Technical Rear Axle Straighness Question

I am still having problems with a noise and vibration from the driveline in my Plymouth that I cannot solve. I have changed out my driveshaft, had it straightened as straight as is reasonably possible, balanced twice, rebuilt the rear end and replaced all bearings, tried different tires and wheels and changed the pinion angle up and down with no noticeable effect. You name it, I've tried it and I still get a bad noise and vibration at 55+ mph and it's really bad at 70. Noise and vibration continues when I push in the clutch, so it's in the driveline.

Also, I have observed it while running on jackstands and can see no noticeable eccentricities or balance problem. I have not run it all the way up to speed on the jackstands because I can't control the throttle and look underneath at the same time.

If the axles slide in and out of the differential easily, can I assume I don't have an axle HOUSING straightness problem? This is an axle housing I have welded on a couple of times but it seems to be straight.

If I dial indicate the axle flange and it reads within a couple thou, can I assume the axle SHAFT is straight?

I hate to open this rear end again but will if needed. I am reposting this in hopes that I get some new perspectives.

Thanks

 

What kind of rear end ? Posi ?

 

Open diff 8.25 Mopar. C clip axles.

 

If the housing was warped, it wouldn't induce a vibration, would it? It might effect the tracking, but I don't think it would induce a vibration. If one of the axle shafts was bent, that could induce a vibration I suppose. But if the flange run-out is within a few thousandths, it would appear that is not an issue.

 

I've had issues with custom wheels as well as Stock wheels in the past that didn't show up even on spin balance. Borrow a full set of wheels and tires off something else and go for a drive. At the least you'll be out some Time, just maybe you'll find the issue. Seems you've done everything else.

 

Put a strait edge on each brake drum about 18 " long, now measure the distance between the straight edges on the brake drums. This is very simular to setting toe in in the front. The distance between strait edges should be the same on both sides of the drums.
I've seen new cars and trucks with bent housing's.

 

Did you try a different drive shaft? I did see you changed out, but was it just to balance. I recently had a dump truck with a drive shaft vibration. Did the usual, new joints and balance. Still vibrated. The owner had another truck with the same drive shaft. Changed the drive shafts between trucks. Neither truck vibrated. Changed them around again. vibration returned. Changed them again, called it fixed.

 

Are the front and rear U-joints indexed correctly relative to each other? Are the pinion and transmission centerlines parallel? What is the operating angle of each U-joint?

 

Have you tried indexing the driveshaft differently in the pinion flange and the output shaft of the transmission? Engine and trans mounts in good condition? Excessive wear in transmission extension housing bushing? Is the slip yoke bottoming out on the output shaft?

 

I'm with pist-n-broke, swap tires.

 

Had that problem once with a sixties Buick, turned out to be the pinion shaft was bent. Just saying!

 

^ Might put a dial indicator on the pinion yoke to check it. Install a u-joint and read off the caps.

 

I tried another set of wheels/tires off one of my other cars.

 

New driveshaft, same yokes.

 

That is what I'm afraid of but the runout at the pinion end of the driveshaft is only about 10 thou.

 

Oddly, indexing the driveshaft in the pinion yoke makes a slight difference but not enough. All the other stuff has been eliminated.

 

I have a similar issue on an 85 c10. New tires, wheels, rotors, drums. Driveshaft balanced. Differential rebuilt with posi unit and one axle replaced as it was bent. My vibration comes and goes depending on curves in road. Happens in neutral as well. As you go through a curve anywhere above 50 mph you can feel the vibration come in and leave again (cycles in and out and is a wobble felt in the seat and i can see the bed shimmying). If you exit the curve during a vibration and the road straightens out, the vibrating continues. If you exit the curve when its not vibrating it will not vibrate again until the next curve. At 65+ it is not as noticeable. Im looking at replacing that other axle even if though the differential shop said it was within specs. Its my last hope.....

 

I checked the dimensions and the axle housing is straight. Sigh.

 

Sounds like the included angle of the U-joints is too much. I chased the same problem on a car for a year before we were able to observe the problem with the car on stands. Check your angles and make sure they are not over 8 degrees total.

 

Has the car been aligned ? Have you pinpointed where the noise and vibration are? Does it change when cornering ? Can you feel it on the e brake handle , trans hump etc ?

 

As we say in the South, you ain't gonna believe this shit. I was sitting under the car looking at everything that could be metal touching metal and trying to figure out where this vibration was coming from. As you know, there is always vibration in the suspension and the driveline. Rubber bushings in the suspension isolate that vibration........when they are working.

As I looked, I spied that one of my rear leaf springs was cocked and, upon further inspection, I discovered that the rubber shackle bushings had given up the ghost. The shackle bolt was touching the leaf spring and the entire shackle was cocked so that the opposite upper corner was touching the chassis. I replaced those with new bushings when I built the car but the quality of the rubber looked like early Chinese to me.

I turned the bushings over until I can get new ones and guess what? Very little vibration and harshness now. I feel like a dunce. I spent a bunch of money and time trying to find out that 20 bucks worth of rubber bushings were my main problem. At least I have the peace of mind knowing that everything else is good to go.

Thanks for all your suggestions and attempts at helping me find this problem.

 

Glad you got it fixed, thanks for letting us know what you found.

 

Okay, the drive shaft turns at around 3.5 times the wheel end speed. Driveline vibrations are higher frequency than wheel end vibrations. There is actually a phone app that will identify the frequency, but it isn't free. If you can find someone with access to a Kent-Moore vibration analyzer you could pin down whether it is wheel end or driveline.

Have you had the balance and trueness of your tires checked? Back in the 70s Ford allowed about 0.060 radial runnout and about 0.040 lateral. If they are okay, you may need to check your driveline universal joint angles.

 

You did not read the entire thread. See post #13.

 

If all else fails, pull both the axles and give the tail shaft and pinion a good rev.
That might at least add one more clue to the puzzle.

 

@Posts #23/24/26 Did you guys read the thread before you posted? In post #21 the OP, rockable posts that he found the problem was bad spring shackle bushings

 

OP, have you thought about looking at the rubber in the shackel bushings?

 

Lol!

 

RING AND PINION SETUP AND OR A BAD RING AND PINION CAN DO THAT FOR SURE. MAYBE CHECK THE RUNOUT ON THAT RING GEAR TOO.

 

Holy fuck....he’s already fixed it....


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