Leaky rear diff 2002 mustang gt

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I have a leaking rear diff that leaks in the bottom left corner no matter what I have tried.
I used a paper gasket with alitttle bit of ultra black rtv to hold it in place. Then it started to leak
In a couple of months. Then picked up a felpro gasket that I followed the instructions on not using any
Rtv and it's still leaking. Both surfaces have been scraped clean of old material and cleaned off with brake cleaner and wiped it dry. I torqued the cover into place per what the manual said which is 28ft lbs. I just saw a couple of drops on the driveway when going to put gas in it. The surfaces are not gouged or has any damage I can see. So I am at a loss

I did not use rtv because the sway bar is very close to the diff over. I have to do a lot of shimmying to get the diff over off.

Thanks

James
 
Make sure both the cover and housing are flat. Also make sure all the bolt holes are cleaned out. How is your diff vent? If it is clogged then you can have leaks. Also when you use RTV how long do you wait to fill the housing?
 
Best solution for differential covers is a Permatex product called "The Right Stuff" and it's available from Amazon:

http://a.co/8B9ziAh

"The Right Stuff" is a gasket-maker product, so don't use a separate gasket with it. I believe newer differentials are sealed at the factory with a similar product. I've never had a leak after using "The Right Stuff."
 
With a paper gasket, lay it out over some flat newspapers. Take your finger and apply an even layer of gasket dressing like if you were frosting a cake. Install the gasket to the differential housing and then frost the other side of the gasket that's facing you.

Do the same with cork gaskets if you ever get any. (don't use it on rubber gaskets)


80016_500px.jpg
 
I let them sit overnight with rtv and the bolts were hand tight.

When I put the felpro gasket I just lined it up with the top 3 bolts. I installed it dry in between the cover and diff.

The cover does not look bent at all or damaged. The diff besides the machine tooling marks their is not
Damage I can see.

I will check the vent tomorrow when I get home from work. Because looking at the pictures of people with that issue. It seams fluid is in the same place both times it started leaking right near the center forward the drivers side. From looking at google the vent is at the top d/s axle.
 
Originally Posted By: Exit32
Best solution for differential covers is a Permatex product called "The Right Stuff" and it's available from Amazon:

http://a.co/8B9ziAh

"The Right Stuff" is a gasket-maker product, so don't use a separate gasket with it. I believe newer differentials are sealed at the factory with a similar product. I've never had a leak after using "The Right Stuff."


Yeah, I have a big tube of this stuff in a caulk gun type apparatus. I keep it in the garage freezer when Im not using it to keep it from setting up.
Its 5 minute setup time. So I lay out a bead on the cover, throw it on, tighten it down to an approximation of 20 ft-lbs. Then I go have a drink or whatever, come back and fill it up. Drop it off the jack stands and drive away. No leaks yet.
 
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Originally Posted By: daemontrym
what the manual said which is 28ft lbs.


Wait.......... you're torquing the bolts on a stamped steel diff cover with a paper gasket to 28 FOOT pounds? Are you sure the spec isn't in inch pounds?
Most stamped steel cover bolts usually get torqued to something like 80 to 120 INCH pounds which is in the 10 Ft. Lb range.
 
Originally Posted By: Scdevon
Originally Posted By: daemontrym
what the manual said which is 28ft lbs.


Wait.......... you're torquing the bolts on a stamped steel diff cover with a paper gasket to 28 FOOT pounds? Are you sure the spec isn't in inch pounds?
Most stamped steel cover bolts usually get torqued to something like 80 to 120 INCH pounds which is in the 10 Ft. Lb range.


This.

Cover's flange is probably bent now.
 
You are torquing them way too high. The cover is probably bent now. Lay it on a flat surface and take a look.

All I use on my Mustang is Permatex Black. It never leaks. 75W140 gear oil.
 
I don't know why the idea that the torque is too high, IIRC from my Ford days the spec is 25-35 foot-pounds (so 30 is nominal).

I don't think I saw it mentioned but tighten in a star pattern, like you are tightening lug nuts. It helps to make sure that the cover seats evenly. And I think all the service manuals call for that as well.

Clean, clean, clean. I use a air die-grinder with a scotchbrite on it for cleaning and it works beautifully. I understand that not everyone has that, so you have to make do with what you have. Razor blades, scotchbrite, maybe even a fine sandpaper. Clean is critical to getting the RTV to seal correctly. Both sides. I use brake cleaner as well but as a final wipe I use acetone just to be sure there is no residue left and I wipe until my rag comes back clean. Then I am ready to seal.

Directions for RTV have changed over the years, the last time I used it, it now says to apply within 5-minutes and torque, no re-torquing necessary. No more waiting for it to skin over or hand-tight then come back and re-torque or any other methods. Not to say that still wouldn't work, but the directions don't say to do that. I do still wait as long as possible before filling with fluid though. Try for a full day if possible.

Don't remember the last time I had one leak. I only need to change when it's time to change fluid.

With all this said, next time I do one I am going to try a lube-locker.

Adam
 
Last edited:
Originally Posted By: ABursell
I don't know why the idea that the torque is too high, IIRC from my Ford days the spec is 25-35 foot-pounds (so 30 is nominal).



The torque spec on the bolts for a stamped steel diff cover is 35 Foot Pounds?

This would be like torquing the pan bolts on an automatic transmission pan to 35 Ft. Lbs.
The connecting rod nuts on a 5.0 Ford only get something like 19 to 24 ft. lbs. LOL. You sure we're talking about the small little bolts around a stamped steel diff cover here? 25 to 35 ft. lbs??
 
Originally Posted By: Scdevon
Originally Posted By: ABursell
I don't know why the idea that the torque is too high, IIRC from my Ford days the spec is 25-35 foot-pounds (so 30 is nominal).



The torque spec on the bolts for a stamped steel diff cover is 35 Foot Pounds?

This would be like torquing the pan bolts on an automatic transmission pan to 35 Ft. Lbs.
The connecting rod nuts on a 5.0 Ford only get something like 19 to 24 ft. lbs. LOL. You sure we're talking about the small little bolts around a stamped steel diff cover here? 25 to 35 ft. lbs??


I don't think most automatic transmissions are cast-iron housings, maybe that accounts for the difference?

I'm admittedly going by memory, but I think the service manual will tell the truth. I did do a little-Googling around and it may vary in the years of the 8.8 by application but is going to be somewhere in the 25-35 foot pound range based on results I saw. It's not unusual to be there. I just did a Dodge and IIRC I torqued per spec on that to 28 foot-pounds.

Adam
 
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I cleaned both sides throughly with a razor blade and scotch bright pad.
I wiped both ends dry with brake cleaner

Lined up the gasket with bolt the loosely put in the rest
Tightened each one to 25 ft pounds in a star pattern
 
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