Crawled out from under my car about an hour ago, after a review of all the advice offered here (thanks) and here's my report:
After many checks, including shaking, pounding and twisting, still no definite diagnosis...only a theory.
First, I went for the low hanging fruit and checked the center drive shaft carrier, which I replaced shortly after I bought the car due to thumping against the body. Vigorous shaking (VS) showed it to be sound and intact.
Next, with trans in gear, I rotated the DS and observed and listened for issues at each U joint. Also did those a while back and they appear sound. Ditto for the big rubber doughnut. No play seen or heard.
Rear transmission mount survived VS with no indication of looseness. Front mounts are the aluminum reinforced type and I checked them a while back, bonnet up, parking brake on, first gear and looking for engine rotation. Solid.
Went to the rear suspension and got hands on everything in sight (including the upper suspension member) applying VS. OK
Next, I disconnected the rear end of the drive shaft from the differential input. When I did this year's ago, to replace a leaking seal, the fasteners were nearly seized and that's when I had to grind down the outer circumference of a 13mm (?) box wrench to fit around the bolt heads. This time two open end wrenches got the job done. Permanent marker used for refitting. There's an alignment lip on the driveshaft side, so a couple of light taps separated the driveshaft.
On a side note, I don't believe checking differential play with the DS connected is helpful (unless all is snug, then no problemo) since rotating everything as a unit is not informative as there are too many variables at play.
Note, at this point, I jacked the rear axle a bit more to free the tires, and placed jack stands appropriately. Parking brake on.
Using just my hand, I rotated the diff input and measured (numerous times) total displacement of the input. Afraid I really exaggerated before, because this time, only 1/4". Vigorous hand rotation of the diff produced no sounds other than a mild bump (is that a sound?).
Decided I needed to apply more torque, so I attached my 00 vice grips to the diff input and rotated again (with vigor).
OK, thought I was onto something and used a stethoscope (RN type) to track the noise. Diff was nominal, axle, the same but a distinct clank when listening at the brake dust shield on either end.
False alarm, unfortunately. I took off the DS wheel and disk and learned that with my PB on full, the axle hub will rotate the captured PB/rotor assembly through about 1/2", with a clunk at each extreme. Confirmed by putting the rotor on backward, covering just part of the PB shoes and with the PB on, could watch the shoes move CW and CCW. Who knew? Or is it just my car. Makes no nevermind anyway, since it does not relate to my issue.
While I had the rotor off, I jammed my vice grips onto the diff input to lock it up and checked axle rotation at the DS wheel. The hub moved about 3/8" total and vigorous rocking produced only the aforementioned bump sound.
Found the cold chisel, whose back end I had ground down to fit the diff filler and checked the fluid level. Seemed a bit low, but with the car on ramps, hard to say.
Put a drain pan in place and dumped my Oreiley's gear oil (I know, I know, I'll look for Redline but wonder if I would be wasting $$$). I'm guessing 10k on the oil (man, I gotta keep records) and it came out quite dark. Also, fine, dark metallic fur on the drain magnet.
Just remembered something else. Last year, I had a buddy rock the car in 1st (engine off, natch) while I bravely stuck my head under the rear end and listened. My recollection is a slightly subdued version of the previously described clank, fore and aft, coming from, as nearly as I could tell, the diff.
Richard, your description of how to disassemble the differential from the driver's side is intriguing and I'll have to read it again more closely. No lift available so everything would need to be done on jack stands, but better than a complete axle drop.
Oh, did I mention? I really think there are gremlins in my differential, although I could be persuaded otherwise. Many times I have gone through a list of suggestions and put options behind, only to discover the problem was one of the items I thought I checked.
A final thought (definately not from Mark Twain): "It ain't what you know gets you in trouble. It's what you think you know that just ain't so."
Steve Waclo Carson City, NV; '87 Spider QV, ES Champion, 2018 Reno SCCA (125k);'93 Honda Nighthawk 750 (105k);'03 GMC Sierra SLE 2500HD Turbo Diesel (155k);'08 Altima Coupe 3.5SE, 6sp (125k)
Last edited by Stevew; 11-09-2018 at 10:38 PM.
Reason: 12 years of Catholic School