I have a 1992 34'Barth Regency with a Cat 300hp engine, 4 speed Allison transmission on a Gillig chassis and 64,00 miles on the unit. When starting from a dead stop, after the unit starts rolling in first gear, there is a distinct shimmy or shaking in the rear end, enough to rattle things in the coach. This only occurs in first gear, after shifting up, everything seems normal. This also occurs when going up my steep driveway, but only at a certain speed in first gear. Any ideas?

Marvin,

I don't think I've ever been within a hundred miles of a Barth Regency/Cat....

Having said that, I HAVE experienced symptoms as you describe in both a Dodge 1-ton and my P-30.....Both times I started my troubleshooting with the U-joints, and both times I was right...(one had a loose U-joint, the other was caused by tired & dry needle bearings.....

If it turns out that's it, please let me know so I can add Regencies to me expertise portfolio

What type of tire tread do you have on the rear tires? A traction tread may cause your symptoms.

I have had similar experiences with worn U-joints, and once with a Michelin tire on which the steel belt was displaced. That one caused a visible ripple in the tire tread.

The previous owner had spent big bucks on new shocks, rear-end alignments, wheel-balancing, etc. It was a mystery to me as well, until one day, while parked, a friend spotted the ripple in the tread. Off with the offending tire, problem solved.

[This message has been edited by olroy (edited August 09, 2005).]

ON some automatics, low fluid will cause a shudder.

Marvin, what have you found to be the cause? Let us know when you do, thanks.

Dale

I haven't found the cause of the shimmy yet, but am checking all the possible causes listed. I have Michelin 11X22.5 tires all around with their standard tread. Will let you know when I determine the cause.

I have not yet tracked down the cause of the shimmy, but have had the Michelin's checked and there does not seem to be a tire problem, the transmission is not slipping and I have had the engine mounts checked and tightened. No luck yet. I have written to Gillig, but no response yet (they are not very responsive). I have had the coach towed twice due to problems and the drive shaft was removed both times, so it looks as if it is pointing in that direction. I am looking for someone not too far away who has some experience in drive shaft problems. Will keep you informed.

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Marvinj31,

I tend to go with the drive line components. With the drive shaft removal having been done twice, you are smart to look there. The Allison tranny's are pretty tough, but since it always happens in first gear, check there if it's not the drive shaft.

I also have a regency and will watch for your future posts. There are not many DP Barths out there so this kind of info becomes valuable to us.

Bill G

The typical drive shaft can only have a certain number of positions. Sometimes just trial and error will eliminate vibration.
You might even get lucky and find some marks on the yoke flanges that would indicate factory matching.

I'm with olroy, bill h, and goodwinw - A driveline problem (like the universals) seems most likely - also have the splines checked for freeplay and lube.

If the motor mounts are really OK (which would have been my first thought - did somebody just look at them while the engine was stopped, or did they put in in gear a apply light accelerator?)

Have you consulted an exorcist?

There's also the possibility that it's not drive train but the engine in that you have a bad/sticky injector; a tech with a stethoscope should be able to pick that up, although that's awfully rare in Cats.

The tire/wheel check out - did they roll the coach slowly and watch for twitches in the tires and wheels, or did they just eyeball the tires while stopped?

Having re read the first post, I keep coming back to the tranny........

We are getting into semantics and parsing, here. I would characterize a shimmy as what an exotic dancer does with her bottom. On a vehicle, that would translate to a side to side movement. My own experience with shimmy has been on the front end.

Now, consider the shudder. That is a low frequency vibration, or a fast shaking. The fact that it occurs only in low, and does it on acceleration or entering a sloped driveway, makes me think it is a shudder that could be coming from the tranny under load.

When the shimmy occurs, does it do it under load, or also when the throttle trails? A driveline vibration is more apt to also be there on trailing throttle, as it is of rotational origin. The shudder that I am imagining occurs only under a throttle load.

Despite the fact that there are indications pointing to driveshaft balance issues, I would consider having a good tranny guy ride and observe. Heck, maybe it just needs servicing.

Also, driveline balance problems usually show up at higher speeds.

I have also seen mystifying problems solved by moving tires around.

bill h, that's an excellent point - he may have a torque converter that's stalling then releasing...but that should show as a fore-and-aft surging...

I wonder if trans fluid levels have been checked (for starters)....

[This message has been edited by Rusty (edited October 12, 2005).]

"This only occurs in first gear..."
My neighbor has a 2002 40' American Eagle with Cummins/Allison and he also has the exact problem. Dealers and Allison shop told him "it's normal" and not to worry about it. It doesn't happen after all is warmed up. This is not a solution, just a comment; you are not alone.

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"You are what you drive" - Clint Eastwood

It's always fun to try to diagnose a problem from a verbal description, & this one's no exception. I've re-read all these posts, starting with Marvin's own words.

Using Bill H's semantic distinction, my Michelin tire problem was a shimmy on start up that developed into a shudder at higher speeds. But it never really stopped. My U-joint problems were in the shudder category, with overtones of grinding. I'll add that I once had a Mercury Grand Marquis that shuddered on torque-converter lockup, but that was a higher speed problem caused by Ford's bean-counters saving 15 cents when they made the lock-up clutch too small. It was expensively cured by replacing the clutch with the larger, later unit.

Marvin's problem is strictly low speed, on start up. He says it occurs after the unit starts rolling. Does it really start after it rolls, or is it just as it starts? And if he holds it in first, does it continue to shudder regardless of speed, or does it stop as speed increases?

If it continues to shudder in first regardless of speed, it points to a transmission problem. If it stops as speed increases, even in first gear, it broadens the problem to engine or driveline.

The odds are still with a driveline problem, more likely u-joints than balance. Perhaps there's improper angularity in the u-joints. Loose, or worn mounts somewhere in the driveline could cause that. Then again, maybe Marvin's description of the problem leads us all in the wrong direction.

FWIW, my 33' on a P-30 also shudders momentarily on start up. Of course, I have a long 2-piece drive shaft with 4 u-joints and a soft-mounted pillow block bearing in the middle ot it, plenty of places for odd twists to occur when the whole drive mechanism shifts as it takes up the torque before things start rolling smoothly.

I've learned to ignore it, remembering the many times I fixed something that wasn't broke in my long climb from neophyte to shade tree mechanic emeritus. I'll continue to check the u-joints periodically, but I'm not going to start replacing parts in hopes of curing the problem. My rig also has about 64,000 miles. Stuff does wear out, and strange creaks, groans, & shudders appear as it does.