I was under the car today working on another problem and I happened to spin one of the rear wheels. There was a noticeable amount of play in the differential before the drive shaft started turning, but the thing that really got my attention was the gravel sound coming from the diff. I immediately panicked and thought the worst.

I drained the diff and checked the drain bolt magnet. It was thoroughly covered in black paste. The oil itself wasn't that bad. I measured the amount that drained out and it seemed correct.

I have 105k miles on the car and have changed the diff fluid every 10k miles (Mobile1 75w90). I have never heard any noises coming from it before, even driving it earlier in the day.

The only noticeable behavior change is the play I mentioned above. I can also feel that through the drive train when I change gears and re-engage the clutch.

So, does it sound like my diff is toast? Is it normal to have that play in the diff? Also, I never launch the car, just to clear that up. I do drive aggressively and do the occasional road course.

I refilled the diff and when I spun the wheel again the gravel noise was almost gone. Still, that large amount of play, and the fact that a good bit of metal goo was on the drain bolt has me really worried that I might have joined the blown diff club.

Thanks
J

 

What diff fluid are you using?

 

Updated with diff fluid type

 

I'm not sure how religious you were with 10K OCI's on your gear oil changes, but it sounds like you may have some sludge in the differential. Sludge occurs in the diff when temperature rise to 180F-200F. Since you mentioned that the noises improved after the oil change, I would look into this first. There is a product that you can use to clean out the sludge safely just by driving 1000 miles and then doing another drain and fill. It's called Auto-Rx. Here's a link:

http://auto-rx.com/

This assumes that you don't actually have something mechanically wrong with the diff.

 

Interesting, I'll definitely look into that. That would certainly account for the goo at the bottom, does it also explain the loose play in the movement?

And yes, as hard as it may be to believe, I really did change the fluid every 10k. Towards the end here recently I've starting thinking that 15k would be more appropriate though. I'd do the tranny fluid at the same time as well.

Thanks for the input,

J

 

ive never heard of auto-rx .... can you get this in stores?

 

Don

 

Wow, awesome. You really are the diff master
Since I thought it might be toast, I was planning on getting one of your super diffs and was about to start researching which gear to go with.

I'm going to do a little research and may end up sending you my diff for bullet-proofing anyway.

Very much appreciate the input.

Thanks,
J

 

LeonGalt Posted on Dec 25 2008, 01:34 AM
This by itself doens't mean anything.
Turning one wheel with the trans in neutral will not by default spin the drive shaft.
If the brake on the other wheel has a slight drag it might but as soon as that brake breaks free there is no telling what will spin first.

Put the trans in 1st and spin one wheel > the other wheel must spin in the other direction without too much noise or effort.
Turn the drive shaft (prop shaft) by hand, that's a better way to feel play.
Especially with the e-brake on: that way you will feel (among others) the backlash.
You'll also feel play in both CV's and play inside the Torsen diff housing with all its gears so don't expect it to be very tight.
Remove the propshaft and pull on the diff input shaft flange, there should be NO forward play AT ALL (that's the pre-load Puppy is talking about).
Go absolutely wild and remove the oil again, look through the drain hole to see the ring gear, now (with the propshaft removed) turn the diff input flange and look at the ring gear: you can see & feel the play = backlash.

 

i have a little play in my diff also. i going to pull the diff and rebuild it. i've never rebuild a diff before, so i have a lot of reading to do.