Technical Clunking noise in the rear axle

I have seen the pinion yoke splines wear and slap back and forth rotationally on the pinion. Have seen the differential cross shaft wear almost half way through at the differential gears, lots of slop but actually locked up the differential during burnouts, spinning both tires equally! In your case HRP, I suspect R&P backlash. Since you mentioned a recent replacement of the rear, maybe the carrier adjusters were not set properly or have moved.

 

I got it, I got it!! - a well worn nut behind the steering wheel - Ha! - sorry, could not resist.

 

Since you were working on the brakes could you have a shoe sticking?


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That might have something to do with it,my pal Earl was driving while I was listening.

I wish it were that easy. HRP

 

I didn't read every post in depth but gimpys made a great point about a locker. A locker will give that "clunk" and make you wonder wtf was that! Especially one that is temperamental.



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I honestly don't think I have a locker. HRP

 

I picked the car up late yesterday, we had it on the lift and checked it front to back checking for loose suspension parts,nuts & bolts and everything is tight.

The "clunk" noise only happens under deceleration. HRP

 

Then just keep yer foot in it!

 

If you have some way to get the car up in the rear and go through the same motions that create the clunk you may be able to reproduce it. Without a load that may not do it though. It really sounds like something rear end related. Maybe pinion bearing?
If you think about it. Acceleration forces the pinion snout up. It should be around -2* static to ensure proper driveline while under load (in alignment). When you quickly let off, that pinion immediately "deflects" back to the -2*. A bad pinion bearing with slop would give you that "rebound" clunk.


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This may very well be the case,I need to find someone that specializes in setting up the rear axle. HRP

 

You should be able to get a feel for how much pinion backlash you have pretty easily.

 

Backlash, yes. Pinion bearing would be a different story.


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Could it be the front driveshaft yoke releasing the splines on the transmission output shaft as the rear suspension unloads? I had an off topic truck that did that...I would grease the inside of the yoke and outside of the trans output shaft splines every so often and it would take care of it.

 

Okay, the above post got me thinking. Your slip yoke could be too short and when you suddenly let off the spline slip bottoms out!


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My F100 (9" rear) had that loud 'clunk' with my 3.54s, so I drove up on the curb with my right side wheels.
Crawling on my back, I went under the rear...grabbed the driveshaft with both hands, and turned it hard.
I had the truck in neutral, my wife blocked the tires.
Holy Hannah! The backlash was obvious, right there in the third member. (differential, 'chunk', 'pig'...)
Moved the truck to the driveway, jacked the rear, wife Joey pulled rear wheels and axles, I undid the circle of 3/8" around the drained 'pumpkin'. ('nother name for it, I won't repeat what I called it)
Pulled it out, had some loose bolts around the Ring/carrier, and excessive back lash.
In went the nice, tight 3.0:1, oiled it and flew it...Wow, like a different animal. No more lightning starts outa the gate, but the clunking's gone...and I NEVER have to refuel. Hardly.

 

I was told there was a new gear installed and I am thinking there may be a back lash problem. HRP

 

I think you are on the right track Danny. Sounds very much like a back lash issue. I would pull it apart and verify, you dont want the clunk to turn into a bang.

 

You've checked everything else so how about the tranny to tranny mounting block? The block could be bolted to the crossmember but bolts loose or missing from mounting block to tranny, the tranny lifts under power and drops back down when throttle is lifted. It is a stretch and even if it happening you probably wouldn't hear it, but its easy to check with a prybar to see if tranny lifts up at the tailshaft.

 

I wonder if the car made the noise for the prior owner as well and he forgot to tell you when you were making the purchase. Have you asked him?

 

Is it an audible clunk only, or do you feel it in the seat of your pants or thru the steering wheel?

 

Not sure what your tranny is, but with an automatic, if the bolts connecting the torque converter to the flexplate are loose, it will make a similar noise.

 

Yes sir,it's more audible,I really haven't driven it enough but I'm not feeling anything unusual. HRP

 

Sounds like you've gone through the easy list and now you need to pull the 3rd member. I'm sorry bud. I wish it was an easy fix.

Is it weird that melting metal in order to be welding brackets is an "easy fix" and unbolting and re-bolting something is the "difficult fix"?

 

Post a video of it if you can do it without getting run over.

 

Did you check to make sure the rear wheels are tight?

 

If it is a backlash problem is that something that I should let a seasoned mechanic repair? HRP

 

Do you own a dial indicator and a magnetic base?

 

What Transmission is in it?
Does it to the clunk in all gears?
At Any speed?
Does it clunk in reverse backing up? If yes getting on or off the gas?


If it is in the rear end- You should be able to replicate the noise on jack stands by slightly dragging the brake or EBrake and letting off the gas. It will be different conditions if the rear is hanging from a lift. If you can't replicate the noise on stands then it's probably in the suspension because you can't duplicate the load and unload dynamics that happen when you let off the gas. It looks like some kind of 4 link- that will give you 32 possible suspects- 8 bushings ends, 8 bolts, and 16 bracket holes. The bolts and holes need to be tight fit with no wear or worbled holes and the bushing sleeve need to fit tight in the bars and around the bolts. No way to tell without taking it apart. The bolts OD should match the hole ID. In other words you don't want a 1/2" bolt in a 9/16" hole. Did The same guys work on/build your brakes? Humm

With it on stands shifting from drive to reverse and back, you should be able to see a bad pinion bearing by watching the yoke and looking for up and down motion. There shouldn't be any.

Few weeks ago I had a u joint that was bad but passed every test a week before. Later found one One of the 4 caps was dry when the tell tail squeak was no longer intermittent

 

My old 66 Fairlane had a similar issue and it turned out to be a failing pinion bearing. When under load it was OK but when not, it was like you have described.

 

2. Shocks: Check the shocks. Have someone lay under the car and watch the shocks while someone else bounces up and down (and lifts up) on the car to run the shocks through their travel. You can put the jack stands under the rear end instead of under the frame to get enough room to get under the car and still have the suspension travel.







2 ;definatly a job for the mother in law-