1991 Caprice 5.0l Differental Oil

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WyrTwister

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I am going to change the pinion seal on the Diff . I bought conventional 80W-90 oil to refill the Diff . Should I have bought synthetic ( is there such a thing ? ) ? I do not plan to drain the diff , just replace what comes out when I remove the yoke & seal .

Thanks , :)
Wyr
God bless
 
I went looking for the best differential oil recently, and ran across a performance comparison test that I believe is valid.

Originally Posted By: ExMachina
Thinking about changing the diff oil out in my car.
I'm assuming the Amsoil comparison at
http://www.lastgreatroadtrip.com/wp-content/uploads/2010/11/gear-oil-comparison.pdf
is "honest". Amsoil wins, no surprise, since its their study, or they are for real. I do admire Amsoil products.
Amsoil Severe Gear 75w-90 it will be, for lack of any better information.
Surprising how poorly Royal Purple and Lucas did !!! And, who wants a GL-5 that tests for foaming??!! Amsoil won it all there.
 
Originally Posted By: ExMachina
I went looking for the best differential oil recently, and ran across a performance comparison test that I believe is valid.

Originally Posted By: ExMachina
Thinking about changing the diff oil out in my car.
I'm assuming the Amsoil comparison at
http://www.lastgreatroadtrip.com/wp-content/uploads/2010/11/gear-oil-comparison.pdf
is "honest". Amsoil wins, no surprise, since its their study, or they are for real. I do admire Amsoil products.
Amsoil Severe Gear 75w-90 it will be, for lack of any better information.
Surprising how poorly Royal Purple and Lucas did !!! And, who wants a GL-5 that tests for foaming??!! Amsoil won it all there.
Amsoil gear lubes are in the top tier that are available, no lie there.
 
For a Caprice of that vintage, you're doing fine. In taxis of similar vintage, we never even bothered with the differential fluid, except in cases of failure, and that was exceedingly rare. The last container left over from the taxis was a Pennzoil conventional fluid of the viscosity you mentioned.
 
Originally Posted By: andyd
80 90 is fine as long as it has an open diff.


I hate to reveal my ignorance , but what is an open diff ? As opposed to what other kind of diff ?

This car was my late Dad's car . it has been in storage 15 - 20 years . I am guessing the seal just dried out & got hard . The car has 46,000 original / honest miles . Nothing is worn out .

------------------------------------------------------------------------------------------

Follow up - Just finished with the pinion seal on the Caprice & got out of the shower . I was a dirty puppy .

I was running out of daylight . :-(

Put most of a " bottle " of 80w-90 oil in the diff , until it started running out of the fill hole . Replaced the plug and tightened it up .

Had my Wife drive the Caprice slowly around the block . While she was doing that , I spread cat litter on all the oil spots on the drive .

Will have to wait to see if it leaks or not .

The seal surface of the yoke has 2 " wear rings " . I used 500 grit sand paper on it , then switched to 1000 grit . I could still lightly see the 2 " wear rings " , but could not feel them when I drug my finger nail across them .

Lubed everything as I reassembled the parts in reverse order .

I had hoped to do this this last weekend . But this last weekend was not good . Worked on plumbing / cold water lines under the house . 3 steps forward & 2 steps back . Ended up creating a leak , where it was not leaking . Praise the Lord ! . It was no longer leaking by the time I crawled out from under the house Sunday PM .

God bless
Wyr
 
The most important thing you can do with that axle is to make sure it has the correct cover gasket with the holes to allow the gear oil to flow out to the axle bearings.

GM installed the wrong gaskets in almost a million 8.5" axles that can lead to early axle bearing failure. At a minimum,,it will render your axle shafts unusable if you ever do have to change your axle bearings.

Get that cover off and see what's going on. Yes, you'll lose all of your axle oil, but you'll save yourself from a big problem.
 
That took me by surprise .

To my knowledge , I am not having axle bearing problems , just the leak at the pinion seal .

Hopefully that is OK now .

If you went to the parts store & bought a cover gasket , how would you know it was correct or not ? Holes to allow oil passage ?

Do you have any photos ?

Now I am really confused . :-(

God bless
Wyr
 
Originally Posted By: WyrTwister
If you went to the parts store & bought a cover gasket , how would you know it was correct or not ? Holes to allow oil passage ?Wyr


The holes issue is a little controversial. If you turn once in a while, enough oil gets to the axle bearings.
http://www.socalss.org/special/holes.htm
The holes allowed some more oil to escape into the axle to lubricate the axle bearings.
Its the rectangular shaped holes on either side. If you don't cruise on the highway a lot, then you can use the non-hole gaskets, if they are still out there.
RDS55028-1.jpg
 
Last edited:
So , oil level is suppose to be at least up to the level of the rectangular holes ?

What really happens if the oil level is a little high ? Too much aeration ? Foaming ?

If the gasket is replaced , is sealant ( Permatex ) recommended , or use dry ?

This is a 5.0 l / 305 ci engine . Were the " bad / wrong " gaskets used on diffs on that car ? I think the 350 ci engine was also used in this model of Caprice .

Do the axle tubes attach to the banjo housing at about the position of the black lines ?

God bless
Wyr

Diff Cover Gasket 2.jpg
 
Controversial for sure, but I've taken apart enough 70-90k mile 8.5 axles that had those incorrect gaskets and ruined axles to err on the side of caution. The surface of the axle where the bearing rides usually looks like smeared creamy peanut butter.

Fill the axle oil up to 30mm below the opening of the fill plug hole. You can use a bent coat hanger as a makeshift dip stick to measure this.
 
This is new to me . I always thought you filled a diff untill the oil came out the fill hole then replaced the plug ?

Thanks ,
Wyr
God bless
 
80W-90 is the right viscosity for both the Posi and the open differential, with the Positrac requiring the friction modifier additive.

It's not necessary to use RTV silicone of any sort as long as the sealing surfaces are clean and not warped or otherwise damaged, but if you want to be extra sure then go for it.
 
The Caprice has been driven around the block a few times & it seems to be not leaking .

Praise the Lord !

God bless
Wyr
 
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