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Topic: Rear end thump, what to do. (Read 1540 times) previous topic - next topic

Rear end thump, what to do.

Hello forum members, I have been doing pretty good keeping Jor's old 34' going down the road. This is out of my knowledge though. I will post pics, I think I have that part figured out. We are at Enid Lake Mississippi. Very nice Corps. campground. Yesterday driving we started hearing some thunking, I just thought something was rolling around thumping in a cabinet. It got worse, wife says coming from underneath. It does seem to thump letting up, and then pressing down throttle pedal. Which I would imagine, could be what I am seeing in pics.
We were headed to Biloxi, but thinking at the every least we should head back towards home, which is about 600 miles to Missouri. Any knowledge and help would be much appreciated. Kim and Elana McCoy

Re: Rear end thump, what to do.

Reply #1 –
So Kim in your first photo you are pointing out the driveline slip yoke. With it raised it is normal to see a shiny metal. Mine also has a layer of grease on it from over servicing both it and the joint about every 7K miles. To the left of the picture on that same shaft is a big round metal disk just past the rear U joint. I would take a prybar and side load it and see if there is any free movement side to side and up and down. Since you say you have a 34 foot coach Im guessing it is a 270 coach with a 8.3L engine and a 3060 Alison transmission. They are problematic for having the dampeners coming loose. Free play will indicate this as I understand
Scott

Re: Rear end thump, what to do.

Reply #2 –
Thanks Scott, I haven't figured out how to put coach info, on my profile. 97 270 34' 8.3 mechanical. I will see what happens when I do as advised, and post outcome. Kim

Re: Rear end thump, what to do.

Reply #3 –
Yup, exposed shiny metal normal-- it extends/contracts to account for movement between axle and chassis.

Check both U joints as well as transmission dampner.

Re: Rear end thump, what to do.

Reply #4 –
Looks like drive line could use a bit of grease also.

Re: Rear end thump, what to do.

Reply #5 –
Quote from: golfnut –
Yesterday driving we started hearing some thunking, I just thought something was rolling around thumping in a cabinet. It got worse, wife says coming from underneath. It does seem to thump letting up, and then pressing down throttle pedal.

"Thunking" is such a vague description.  Do you hear a thunk once upon changing direction?  Say when you go from coasting to accelerating?  One thunk is okay.  Steady vibration deserves some observation and analysis.

The shiny area your yellow arrow points to is the drive spline in its extended position.  That's a part that's often overlooked when running around with the grease gun, because if it doesn't have a grease fitting of some sort it needs to be pulled apart to be re-greased.  If there is a problem with the drive shaft as others have said you can grab it in you hands and move it.  If it doesn't move, no problem.
One thunk?  Keep driving.

Re: Rear end thump, what to do.

Reply #6 –
I can turn dampener and u joints slightly left and right. When I turn forward facing u joint, on rear end side, slightly to the left and then clockwise I can here a clunk?? Seems to be inside housing, normal??  will post pic.  Not sure where to pry on the dampener. Anyone have a pic? So use a steel bar? Thanks for all the reply's!!

Re: Rear end thump, what to do.

Reply #7 –
The damper does'nt come loose, the bearing in the trans housing does and may need to be tightened  and or replaced,had mine
repaired in Memphis at a very good shop,there is an elbow towards the bottom of the trans under the damper,you can gently put the pry bar there and check end play,grease the u joints and shaft and see if that helps with the clunk,make sure the trans fluid is topped off.

Re: Rear end thump, what to do.

Reply #8 –
Quote from: Old Toolmaker –
The shiny area your yellow arrow points to is the drive spline in its extended position.  That's a part that's often overlooked when running around with the grease gun, because if it doesn't have a grease fitting of some sort it needs to be pulled apart to be re-greased.

Every Foretravel driveshaft I have worked on/inspected DID have a (one) grease zirk on the spline and two on the U joints.  Grease either of the U joint zirks, as both are drilled to the same center of the cross.

Re: Rear end thump, what to do.

Reply #9 –
Quote from: golfnut –
I can turn dampener and u joints slightly left and right. When I turn forward facing u joint, on rear end side, slightly to the left and then clockwise I can here a clunk?? Seems to be inside housing, normal??  will post pic.  Not sure where to pry on the dampener. Anyone have a pic? So use a steel bar? Thanks for all the reply's!!

That would be the gear backlash and normal doing what you describe. The bearing Scott talks about is at the other end of the driveshaft and in the tailshaft of the transmission. You need to find a place to pry that damper sideways or up and down.

Re: Rear end thump, what to do.

Reply #10 –
As I recall from earlier threads, if the transmission dampner needs replacing, several have used the Allison shop in Longview, TX.

Re: Rear end thump, what to do.

Reply #11 –
Also make sure your differential lube is topped off.

Re: Rear end thump, what to do.

Reply #12 –
Quote from: wolfe10 –
As I recall from earlier threads, if the transmission dampner needs replacing, several have used the Allison shop in Longview, TX.

Stewart and Stevenson?

Re: Rear end thump, what to do.

Reply #13 –
Sales + Service Locator


Stewart & Stevenson Power Products, LLC
4935 Whitehurst Drive
Longview, TX 75602
  903-758-5562

Re: Rear end thump, what to do.

Reply #14 –
Of course pry bar is one thing I don't have, and grease gun LOL. I do have this, just don't have any idea how much muscle to use. Is this where to try for movement?

Re: Rear end thump, what to do.

Reply #15 –
Yes see if there is play there. It should not move.

Re: Rear end thump, what to do.

Reply #16 –
Quote from: golfnut –
I can turn dampener and u joints slightly left and right. When I turn forward facing u joint, on rear end side, slightly to the left and then clockwise I can here a clunk?? Seems to be inside housing, normal??  will post pic.  Not sure where to pry on the dampener. Anyone have a pic? So use a steel bar? Thanks for all the reply's!!
That would be the pinion bearing and if it were problematic you could wiggle the drive shaft up and down.  Turning from one side to the other is the backlash between the pinion and the ring gear, and not to belittle your concerns, but I'm wondering if what you're hearing is normal.  Sometimes as we become used to a new machine, as we become comfortable in its operation we begin to notice "new" noises and vibrations.  These were always present but buried under the noise of all the new sensations that come with new machinery.

Now the output bearing on the automatic transmission, if you can find movement there, you have something to be professionally addressed sooner rather than later.

Re: Rear end thump, what to do.

Reply #17 –
I leaned on it pretty good, I am not getting any movement. I will check tranny fluid, stop somewhere buy grease and gun, which I was wanting something better anyway, see what happens I guess. Any more words of wisdom, please share, I appreciate it very much. Thanks

Re: Rear end thump, what to do.

Reply #18 –
I have put about 4 thousand miles on the coach, we haven't heard this before, it is pretty distinct. No movement on the dampner that I can produce. The dampner and yokes will slightly turn counter clockwise and clockwise. Thanks Kim

Re: Rear end thump, what to do.

Reply #19 –
I will see if I can move shaft up and down.