Fleetwood Discovery shaking underload

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Bicycle Guru

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Hi guys, My family bought a 1998 Fleetwood Discovery (frieghtliner chassis) with a Cummings Diesel engine and Allison tranny 2 years ago. I've noticed it is starting to vibrate very badly when giving the engine any load. Going uphills is a nightmare that vibrates the whole coach. Recently the driveshaft ujoints failed and were replaced but it still vibrates and I'm thnking the vibration might have led to the driveshaft problems. I know it's pretty hard to diagnose online, just wondering if there's something I should be looking into that might be common on these. Transmission? Motor mounts? Thanks for any help!
 
First-Welcome to the site! There's a lot of good folks here, and the library is a wealth of information.

If the driveshaft wasn't phased correctly when the u-joints were repaired, it could cause vibration, but it would also vibrate when it isn't under a heavy load. The other things you listed, motor and transmission mounts could also cause a vibration. The best thing to do would be take it to a truck shop and have them make a diagnosis. It could be something simple like a clogged fuel filter to something major.

Oh by the way, someone will correct you, so it may as well be me-Cummins, not Cummings.
 
I'm wondering since you notice vibration under load if you have a bad injector.  Diesels will vibrate if you have a bad one.
 
Diesels will indeed shake a little with a bad injector, but based on the OP?s description of the level of vibration I?d guess it?s driveline related. The fact that the ujoints ?failed? and were replaced, and the problem still exists, would make me suspicious of the work.


I had both a ujoint issue and an injector issue. The injector did occasionally cause a perceptible shake but the bad ujoint (due to poor maintenance by previous owner) caused significant vibration. kdbgoat?s advice is good, get it to a reputable truck shop.


One thing, the transmission front seal can be damaged by heavy driveline vibration. I had a brand new seal in my Allison (replaced during delivery inspection), and after my vibration incident the new one started seaping; just replaced it again. Not too big of a job, couple hundred bucks if I recall.  Have a close look at that seal while you?re having whatever you find repaired.
 
Heli_av8tor said:
What do you mean by ?phasing? a drive shaft?
Click to expand...

These guys can explain it a lot better than I can. Look at the balancing section too.

https://www.drivelinesnw.com/part-trouble-shooting/vibration-analysis/phasing/
 
I'm no expert, but I don't think it's the driveshaft/u-joints. It drives fine at half throttle at any speed. Only when given power does it vibrate the coach. It seems to pause vibrating when shifting gears so that's what leads me to believe it might be transmission related. Need to just take it to a shop, but would rather take it to a diesel mechanic than an RV repair shop that charges out the butt.
Had a rear airbag bust in the driveway so in the middle of repairing that now.

PS. The driveshaft was repaired by a driveshaft expert, Raneys, in the Ocala, FL area. I'm hoping they knew what they were doing.
 
Bicycle Guru said:
I'm no expert, but I don't think it's the driveshaft/u-joints. It drives fine at half throttle at any speed. Only when given power does it vibrate the coach. It seems to pause vibrating when shifting gears .
Click to expand...

I'm also no expert but I disagree - that sounds exactly like u-joints, at least in my experience. When my u-joint was failing it would vibrate terribly under a load. As it worsened, it also started vibrating during exhaust braking (which of course is also a load on the driveline, just in reverse). If I would back off the throttle climbing a hill (taking off the load) it would stop vibrating. If I would switch off the exhaust brake going down a hill (taking off the load) it would stop vibrating. At half throttle on flat roads, there would be virtually no vibration.

Bottom line, needs to be fixed. We can all speculate until the cows come home. A good truck shop will have the answer very quickly, especially if it's happening consistently
 
I'll jump on the bandwagon - some sort of driveline problem. Not U-joints, since that has already been done, but something.  This is a diesel pusher, so the drive shaft is extremely short, but the angle could still be out-of-spec, or some other drive shaft alignment issue. For example, improperly set suspension ride height can cause driveline problems.

It needs the attention of a real rear diesel driveline pro, and they aren't all that common because most trucks for front engine. Mostly just transit buses and motorhomes have rear engine and tranny.  I would be looking for a competent truck & bus chassis shop, or better yet a trip to the FCCC Factory Service Center in Gafney, SC. 
 
Gary RV_Wizard said:
. For example, improperly set suspension ride height can cause driveline problems
Click to expand...
An over-the-road semi tractor with full air ride suspension will exhibit the same characteristics being discussed  if the leveling valve fails ( or adjustment rod gets bent) and allows bags to overfill, throwing driveshaft angle off.
 
Yeah, ride height would be the first thing to check and is fairly easy to do once you find the specs for the chassis. FCCC can help with that - just call 1-800-FTL-HELP and have the last 6 digits of the VIN  ready. They can look up the specific chassis specs.
 
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