What was that about differential gaskets with slits?

The posi diff on my 96 is banging on slow tight curves, like backing out of a driveway. Added additive to no effect. Time to clean it out and replace the lube, BUT somewhere in a forum I saw mention that there are good gaskets (with slits) and bad gaskets (without slits). Now I can't find the post.

What's the score with the gaskets? I seem to remember that bad things happen to...inner wheel bearings? if the wrong gasket is used. Is there a GM part number that guarantees the correct slitted gasket? I've never seen one, so I don't know what to look for.

As well, any thoughts on the best lube and the best additive? Thanks for any illumination.

80w90, with GM posi additive.

This gasket from Fel-Pro:

jayoldschool wrote:

80w90, with GM posi additive.

This gasket from Fel-Pro:

Thats the gasket I have. I seem to recall there are little tabs on the diff cover, or housing that the gaskets mates to.

I'm not sure you can even buy the old style gaskets that cover the "ports" that feed the outer axle bearings, so that shouldn't be an issue any more.

I just use conventional rear gear fluid, with GM limited slip additive. I've not had the best luck with synthetics running clutch/friction type limited slips differentials.

Mike

Thanks to everyone. Will let you know how it goes, if it goes.

Interestingly, someone told me it might be better to omit the gasket. They had leaks with the gasket but no leaks using just sealant. Decisions, decisions.

BuickBarry wrote:

Thanks to everyone. Will let you know how it goes, if it goes.

Interestingly, someone told me it might be better to omit the gasket. They had leaks with the gasket but no leaks using just sealant. Decisions, decisions.

I'm running just a gasket and haven't had any leaks. They key is to make sure your diff cover and housing surfaces are clean and level.

yeah clean both the cover and the housing with a razor blade to make sure it's clean/

If you end up with a gasket without the holes you could make them easily with a hole punch.

Also, learned this trick some where.....lightly coat both sides of the gasket with wheel bearing grease. The paper will absorb it. Why that is good is that when you unbolt it again, it won't stick and you can reuse it with no leaks.

Yeah, so we drained it and ordered the correct GM gasket w/correct part number. When the gasket arrived, it had had no slits, so some of those wrong gaskets are still out there under the correct part number from your friendly GM parts counter, at least in Canada.

Got the correct Fel-Pro gasket, drained the diff, cleaned it twice, no visible wear or bad cogs, refilled w/ 3 liters of synthetic 75/90 and 2 hits of GM LS additive. Result: no difference. Still does nok-nok-nok on very tight turns, esp if the rear wheels are on different levels, as in backing out of a driveway. Is it the synthetic lube? No idea. At least there are no leaks. I quit. For now.

Drain the expensive synthetic, and refill with conventional oil and additive.

Yeah, I feel bad. We should have said no synthetic.

I kinda did.

Interesting to see so much talk and time on something simple as a gasket,.which doesn't necessarily need to be used,.
10 secs work with an exacto knife on the gm gasket,.. and its all good,.

Me personally i use silicone to seal a diff cover,.but,..

do what you want , you're gonna anyway.

Those holes are not for lubrication anyway - they're for spreading the housing at the factory to make differential installation easier given that it needs some preload. If the differential tube bearings needed dedicated lube passages, it would have been a lot simpler just to grind a slit in the side of the carrier bearing area for oil to travel through.

As long as the fluid level is at the appropriate level, the tube bearings will get enough oil.

I believe the real problem was that the pinion yoke leaked and so the fluid level went down and as a result the tube bearings didn't get oiled and the axles got chewed up.


Thus, whether the gasket has holes or not is a secondary concern. Nick's point says it all - if you care that much, then cut two holes with a knife and git-r-done.