Ok on my 1995 Z28 I have a Strange Engineering 12 bolt rear end with 3.73 gears and posi differential (not sure which one).

After it is driven 25 miles or more it makes terrible noises when I do slow turns into the driveway or in a parking lot. The rear end clunks and groans and I feel a shuddering when moving forward. It is loud and makes you think the rear end will fall out of the car any minute.

Things are fine while driving straight, no noise and I don't feel anything out on the highway though any noise would be covered up by wind noise, exhaust, etc.

I've got Founder's Performance LCAs and Panhard Rod. The LCAs are mounted on the lowest hole of the mount on the rear end. That's the only place they can go as they are too long to mount higher.

I'm using the manufacturer recommended Lucas 85W-140 gear oil with GM additive. I also have a B&M rear end cover but I'm not using the end cap bolts to support the end caps right now.

It's a DD with no racing.

Could the LCA geometry be causing some strain on the rear end or is the posi unit failing?

 

How many miles on the 12-bolt? How many miles when it started making noises?

Based on one of my old posts on another site, Strange's FAQ recommended 85W-140 for drag racing applications and 80W-90 for street applications, plus the limited slip additive. They indicate to use non-synthetic lube, but two different highly experienced shops have used synthetic in my Strange 12-bolt with no unusual problems. When the person in the other thread asked Strange, they replied that he should use 75W-140. Confusing.

Might be worth a change to 80W-90 plus additive to see if it helps.

When I bought mine 18-years ago, Strange installed Eaton disc-clutch posi units.

Rear gear oil for 12 bolt 4:10 33 spline strange? - Drivetrain - Firebird Nation

 

Thanks for the reply from last year. Can't remember if I saw it then or not. I took the car on a road trip out west right about that time. It made lots of noise but no actual driving problems. Then other car problems occurred and have just gotten car back on the road in the last month or two.

I've pretty much decided to buy an Eaton Truetrac carrier and have it installed. Any input?

 

No experience at all with the Truetrac.

 

Not sure I wouldn't throw in another bottle of GM additive just for grins, before you spend a bunch of money. The noise on slow turns makes me think the clutches are sticking.

 

^^^agree. Depending on type of posi,as if an Eaton clutch plate type,the grab/ungrab/grab/ungrab sequence can be noisy.

 

I had put in 3-4 bottles of AC Delco additive. I have a B&M cover on the differential. Total capacity is about 4 quarts of gear oil. I recently changed the fluid and added 1 bottle of Equa Torque additive. A mechanic suggested driving the car in circles in reverse. He said he's seen that help some rear ends as it forces the fluid in the other than normal direction and helps "clean" and lubricate the clutches. I did that and it seems to be better. At present I'm not planning on replacing the carrier. Thanks for the responses.