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Chaplain Kent · 09-19-2005, 08:18 AM

On my last two trips there has been periods of chassis vibtation. First time I thought it was a flat tire, though all tires were fine. I later checked air pressure and all were good. The next time it happened I stopped again checked all around found nothing out of place and continued on. The vibration continues for about 4 to 5 minutes then stops. There are no indications of engine changes, gauges all read same and the engine sounds fine. Speed makes no difference, though I can feel the vibration in the brake pedal when slowing.
I hate to bring an intermittent problem into a mechanic without some idea as to what it may be. I also am concerned to continue driving if there is a serious problem which needs addressing.
Thanks for the ideas.

85MH325 · 09-19-2005, 08:26 AM

If you can feel a vibration in your brakes, you may have warped front rotors. I ended up having to replace the brakelines, rotors, AND calipers on my '85. If you have a front caliper(s) that is sticking for whatever reason, it will overheat the rotors and cause them to shake the coach even when your foot is off the brake. Having a caliper (or calipers) or a master cylinder that is sticking is a serious problem. Eventually, it will lead to total brake failure. What actually happened on mine was that the brake lines had so deteriorated that they acted as a one-way valve, not allowing the brake fluid to return to the master cylinder reservoir after they were pressurized for a stop. That ultimately caused the calipers to fail and warped the rotors.

A tell-tale sign of caliper sticking is hot wheels... they can get VERY hot...

Roger

74Argosy24MH · 09-19-2005, 09:43 AM

Strange. If you feel it in the brake pedal logical thought would be a rotor or drum warped. But usually these don't have any feel other than in the pedal. Do you feel pulsations in the brake pedal every time when braking?

Other possible sources are tire/wheel balance and driveshaft balance (u joints and carrier bearing wear also).

John

ALANSD · 09-19-2005, 10:01 AM

I would think to check the driveshaft also. Has the shaft been lubed? There are fittings on it that many people miss greasing.

85MH325 · 09-19-2005, 12:15 PM

Quote:

Originally Posted by 74Argosy24MH

Strange. If you feel it in the brake pedal logical thought would be a rotor or drum warped. But usually these don't have any feel other than in the pedal. Do you feel pulsations in the brake pedal every time when braking?

Other possible sources are tire/wheel balance and driveshaft balance (u joints and carrier bearing wear also).

John

What was interesting about the brake line problem was that it also was intermittent... until finally a caliper overheated and seized. It would intermittently vibrate the motorhome like crazy though prior to seizing. Drove me nuts. Then, we still didn't catch that it was the brake lines until I ruined a SECOND caliper! The brake lines were ballooning out from being soft, and then the lining had peeled back inside acting as a one-way valve. Eventually they'd bleed back down. It was really frustrating until I found a guy who regularly worked on Chevy heavy truck chassis... he knew exactly what to look at. Apparently mine must not have been an isolated case.

Of course as John and Alan suggested, it could be U-Joints or the driveshaft as well. Or a tire balance problem, although tires will normally be repeatable at a specific speed...

Roger

swebster · 09-19-2005, 01:54 PM

Any other clues? Does it happen at under engine acceleration or deceleration? Vibrations in the steering wheel? High pitched, low pitched? Does it "feel" like it's coming from a specific side of the coach or the front or back?

I replaced all of the UJoints, carrier bearings, front wheel bearing, front calipers, hoses, roters and pads, etc and have only now removed the last of my annoying chassis vibrations and feel like the braking system is working correctly.

I'm thinking rotors or loose wheel bearing. Maybe you could jack it up and spin each wheel by hand, look for end play in the dub, etc. Then pull the wheels and look at the brake components for out of round or true.
Had a strange vibration in my driveshaft mounted parking break that took forever to find and eliminate. It was driving me insane...whiiiiir, whiiiir, whiiiiir, I can still hear it in my sleep sometimes

Roger - very interesting information about your brakes. I personally work hard to get over spending money on the stuff that's "under the water line" but know it's the key to a safe and happy Airstream. Your story makes me glad I replaced everything.

Chaplain Kent · 09-19-2005, 03:44 PM

Thanks guys for the ideas. The brakes were completly
replaced about 10,000 miles ago, including rotors, MC and lines. The drive shaft was aligned/ balanced by the PO just before we took delivery but we do have our new engine. Could this have thrown it off needing to be done again?
Speed does not affect the shaking, nor does it make a difference whether I am accerlerating or slowing down. There appears to be no pattern as to when and how long it happens and continues. It feels like it is comming from the front and evenly on both sides.

swebster · 09-19-2005, 04:09 PM

I'll bet there is a GMC truck shop in your area that works on Medium Duty and Heady Duty trucks. When I was chasing vibrations I talked with the service manager at our local repair facility. He said they have a lift which allows them to run the chassis up to speed and using sensor pinpoint the source of chassis vibrations. I don't remember the cost but it was not super expensive.

Might be a good way to find the source.

I have to wonder...anything about the new engine/tranny feel funny? Flywheel, trans yoke? IT's soooo hard to find these things when they are not obvious.

85MH325 · 09-19-2005, 04:34 PM

Hmmm... do these things have ball joints? Hmmm...

Roger

Orland Dewey · 09-19-2005, 04:37 PM

Hello,

O Dewey here, Last February while heading to Florida with my 1985
325 MH I had a very serious vibration sometimes and sometimes not.
After arriving at our campgound I jacked up the front end and took both
tires off and loaded them into the van we pulled and went to a gmc and
a/s dealer in Brooksville,Fl.

The problem was the internal sending unit that tells me if I have a flat tire
had busted loose from the rim inside of the tire. This is a pretty good size
pc of material so if you have this system on your MH check it out.

Hope this is of help!

ODD (Mixednuts)

overlander63 · 09-19-2005, 06:21 PM

Quote:

Originally Posted by 85MH325

Hmmm... do these things have ball joints? Hmmm...

Roger

Roger, I THINK they have kingpins. This would cause intermittent vibration, but you should feel it in the steering wheel. Something it may be, is an inner wheel bearing staring to go bad. Put the front wheels up in the air, and try to wiggle the wheel around. If it moves more than about a 32nd of an inch, you have either bad bearings, bad races, both, or maybe just need to have the bearings adjusted. If the bearing was bad, it would be able to be felt in the brake pedal when braking, you may also notice the coach tending to wander off one side of the road, also known as "pulling".
It's too bad Kent is so far away, I could take a look at it this weekend at the Forum rally (shameless plug).

74Argosy24MH · 09-19-2005, 07:27 PM

If you have leaf springs you have king pins, coil springs and you have ball joints. Check your tires also for tread separation.

fangthorpe · 09-20-2005, 01:23 PM

Jack up the front end - got levelers? - and shake the tires in and out top to bottom HARD and try to find something loose. Easiest find would be a loose wheel bearing - you'll get that right away and that will give your symptoms - but the ball joints are a tougher find. Unless I am mistaken, the MOOG joints are a ball captured in a metal cup with a small very tough spring on top so the joint doesn't flutter when unweighted. This makes a bad ball joint feel like a good one because it forces the ball down into the good lower cup - where it doesn't ride and where there's no wear - when you unweight the vehicle to inspect it. Maybe you even use a long 2X4 or a pipe to try and find play like they do at circle track tech. One guy levers and the other guy puts his fingers on the joint to check for play. Balljoints can make you crazy. I bet on bearings though. I think you'd get more in the brakes with the bearings and more in the steering with the joints.

If your coach porpoises a lot, you could be cupping the tires and boogering up the wheel balance too. Run your hand over the tires and see if they're smooth.

Good luck.

Chaplain Kent · 09-22-2005, 06:04 AM

I jacked up the front and found no play in the front wheels. The tires are fairly new and have no evidence of separation or wear. My bet is the driveshaft alignment. It goes into the shop today and at least I have something to tell them. I hate it when I need to leave a vehicle and act like I know nothing. Thanks again and stay tuned for the verdict.

Nye Thatcher · 09-22-2005, 09:27 AM

I have experienced an intermittent problem as you described. It turned out to be frozen caliper slides. The calipers are made in two parts. One part moves on the slide when the brakes are applied. If they are beginning to freeze. the seals on the pistons are unable to fully retract causing a heat build up. IF this is it, it is easy to fix with a wire brush and a good penetrating oil, with the wheels removed. (wheels may turn freely when cold). Good luck, nye

Chaplain Kent · 09-24-2005, 08:03 AM

I picked Chummy up from the shop and they reported that everything checked out fine. The mechanic can find no reason for the vibration and since it is intermittment, it does not happen on a road test. I listed all the suggestions given and he stated that they checked them all plus more, including wheel balance, a bent rim, loose wheel, engine mounts, and on. This may be one of those things that has to get worse before it gets better.

john hd · 09-24-2005, 08:22 AM

chaplin

one other area of remote possibility would be the steering gear box.

we had a batch of chevys at the power company that would develop cracks in the frame where the steering box mounted.

the steering box would flex at the mounting bolts and cause vibrations and shimmy in the steering.

just a stab in the dark at your problem. could be worth a look.

john

GlenCoombe · 09-29-2005, 05:54 AM

I'm going to persue my own chassis vibration and figure to start with the least expensive item on the list. My tire man took a ride with me yesterday and declared it not to be a tire related vib.
I'll have the U joints changed in the next couple of weeks and also look at the drive shaft brake at the same time.
The vib comes on at about 45mph and is gone at 55. Seems to jump up more on deceleration but that could be my imagination. The vibration is not enough to really shake anything but I can feel it.

overlander63 · 09-29-2005, 04:44 PM

Quote:

Originally Posted by GlenCoombe

The vib comes on at about 45mph and is gone at 55. Seems to jump up more on deceleration but that could be my imagination. The vibration is not enough to really shake anything but I can feel it.

45-55 vibration is usually a bent wheel. 55-65 is usually tire balance, and a seperated belt in a tire will normally show between 15-25 mph.

swebster · 10-02-2005, 03:19 PM

Glen,
Check the bolt holding the trans yoke in. You can see it once you remove the driveshaft brake. (Be sure you block the chassis well before disconnecting the driveshaft). I have this same vibration and it goes away when I periodocilly tighten this bolt.

I'm considering replacing the yoke and trans tailshaft for a more permanent fix.