Hi yal. so im having some humming coming from my rear its not to serious an its only while on the throttle , which leaves me to believe its the ring/pinion. no signs of metal in a fluid change. but i did notice chattering or sort of the car jerking in the rear like it was trying to lock when id make a hard right turn from a stop going up a hill lol i know odd situation but it happen more then once. i basically want to do new gears an install kit new spiders. I need to know tho its a 10 bolt. what is it tho , a 7.5&7.6 or 8'. what splines without pulling axles. Im looking for a good kit with everything that really wont break the bank. its more of a street/track car. i want to up it to 3.73 also. the Car is a 1995 z28 A4. From the window sticker it also says performance axle upgrade so i dont know if that makes anything different. Any suggestions will be greatly appreciated. an i am having a professional do the install. thank you very much.

 

The stock/base rear with the V8 and auto trans was a GU2 2.73:1 rear axle ratio. The GU5 Performance Rear Axle is simply a change to 3.23:1 gears, nothing else related to the rear (included selectable 1st gear and 150 MPH speedo if equipped w/ Z-rated tires).

Common designation for the 4th Gen rear axle is 7.5/7.625" 10-bolt. Sort of a weak link.... GM pulled it from the parts bin for the 4-cylinder S10 pickups.

Chatter in a hard turn is often the result of not adding the GM limited slip additive when the gear lube is replaced.

2-part article on 4th Gen 10-bolt upgrades. Get's expensive, and doesn't get you much. I believe they determined almost $2,000 worth of upgrades would allow them to run no more than 450 flywheel HP with an auto trans and sticky tires on a well-prepped track. Beyond that, you are looking at complete replacement - 12-bolt, S60 or 9-inch. Some people get lucky with the stock 10-bolt and have taken the car into the 10's. Others have blown the up with a stock engine.

Strengthening The Rearend From An LS1 Firebird Formula - Hot Rod Network

http://www.hotrod.com/articles/hppp-...arend-rebuild/

 

thanks for the reply. I did add that bottle of GM lube. it was like 20$ for a tiny bottle. But basically your saying Im better off with just buying the regular replacement parts , ring , pinion , rebuild kit with bearing shims ect.... then going an buying some fancy kit for it ? because it does need to be addressed. I dont want it to blow out on me. also is there any way to tell what spline axle it has i know it has that GU5 the chart in the glove box as you stated. so that tells me the axle ratio but all the replacement parts state a specific series an spline. i believe its a 3-series but still in the dark about the spline count. I just want to be 100% before ordering all the parts an then tearing down an running into problems.

 

If you plan to rebuild it, with a new carrier and gears, you will need a master rebuild kit.

What I tried to point out is that if your long-term goal for the car is some track use, and more than 450 flywheel HP, a complete, upgraded rear axle assembly might be a better choice. If not exceeding 450 HP, do a rebuild, recognizing that as HP and abuse increases, the probability of grenading the stock 10-bolt increases.

A new, stronger rear axle is a major investment: $2,500 - 3,000.

4th Gen ring gear is 7.625" diameter and axle spline count is 28. See chart in Part II article linked above.

 

^^^everything Injuneer said.
Did you add the $20 bottle yet ?, a fluid change(regular non-synthetic GL5 use) with the additive MIGHT eliminate some of the stated symptoms.
You never stated how many miles on it, the Auburn cone clutches wear with time,150,000 miles they're beginning to near the end of their service life.
The 3.23/Auburn rear behind an automatic typically just wear out and don't experience catastrophic happenings.

 

Hi sorry i didnt specify the rear only has 54,000 on it. but they have been hard driven miles. an yes i added that gm fluid at the time of the fluid change. Im also wondering the car is lowered but i do not have a rear adj panhard bar could that possibly be throwing the driveline off an causing the noise. to the eye the tires look centered. an basically the car is going to stay under 450hp. i am leaning just toward a master rebuild kit , new spiders, ring an pinion. just a different ratio to 3:73. the car has est 350hp. i have greddy cold pipe with stock air box but with the holes drilled , corsa exhaust , TPIS throttle body , hyper tech tune ,160" thermostat , an comp cam.

 

As others have written, the rear end is the weak link. If you get bigger, sticky tires, and get it to hook, you're going to start breaking things.. Always cheapest to break traction, parts cost more.

On your chatter, some people have good luck using synthetic gear oil, doesn't seem to need the GM friction modifier. OTOH, wouldn't hurt to add it. At least it means your limited slip is still engaging.