Slipping Posi: What are my options?
 

Well I went to Island recently and ran a new personal best of 13.2 at 103.5 mph. When I was getting ready to go the second time I did my burnout in the water and noticed that only one tire was spinning. I ignored it and ran 3 more times. Sometimes both tires would start spinning then as the radials warmed up just one would spin. So I am wondering what my options are at this point. I tried to research it and I've seen that the rear in my car cannot simply be rebuilt? I was thinking of just buying a new Posi unit and throwing it in, but I don't want to do anything before actually knowing what is wrong. Someone told me that if I change the fluid it may cause the clutches to stop slipping internally.

So I pretty much don't know much about rear's at this point but I am learning a lot through research. What do you guys think I should do first?

you could drain the fluid and add gear oil with no GM addative. But the real fix is a new stronger rear

I may try and flush the old fluid from my differential. I found this on Tech and its a killer deal question is, will a carrier from a 98-02 Camaro fit in a differential from a 93-97 Camaro? http://www.ls1tech.com/forums/parts-...-rear-end.html

well it depends if it is a 2 series or 3 series carrier and if that is what you have. the guy doesn't seem to know much about it. you would be better off pulling your rear apart and seeing what is the matter then replacing the correct part.

How do I find out what series carrier I have?

What gears are in your car now?

And thats not so much a killer deal. SLP years ago was selling them brand new for around 100 bucks as "Take out units". Not to mention the price of the shim/installation kit with labor.

Im not trying to scare you, but its not a "Pull it out and put new one in" kinda deal

No I understand that. I have 3.23's in it now.

I believe cars that came stock with 2.73 gears use a 2 series carrier. Cars that came with 3.23 or 3.42 gears from the factory will use a 3 series carrier gear.

Right.....3.08 was the break, I just always forget which side of the break the 3.08s fall on.

- Justin

Is it at all possible that the drag radials are just too much for the rear? I was talking to my friend about this and we were wondering that. I know the clutches are meant to slip under some conditions, maybe the added stickies at the lower tire pressure made them raise the white flag. Other than taking apart the rear itself and doing a burnout is their any other way of testing whether the posi is working or not? Sorry for all the questions, Im a newb when it comes to rears.

Slightly off topic: Did 4th gen cars ever come with a clutch posi from the factory? I thought it was only Auburns and Z-T's.

That sounds pretty normal. When I take my cars to the track in the burnout box with the stock rear ends it sometimes doesnt spin one tire. When I do a burnouts in a parking lot or what not they leave down 2 nice tire marks but one will start before the other. I think its the way the ZT is made. I would change the fluid, and maybe get a T/A cover.

You can get a auburn pro, Eaton Posi, or locker for the 10 bolt but the best bet is get a 12 bolt. I built a 10 bolt for my old V6. Cost about 1000.00 to build with Moser axles, Eaton Posi and a T/A cover and it broke about a 1 yr later with about 12,000 miles on it. Took it to the track 4 times. Sold the Rear to a buddy when I got rid of my V6 and he put it in his Bolt on 305 1988 Formula. The rear broke in his car at the track running a low 15 I believe.

I dont think so. They came with the Zexal Torson which have Spider gears. They really dont wear out, They just break.


Does your rear end make any noises? Howl, Grinding while at cruising speeds? Notice any oil buildup on the inside of your rear wheels?


I believe if you jack up the car in the rear so that the rear end is hanging there. Chalk off the front tires of couse and put the car in neutral. Spin one wheel and the other should spin in the same direction if its a Posi rear. If you spin the one wheel and the other spins in the opposite direction then you have an open differential or a broken ZT unit.

I am a little rusty on the rear end because Its been 5 yrs since I have had to deal with rear end issues. So if someone sees a fault in what I am saying please chime in. I broke 3 rear ends in my old V6 from 2003-2005 and 1 rear end in my T/A in 2005. I am a little rusty but I believe thats the way I checked to see if my Diffs were still good to go when I had the car on a lift or what not..

That makes sense. I was just wondering if there was some slipping going on. I think the drag radials are just too much tire for a stock rear with 112,000 miles. It drives fine and doesnt make any weird noises or anything so I am really lost. I will try your method to checking the posi and see what happens.

Your best bet is to purchase a complete Rear from a Z28 or T/A. You can get them for as little as 100.00 and its a lot easier to swap rear ends then to do a differential install .

2.73 and 3.08 were 2 series and 3.23 and 3.42 were the 3 series. If you can get a 2 series I hear that they are better and the gears are stronger. They make aftermarket gears for the 2 series but in the end its a 10 bolt and it will break..

So we drained the rear (it was really low) and we refilled it and put some additive in there. Surprisingly it seems to have worked for now. I did a burnout and both spun evenly. So I think for now I am good to go. We will see what happens Friday at Island :)

The additive it what helps the posi "slip" for normal driving/turning.

So like I said, if it still one wheels again you can try to refill without the additive.