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Discussion Starter · #1 ·
I took my 94 stock trans am to a rear end shop yesterday to get some much needed questions answered. Supossedly I was told by a rear end shop in San Diego that I have a bent axle caseing due to the fact that my rear tires do not sit flush/perpendicular to the ground. This is whats causing poor control on the rear end during wet road conditions, I'm told. So I explain all this to the shop guy yesterday, give him all the detailes I can, and aside from being the rudest SOB I've incountered in a long time, his only suggestions for me was to find another axle assenbly which he said would be very difficult where I live (Reno NV) or sell the car to someone else and make it there problem. Sorry, not going to do that.

So here are all the details that I can give you in this matter, and I hope you can help with better solutions

1: Growling noise coming from the rear end during tight left and right turns, sound like a tire hitting the inside wheel well, but no indication of that happening, AND IT DOES NOT HAPPEN ALL THE TIME, AND NEVER WHEN TRAVELING STRIGHT.

2: Outside edge of rear tires wearing quicker then inside edge, less then 3000 miles on this new set of tires and edges are wore down.

3: poor hadling on wet roads, feels like I'm loseing control of the car.

4: rear ends feels like its slipping to out side of a turn when I go over RR tracks, either left or right..

5: PO had the pumpkin replaced back in 2009, and a recent check by the pontiac dealer service center says that my axle is OK (I dont believe them). I've been told to go to a body shop and have the rear alex mesured to see if it real is bent.

I really need help on this matter, as I would like to keep the car, but if I have a mojor work job ahead of me I need to know and be able to tell a shop just what I need done.

Thanks so very much in advance for any help.

Tony
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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The tire wear could be due to excessive camber (axle tubes bent downward) or due to excessive toe-in (axle tubes bent forward). An alignment shop will be able to check for both conditions, along with thrust angle (axles not perpendicular to centerline of chassis).

Solid rear axle housings can be straightened. Used replacements should be readily available from a salvage yard. All 93-97 rear axle assemblies from Firebirds and Camaros are physically identical. All assemblies from a V8 model will have disc brakes and a limited slip diff. Some, but not all, V6's have options for discs and limited slip. The possible mismatches:

- auto trans V8's can have either 2.73 (RPO GU2) or 3.23 (GU5) gears. Manual trans cars are 3.42 (GU6)

- 93 and 94 rears are all ABS only with 3-channel sensor system. In 95 they made traction control (TCS) an option. So 95-97 can be either ABS only, or ABS + TCS. The latter has 4-channel wheel speed sensors and are not compatible with your 94

- 98-02 have the same possible mismatches as above, but will fit. The only issue is the way the E-brake is actuated.

When you hit a bump with a limited slip rear, it is normal for the rear to move slightly to one side.

The noise you hear when turning could be due to lube refill not including the mandatory limited slip (LSD) additive.
 

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Discussion Starter · #3 ·
Thank you Fred, I believe the diffenitive term here in the first 2 sentences is BENT. Is it your opinion that the axle tubes could be bent? And just so I fully understand your saying that a good alignment shop (not tires plus) should be able to tell me if the tubes are bent? If you have time to answer this what would have to have happened to cause the axel tubes to get bent.?

Could the rear wheel bearings contribute to any of htese problems I mentioned?

My ABS system is dead accordng to the pontiac dealership and they told me the control module is no longer availible.

Normal on the side slip, one less thing I need to worry about.

Lastle what is this LSD additive as I've not heard of it and where can I get it?

Many thanks for taking the time to help.

Tony
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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Yes, the axle tubes can be bent. Serious Auto-X racers have been known to intentionally bend the axle tubes to increase camber.

An alignment shop can only tell you if the wheels are aligned correctly. They should point straight ahead (no toe-in) and have no camber. If they do exhibit either an alignment shop should be able to tell you if the degree of misalignment it serious, and if it would cause the problems you are experiencing. As far as I can see, the only way they could exceed acceptable limits would be bent axle tubes.

EBCM (electronic braking control module) is the computer portion of the ABS system, and should be readily available in junk yards, or on forum parts for sale listing, ebay, etc. A lot of people delete the ABS on drag cars.

Limited slip differential (LSD) additive. Use GM brand, Part # 88900330 (replacement for 1052358)

http://www.jegs.com/i/Chevrolet+Performance/809/88900330/10002/-1?CAWELAID=230006180000978842&CAGPSPN=pla&gclid=CMerktjKpcsCFRNahgodcIYApA
 

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Discussion Starter · #5 ·
Thank you Fred for your insight, the only thing you did not comment on was the wheel bearings, any chanch of these causing anyof the problems?

Tony
 

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Discussion Starter · #6 ·
So I dug into the axles yesterday and pulled everything apart. I replaced the bearing and dust seals, checked the axle themselfs with a long stright edge and found them to be not bent as fall as I can tell. Bearings were a little sloppy. there ws about a tablespoon of silver particles on the magnet. Refilled the punpkin with the LSD additive and good gear oil. No more noise in tight turns, rear end seem more solid. looking at the wheels as they sit on the ground and they look like there sitting flat with a slight tip towards the outside edge, is this the normal appearence??? I think its fixed but not sure, need some wet roads to really check and see if the rear end is stable.
 

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The tires should make a 90-deg angle with flat pavement - straight up and down. Put a level across the outer edges of the wheel rim, not the tire. Tire can have bulges in the sidewalls. Do you mean the top of the tire seems to be leaning outward toward the outer edge of the fender?
 

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Discussion Starter · #8 ·
So Sorry for the long delay in getting back to you Fred, and again I want to thank you for your insight and knowledge. Since the last post in March I have been busy with other things and have just gotten around to getting a few last things done to the rear end and could use you opinion on the changes I have made.

First off I took the Bird to a good alignment shop and they did a through exam of the front and rear end. As far as Toe for the rear, there is none, they are perfectly straight front to back. As far as Camber there is about 1 degree of negative camber. The Mech told me this is not bad at all and he did not think that it would contribute to the radical tire wear I have been getting. I showed him the old bearings and told him about the lack of any LSD in the rear pumpkin. He said that both of these things could contribute. He also pointed out that my rear bump stops were gone, indicating that I have probably been bottoming out. He noted that the front end was all new and was aliened very well but the rag joint is shot and needs to replaced.

So I went ahead and removed the old springs which I think were oem and installed new coil springs, the old springs were about 2 1/2 inches or more shorter then the new ones. I also replaced the bump stops. even though I replaced the shocks when I bought the car I put cheap ones in. So along with these new springs I installed some good Monroe shocks from summit racing. I also replaced the rear tires as they were down to the cord. so all parts in the rear are now new.

Ok, so here are 2 questions.

The springs, other then aliening the top of the spring into the groove and the stop in the top bumper, Is there anything that needs to be done at the bottom? I did not see anything at the bottom that told me they needed to be aligned in any particular fashion, I just made sure they were well seated on the raised lip.

During road testing, other then the smooth ride, it felt like the rear end was floating a bit, sorry I cant think of any better way to describe how it felt. Maybe that perfectly normal with the right size spring and better shocks.

So that's it, hopefully I'm finally done with the rear end and I can turn my attention to replacing the front fender and getting it painted.

Thanks again Fred for your input its much appreciated.

Tony
 

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I showed him the old bearings and told him about the lack of any LSD in the rear pumpkin. He said that both of these things could contribute. He also pointed out that my rear bump stops were gone, indicating that I have probably been bottoming out. He noted that the front end was all new and was aliened very well but the rag joint is shot and needs to replaced.
Not sure why lack of LSD additive would contribute to edges of tires being worn down to the cord in 3,000 miles. I know people that run a spool (no differential at all) and don't experience that level of tire wear. If it was that bad you would have noticed serious chatter on every turn.

So I went ahead and removed the old springs which I think were oem and installed new coil springs, the old springs were about 2 1/2 inches or more shorter then the new ones.
Are you sure you got the correct rear springs? Was the rear of the car sagging badly? The only way a spring could be 2-1/2" taller than the old springs, yet compress to the same ride height as the old springs would be if you got much "softer" (lower spring rate in lbs/inch) than stock. Softer springs would account for the "floating" feeling. Good shocks should control the up and down movement. Not sure how good the Monroes are. Don't know anyone who used them.

The springs, other then aliening the top of the spring into the groove and the stop in the top bumper, Is there anything that needs to be done at the bottom? I did not see anything at the bottom that told me they needed to be aligned in any particular fashion, I just made sure they were well seated on the raised lip.
When I did my rear springs, one upper rubber mount stayed in the chassis and one fell out. Just seated the spring coil in the notch on the one that stayed in. On the one that fell out of the chassis, there was enough of a pattern on the chassis sheet metal and the top of the rubber mount that I was able to insert the spring in the mount and put the assembled spring/mount up into the chassis in the original position. Both sides should probably be aligned in the same position. Bottom is whatever results from aligning the tops.
 
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