Diff cover gasket help please
 

New to the forum. Got my first Pontiac. It's a 68 Bonneville with the 400. Just got it at auction so trying to check everything out prior to putting it on the road.

As part of that, I drained the rear end lube. Had gone to my local parts store and purchased a cover gasket. It had 12 bolt holes whereas I only have 10 bolts. Got on the internet and thought Felpro RDS 55028-1 would fit. Also thought a Motive Gear 3993593 fit. It turned out to be the same fit as the Felpro and neither fit. Although these gaskets have 10 holes, my diff & cover are slightly larger in diameter than these gaskets.

I'm stumped for the moment as to what part to order. Can anyone tell me what to order?

Also, do I perhaps have some odd, non-standard setup? Are there casting numbers or such on the diff that would identify it as appropriate for the car?

Thanks in advance for any help,
Bruce Clarkson

Adding a post with a picture of ID #s on the diff.

I wouldn’t even fool with the gasket and just use some gasket maker like Right Stuff black .

Our host has the gasket:

https://www.amesperf.com/parts/searc...s/?term=pr524d

Looks like the 8.2" 10 bolt rear end. Like previously state tho, Just RTV the cover on. I use the brand called "The right stuff" Put on cover, and install cover loose. Just till RTV makes contact with both surfaces. Let sit 20 min to skin over. Then tighten bolts

I have not used a gasket back there in 35 years.

Like others have posted just clean it all off well. Spray it down with brake cleen and use a gasket maker.

Let it set up for 20 minutes and put it on.

GM has a service bulletin about synthetic gear lube destroying the OEM Silicone RTV sealer used on AAM axles.

It may be that AAM was using the crappiest Silicone RTV on Earth. It may be that AAM was using the cheapest, rawest gear lube on Earth.

But ever since I saw that, I've gone back to actual gaskets on gear-lube applications. Note, however, that Permatex has a specific RTV 81182 for gear lube.

https://m.media-amazon.com/images/I/...AC_SL1500_.jpg

I'm maintaining the diffs in my 2005 suburban now and found these after I already purchased my gasket/sealant. If I had known earlier I may have given it a try. $26 isn't bad...

https://www.lubelocker.com/collectio...gaskets?page=2

Just to add to the confusion, the big cars (B-body) 65 - 70 has a rear end with the ring gear attached with 12 bolts, but the rear end cover only has 10. I doubt anyone has attempted to install an 8.2 to a full-size car as there are no aftermarket kits that I am aware of and regardless would be a step backward on reliability. The B-Body 12-bolt rearend is a bit of an overlooked and underappreciated piece with little in the way of aftermarket support.

As mentioned, the 65-70 full size rear ends for Pontiac are an odd duck. I had a hard time finding that paper gasket 20+ years ago. I don't know if they are available anymore. You may be stuck with a liquid gasket. (RTV) Changing the entire rear end to a 12-bolt B-car axle is not a simple bolt-in. The majority of the Chevy B-body 12-bolts are not a 4 link suspension. Most are 3 link, using a Panhard rod, (diagonal link) on the top instead of 2 upper control arms. So some welding and brackets would be needed. Also, not sure if Chevy axle length is the same or close.

Could always make a gasket, or is it a lost art?

George

I got in the habit of checking the Fabcraft Metalworks site when I was setting up a big car rear with their 3.55 gearset. Their prices are competitive and sometimes lower than other suppliers, and they know Pontiac parts. I've found that companies that should know what goes under our Pontiacs simply have no clue. Visit the Richmond site and you might be told the Bonneville came with an 8.2 BOP rear the same as GTO, or even told that Chevy 10-bolt stuff will fit. Good that you can go to Fabcraft and get correct parts. Here's the gasket on the Fabcraft site: https://fabcraftmetalworks.com/produ...lera9-8080-12/

They're pretty quick getting stuff to me also. Not quite Summit quick, but equal or better than the others for shipping.

Also, the gasket looks about the same but the 8.2 gasket would just about fit inside the big car gasket.

That's a great find! I bought a bunch of stuff from them for the larger 9,3" rear ends. Didn't realize they had that gasket. Thanks.

The Lubelocker has gotten cheaper every time I've serviced a Dana 60 and 10.5" Ford axle. I'm on my 3rd service each using the one gasket, no leaks no sticky stuff.

I gave up trying to procure this gasket. I got yet another gasket with the right number of holes that was almost but not quite the right size. I got the Permatex stuff in the green tube. For the last 48 hours, it's held just fine. I don't anticipate a problem. Thanks to everyone for their suggestions.