REAR END TROUBLE

[ONLNTM5]

Hey guys,
My son has a 97 Firebird, with a 3:42 (I think that’s right) rear end, non-posi, with the Traction Control System, and we recently had the rear end bearings and seals replaced, as well as the rear wheel bearings. The “shade tree” mechanic that did the job, said that the gears looked ok. I looked at them and they did look ok, but I am not an expert, but he is supposed to be, since he is a retired mechanic from the Pontiac dealership. Anyway, before he did the job, the rear end had a high pitched roaring noise coming from the right rear, on acceleration, but now it has noise on deceleration. He said that it was because of the “old” gears, and that they would have to be replaced to completely get rid of the noise. What is strange, is how the rear end just started making this noise in the first place. We had the fluid checked whenever it started making the noise, and it was full, so that wasn’t the problem. So, does this story wash? First we are told that the gears look ok, and then, we are told that it’s the gears that are making the noise. Does this sound right, or did we just get ripped off? I didn’t think we were ever going to get the car back from this guy, so whatever we do from here on out, will be either be done by me or someone else. The bottom line is, what can be done to get rid of the noise?
Any advice would be very much appreciated.
Thanks,
Bruce

[Mike71]

it sounds to me like the backlash(correct term?) is not set properly now..i read about it alot on a 4x4 forum i belong to..it usually happens after they have changed to differecent gears and they did not set them up properly..

[SteveH95Formula]

try adding the GM limited slip diff. additive even though you claim it is not a limited slip diff. I don't think it would hurt to try it.

[Kevin - Blown 95 TA]

Well, you should start by opening the rear cover and mark the ring gear with the yellow grease to see where the pattern is. Then, if you can borrow a dial indicator, you can look at the backlash - it should be 5-6 thou. Get a book on rearends or download some pics from the net to compare the pattern to. These clues will tell you what's wrong.

In a rebuild with new bearings, etc., it can be a little hard to get the gears back exactly like they were, and if they were in there wrong to begin with, and they were broke in that way, then it might be hard to get them back to perfect. The mechanic might have set them up by the book, but they got funny wear on them from before. I'm not saying that's the case, but it well might be.

[Joe 1320]

As was mentioned, most likely the backlash is not correct. Whenever the rear is taken apart, all the clearances should be verified and reset. Most often these backyard semi-rebuilds give you the result that you see. You may end up needing a new ring and pinion of you cannot correct it. Have specialty shop set the backlash.

[ONLNTM5]

Thanks for the ideas on what the problem might be. It sounds like it might possibly be the backlash. I'm not really sure exactly what the backlash is, or maybe I just forgot. Anyway, how much damage could be caused by not having it set properly? I wonder if it would be worth trying the GM limited slip additive first, to see if that would quiet it down. Can you get the additive anywhere else besides the dealer? Also, does anyone know about what the average charge might be to have a professional to set the backlash?

[Mike71]

even if the additive quiets it down all its really doing is putting the problem on the back burner..i would just fix it right the first time and never worry about it again

[Valyndiir]

Thanks for the ideas on what the problem might be. It sounds like it might possibly be the backlash. I'm not really sure exactly what the backlash is, or maybe I just forgot. Anyway, how much damage could be caused by not having it set properly? I wonder if it would be worth trying the GM limited slip additive first, to see if that would quiet it down. Can you get the additive anywhere else besides the dealer? Also, does anyone know about what the average charge might be to have a professional to set the backlash?

Backlash is the gap between the gears. Too close or too far makes the gears wear incorrectly. Basically what will happen, assuming the backlash is set incorrectly, is that the ring and pinion gears will wear eachother much faster than normal and possibly throwing teeth. I have had my run-in with these rear ends and I would recommend having a shop look at it. Integral differentials are no fun to play with. Limited slip additives are friction enhancers(i believe). I had to add this to my Moser 9". According to Moser it is required for the friction plates to catch properly. That is heresay so it may not be perfectly accurate. However, I don't think it would damage anything to add it.

[TraceZ]

You might want to compare the price of getting a salvage rearend from a wreck to fixing yours. I'm assuming the car is a V6, since you say it is without positraction. Used low mile V6 rearends are a dime a dozen because nobody really wants them. It is at least worth looking into if there is a salvage yard close by.

If the gears in your current rearend are worn, you could spend $200 getting it all professionally re-installed and still have problems. Then you'd have to buy new gears and start all over.

I bet you could get an entire used low mile V6 rearend for $200. Like I said, it is at least worth looking into.

[ONLNTM5]

We checked at a local junkyard for a rear end, and were told about $200.00-$300.00 for one, until I told him the car had the Traction Control System. He was like “are you sure?”, “a 97 model shouldn’t have that”. He then told me that a rear end with the TCS would be $800.00-$850.00. Also, I have to say that these people were about as rude as anybody could be. Its been a while since I dealt with a junkyard, in person, and I had forgotten how rude some of these people can be. All that I wanted to do was go out and look at the different cars that had the rear ends, and look at the rear ends while they were still on the cars. I guess they don’t want to bother with that, though. They just want to sell you what they want to sell you. I finally got them to show me three cars with rear ends and the guy that took me out there, looked right at me and told me that this one car with a 3800 engine was an 8 cyl. I finally convinced him that it wasn’t.
I have bought quite a bit off of EBAY, including my 99 Camaro, and there are not usually very many rear ends available, but I did find this one this morning-what do you all think about this?:

eBay item 7927585507 (Ends Oct-18-04 05:46:38 PDT) - 2001 PONTIAC FIREBIRD REAR END USED

I have become quite wary of EBAY sellers though, because I have been ripped off several times. Fortunately, I was able to work things out with all but one EBAY seller (EDEMERSON).
Does anyone know if a non-TCS rear end can be installed in place of the one that is on the car now and do you have to match the same gear ratio? Also, Kevin, do you know, without going to a whole lot of trouble, where on the net that I might find some pics of rear end patterns, like you mentioned? By the way, I misspoke about the rear end being a 3:42. It has an axle code of GU4, which I believe is a 3:08, so the one on EBAY is the same ratio.

Thanks

[ONLNTM5]

Well my link didn't work for the EBAY item. Can anyone tell me how to get the link to show up as a clickable link?

[ONLNTM5]

Well, here is a cut and paste version:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7927585507&fromMakeTra ck=true

[Kevin - Blown 95 TA]

Let's see if this works...



BTW, you might just post a WTB ad on some of the forums. Plenty of guys like me have ripped out perfectly good rear ends to put in 12 bolts or 9" and sold ours for $300-350 or so. Better than taking a chance on getting another junky one with worse problems than yours has.

[ONLNTM5]

THANKS KEVIN,
That illustration gives me a really good idea of the back lash. Now I understand what it is.
I believe I could handle something like that, but I am not sure about a couple of things:

Where do I get the yellow grease that you mentioned -

I found dial indictors on EBAY, but exactly how is it used to determine the back lash? I am assuming the gap between the pinion and ring gear?

How do you adjust it once you determine that it needs to be adjusted?
Thanks

[Kevin - Blown 95 TA]

THANKS KEVIN,
That illustration gives me a really good idea of the back lash. Now I understand what it is.
I believe I could handle something like that, but I am not sure about a couple of things:

Where do I get the yellow grease that you mentioned -

Any place that sells the gears & install kits.

I found dial indictors on EBAY, but exactly how is it used to determine the back lash? I am assuming the gap between the pinion and ring gear?

Set it up against the face of the ring gear tooth & rotate the ring gear forward & backward - measure the travel.

How do you adjust it once you determine that it needs to be adjusted?
Thanks

Carrier shims, unless the pattern shows that the pinion depth is wrong.

You need to do some research - suggest looking at back issues of car Craft & other car mags - they cover this every couple years, otherwise get ahold of a factory manual.