U295 weird vibration

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U295 weird vibration

June 10, 2024, 03:34:57 am

Hey, all,

Greetings from the start of our summer road trip. This is the first "serious" distance we've made with our U295. We have Chris White's old coach, with the CAT 3126 he pretty much rebuilt himself.

I've noticed this annoying thing that I'd love your advice on. We don't like (or want) to drive very fast, so I set cruise at pretty much 62mph and kick back and let almost everyone else just go buzzing around us.

It seems like there are basically three scenarios (and, apologies here if I'm oversimplifying):

1. The engine needs to make power, either to keep us moving along on a flat section or to get us up a hill.

2. The engine doesn't need to make any power, because we're going slightly down hill already at the set speed.

3. The coach is going down too steep of a hill, and it's time for the retarder to come on and bring things back under control.

In scenario 1, the coach drives great.
In scenario 3, the retarder kicks in and works great.

But in scenario 2, we get a pretty strong vibration in the rear. Enough to start to loosen screws on various things inside the coach, LOL. Not enough to shake my eyeballs or vibrate the mirrors or anything. But it has definitely tested how firmly our shower frame is screwed together, caused some power panel screws to accelerate their backout, and so on. We have been on a hunt, securing various things that otherwise don't rattle but can't help but succumb to this buzz.

If I slow down to 59 or 58mph, this problem basically goes away. It might still be there, but if so it's very subtle.

The Allison computer shows 6th gear the whole time.

I haven't tried going much faster than 62mph, because we don't want to go that fast anyhow. :-) But, anecdotally, when passing or occasionally going downhill a little faster if I wasn't paying attention or didn't have the retarder set high enough, then as long as either we're making power or using the retarder, it seems pretty much the same at higher speeds.

The tires are brand new, if that matters.

I adjusted ride height all the way around prior to our trip; I think it's pretty close.

I read the P3 bearing threads, and we are in that window of coach and years. I don't know that Chris had any work done there, but it may have predated his ownership, too. But, those reports seem to suggest problems at or above a speed in a more consistent and continuous way. We only seem to have this buzz in the "coasting" scenario.

Any other ideas? I might not even have this properly characterized, but I've had 1,500 miles of freeway to play around with it in the last few weeks, so I'm feeling pretty confident that I'm describing it semi-accurately... maybe!

Re: U295 weird vibration

Reply #1 – June 10, 2024, 06:25:19 am

The bearing in the trans may be loose,can check it with a pry bar,have it checked by a Allison shop that knows about the problem,
a vibration will only get worse.

Re: U295 weird vibration

Reply #2 – June 10, 2024, 08:21:05 am

That's a pretty outrageous vibration you describe. Definitely need to get it checked out sooner rather than later as John recommends.

Re: U295 weird vibration

Reply #3 – June 10, 2024, 10:02:54 am

Sounds like vibration only occurs when there is no torque on the driveline.
Maybe you can find somewhere you can back up to and have space to crawl under while still in ride height and check u-joints for play and both ends of driveline. Grease u-joints and spline while there. When practical change gear lube in rear end, pay attention to drain plug for metal wear.

Re: U295 weird vibration

Reply #4 – June 10, 2024, 01:00:00 pm

Try 5 gear to isolate the rotation speed.
It should correlate to wheel speed , out put shaft if the trans speed , or crankshaft speed.
Once you figure the speed out. The failure points get smaller .

Re: U295 weird vibration

Reply #5 – June 12, 2024, 01:18:28 am

Okay, thanks all. Good ideas, sounds like it could be a variety of things. I especially like the idea of trying to determine which "speed" is the culprit, to narrow things down a bit.

Aside from that, what do you think about just staying under the vibration road speed for now? If that is likely to be okay for a few thousand more miles, 4mph slower would be a small price to pay vis a vis our planned schedule.

Re: U295 weird vibration

Reply #6 – June 12, 2024, 05:43:35 am

Sounds like you want to stick to your schedule no matter what,at least do what Doug said and go from there and hope there is a shop nearby when it gets worse,it's not going to go away.

Re: U295 weird vibration

Reply #7 – June 12, 2024, 02:13:34 pm

Drive around the vibe is always a good idea .

Re: U295 weird vibration

Reply #8 – June 14, 2024, 12:56:54 pm

Okay, the vibration starts around 61mph regardless of 6th or 5th gear. It will continue even through the gear changes. Rpm is 1750something and about 2000 respectively.

So that's a hint, at least.

Re: U295 weird vibration

Reply #9 – June 14, 2024, 02:49:23 pm

Yup, suggests drive shaft or transmission output shaft or rear axle.

Re: U295 weird vibration

Reply #10 – June 14, 2024, 03:26:27 pm

Have you checked for play in harmonic balancer on output end of transmission? Gently prying up on it....lifting it....should show little to no play, ideally zero.

Re: U295 weird vibration

Reply #11 – June 21, 2024, 10:16:27 pm

Adding all suggestions to the list... to give to the shop we work with when I get back to Oregon, since I don't know how to do any of these things. :-) Many thanks.

Re: U295 weird vibration

Reply #12 – June 22, 2024, 01:01:44 pm

Hope you make it back in one piece.

Re: U295 weird vibration

Reply #13 – July 13, 2024, 02:52:54 am

Okay, just a quick update on this vibration.

It has... stopped? (!)

We had a couple weeks of actual camping, rather than driving. And, now that we've started heading back west, I noticed on a downhill run at some point yesterday that we were going 62 or 63 and there was no shaking. I can now go even 65mph and it's smooth as silk. I've really not done anything at all in the engine bay, the toad is in the same spot, our loadout is roughly identical, and so on.

So now I have this weird mystery of a thing that has (at least temporarily) fixed itself. I haven't decided if I like that more or less than just having it easy to point at and say, "please fix this!"

Re: U295 weird vibration

Reply #14 – July 13, 2024, 09:39:33 am

Quote from: nebster – June 10, 2024, 03:34:57 am

The tires are brand new, if that matters.

I read your vibration free but in re reading something came to mind.
Did you have the vibration before the tires were changed? If you did then disregard this. If you didn't I would get the wheels retorqued. I would not put this off. Had the same issue with a friend's work truck. It too became vibration free for two months till the left rear wheels were set free from the lugs being cut through. I only learned of his issues after failure.
If a undertorque is found I would remove affected wheel to inspect lugs, wheels for damage not just torque them up and go.

Re: U295 weird vibration

Reply #15 – July 13, 2024, 11:32:42 am

Quote from: dsd – July 13, 2024, 09:39:33 am

If a undertorque is found I would remove affected wheel to inspect lugs, wheels for damage not just torque them up and go.

Wow, scary. That's easy enough to check, so I'll do that right away.

I don't remember if the problem was there before the new tires, but there wasn't much driving before them. It's possible it ensued after they were swapped, for sure.

I did watch the (poor job) the tire-changer did with the new tires. I say "poor job" because he used a gun set pretty high instead of a torque wrench. I almost retorqued them myself when I got home, but I decided just to let it lie.

Re: U295 weird vibration

Reply #16 – July 13, 2024, 11:36:50 am

With your coach being a '97 you will have Budd wheels which means you have an inner wheel nut and an outer wheel nut that attaches to the inner nut. So 2 places to have a problem .

By the way what is your coach build number.

Mike

Re: U295 weird vibration

Reply #17 – July 13, 2024, 12:43:33 pm

Quote from: Pamela & Mike – July 13, 2024, 11:36:50 am

With your coach being a '97 you will have Budd wheels which means you have an inner wheel nut and an outer wheel nut that attaches to the inner nut. So 2 places to have a problem .

By the way what is your coach build number.

Mike

Thanks for mentioning. Was curious if that year was BUDD lugs.

Re: U295 weird vibration

Reply #18 – July 13, 2024, 12:49:51 pm

Quote from: Pamela & Mike – July 13, 2024, 11:36:50 am

With your coach being a '97 you will have Budd wheels which means you have an inner wheel nut and an outer wheel nut that attaches to the inner nut. So 2 places to have a problem .

By the way what is your coach build number.

Mike

Just to be a little more simple in the explanation it is possible to have the first wheel installed and under torqued and install the outer wheel and nut then torqued up. Just checking the outer nut will not insure the inner is tight. Mike or someone competent will hopefully correct if I'm wrong.

Re: U295 weird vibration

Reply #19 – July 13, 2024, 12:51:16 pm

The change was during the '98 run. Coach 5209 was equipped with Budd wheels and 5212 has metric wheels. I have not found #10 and 11 but that is close enough.

Mike

@ Scott, I couldn't explain any better as that is correct.

Re: U295 weird vibration

Reply #20 – July 13, 2024, 02:29:58 pm

Got it. So to confirm things are right, it's a requirement to remove the two outer wheels?

Re: U295 weird vibration

Reply #21 – July 13, 2024, 02:32:06 pm

Short answer Yes.

Mike

Long answer: Once you see how the outer nut screws to the inner nut when the outer wheel is removed it will be clear.

Re: U295 weird vibration

Reply #22 – July 13, 2024, 02:52:07 pm

A little more info for you.

You don't have to pull the outer wheel completely off to be able to check the inner stud/nut. Some people remove one outer nut off one at a time and use the square socket to check the inner. I prefer to remove all the outer nuts and then check the inner ones. My opinion is this helps to make sure that both the wheels are seated properly on the lug nut tapers. There are all kind of arguments as to how to check the inner stud/nuts.

Mike

Re: U295 weird vibration

Reply #23 – July 13, 2024, 11:28:22 pm

Hmm, I haven't removed anything, craneman.

Re: U295 weird vibration

Reply #24 – July 14, 2024, 02:04:55 am

Sorry must have been a different thread. I will look for it.

Found it.

Cracked Bellhousing....Again

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