Rear Differential Leak 98 Jimmy

[scrnchr]

1998 Jimmy with 128,000 miles

In the last few days, when I am coasting slowly and give it some gas, I sometimes hear a "clank" which I thought
was coming from the rear end or transmission. Then I noticed dark fluid dripping from the rear differential. I crawled
underneath and see that the fluid is dripping from what I assume is a gasket under the rear cover of the differential.
Here is a photo:




Here are my questions:

1. Any chance that just tightening up the bolts will stop the leak? I know, "Try it", but I'd like to hear of your experiences.

2. How do I check the differential fluid level and what fluid would I add? I've worked on boats but not trucks.

3. If it still leaks, can I remove the rear cover or does it somehow support any of the internals?

4. Where do I buy the new gasket and should I coat it with a gasket sealer (like permatex ultra black) before installation?

5. What's the capacity of the differential for when I refill it? Any bleeding required or does it always fill without air pockets?

Thanks in advance for any input you can provide.

[96S10BlazerGuy]

Quote: Originally Posted by scrnchr

1. Any chance that just tightening up the bolts will stop the leak? I know, "Try it", but I'd like to hear of your experiences.

Possibly, but doubtful. Try it and if it doesn't work replace the gasket.

Quote: Originally Posted by scrnchr

2. How do I check the differential fluid level and what fluid would I add? I've worked on boats but not trucks.

There is a plug the cover, remove the plug and stick you finger in the hole (make sure you let the rear end cool first) if you can feel oil then it's full if not then add until it reached the hole.

Quote: Originally Posted by scrnchr

3. If it still leaks, can I remove the rear cover or does it somehow support any of the internals?

You can remove the cover without disturbing any of the rear end internals

Quote: Originally Posted by scrnchr

4. Where do I buy the new gasket and should I coat it with a gasket sealer (like permatex ultra black) before installation?

Any parts store will carry the gasket, and you can coat the gasket with Permatex if you like but it's not necessary.

Quote: Originally Posted by scrnchr

5. What's the capacity of the differential for when I refill it? Any bleeding required or does it always fill without air pockets?

About 2 quarts of 75w90 gear lube should do it... just fill it until it reaches the plug hole as described earlier.

[cpolaris502]

You could try tightening it but that looks like its a pretty good leak. its always worth a shot though.

There isnt really a way to check it without just adding more.

The rear end cover comes right off, the only thing that will come out is the old fluid.

Any parts store has the gaskets for it, it looks like that the 7.5" diff. When I changed my fluid i just used the gasket with no sealant and it hasnt leaked at all.

I think the capacity is 2 quarts. it says in the manual. If you dont know when the fluid has ever been changed then its definetly a good idea to do that. The fill plug is up on the front right side of the diff i think.

[scrnchr]

Coolness! Thanks guys for those super fast replies. I will give it a shot.

[96S10BlazerGuy]

Let us know what you end up having to do.

[scrnchr]

I'll post how it ends up. Bought the gasket and gear lube today.
I figure if I'm going to put it up on ramps I might as well change
out the gasket and lube.

[scrnchr]

btw, I saw this on another website:

"When adding oil to the rear axle, be aware that some locking
differentials require the use of a special gear lubricant additive."

Does that apply to my Jimmy?

I bought 2 quarts of lube, they had 80w90.

[scrnchr]

I ended up fixing it twice. GM in all their wisdom used a special
5/16-18 x 57/64 bolt for the cover bolts. They aren't very hard,
and with 11 years of winter rust on them they got chewed up
when I took them out, even using a torch. I put the cover back
on along with a new $5 gasket from Napa, tightened down those
crappy bolts as best I could, and found a nice leak the next day.

Bought a new cover and a better gasket from GM. Bought ten
5/16-18 x 1 Grade 8 bolts with washers and lock washers from
the hardware store for about 6 bucks. GM wanted $9.32 PER BOLT!
(Yeah, I wonder why they're having trouble...) Put it all together
and now it seems to be leak free, knock on wood. Used Permatex
Ultra Black on the new gasket both times. Cleaned up the mating
faces good with a putty knife both times.

It's a real pain to get the new gear lube in, with where they put
the filler hole. I finally realized I could use the gear lube pump
for my boat's sterndrive. That made it a LOT easier.

Thanks for all the input! I think this one may be fixed. Now I'll
post one about the radiator.........

[scrnchr]

still no leaks!

YAHOO!

[cpolaris502]

Nice, its always fun fixing an annoying problem. Now if I could just get my exhaust to shut up.