Rear diff (pumpkin) cover

[Petey]

At 100K I started working from the front to back and doing maint. Plugs and front diff are done, I have the transfer case fluid(smurf blood?), debating on having a place do the trans fluid again (I did it at 50K)

Now my question.

I think my cover is rotted and stating to leak it feels wet, however 2 years ago I painted the rear axle with POR15. Yet all the bolts are shot, I started at 15mm and now down to 12-13mm without getting a good bite to break them free.

Before I go any further I want to have on hand new bolts and a cover. From what I see the original cover is no longer available. I have the SWB 4.2 without the g80 (GU6). The one for the LWB will fit all it is just deeper, correct? Does it comes with a gasket and bolts? What is the P/N for that?

Tricks to get the bolts loose? Vice grips, stripped bolt extractor?

 

[Sparky]

I don't know the part number or what it comes with, but yes the 8.6 cover will fit as long as it is from this platform (it is a non-standard housing compared to all the rest of the 8.6 axles out there). It is just deeper.

 

[Mounce]

PS the bolts are 13mm pre-rust

 

[Reprise]

Given I'd been on this subject recently, I did some more research, and found the following on the old site:
http://forums.trailvoy.com/archive/index.php/t-22973.html

(for the nostalgic, Roadie participates in the thread, although he's not the OP)

The short version: (and I need to update my own thread again...)

- Both of the covers have the same bolt pattern (placement)
- Both covers use the *same* gasket, per GM, as a result (?)
- The 8.6 cover is a little higher (makes sense, the ring gear is bigger)
- The 8.6 cover actually has '8.6' stamped into the housing, on the RH side (now I want to get back under the truck with a wire wheel)

GM part # 12479379 is the 8.6 housing cover.

There are some Photobucket pics at the link - if you use Chrome and have the Photobucket add-in, you can see the pics there.

Here's a screengrab of the 8.6 cover with the stamp on the housing (orientation here is LH side on top):


As far as removing the old bolts:

- Get some PB Blaster and soak all of them well. Leave it for a day to be safe.

- Since the torque spec on those s/b 18-20lbs, it shouldn't take too much to break them. A breaker bar should get them for sure.

- Use a 6-point socket or box wrench or one of the newer tools that grabs fasteners more securely. Just don't use a conventional 12-point on iffy bolts, as they can round off the corners of the bolt head.

- If you feel one or more of the bolts 'getting tighter' while removing, stop, apply more Blaster to the threads, and reseat the bolt. You may need to apply heat to completely remove it. If you decide to keep going and 'gorilla' that bolt, it will likely snap.

The nice thing about the cover bolts is that there's a lot of room to work in there, comparatively speaking. Drop the spare tire and it's pretty roomy. Take your time and you should be OK.

 

[Mooseman]

The FAQ's are your friend:
Rear Differential Cover Bolt Size
How to identify gearing and differential size

 

[Petey]

Thanks

I'm finding P/N 12479377 I'm wounding if that's the beast W/bolts.

I'll start soaking the bolts now in hopes but the problem I have is, I started at 15mm and been working my way down and still not getting a good bite on the bolt with a 6pt socket. The bolts are that bad I'm now working some place between 11/12 mm. Also I may have POR15 them in place.

 

[Mooseman]

You might need to use a reverse twist style bolt remover if they're that bad.

 

[Chickenhawk]

I had to grind flats on two so that I could get a good bite with the jaws of vise grips. The last one was the only bolt left, so I was able to twist the cover slightly around to break it loose. I was using a new cover anyway, so if I bent the old one, it was no big deal. And, in answer to your question, as far as I know the GM part 12479377 fits all years of trucks with the 4.2. Very important to note that it comes unpainted, and with new bolts and a new rubber gasket. It saved me a ton of time and was actually cheaper from an online GM dealer than just the gasket at NAPA. I also painted it black before I put it on, and just for fun, painted the bolt heads stainless color.

 

[Petey]

I got all 10 bolts loose today. I think the POR15 didn't help me any either. I had to use a bolt extractor on 9 of them to take them out but I ran them back in to snug with a 13mm socket just so I can drive to warm up the fluid and stir things up in there before I drain it. The very bottom one put up a good fight. Wound up using the grinder to make 2 nice flat sides and then put vice grips on it after using the torch. It backed right out and I put a new bolt in there so I could drive it.

 

[Petey]

New cover is painted and on with new bolts and filled!!!

a little more than 2 qts went into the rear and a little less than 1.5 came out. I think I may have a pinion seal seeping.

a little less than 1 qt went into the front and 3/4 came out.

Both were black but clean other wise.

 

[Mooseman]

a little more than 2 qts went into the rear and a little less than 1.5 came out. I think I may have a pinion seal seeping.

Which cover did you use? If it's the 8.6, it's the bigger cover and it takes more.