portland area guys/gals, need some help..

hey guys. i've got a knocking noise coming from the rear of my Z (99 Z28, mods in link in sig). the noise is proportional to the speed of the car, and is only audible at slow speeds, either decelerating in gear, or coasting in neutral.

i took it to they guy who's worked on my car before (in lake oswego, formerly mgees auto service). he took the rear apart, and said he couldn't find any problems. while he had it all apart, i had him go ahead and replace all the bearings (axle bearings, carrier bearings, and pinion bearings). he said all the bearings were fine, but replaced them at my request.

of course, the noise is still there, and driving me crazy. it's to the point that i don't even want to drive it any more because of the noise.

right now, it's on jackstands in my garage. i'm going to pull the axles just to look at them, and maybe the axle bearings (even though they were just changed). anything beyond that would be out of my comfort level doing on my own, unless i had some help.

so my question is, are there any local shops out there who are very experienced with 4th gen rear ends? anyone in the area consider yourself a 4th gen rear end expert? if so, let me know. i'm really not expecting to find anything wrong by myself, since my mechanic couldn't find anything wrong.

also, are there any local meetups anytime soon? if so, maybe i could get someone else to listen to the noise, and maybe it will be something you have heard before....

i'm almost ready to take this thing to the STEALER!!!:cry:

It could be a couple of things. At any rate, don't take the car to a dealer. The labor rates and diagnostic fees will kill you where you stand.

I had the same problem in my 2000 Z28. It was usually at lower speeds up to 35mph, coasting, in neutral, and amplified if I was taking a slight left turn. I put a ton of miles on the car, and it never got louder. I had it checked once, and same as yours: Everything was fine.

I've heard that sometimes the axles can become pitted. Even if the bearings are replaced, the pitted axles will produce exactly the noise you are talking about as they turn inside the new (or old) bearings.

If you have the know-how, pull your axles out and inspect them for wear or any sign of pitting.

If not, then you can chalk this up to the f-body's extremely strong, well-built rear end :p ...or you can go to the dealer who will say everything is fine in exchange for $70.

It could be a couple of things. At any rate, don't take the car to a dealer. The labor rates and diagnostic fees will kill you where you stand.

I had the same problem in my 2000 Z28. It was usually at lower speeds up to 35mph, coasting, in neutral, and amplified if I was taking a slight left turn. I put a ton of miles on the car, and it never got louder. I had it checked once, and same as yours: Everything was fine.

I've heard that sometimes the axles can become pitted. Even if the bearings are replaced, the pitted axles will produce exactly the noise you are talking about as they turn inside the new (or old) bearings.

If you have the know-how, pull your axles out and inspect them for wear or any sign of pitting.

If not, then you can chalk this up to the f-body's extremely strong, well-built rear end :p ...or you can go to the dealer who will say everything is fine in exchange for $70.

the description of the problem you were having sounds EXACTLY like my symptoms. did you ever find the root cause or get the noise to go away?

actually, i have the axles out right now, and they look just fine. both axles were replaced 2 years ago when i had my 3.73 gears installed. the surface that rides on the rollers is perfectly smooth and shiny. no problems there.

at this point, i'm not sure what else to do besides live with the noise. i guess i'll put it all back together tonight. i found another f-body guy in vancouver (wong's) who said he would listen to the noise next week. don't know how much good that will do, since everyone who hears it says it sounds like axle bearings.

i'm about $500 into this job so far (paid the last guy to replace all 6 bearings and both u-joints), and the noise is still there. i don't know how much more i can spend on this "problem", that may not actually be a "problem". hell, every time i open the differential, i just spent $20 on fluid and a gasket.....

well, i guess i'm just venting now. i'll stop.;)

so anyone else know any good 'rear-end shops' in the pdx area?

Beyond knowing that the problem never got any worse, and that it had nothing to do with the bearings, no, I never found the root cause. Wish I did, that way I'd be more helpful to you :D

I bought my 2000 Z28 w/ 49k on it and drove it to 61k with the noise present and no problems. It never got louder (or quiter) despite a fluid change and inspection of the bearings/axles.

If you find out what it is, let me know--that way, if my 98 ever starts acting up, I can fix it right away.

buttoned everything up last night, and test drove her, and the noise is still there.....:mad:

i'm wondering if my 3.73 gears could be to blame (even though they look fine on inspection)? i had them installed about 2 years ago. it's hard to say exactly when this noise started, as my cutout is usually open, and i recently closed it, which allowed me to hear this noise crystal clear.

maybe i should put some 4.10's in and see what that does......:shrug:

My 3.73s slightly whines at about 40-50 mph on slight accel and decel. Its a takeout complete 10 bolt from another car, which got new ring and pinion 3.73, rebuild kit(bearings, seals and such), and a T2R diff. The shop did it over twice, and got it check by another guy, and they said its as good as its going to get. I don't even think twice about it now, 20k later.

Although I think my diff may be making knocking noises on slow speed decel now. HOWEVER, I do have a much more aggressive T2R diff in it. Makes a regular T2 feel like an open unit in turns.. Makes powering out of turns awesome! :D

This was done at paceway frame and axle.. I don't have any other shops to compare it to.. They do at least know how to do a custom front alignment for a fbod, if you want neg camber for autox and such.

But I think if I need any 10 bolt work done again, I'm going to try mcgee's auto next time.. I did a dyno day at their shop and seem to be nice. One of the guys that works there is also working on putting an LS1 in an old 30's Buick for his wife daily driver!

Hey man, you don't happen to ride around shute road/helvatia area on your GSX-R750?

I remeber a month or two ago, I saw a blue/white GSX-R rounding down a backroad sweeper around that area, while I sat on my bike and just watched pass by while I was on a side road to take a right..

I just got my red 2006 SV650S as my first bike a few months ago and trying to learn the ropes. :)

I got a 99 black Z28 too.. I don't remember seeing your car around though..

check the suspension bolts. i had that issue once, lower control arm bolts werent to spec.

Did you inspect the gears very carefully? I'd look for hairline cracks in the teeth. My 4.10's made that same noise before I lunched 4 teeth off the pinion gear and 3 teeth off the ring gear lol....

Also, have you inspected your U-joints? I've heard U-joints make that same noise when you could swear it was coming from the rearend. I'd replace those next, just because it's a very easy way to elminate that as a possible problem, or swap it out with a known good driveshaft.

Good luck with it.

Mike

I assume that the gears are aftermarket...and were installed by someone else---perhaps they were installed incorrectly including pinion depth, backlash, pionion preload, and carrier preload.

I.e, you can have all new parts, but if not installed correctly, you are going to have problems.

Of course you first have to be certain it's the rearend making the noise.

You might check with Oregon City Transmissions---either they can give you some suggestions or recommend someone who can.

BTW, if you have to go into the rearend again, might I suggest you get some OEM 4.10s and have them installed with ratech solid pinion spaces. JMHO:cool: