normal position since the weight is applied to the rear wheel area like it normally would be going down the road. The bags are not in the system changing things and we are not abnormally hanging the rear weight on a single point rear trailer hitch. On every coach I or Chuck have done this way, when we put them on the scales we have found that the weight on all of the wheels is within specs after driving them a few miles on relatively level highway.

The real way we like to do it, if we have a set of scales available at the time, is we make the front side to side weights as close to equal as possible rather than adjusting strictly by height. When we do it this way (by weight) we also find that the ride heights are also equal. Once they are equal, if the front is a little low or high we can adjust both bars the same number of turns up or down to fine tune the final front height.

Either way will come out very close. So if you do not have scales, block the rears at the EXACT height and adjust the fronts exactly equal at the correct height. Then bring the coach to a GMCMI rally, or Bean Station, or run over a set of commercial scales, or come by my hangar, and we will check it out for you. Also many state highway weigh stations leave their scales turned on even when they are closed. They display the weights if you simply drive over them. Many truck stops also have Cat brand scales available for a few dollars. I have also weighed coaches for free at a local scrap dealer and a local grain elevator.

A poster on Facebook implied that a front tire blow out with the One Ton conversion would be hard to handle. Our left front tire blew on the way to Chippewa Falls. We were passing another vehicle on I-35 north of Kansas City, doing about 70 mph when KA-BANGITY-BANGITY-BANGITY-BANGITY that didn't stop until we pulled over onto the shoulder and stopped. My first though was a broken drive axle or CV joint as the banging was right under my seat. One look revealed a blown tire. There were absolutely no control problems. The noise was the broken steel belt hitting the floor under my seat

Background information. After installing the GM 502, we adjusted the ride height, which took all the available adjustment on the left front torsion bar and was still not perfect. On one of the first test runs, pulling out of a service station with a steep ramp we noticed the upper aft corner of the right windshield popped out of the rubber. Later noticed the lower left windshield was coming out too. Ended up with both of them cracked and then replaced. New ones didn't fit well at all, top center of opening was displaced from bottom by 1/2" or more. Humm, I hadn't noticed that before. Later when we weighed the coach at Dothan, left front wheel was 1250 lbs more than the right front! Rear unbalance was the opposite, about 450 lbs, not near as bad, or about 12 psi difference on the suspension air pressure. Borrowed the scales and readjusted the torsion bars to within 200 lbs unbalance front left to right. Noticeable improvement in driving! When back home, more adjusting and got it to almost perfect left to right and just a lb or two difference in rear suspension air pressure. Windshield center post now lined up much better. Ride height in spec. Time and many miles pass.

About 200 or 250 miles before the blow out I noticed a high frequency vibration that seemed to be in area of left front. Checked every thing I could think of and found nothing . Drive axle bolts tight, no temps out of line, (didn't closely check tire as the vibration seemed to be too high frequency). Tire was a Goodrich Commercial TA, 6 years old, that showed no age or other distress. I'll report later how many miles it had after the overload and before it failed. I don't think age of tire had anything to do with the failure. Tire store 8 miles away had a perfect match in stock!

Total repair cost - approximately $3500. Expensive stupidity!

Hal Kading 78 Buskirk Las Cruces NM