I Can't Seal up the 8.8 for the life of me!

[Creager]

Heh... This feels like a stoopid question.

I’m not sure what I'm doing wrong here! hehe, and Mobil1 synthetic gear oil has a tendency to inflict trauma on my wallet.

A week or so ago I discovered a small, small leak from the cover of my 8.8. I was like... 'Ok, I’m fixing that,' and went to work.

Drain oil, remove cover, inspect gears, spend mucho time cleaning/scraping old gasket, clean surfaces with laquor, let dry, thin layer of RTV around cover, thick bead around the inside lip, torque to 25-35ftlbs in pattern as described in the book, and let RTV dry for a couple hours.. then refill!

Round one, she leaks again! But only worse!

So I’m like, OK... le'me try this again... this time with fresh tube of black RTV

Round two, holy crap! It’s leaking after a second try!

At this point I’m trying my damn’dest to keep that oil in the diffy, $15 a quart!

So round three, I try one of those fel-pro gaskets from advanced, $5.

hehe, (goonie voice) its still leaking!

Round four, I go to the pull-a-part yard and grab a cover off a 91. Cover looked good, no cracks, didn’t even look as if had been removed before. I used a fel-pro gasket again...

So with the new cover it seemed to stay, but only for a little while! Oil didn’t leak for a good week, until the other day when I get out the truck and I’m like, 'ohhh no, what the... is that smell?' I couldn't even evade the smell of gear oil! I check out the rear diff and discover a thick trickle of oil protruding from behind the cover. (not a small leak, an extensive, annoying one!)

I know I’ve sealed this thing up in the past without it leaking!

The breather hose/tube is clean, the pinion seal is clean of oil. I just can’t get this thing to stay sealed! How long do you usually give the RTV to cure? I shouldn’t need RTV if I’m using a cork gasket, right?

 

[hunterdan]

I would try applying a bead of blue RTV around the diff, and on the diff cover then sandwich a gasket between the 2, usually I just use the RTV along with a gasket and not have any problems. Make sure that you apply the RTV around the bolt holes so it can not leak around them. Just make sure you do not use a lot of RTV so none squeezes inside the diff housing.

Dan

 

[FireZapper]

I usually leave it overnight. Not really need too but I have the time so....

Also do not smear the bead at all. Leave it tall and like above, go around every bolt hole. I let the stuff sit for 2 or 3 minutes before putting the cover on the diff.

 

['97 V8]

You need to let the rtc sit on the diff for around 2-3 mins, then place the cover on. It will be a liquid solid in that tate and seal it up nicely.

 

[IZwack]

When I still had the 8.8, I left the RTV for maybe 10 mins and then put the cover on. No leaks and didnt use a gasket.

 

[Stic-o]

I usally use the grey RTV as the gasket, and only wait about a 20 min for it to dry. Worrks like a charm

1st of all your using Synthetic...Which will find a leak if there is one anywhere.

and the other thing is maybe your cover is bent? That could be the problem.

When I put on the RTV I spread it out flat like peanut butter with my finger.

 

[JDraper]

Are you sure all the mating surfaces are flat and clean? If the cover is warped, it will be a royal pita to seal properly.

 

[CDW6212R]

Something else is being missed, there's probably a crack or groove that is not being coated.

No gasket is necessary, use Ultra Black or Ultra Gray, or any other color of Ultra RTV. Those are high heat; plain RTV is cheap, and why save $1 for a lesser product.

Clean it all well, that's the hardest part. Use a razor blade and throw it away when done. Flow a 1/4" bead around 95% of the diff. surface. Spread the RTV slightly with a finger, to cover the whole perimeter, not necessarily to every edge of the surface. Wipe the cover last with brake cleaner, give it ten seconds top dry, and bolt it on.

Don't go nuts with torque sequence or a wrench. Tighten them all by hand first, then run them down to touch with a socket. Tighten them lightly by hand, 3/8" ratchet with wrist strength, don't put your arm into it, and they should not be so tight that you cannot turn them more. When you see a full squeeze of RTV your final check is done. Let it set for 30 minutes or longer if possible. Good luck,

 

[Creager]

Yo, thanks yall.

Yeah 25-35ftlbs seemed like way too much to me.

The one thing that is concerning me is the ridge that is cut around the circumference of the cover. This gully is filled with RTV from the factory, in the past i simply used the razor to get this surface flush with the rest of the cover, I wouldn’t actually clean it out. These few past times though, I scraped this ridge clean and refilled it with a light amount of RTV. Not sure if that could be causing problems.

 

[dkchrist]

breather maybe plugged?

 

[410Fortune]

yeah check your breather.

I had a 8.8 that I could not seal up as well, yes the surfaces were clean 100%, yes I used black rtv on both surfaces and let it tack up before installing the cover, yes I waited for it to dry before filling, over night in fact...it still leaked, I have drained and filled countless Ford rear diffs...

Warped cover? small cut in 8.8 case and mating surface? Who knows it still wouldnt seal up.

I went to Carquest and got an 8.8 gasket (call first not all stores have these), I re-used the day old synthetic lube, light coat or rtv on both sides of gasket, no leaks no more.

Sometimes when your metal cover is not sealing up a paper/cork gasket is needed to take up the gap and get a seal

 

[Blee1099]

If your 8.8 case was like mine, I'm sure the lip on the bottom wasn't all that great if you wheeled it.. I had to use a hammer and dolly to straigthen it out to get it to seal right.. I've always been told on diffy covers to add a gasket plus a little rtv so the gasket is sandwiched between two layers of rtv.. Maybe over doing it but I like you had an issue with leaks after wheeling a few times.

 

[Rick]

x2 on the RTV with no gasket.

 

[sn0border88]

sounds like the housing has an issue if you tried another cover. I just use plain old blue RTV, nothing fancy, no gasket. Maybe just dont use synthetic oil? I dont see any reason to, you dont have a ton of money in your diff and you arnt some high end race car. Just get plain ole 80-90 with some LS additive if you have a Limited slip.