vince vette 2

I made a couple recordings, but apparently m4a audio files cannot be uploaded to these posts. If someone can convert them I can email them the originals and get them posted.

Hamerdown

My 81 140,500 miles at times will 'clunk'
Over the decades (bought it new) I would routinely drain the Differential Gear Oil (I drilled and tapped the lower aluminum case and used a plug) and always added TWO bottles of the GM Limited-Slip additive and then found a big parking lot and made several figure-8's...this made it quite.
When it starts 'clunking' again I'll make a few 'tight' figure 8's in a parking lot and it gets quiet again.
Local Vette shop stated the clutches sometimes get sticky then unload and that causes the noise...seems to work for me.
BTW...back in 2014 I dropped the Batwing, pulled diff out and went all through it, checked the wear pattern and it was fine, backlash was a little extreme but well within the parameters...clutches even looked good as so did the two large bearings-and races (routinely changing Diff Oil must be why) and Installed new oil seals, rebuilt Stub Axles with hardened ends and the new-harder center-pin (the OE center-pin had a hex pattern wear all around it) and rechecked wear pattern at the gears and all was good.
Just for giggles go do some figure 8's in a parking lot to see 'if' that quiets the 'clunking'.

vince vette 2

Thanks for the suggestions. The rear end was just rebuilt by Bairs. They did recommend two bottles of additive. I also did some figure 8's. The Bair's tech was surprised with my Dana 44. After 90,000 miles everything looked good. He felt it had to have been worked on previously. But to my knowledge it was only ever in for new seals. Go figure.

garrettb

I was able to get the audio files converted. Recording 3 is probably the easiest to pick it out. It's definitely a similar sound to what I am hearing when slowing down.

vince vette 2

Thanks for getting these converted.

Now I'll ask the experts to weigh in on likely sources. As per early notes. The recording with the more obvious knocks starts out slowing from from around 35 or 40 and the knocking picks up during deceleration from 25 to 15, off throttle, in drive, no brakes.

The recording with less detectable knocking is deceleration under 15 mph.

DUB

After listening to the audio files on this. I have a couple of questions.

When you had the half shafts out...did you spin the rotor and 'feel for any bumps or bad spots in the bearing when it was being turned slowly?? I normally try to do this with the caliper not installed so it is not causing any additional drag on the spindle/rotor when doing this. I can often times pick up a galling feel in the bearing and when I take it apart it is confirmed that the bearing race is damaged due to really bad galling in one or more spots.

Does this sound happen ...literally ....the instant you take the car out for a drive...OR...does it seem to begin to show up the longer you drive it???

Assuming that the U-joints are still good. Way back in the day my Dad suggested I use another U-joint due to it being cheaper but it was in a box that said it was BRUTE STRONG. Well...I did and in 6 months I was replacing them and putting the SPICERS I had been using right back in.

The sound comes on when the car is under a load and then also when it is not...so that obviously is telling me that it has something to do with a component that is turning. So this is what is directing my comments in the direction they are.

I am NOT the 'guru' of rear differentials but hopefully GTR1999 ( Gary) can chime in and let us know if it is still possible that the bearings for the carrier or pinion can case this issue due to you currently have an issue with the rear differential. Not saying that is what it is...because if I read what you wrote...you really did not have a huge issue with the differential...unless BAIRS found something while doing the set-up.

I doubt it has anything to do with the differential or U-joints due to when the car is in motion...they parts that can be bad are now in a position of being interlocked or engaged...so-to-speak...and thus the noise is not there.

MY GUESS....it is the wheel bearings due to they have not been addressed. Because the sound does not sound like exhaust hitting the frame...especially if you have made attempts to make sure that it cannot hit the frame and that ALL of the mounts for the exhaust are correct.

DUB

GTR1999

Vince
I can't pinpoint the issue from those sound bites, sorry. Bairs is the place I would send any 80-82 diff to for repair, they are good, have the tools, knowledge and back their work up. If you contacted them and they told you the diff was good but has a gear whine they will cover it and not try to tell you otherwise so I would pull the diff out of the equation. As Dub mentioned, if your bearings are original, the grease may be gone by now, I have seen it on low mileage original cars. You are a capable guy and I can coach you it you want to check the rear bearings. Think about it, there's not a lot moving back there- drive shaft- diff- wheels. Suspension- bushings, shocks, springs. Again knowing your training a systematic approach from the trans back should show any obvious external issue.

vince vette 2

Dub, GTR,

Thank-you both for your continuing advice. Concerning Dub's questions/points:
- I did not spin the rotors while with the half shafts off, at least not with the intent of finding an issue with the bearings. I did use the backside tool to press some grease into the bearings - GTR, I know you're not a fan of that and understand the reason. As I expected to pull the TA's this coming fall, I was just buying some insurance for the few hundred miles I might put on this some (which is getting to look optimistic). I pumped in only half the GM recommended amount as I did not want to risk pushing something out the other way. I did spin the rotors after putting the spindle yokes back on, but it wasn't slow enough to notice anything subtle. I was looking for a gross screw up.
- On the issue of it happening literally on taking it out - It is certainly soon - within 1/2 mile, but maybe not literally. I'll check this weekend.
- U-joints are all new with the work this winter. They are all Spicer non-greasable.

Putting the comments from both of you together along with the facts that this noise was there before all the work I did, which suggests it lurks elsewhere than things I or Bairs touched. Also, since it did start out as barely audible when I first detected it sometime in the 90's and got progressively worse, it would indicate wear. I to am suspecting one of the spindle bearings even though it's not the traditional grinding.

My plan then now is to check on the timing of when the noise starts and I'll report back on that. Meanwhile, this weekend I'll recruit my two sons to help pull out of the basement all the steel that makes up the quick-lift and help me assemble it. Then get the vette up on it and see what kind of view I can get of the TA bushings and also pull the half shafts and calipers to then turn the rotors to get a sense of any bearing issue. That may take some time as my wife is still waiting for the water softener I promised to plumb in.

GTR1999

Vince if you want to drive to CT on a Sat when I am building a set of arms I'll show you how to build them.

vince vette 2

I'd be interested in seeing it. If there's a small airport near you I could fly up. Likely sometime later in the year. I have some travel in September and October.

vince vette 2

The latest update.

Dub, in answer to your question, does the knocking start literally as soon as I move, I can say for certain within 100 ft, pretty much as soon as I get up to 10 or 15 mph and then let off the throttle.

Now for today's development, having recruited my two boys to help get the quicklift out of the basement and assembled, I took one of them out for a short drive. Short mainly as there is a new sound associated with the engine. I'm not going to deal with that for now.

But on the drive, at about 20 mph I put it to the floor - not a flat out stomp, but aggressively. At just passed 55 I came off the throttle and just as I did heard something like a crack and for a split second it seem the car was about to come to a hard stop. It threw us both forward slightly in our seats. The whole event was under a second. I wasn't even sure something had actually happened until my son said to me "what was that". There was no swerving or darting. It was all perfectly straight. I guess the closest analogy would be like the brakes were tapped for an instant and let off.

Sorry for the bizarre description, but I have no better description.

DUB

That is odd.

How did the rest of the ride go after that incident?

Would you say that it would be similar to having a manual transmission and you going fast and then pushing in on the clutch...and how the car can somewhat nose dive while it loosed the pulling power of the clutch? If so..I wonder if it is transmission related.

I have seen ring gears and pinion gears that have snapped a tooth off of them but usually when I encounter them the portion of the tooth of the gear can get caught up on the ring and pinion and lock up the entire rear end.....so that is not it...due to your rear end did not lock up the wheels.

DUB

vince vette 2

The ride after the issue was the same as previous rides. The usual gear noise and and knocking.

It may have been somewhat like that instant when you push in the clutch, but more abrupt though much shorter. I could see it being auto-trans related. With the 3.07 gears with the pedal down it would shift to 2nd right at 60 mph with the RPM hitting 5200. I wasn't watching the RPM, but with 3.54's if it was hunting the same RPM to shift it would to it about 15% slower. That would mean it wanted to shift at 50. When I said in my previous note it was just passed 55 I came off the throttle that's when I was fully off. But I started coming off as it passed 50. Maybe I scrambled the tranny's fluid dynamic controls by coming off throttle just as it was ready to kick up a gear. Or maybe the speed gear I left in the tail housing decided not to play nice with the vacuum accumulator, the only other thing back there.

The tranny has had an event or two in its life. One was a time that I pressed the brake to come to a stop and it simply didn't disengage. It stuttered a couple times under the load and stalled. I started it and off it went. I changed the filter and fluid and it never recurred. But automatics are a mystery to me.

vince vette 2

Got off other projects finally and back to this. Pulled the passenger tire to get a look at the trailing arm bushings. Opinions welcome - could this be the source of the knocking I'm hearing?



long view - looks like shims are where they should be



closer look at the wheel side (right)




closer look at the half-shaft side (left)

A side note - many years ago (as everything about this car is) I brought the car in for an alignment. I had a lifetime deal with Goodyear. When they were done the tech said I made out on the lifetime deal as they needed to put shims in to get the rear setup. I speculate that was probably with about 60k to 70k miles on it. Just noting it in the event it matters. As for the driver's side I didn't pull a wheel off yet.

DUB

The trailing arm bushing is SHOT. Make NO Mistake about that.

When I see rubber coming out like what your photo shows and the yellow arrows are pointing to, THAT is an instant indication that you have a problem.



In the photo below....I can sea gap...which is ALSO an indicator the bushing is shot.



DUB

vince vette 2

Thanks Dub, I think I knew I was going to have to pull the trailing arms in the near term if for no other reason than to redo the bearings and such as at 90,000 miles with minimal maintenance they were on borrowed time. I was just hoping that was 2 years out. Guess I should have looked in there when it was all apart 6 months ago. Hopefully this is the source of the knocking noise I've been hearing.

On the bright side, since Bair's agrees that the noise in the rear end is not acceptable and will rebuild it again, I have to pull that out anyway. I't not too much more to pull the trailing arms. And I get to do it all on my quick lift this time. Gotta be better than on blocks of wood. Though I'll need a lot more jack to get the rear end out and back in. Not sure how I'll tackle that yet.

GTR1999

VInce call me anytime if you are going to rebuild the arms at home and I'll walk you through the whole deal.

vince vette 2

Gary, thanks. I'll see what kind of mood I'm in once I get them pulled off. As a starting point though, what specialty tools will I need beyond a magnetically mounted dial indicator which is all I have?

DUB

A spindle knocker to remove the spindle. Some may use a hydraulic oppress...but you have to figure out how to support the trailing arm so you do not damage it. I have always used the knocker tool and it has never failed me.

A bearing removing tool to remove the outer bearing off of the spindle.

A set-up tool so you can get your bearing set up when they are dry.

A spindle installation tool to pull the spindle in your set-up...OR...as some use a hydraulic press to press in the spindle.

You will also need the trailing arm bushing press to compress it so you can stake the sleeve.

DUB

GTR1999

DUB covered it. I use the knocker tool all the time even though I have a press. I have to go back through my old threads and pull the press reference out if I haven't yet. I always use the press to install, have the tool somewhere but never used it once. You can make up a bushing press. Some guys have the tools and may loan them out, I wish I could be I use them all the time.