Last Saturday night during one run of drag racing, only one slick was turning during the burnout.
Yesterday morning, after taking the car off the trailer, I "tested" the posi in my driveway. Both tires put down equal patches of rubber.
This complete rearend is one year old...3.73 gear, Eaton posi w/800 lb springs and carbon fiber clutches.
Since new, I've been running Redline gear lube. I was told at the track that synthetic lube is no good for the Eaton unit's clutch pack.
Yesterday, I changed the rear lube to a standard gear oil (no posi additive), making sure to clean out the housing really good. The old stuff smelled burnt and was very thin.
Is it possible I damaged the carbon fiber clutches just by using synthetic oil? Or, were the clutches just slipping after getting hot. I tested the posi again after the oil change and all seems fine.
I'd hate for it to go out again after a couple of rounds this weekend...
Any opinions?

Interesting, I put Lucas synthetic in mine. Seems to be working fine.

I dunno about running without posi additive though...doesn't sound like a good idea.

not sure but I don't think you need the posi additive for the carbon fiber clutches

This is very common for drag cars. You will see many of them spinning one wheel in the water. It is very hard on a posi to do a water burnout. If you plan on drag racing often then I recommend switching to the steel clutch plates and no oil additive. This will help it lock up easier. The clutches need to be set up as tight as possible. It will pop a lot when driving on the street, but you can't have it both ways. If this will be mostly a drag car then a Detroit Locker would be better.

It is very hard on a posi to do a water burnout. If you plan on drag racing often then I recommend switching to the steel clutch plates and no oil additive. This will help it lock up easier.

Would it be OK to just run dino gear oil and NO additives with the carbon fiber clutch pack?
Is it true that synthetic oil is harmful to the clutches by allowing too much slippage?
Right now, after the gear oil change, all seems well with the posi.

The car is run on the street about 75% of the time.

You can run it without the additive. It will pop when driving on the street, but the clutches will lock up better. I have run Amsoil synthetic in many of these without any problems.

big gear head,

Is there any "disadvantage" to running (mainly on the street) an Eaton rear with the steel clutch pack, shimmed tight and do away with the springs?

I have seen that some places do this and is better for a "strip type" car but I was wondering if this setup would be okay on a car that see's more street miles than strip time.

Thanks in advance.

Tom's Differentials has been building them that way for many years now. I don't see any problems with it, except that you might have to tear it down more often to shim the clutches as they wear. The preload springs will help make up for some wear, but people who drag race are use to tearing down their engine, transmission and other parts every season to freshen everything up. I think the steel clutches are better for racing because you can get more of them in the case for increased friction area.

Thanks for the input, BGH! :beers: