So I have one of those famous RVs with the "fake" duallies. It is actually duallies on an '82 4X4 pickup axle. As a result of known incidents with these axles, I keep a close eye on the whole thing. Recently disassembled the whole axle after some grinding noise and brake problems. I found that the thin internal bracket thingy (which I was unaware existed) had come loose been sucked into the diff and chewed to bits. Brakes were just shot. So I bought a used diff from a solid place in Denver (Yoda Jims) and got a new bracket, rebuilt the brakes, replaced the axle bearings while I was at it, and put it all back together and now...

I have a rhythmic loud metal clunk coming from somewhere back there. It occurs only under load when driving or gear braking. If I push the clutch in its gone. I disassembled the whole thing again and inspected everything. The diff seems okay, bearings are tight, etc. Back together, still there. It does not occur when I have it in drive with the back end up and wheels spinning.

U joints (non-greaseable) are very old and one is slightly sticky in one direction, but seems like the clunk is too loud to be from that. Am I wrong? Probably gonna replace anyway. It has the two part driveshaft with the middle support bearing which seems fine.

Or is the used third member defective?

Or is its not adjusted in some odd way for the weird setup with the four tires?

Or, somewhat likely on this old boy, the noise is coming from somewhere up the driveline and a completely coincidental unrelated problem? The finger in the dike syndrome of a 28 year old vehicle. But the sound does not seem related to RPMs in the engine or tranny or specific to any gears.

Drives okay, although it sounds like its gonna break any minute.

This beast does not fit in my garage, and its started to snow for real, so I want to minimize my time underneath and get it right next time.

Thanks for reading this far! Appreciate yer help in any way!

 

Pics!!

 

A small pic from above Moab, Utah

 

Sweet! You should make that thing a 4x4!

 

Did you check the set up on the new differential at all before you installed it? If not, I'd pull it and check the whole nine yards (Back lash, Carrier bearing preload, Pinion bearing preload, and check the contact pattern.)

 

I have read a lot about Toyota motorhomes, and it appears the main problem with the non-full floating dually axle is the axle shafts are over-stressed and crack / break. Did you check the shafts to make sure they were not bent or cracked? The clunk could be coming from a u-joint, but it should be noticably loose, not just old. I also remember reading about failing bushings on the rear of automatic transmissions on the back of these motorhomes. That might be something else to check.

Personally, I would not bother with the stock axle for safety reasons. I would get a replacement full-floating dually axle from a Toyota motorhome, uhaul, flatbed, etc, or some other full-floating axle and fabricate it in. I have a dually axle from an '80 with 45k if you want to take a road trip to California .

 

So replaced the U-joints and the noise was different but still there. So I jacked it up again and found that it still wouldn't clunk without being under load, but I could get it to make a couple clunks if I released the clutch hard. I had an assistant do this while under the vehicle- a little scary just up on jackstands in the yard!- and found the noise up by the clutch and tranny. Drained the tranny and found a bunch of metal. Its a used transmission and figure its dead. The clutch parts all looked fine when I pulled it.

In addition to the axles being problems on these things, the transmissions were also not really designed to push duallies and all that weight. The thing is tiny, an L45 I think, I bench pressed it out of there and I only weigh 140!

Gonna get another transmission and proceed.

Does anybody know specifically what might cause a clunking in the tranny in all gears under load?

The axle is the weak link in the whole thing, I know. I keep a close eye on everything back there. I use this RV in a strict self-imposed low mile radius around my home in Colorado, or in Moab, Utah because she's a rickety old mama in many ways. Maybe next summer I'll get up the guts to start in on replacing the axle if I can find something.