Revcon Forums

Heavy front vibration problem - Torsion Bars
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Author:  Marks_WT [ Thu Jul 14, 2022 4:08 pm ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

I have started a new post on my ‘85 Duke’s restoration project over in Slant-nose Renovations but since this post is about torsion bars I thought I’d put some information here. I have pulled the drive train subframe out and completely disassembled it. Torsion bars in my wide body Revcon are 56 5/8” long. 1 3/8” diameter. 1 1/2” across flats.
I picked up a torsion bar unloader from Amazon about a month ago for $20 it worked very well and seemed well built.
As far as the bars, I did some internet searching and found some that looks like they will work. I’m in the process of getting measurements of the lower A arms of a 2014 chevy Silverado 3500 to see if distances from inside pivot point to ball joint, and inside pivot to center of torsion bar mount are similar to the Revcon. This will affect which bar strength will be needed. Also need the measurement across the flats of the hex ends.
I’m including screenshots of GM torsion bar information that I found.

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Author:  Austro-Revconeer [ Thu Jul 21, 2022 7:02 am ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

Thanks for supporting the cause.


The Revcon is back on the ground. I took the correct ride height from the manual of the blue GMC Motorhome pork chops.

GMC Ride Height R. Forum.jpg
GMC Ride Height R. Forum.jpg [ 68.56 KiB | Viewed 2254 times ]

Driver' s side and passenger side heights are almost equal, but we can' t get rid of the difference of about 1 inch between the two sides. If you lower the height of the passenger side, which is a little bit higher, the driver' s side goes down too. But this difference has already existed before we installed the new torsion bars. It was the same with the old bars.

Result of the test drive: The front suspension now works as it should, the ride is smooth, the ride height stays the same, no sagging. This problem seems to be solved with the "good old used" bars from Applied GMC.

But - and this is a great disappointment:

The vibrations are still there, starting at 58 mph. Very interesting: At about 62 mph the coach shakes badly, but it' s getting significantly better when exceeding 68 mph.
The speed limit for my Revcon on the German Autobahn ist 62 mph, so I didn' t dare to drive much faster in the past and I was afraid of the vibes too.

I took a ride along the Autobahn today together with my mechanic at 80 mph. Left the hatch for the engine compartment open and watched closely from above. No abnormalities.

The source of the vibrations seemed to come from behind, passenger side. My mechanic left his seat while driving and went through the coach in order to identify the origin of the vibs.

As you know, we balanced the front wheels in July 2021. This time I wanted to have ALL wheels and rims checked, especially the rear ones on the passenger side.

The wheels are from 2018. Firestone Transforce HT.

Vibration Transforce Tires R. Forum.jpg
Vibration Transforce Tires R. Forum.jpg [ 62.33 KiB | Viewed 2254 times ]

Firestone Transforce HT (9.50 R16.5 LT 121/117R) are on my Revcon...interesting information from SCOUTII, German Astro Van Forum.

Result of the tire balance:

Balancing 1 R. Forum.jpg
Balancing 1 R. Forum.jpg [ 113.45 KiB | Viewed 2254 times ]

Author:  Austro-Revconeer [ Thu Jul 21, 2022 7:23 am ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

3 of the 4 tires on the tandem had a big unbalance.

Balancing 2 R. Forum.jpg
Balancing 2 R. Forum.jpg [ 67.33 KiB | Viewed 2254 times ]

The front wheel rim on the driver' s side had a radial run-out and couldn' t be used anymore. So we took the spare from the roof and switched the rims.

Balancing 3 R. Forum.jpg
Balancing 3 R. Forum.jpg [ 105.59 KiB | Viewed 2254 times ]

There were tubes inside of the tires.

Balancing 4 R. Forum.jpg
Balancing 4 R. Forum.jpg [ 87.94 KiB | Viewed 2254 times ]

Didn' t know that. Ist this the way it should be? Tubes in tubeless tires? The steel rims (16.5 8.25) are standard.

These tubes are inside, because the former owner was told that the standard steel rims of the Revcon are not suitable for tubeless.

Opinion of a German tire dealer 20 years ago and so the former owner always drove the Revcon with tubes in the tires.

However, The young mechanic worked for three hours to get the job done. All 6 rims and tires are now inspected and balanced.

But it didn' t help. I left the repair shop and the vibrations started again.

They are less intense when reaching 70+ mph.

I' m pretty sure now that the cause could be a tire, rim or balancing issue.

Author:  Marks_WT [ Thu Jul 21, 2022 7:45 pm ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

Sorry, hope I didn't scare anyone about the price of torsion bars. Yup "Sway-a-way bars are expensive, I've found them on GM websites from $225- $250 apiece.

Author:  Austro-Revconeer [ Thu Jul 21, 2022 10:18 pm ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

Didn' t scare me...I paid over 2.000,-- USD for two old used bars. :lol:

Author:  tttphd [ Fri Jul 22, 2022 12:59 am ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

Inasmuch as you have not resolved the vibration, I assume you used my earlier suggestions especially about raising the front wheels and running it up to speed. In any event, Revcon utilized a special procedure for balancing the front and rear wheels. This can be found on page105 of the manual for the slant nose. May I suggest you read this information
It might help inasmuch as it is not the method used today on most vehicles although I am not sure it applies to a 1979 but it is worth reviewing.

Your middle name must be Perseverance.

Good luck!

Author:  Austro-Revconeer [ Tue Jul 26, 2022 4:54 pm ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

Yes, thank you for your advice!

My middle name is Christian. :lol:

Went to the tire shop in the morning...the mechanic took off one wheel again and checked the rim. The original Revcon rims haven' t got any humps, so they need tubes - that' s what he said. I personally still don' t understand why they have tubes. GMC Motorhomes don' t use them. Also no idea where I can get good used original Revcon rims from. The German rules for historical vehicles are very strict. If I put on new rims, I will lose my "H" license plate. I must contact a German TÜV (technical inspection station) inspector, who is a specialist in U.S. Cars imports and maybe there might be a solution. New tires and new rims imported from the U.S. means a lot of paperwork and red tape. And in the end it could still be illegal. It' s easier in Austria, I just put on new rims from the U.S. on my GMC Safari Van and nobody cared about it, but the Germans seem to love paperwork. :lol: Remember? The coach is registered in Germany and I have two U.S. cars with Austrian license plates too... ;)


Author:  tttphd [ Tue Jul 26, 2022 7:07 pm ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

According to the manual, the tires and rims have to be on the vehicle when being balanced which is the earlier method of balancing tires. This method not only balances the tires and rims but the drums, disc's and other driving parts as well. If any of the parts are out of balance, you will get vibration. By raising the front of the vehicle and running it up to speed, you can check the front parts. However, this does not check the rear parts. By using the proper balancing equipment, you can check and balance all parts. Check the internet for balancing tires on vehicle. Moreover, be sure to support your vehicle under the A arms.


Author:  Daveinet [ Tue Aug 16, 2022 1:29 am ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

How in the world would they ever know you put new rims and tires on it. Is the tire size tag a government supplied tag, where it could not be easily forged?

Incidentally, if you have vibration in the rear, the drums are likely out of balance. This is a well established fact in the Revcon world. Revcon specified the tires be spin balanced on the vehicle, to compensate for the drums. The other option would be to use Mercury or ballbearing automatic balancers. I had a set on the front of my Revcon. I bought the Mercury balancers. They only drawback was that above 80 mph, the mercury would flatten out and not work as well. They also would take about a 1/4 mile of stable speed to balance out.

Author:  Austro-Revconeer [ Tue Aug 23, 2022 3:43 pm ]
Post subject:  Re: Heavy front vibration problem - Torsion Bars

Thanks, TTTPHD and Dave for your advices!

Manual 106 R. Forum.jpg
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I will be back in Saxony next week. There is only one old tire specialist, maybe he is able to balance the rims on the vehicle. It´s the only contact which I have got a the moment. The other shops don´t use this old method anymore... :roll: It´s not so easy to get this done, here in "good old" Europe.

Maybe I would have to buy the equipment by myself, if I found out where.

And where can I get ballbearing automatic balancers, which fit for my rims?

This company for example don´t have any:

I have already contacted them. They used to offer sets for the GMC Motorhome, but my rims are not identical.

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