Saturn5

I know the general consensus is going to be "put a stronger rear end in it" but that's not what I'm looking at right now.

Some history:
I have a 2000 Trans Am M6 with 152k miles. I recently had the rear end rebuilt by a local garage and after multiple trips back and them working on it for several weeks, it's still noisy. I had all of the bearings, ring & pinion, axle bearings/seals, etc. all replaced. I did a proper break-in of the gears as well. When I was taken in most recently, it's been about 1000 or so miles on the new gears and he said the wear pattern looks good and there's no sign of improper break in. He replaced a pinion bearing and race this time around. (I don't know for sure if they were skipped during the rebuilt or not included). It's quieter, but still makes noise. I have done some searches and the overwhelming response is always to put something else in it. I get it, but that's not what I'm looking for right now.

So given that history I'm looking at a couple of different options.
1. Replace the entire rear axle assembly with a remanufactured unit. "PowerTorque" brand is available at O'Reilly auto parts and I'm sure others.
2. Find a different shop to fix the rear end that's currently in it (assuming there isn't some wear that would make it not rebuildable).

Does anyone have any recommendations on a reman brand, or failing that a shop within 100 miles of Raleigh NC that can handle the job? The shop I went to I've been using for a while and they have a good reputation, but this is looking beyond their ability.

FirstYrLS1Z

iTrader: (4)

What brand gears did they use ?
How noisy ? slight (not as quiet as stock new car) OR loud ?

RockinWs6

Ditto, I know this sounds odd but its not that hard to set these up. Maybe they need a little coaching, IMO anyone with basic mechanic skills can do a rear with a little knowledge.

Saturn5

What brand should he have used? I'm sure these were just stock replacements, not some premium speed-shop brand.
Define "slight" and "loud." Initially it was loud enough to hear at highway speed with the top down. It's quieter now that he replaced the pinion bearing and he did say the wear pattern on the ring and pinion looked good and they looked to be broken in properly. He also said the ran it on the lift and the noise sounded like it was coming from the pinion bearing area. He also mentioned the pinion bearing race was shiny on one side and looked brushed on the other. Both bearing and race were replaced, IIRC. As before, the noise starts to become audible at about 30mph and gets louder up to about 70mph when road noise starts to drown it out. The noise is primarily under throttle. I don't know how many rear ends he rebuilds, but this is a reputable shop that has a large local following and has been around for over 15 years. It's a small operation, but he has a reputation for quality work. I, and friends, have had a lot of work done there over the years. But, maybe this is outside his expertise. It's possible.

I know some people say "some" noise is normal. (how do you quantify "some"?) I don't disagree, but it's louder than the original rear end was when it was completely shot. If it was quiet from the factory, I don't think it's unreasonable to expect that with the rebuild.

FirstYrLS1Z

iTrader: (4)

There are many brands to choose from,Motive,Richmond,Yukon for a few. And typically within a brand there are different qualities as for regular use and performance use. Motives seem to be the preferred and Richmond is considered to be 'noisy'.
Factory rear ends for the assembly line are built by AAM (American Axle Manufacturing) in Detroit. Their 'quietness' is difficult to obtain when rebuilding.

rising_4rm_ashes

iTrader: (2)

Would REM Polishing possibly help with that issue? Just a suggestion.

Saturn5

Thanks for the info. I'll check on the brand of the gear set and see. If it's difficult to get factory rebuilds to be as quiet as OEM, I may lean towards getting a low mileage used diff and swap the entire unit out if I end up having to spend more money on it. I would like to keep the stock rear for at least another year or two. I don't know what my long term plans for the car are going to be - either put serious money into it with an engine swap/build, which would get a beefier rear end, or sell it to buy something else. Right now any money spent is lost if I sell it, so I'm trying to minimize cost for now.

FirstYrLS1Z

iTrader: (4)

Swapping out an entire rear end is relatively easy, I'm 72 and I do it in the garage on jackstands, just got doing one, pulled out the 3.23 rear (was in for the past 7 years) and put the 4.56 rear end back in.
Since you're an M6, finding a decent quiet used one would be 'iffy'. M6s' cause rear problems because of the stick shift/clutch shock loads.
Also 3 channel ABS only and 4 channel ABS & TC rear ends are not interchangeable because of the locations of the sensor ring (s).
Mine is 3 channel and I've accumulated many complete rears from M6s'. Given to me from friends in the group just to be able to clear it out of their garage. The 4 channels I always sold for $125 just to get rid of them. Typically they sell for $300-500 and that's with unknown quality/noise.
A 3 channel rear can be converted to 4 channel by swapping/using the axles and backing plates from the 4 channel and using them in the 3 channel rear. A 4 channel rear CANNOT be converted/changed to 3 channel without housing machining and acquiring the proper sensor ring.

Saturn5

Great info, FirstYrLS1Z! Thanks. I wasn't aware of the interchangeability limitations between 3 and 4 channel rear ends.

The main reason I'm holding off on a non-stock upgrade for now is I don't know the future plans for the car yet. I may decide to keep it and upgrade the power substantially, which will require a beefier rear. Or I may trade it and get something else, so that upgrade money would be wasted. I'm not doing anything major with the car for probably a year or more and I don't want to the car to just sit for a year waiting for my life to catch up to it.

I appreciate all the info, guys! It really helps.

01ssreda4

iTrader: (96)

What kind of noise is it? Is it howling or what? Trying to give a suggestion as i rebuild diffs quite often but I've never had one make noise from 30mph and up? Why was the diff originally rebuilt?

Saturn5

I took it in originally for what I thought was rear wheel bearing noise - only did it when turning and sounded like it was coming from the rear. Also the rear end felt "loose" - almost like you were towing a trailer and had some trailer sway. (New LCA's, shocks, springs - all properly torqued and re-torqued).

When I took it to my shop he said the rear end needed to be rebuilt, gears, bearings, etc. When he took it apart he said he could see the wear pattern looked sloppy on the pinion bearing (don't remember his exact words, but essentially that's where the sway feeling was coming from). After the rebuild the sway feeling is gone. Now when I drive it once I get up to about 30mph I start hearing what sounds like a whining or gear type noise. It may be doing it at lower speeds but isn't loud enough to be noticeable until around 30mph. It gets louder the faster I go up to about 70mph or so. It only does it under throttle and being in a different gear (M6) doesn't change the pitch. It is directly proportional to vehicle speed but doesn't do it when coasting.

I'm not sure how you would differentiate a "howl" from a "whine," etc.

I've had some suggest since he just used standard replacement gears, it may be that they're just noisy and the fix is to replace the gear set with a better quality brand. I'm going to take it back to the shop to have him look at it again since it won't cost me anything, but if he can't fix it after 3 tries, I'm either going to have a known expert rebuild it again or I'm going to replace the entire rear end. So I'm also looking for recommendations for mechanics who can do the job right. This isn't a drag car so I don't see a need to upgrade to a beefier rear end at this time, not to mention I've also heard a lot of people talking about how the stronger rear ends can also be noisy. I want it to be as quiet as it was from the factory. Maybe that's expecting too much?

01ssreda4

iTrader: (96)

30-70 noise could be a bearing but Im leaning towards a crappy gear pattern. However, not all gearsets are the same. He may have put it in with the best pattern possible with that gearset. I am hesitant when rebuilding rears about what gears people bring me. Ive had really good patterns with Motive brand and i generally recommend those to people. I can almost get the shim packs right and produce a great pattern on the first try every time, which = easy/quick money for me and a happy customer. For the quietest set, you want the motive blue box, part number will start with GM75xxx. The three Xs will be the ratio of the set. Also, oem GM/SLP gears should be silent.

Side story, I had a rear rebuilt when i was a teenager. It came back with a slight howl from exactly 40-50mph on coast/decel. I took it back and he said it was "normal" and nothing to worry about. That rearend went another 100k+ miles with the same howl. Looking back now, the shop bill was about $650, and there is no telling what kinda gears they put in, wouldn't surprise me if it was some used set they had on the shelf, which would make that a hefty profit on their end.

FirstYrLS1Z

iTrader: (4)

^^^ gear sets can go a long way when set for the best 'wear' pattern. That might not be the best pattern for noise but I'd rather have a long lasting/slightly noisy gear set than a quiet/soon to wear out gear set.
My 4.56 set (used picked up at Canfield swap meet for $25) still going strong after many years. It's always had a 'hum' that never increased in intensity.

dlandsvZ28

Is it possible he was lazy and didn't replace the crush sleeve.

GM techs are notorious for using the same one even though the manual calls for a new one, even for a seal replacement. Even on my 98 when it was under warranty. The service mgr argued with me but they finally did it right and replaced it.

Since then I had my ten bolt rebuilt with a Ratech solid pinion spacer instead of the crush sleeve along with a complete overhaul - Motive and Ratech parts.

Some noise can be amplified thru the torque arm and transmission mount as well. So would check them for wear or disintegration while it's in the shop.

Saturn5

Thanks for the info. I'll talk to my mechanic. If a new gear set is the solution, I'll make sure to go with the Motive Blue box part. He's already put a ton of labor into it, so I'm sure he doesn't want to see me bringing it back over and over any more than I want to take it back.

dlandsvZ28

Notice you have a 6 speed. After 18 years, the transmission mount can get real loose. IMO I would not replace with poly. If you do replace it, make sure YOU compare the new with old. Some OEM aftermarket replacements are NOT the same height and can affect pinion angle.

Saturn5

Last year when I had a new clutch put in, I had all new engine and transmissions mounts done at the same time. I figured the car has 150k miles, there's no point in checking if they're good or not - just replace them while the tranny is out. (and I didn't want to replace the trans mount and not the engine mounts) So even if the mount changed the pinion angle, it had the new mounts when the rear end was rebuilt.