Differential cover, bolts and gasket for 8-inch rear end

[Chickenhawk]

There have been many posts asking about the rear diff cover, so I thought I would just address some of the questions in one new post based on recent experience. Aftermarket rear diff covers for the 8-inch rear end that comes on most short-wheelbase 4.2-litre Trailblazers and Envoys seem to be in short supply. Even Rock Auto was out of stock. The GM part seems to have a lot of conflicting information.

My rear end was dripping from the bottom and it appeared that the RTV sealant had failed. (Long story, but I when I stripped out the inside of the factory diff fill plug, the shop who got it off by welding a socket adapter to the plug put in a new plug for me with a hex socket instead of the 3/8" square hole and refilled it with fresh fluid.) The diff cover was also rusted quite badly, so wanting to avoid an hour of work just to scrape and clean the old cover, I just ordered a new factory cover from an online GM parts retailer.

It had to come from the warehouse, but I had it in my hands in just over a week. I ordered GM part number 12479377, and the nice thing is that it also came with new bolts and a new factory gasket. I actually paid less for the cover, factory rubber and steel gasket and all new bolts, than what the local NAPA wanted for just the Fel-Pro gasket. It came to $52 Cdn, plus shipping.


I also checked into the PML covers for the Torsen differential, and it fits. It has a larger capacity but according to PML, there is still 1/16" clearance between the cover and the panhard strut. It even has a drain plug, and can be tapped for a fill plug in the cover too. The only reason I stuck with the factory cover was the cost was just too much for a diff cover that was going to be hidden behind the spare tire anyway.
https://www.yourcovers.com/diffcover_11035.phphttps://www.yourcovers.com/diffcover_11035.php

Tonight, a quick coat of primer and glass black paint, and then I wait for the weather to warm up enough to crawl underneath. I am hoping a brand new cover will turn a 2-hour job into a simple one-beer effort.

 

[Capote]

There have been many posts asking about the rear diff cover, so I thought I would just address some of the questions in one new post based on recent experience. Aftermarket rear diff covers for the 8-inch rear end that comes on most short-wheelbase 4.2-litre Trailblazers and Envoys seem to be in short supply. Even Rock Auto was out of stock. The GM part seems to have a lot of conflicting information.

My rear end was dripping from the bottom and it appeared that the RTV sealant had failed. (Long story, but I when I stripped out the inside of the factory diff fill plug, the shop who got it off by welding a socket adapter to the plug put in a new plug for me with a hex socket instead of the 3/8" square hole and refilled it with fresh fluid.) The diff cover was also rusted quite badly, so wanting to avoid an hour of work just to scrape and clean the old cover, I just ordered a new factory cover from an online GM parts retailer.

It had to come from the warehouse, but I had it in my hands in just over a week. I ordered GM part number 12479377, and the nice thing is that it also came with new bolts and a new factory gasket. I actually paid less for the cover, factory rubber and steel gasket and all new bolts, than what the local NAPA wanted for just the Fel-Pro gasket. It came to $52 Cdn, plus shipping.

View attachment 83098
I also checked into the PML covers for the Torsen differential, and it fits. It has a larger capacity but according to PML, there is still 1/16" clearance between the cover and the panhard strut. It even has a drain plug, and can be tapped for a fill plug in the cover too. The only reason I stuck with the factory cover was the cost was just too much for a diff cover that was going to be hidden behind the spare tire anyway.
https://www.yourcovers.com/diffcover_11035.phphttps://www.yourcovers.com/diffcover_11035.php

Tonight, a quick coat of primer and glass black paint, and then I wait for the weather to warm up enough to crawl underneath. I am hoping a brand new cover will turn a 2-hour job into a simple one-beer effort.

I actually have both those links saved apparently, forgot I found those a long time ago. I would use a PML cover on my 8" diff as well, but since I've got an aftermarket Massive panhard bar, there would be no clearance for it.

 

[Reprise]

I actually paid less for the cover, factory rubber and steel gasket and all new bolts, than what the local NAPA wanted for just the Fel-Pro gasket. It came to $52 Cdn, plus shipping.

That's insane. I think I paid $10-15 for a Fel-Pro (from Rock Auto, no less). I do have the larger carrier, but most of the run, to your point, was SWB / 4.2, with the 8" carrier. So those should cost even less than mine ?

Going off topic - with a (current & historical) exchange rate of about 20% in our favor - why do the same things cost so much more in Canada? (I know, there is VAT, etc. - but it's not the difference between $15 (US) and $52 (CDN) - actually more, per your statement.)

 

[Mooseman]

Going off topic - with a (current & historical) exchange rate of about 20% in our favor - why do the same things cost so much more in Canada? (I know, there is VAT, etc. - but it's not the difference between $15 (US) and $52 (CDN) - actually more, per your statement.)

That is one of the universe's great mysteries. Even when the CAD $ was higher than the US $, we were still getting gouged. Case in point, snowmobiles made in Canada were still more expensive here than in the US and the manufacturer would punish US dealers that would sell to Canadians. But because of the Internet, the knowledge is coming out.

 

[Chickenhawk]

NAPA traditionally runs high prices because so few people end up actually paying their retail listed price. They give jobber discounts, CAA discounts and discounts sometimes just for the asking. I am not sure of the difference between the Fel-Pro gasket (RDS55479)
for the 8-inch rear end or the GM gasket, part # 12479020, but NAPA was $60. (I suspect they might even be the same gasket.)

Mind you, the cost of shipping the cover from the online dealer in Red Deer Alberta pretty much negated any savings, but I am lazy and the thought of just scraping the diff housing and slapping on a brand new cover, with a new gasket and new bolts, might shorten the job to 20 minutes. (One beer.)

Of course, using the Chickenhawk method of timing a job, I take the most pessimistic view of how long it will take when i need to crawl underneath a truck on ramps, fetch another tool out of the basement every five minutes, come in to warm up with a coffee, and deal with rusted bolts ... and then multiply it by three. So my one beer job is actually three hours.

 

[Reprise]

So my one beer job is actually three hours

Or nine beers, at a rate of 1 beer = 20min

I was curious and went back and looked up my RA order - and it wasn't a diff gasket I ordered - it was a rear main seal kit (that I haven't installed yet, obviously - and may not need to - but that's another thread.)

I looked up the Fel-Pro equivalent of what you got - and it lists at $21 - $32 USD (RA vs. retail parts store.) It looks like only a rubber gasket is available for that particular carrier. NAPA online was $40.00 even.

Apologies for misidentifying / causing confusion.
Appreciate the 'lesson' on price disparities between US <> Canuckistan.

As for my own diff - I had opened the fill plug on mine, and was about to change it out a couple of months ago. But when I saw it was filled perfectly (meaning: no leaking), and I wasn't having any problems with the rear whatsoever, I decided to postpone the job until spring (I had just finished a ton of other work on the truck, and I guess I wanted to get the thing out of the garage so I could get the car back in there before the snows came.)

My 8.625 carrier has a reusable rubber gasket; if it had not sealed properly after reinstalling it, I'd have broken out the Permatex (making my own job about 3hrs, and nine beers, by the time I stopped cursing at the leak, re-draining, R&R the gasket, etc.)
And that's why I hadn't purchased a new gasket of my own.

 

[littleblazer]

Well see there's the problem, 20 minutes is a two beer job at the least.

Being serious for a second, you got the and the reusable gasket as well as bolts for $52? I think I paid $38 for the gasket on mine. (Inner steel was rotted leaving soft apots. With my luck it would have seeped if I had reused it.) That is a good price.

 

[Capote]

A lot of guys don't even use the seals, they just use Permatex "the Right Stuff". That's what I plan to do anyway.

 

[Chickenhawk]

Yup, cover, new bolts with threadlocker, and gasket. All in the same GM box for $52.

 

[Sparky]

What's weird is how this platforms 8.6" diff is the same guts as any other GM 8.6", however the diff housing and cover doesn't match the standard GM 8.6" rear out there. This platform's rear end housing is unique to itself. The 8.0" and 8.6" in the GMT360 series have the same cover bolt pattern, just the 8.6" cover is deeper (and the 8.6" housing is deeper also).

You can use the 8.6" cover on the 8.0" rear end. Just has some extra space inside that will result in needing a little more gear oil to fill it.
You cannot use the 8.0" cover on the 8.6" rear end. Someone here a while ago bolted one on by accident because it appeared to fit but as soon as he moved the vehicle the ring gear tore a hole through the cover. Oops.

 

[Chickenhawk]

Wow, that is great to know! I never knew the 8.6" cover would fit. I wonder how much extra depth it has. The PML cover is designed for the Torsen diff, and it barely clears the panhard rod.

 

[Capote]

Interesting info @Sparky, didn't know this.