KenRudd

I have two related questions:

First

I am getting a clunk while braking, coming from the rear passenger side. It does not happen when shifting, accelerating, letting off the gas or cornering, only when I apply the brakes. Hopefully that rules out a transmission issue and maybe CV issues. I have the rear wheel off, and I don't see anything obviously loose. I particularly checked the caliper bolts and the bolts from the CV into the diff. Any ideas?

While investigating this, I was looking at the play when turning the rear wheel, specifically, how far I can spin the one side before the other side begins to spin. To me, there seems to be a lot of play, but I have no point of reference. So, because a video must be worth 10,000 words, here is a video of what I see ( You may want to open this in its own window to make it easier to see) :


Is this too much play? Would this cause the clunk only under braking?

Bill Ball

Ken:

My open diff has a lot of play - maybe as much as yours. See my little movie. That's about 1" of play at the outer edge of the tire. I have no brake issues. In fact this play has never caused any known issues and has been the same since I bought the car 12 years and 160K miles ago. Still, it is more than a few other 928s I checked (they may have had limited slips). That concerned me, so I pulled the diff cover and found the ring gear backlash was within spec. The movement I found was in the small gears which rocked on their axes. I bought new small gears, shaft and bearings quite a while ago but have not installed them to see if that would reduce the play, since as far as I can tell the diff play isn't a problem.

KenRudd

Bill,

I appreciate it! So the differential play is a red herring it seems.
The clunk hunt goes on...
The good thing about this type of work is it give me time to attack more cosmoline, repair the crumbling brake sensor wires, measure rotor thickness, all the the fun WYAIT stuff..

Bill Ball

You should determine if some of the play is in the CVs (they should have NONE), although you would expect more than a braking clunk. Mine are fine.

You know, it's odd...if I move the car back and forth w/o the emergency brake on in Park, I can hear a clunk in each direction, but I never get any noise when driving. You'd expect an acceleration clunk as well as braking, but I'm not aware of any.

KenRudd

No measurable play in the CVs themselves. I tested this by wedging a big *** screwdriver up between the bolts at the differential end ( effectively locking that end in place) and forcefully trying to turn wheel in either direction. No movement.

Speedtoys

Can you force any play in the bearing pin in the LCA?

KenRudd

You mean this, ( #22), right?

Could not force any movement there.

Unrelated, while looking at that page in PET, I see that there was a change in the wheel carrier/bracket between 88 and 89. What changed?

KenRudd

Issue resolved.
" I particularly checked the caliper bolts"
Um yeah, not as good as I thought I had.
I had originally checked with just the car jacked up and the wheel off, so essentially not looking, but feeling around with a wench behind. At that time I did not really get under the car.

Put the car up on ramps so I could really look around under there. When I got under the car, I could actually see the bolts, and it was clear the bottom caliper bolt was moving slightly. Took care of that issue and now: blissful silence.

I'm admitting my initial oversight mainly to save the next guy some time...

Also made progress in my ongoing battle against cosmoline, so I got that going for me, which is nice...

KenRudd

David,

I was was really, really hoping it was not a drive train issue, as that is an order of magnitude more of a PITA than a brake issue.

This morning I was getting more suspicious of something in the rear drive train, as the actual noise, from in the cockpit, sounded like it was coming from the right side of the transmission hump by the rear passenger seat, which would jib pretty well with a torque tube issue.

However, it was almost certainly the bottom brake caliper bolt, as I torqued that up, gave the car a good test drive and the noise is very gone. I suspect that the caliper was slipping slightly , and the actual clunk sound was transmitted to the suspension mounts right around the same area as the transmission hump, which is what I was hearing.

cold_beer839

Man you must read that post in the 20 seconds it lived before I deleted it (once I read you last post that you had solved the clunk issue).

Anyway, I have been told that if the dampening weight in the TT comes loose, it will 'clunk' inside the TT when the brakes are applied firmly.