Just a quick question. I'm about to put the cover plate back on my 12 bolt type C rear end. Trying to decide whether to just use sealer, gasket or combination of both. Wondering what other people have most success with.

 

I've always used a fel-pro gasket with a dab of sealer on either side, she hasn't leaked in 3 years of hard use.

 

Another question just came to mind. Do all these anti-spin rear ends take 80w90 with some special additive, or are there some that don't need the additive? My rear end didn't come with a tag on it, so I kind of hate to assume.

 

To the best of my knowledge all ltd slips need the additive.
I sealed mine with a gasket & black RTV.

 

x2 on the above.

 

1. You can use either a gasket with sealer or make the gasket out of silicone products like RTV or Permatex. I used just a gasket on my cover last year and it leaked very quickly even with proper bolt torques. Put a little sealer on each mating side of the gasket and it won't do that.

2. The car should be level when you're adding the gear oil. Use 80/90 and about 1/2 way through your fill, add the tube of posi/limited slip additive. You need this for the clutches or the diff will 'chuck' when turning corners. Then fill the diff the remaining amount with the rest of the gear oil. It's full when the fluid starts oozing out the fill bung. Put in the bung, tighten and then wipe or spray down with brake clean to get rid of the extra oil. Your owners manual will have the specs for how many pints of gear oil you need, I think it's going to be around 4 not including the posi additive.

Some folks like using synthetic (70/90) but it's really too slippery for the older style units like this, especially if you're adding posi additive. It would be fine for the new Auburns etc, but IMO not on an O style 12 bolt.

Get a Limited Slip tag and put it on one of the bolts so it's properly identified for the future. Someone probably lost or bent it taking it off last gear oil change. Nice - 3.73's.

Fel pro makes one of the best gaskets! I used one to replace the cheapo one that came from PP for my W27 cover. It sealed up that diff really nice - no leaks and I'm happy. Price and availability for felpro was also really good.

 

I could be wrong, but I think it's a Chevy 12 bolt. Thanks for the advise everyone. Just picked up a Fel-Pro gasket and going outside to put it on.

 

pitch the gasket, use The Right Stuff, believe it's from Permatex

if it's a limited slip, you need the GM limited slip additive. it's still available from your local dealer in a 4oz bottle.

 

It doesn't matter whether you use a gasket, a silicone sealer or an anaerobic (flange) sealer. The only thing that matters is a clean, oil free surface. And that is the trick to getting a sweat free seal on any joint.

Buy a can of aerosol brake cleaner. Spray both surfaces liberally, blowing them dry with compressed air each time. Don't touch the gasket surfaces with your fingers after that. With a clean, dry, oil-free surface like that any of the gasket choices will result in a perfect seal.

Of the gasket material materials, anaerobic is the most forgiving of oil on the surface. Silicone the least. Gasket material somewhere in between.

Steve g

 

Got it put on today. Wiped the metal surfaces clean with a dry cloth. Clear siliconed (RTV) the housing. Put the gasket on. Siliconed other side of the gasket and stuck the cover plate on. Letting it sit for a bit. Maybe tomorrow or Sunday I'll put the 80W90 plus some additive in. Might even check around to see where you buy a tag that says "Use Limited Slip Fluid" or something like that. If it leaks, I'm out $8.25 for the gasket. Could probably re-use the fluid. Hoping for the best, and thanks for all the assistance.

 

You are correct that is a chevy 12 bolt c type as you stated.

 

Here's one.
http://www.ebay.com/itm/NEW-GM-POSI-...178b89&vxp=mtr

 

Wiping it off with a dry cloth will not get the oil off the surface. It may not drip, but it will sweat. You ideally need brake cleaner, but could use lacquer thinner and a dry rag. Even solvent will leave a residue.

Steve g

 

Rubbing alcohol will work,if you have that around the house.The 12-bolt Chevy cover has the ribs in between all the bolts.I like to use a gasket,with rtv silicone on each side.
I use the thicker 85/140 oil.We are not driving these in the winter,and it's a good oil. Do NOT use synthetic with a posi rear.

 

I think I have a can of brake parts cleaner on the shelf, but when I read your comment I had already put the cover back on. Had I been just a little slower....
I'll remember for next time. Always more cars coming !!

 

Thanks Charlie,
I sent them a message. Think I'll probably order one.

 

Just thought of more questions. What happens if you put too much additive in? If you ended up with two bottles instead of one mixed in with your 80W90. would it cause grief?

 

I would say no. The gears won't care, and the posi probably wouldn't either. It may make it not grab as well, but that's all I can think of.

 

It very nearly worked. They wouldn't sell to me in Canada from e-Bay, but refered me to their web site. Went through the web site trying to order and it came up "minimum purchase $25". Too bad, they look like nice tags at $5 each. Maybe I'll make one out of a chunk of aluminum.

 

You can buy these tags from other vendors who do ship to Canada. In fact you can probably still buy them from GM in your area. Check them or a local differential shop.

 

Thanks Allan,
A funny thing happened an hour ago. I was whining about it to my neighbor who's a retired aircraft machanic. He said "Quit your whining and make your own".
He went and got me two boxes with numbers and letters in them. I cut a piece of old eavetrough aluminum and whacked some digits into it. Next, I drilled a hole at one end and put it on. It won't look factory, perhaps, but it gets the message across.

 

eavestrough eh! a real canadian would use a beercan

 

The recycling truck had just gone by, and I was all out of empty Labatt's .5 cans.

 

Labatts .5???? You gotta be kidding me. That's only 'near beer'.

The one thing I do like about your creativity is you put the gear ratio on the tag. That's especially helpful if you ever sell it.

 

Quit drinking 22 years ago, October 17th in fact. My first wife never saw me sober. My second wife has never seen me drink.

 

Congratulations! That's an accomplishment to be proud of.

I apologize if my comment was hurtful in any way. I on the other hand have yet to find a way to break my cravings for Nachos....

Just an FYI, although I didn't do any more than wipe the surfaces dry on my diff cover, I used permatex 2 on both sides of the gasket when it was installed and it has not leaked or sweated anything out since. In the car world there's always more than one way to do things, and most of them are right and give great results.

 

Your comment was not hurtful at all. Everybody I know, including my wife partakes of the fluid, even the people that convinced me to quit, all those years ago. What I've done is shift my focus onto coffee, and boy, that'll probably wipe out my innerds faster than anything.

Now that I've got the rearend in shape it's time to pick another part of the car to play with. Thanks to all for joining this thread. I've had some fun and learned a bit, too.

 

Any one got a P/N on correct Fel Pro gasket?

For the 71-72' 10 bolt 8.5 Corporate rearend diff cover gasket,
p/n FelproRDS 55028-1 ?