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Sonoma rear diff leak

491 Views 36 Replies 12 Participants Last post by  Innate
Hey all. I just discovered this fluid mark on the Sonoma's rear diff cover.
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Last I checked the fluid (about a month and a half ago), it was at an appropriate level. Not sure why there’s this wet mark now. Any ideas?
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Thank you all for the replies. @Joe Cool now that I think about it, I could’ve sworn I saw a teeny tiny hole in it in that general area last time I got up close to it. But I thought it may just be a breather or something. I will get underneath it again and check again (make sure my mind isn’t playing tricks on me🤣). I do agree that it’s very odd. And, luckily, the plug on mine works good, so it shouldn’t be any problem there. Anyone know where I can find a good replacement for the cover?
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Thank you. Looks like that one GM kit might be good… replace the cover, gasket, and hardware
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You mean GM 19333218, the kit that doesn't fit yours?

You've got a 7.625" gear, right That GM kit is for an 8.5/8.625" gear 10 bolt.
Shoot. I was just about to ask that. I’m not sure exactly which one I have. If this info helps, it’s a 4WD 02. With the 3.42 (GU6) and Positraction (G80)
Standard question....can you post a pic? If the axle tube narrows a couple of inches past the center section, it would be an 8.5".
Eh...never mind.

Here are the differences...
Thank you very much sir, good info there
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Here’s some better pictures. Thanks again everyone for the fast and good responses!
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Quick update. Before I went in for the night, I decided to check the diff’s fluid level. It was right up to the top, so at least that’s good. I also looked closer at the moisture spot. And lo and behold, there’s a tiny hole that looks like the diameter of a thumbtack right in the middle of the moisture spot. Definitely the culprit. There also is two little dents, (one of which the hole is in the middle of) on the cover. Now, this would be a very easy fix, just replace it and be done. But, the problem is that the bolts holding it on are in such bad condition, that I fear they’re gonna just either snap off, or the head will completely round. Idk what I’m gonna do. Anyone got ideas? I do have a mig, so if I attempt it, and they snap, I can weld a nut and all that.
Your axle tubes look like the 7.625 to me.

ZR2 trucks got the 8.5 inch gears. Most 4.3L v6, 5 speed manual Blazers and Jimmys got it as well. Some 4.3L V6, 5 speed manual pickups got the 8.5 inch gears as well, but that seems to be hit or miss.
Yep, that’s what I was thinking it was. I’ll just piece together online what that GM kit comes with👍
Suggestion...
Don't know how much life is left in this rig, since it looks like you live in the rust belt (!)
You can buy a cover with a drain plug built in. It may be more than you'd want to spend, but they work very well.

If you are really cheap, you could spray the area with brake clean, sand the bag out of the cover near the pinhole and JB Weld the area. I am sure that would solve your leaky cover.
The key is making sure that the area is oil free.

Hope this helps...

Confucius say: JB Weld work good. :p
The weird thing about this truck, is that certain things are extremely clean (rockers, frames not scaly etc), but then you have this pretty crusty diff cover. I did think about the JB fix as a stopgap… maybe I’ll do that, until I get parts in.
^^^ I wish I was in Baton Rouge. I have at least 3 covers from different projects that I could send you for free. Just pay postage. I think I may be back there for a few days this coming weekend, if you still need a cover, I'll dig one out.
IIRC, they look like new. Nor rust at all.
Thank you buddy. I’ll keep everyone updated on what I’ll do with this/when I get parts👍. Just finished up spraying it down with penetrating oil. Hopefully if I do that for a while, it’ll help
I'm impressed, not many people know about Kroil. It's expensive but worth the cost.
True. It’s some good stuff!
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Decided to slap some JB on it, as a stop gap measure. Cleaned up/sanded the spot, and just put it on. Hopefully it works fine. I’ll keep everyone posted when I get the new cover👍
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