Rear Differential Cover Replacement
 

I hate to say it, but my diff has a leak and I have no idea for how long. I really hope I didn't kill it. The entire lower quarter of the cover is soaked, and there is a wet mark in my parking spot under it. Never noticed till now.

Anyone have tricks to doing this with it on jack stands? My father did this on his S10 and said it was easy, but it looks different. Mine has what looks like a rusty pipe in front of it. Will this get in my way or can I wiggle the cover out. Every single bolt looks like it has a nice coating of thick rust and dirt build up. How do I tell which cover I have, that auto store said there were two different sizes. Finally, is it safe to shoot PB Blaster on the bolts to loosen them up?

Before you do anything, first make sure you can remove the filler plug. The rusty pipe would be the stabilizer bar. Should be able to do the cover gasket with the stabilizer bar in place. To get the correct gasket take the old cover to the parts store with you. In Michigan, I would buy a new cover as it may be rusted out - they are pretty cheap. When you scrape the old gasket from the housing, make certain ALL of the old gasket is removed (not just what is convenient). Old rear end cover gaskets are notoriously difficult to scrape off. Yes, PB Blaster is fine.

I'll attempt to remove the filler plug today after work then. So what if that plug doesn't come out? Am I just SOL? Will I need a drip pan or will little to no oil come out?

Defiantly wasn't going to get used here when a new one is only $11 - $20.

Its just a 3/8s drive fill plug. Use a breaker bar for leverage. No oil will come out of it. The oil comes out when you remove the drain pan

If you can't get the original fill plug out, then you can get rear covers with fill plugs incorporated into them (but they are more expensive). Better to know how you will fill it up after repairs, at the beginning of this process. Yes you will need a drain pan when you remove the rear cover. A quart or so should come out. When scraping gaskets and rust, take care to not get stuff into the inside area (bearings and gears ya know!) - you can stuff shop rags in the top area and let them hang over the gears. Plan on taking your time and expending considerable effort scraping all the old gasket material off the rear housing sealing surface. If you eventually get the surfaces clean and oil free using carb cleaner, you can put a thin film of RTV sealer on both sides of the gasket to seal things up and then let sit overnight. But don't waste your time unless it is absolutely oil-free. RTV doesn't adhere in the presence of oil. Get ready to get greasy with some really smelly stuff!!!

The videos I saw doing this jammed a white rag into the diff when the cover was removed to prevent shavings from getting into the diff, I plan on doing that. I don't have carb cleaner laying around anywhere, but have been told brake cleaner (which I have plenty of) is good for almost anything could I use this instead to clean off the area the gasket goes?

Sure, brake cleaner will work too - but scrape it down to bare metal first. The gasket material is REALLY tough stuff. I like to sharpen a putty knife with a file to a razor edge and scrape with that. I have found it advantageous to be able to tap on the end of the putty knife with a small hammer when going through the tough stuff, so get a putty knife with a blade that goes all the way through the handle with wood riveted on both sides.

If you're a "Super Lucky Ace" and all the stars align correctly and the moon is in the third house the gasket might be stuck to the cover and come off the rear end housing clean. But I have never ever seen that happen!! Chances are it will be adhered to both the cover and the rear housing - and will tear around each bolt hole leaving super hard gasket material there. Not a big deal - just be prepared to work at it and make sure surface is clean and down to metal.

FYI - now is the time to replace your disk brake backing shields if they are rusted off. Axles need to come out and this cover needs to come off for that to happen.

How long can I leave the differential exposed? I'm going to try to remove it tonight, but doubt I'll get it all done by days end. There is no rain in the forecast until Thursday and it will be in a garage just in case it does rain.

Also never left the Blazer rear end on stands for this long. It is safe for it to just stay jacked up for a couple days right (I'm left to assume yes, but better safe then sorry)? Potentially putting entire car on 4 jack stands for other work (2 2-Tons for rear, 2 3-Tons for front). Makes it easy to slide around under the truck if it is all lifted as high as I can. Where are good points for the stands? I usually put them on them right next to the scissor jack hole (the spots where the provided jack bump fits nicely) on the frame. However I have never lifted the whole truck like this before.

Should be fine leaving the cover off over night. The residual diff fluid on the gears will prevent any surface rust. The garage is going to smell like gear oil though lol

Put the rear axle on jack stands and the front frame rail on jack stands. Have done it many times, never had an issue. Most recently was when I did the brakes on my father's F150, did all 4 at the same time so I only had to make one trip to a guy he knows that owns a shop to have all the rotors turned. Sure looked funny in the driveway lol but made it much easier.


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Well, tried to remove the plug yesterday with a foot long ratchet with no luck, it slipped right out. Only tried once, it was getting dark and I didn't want to strip the plug any more. Going to hammer in the drive extension tonight and hope for a better grip. Any other tricks to getting this thing off?

You might want to take it to a good shop (one that has confidence in taking out frozen fill plugs) before the plug gets too damaged. Your skills are just fine for replacing the cover, but getting out frozen rusty fill plugs can be very tricky and require heat and/or welding. Other option is to go ahead and buy the cover with the fill plug built in.

I have the feeling buying the cover with a plug will be significantly cheaper then paying a shop to do it.

Edit: After a quick look on rock auto there is only one size with a drain plug and odds are it isn't mine.

Would a shop even just replace a bolt, and wouldn't they torque it in?

How do I determine which cover I have? If it is the 8.5" then I can get a cover with a plug. And if I got the cover with plug would it still fill the same amount in? It looks like the plug is near the center on of the cover, and therefore would only fill it about half way.

To ID the rear look at the tabs below the center section.
https://www.gmbbodyforum.com/t333-ho...8-5-8-75-8-875 Also on the S10/blazer 8.5/8.825 rears the axle tubes go down in size after coming out of the rear. The S10/Blazer 7.5/7.625 tubes stay the same size all the way to the brake backing plates.

The rear does not fill completely with rear end lube. Too much and you'll have it coming out the axle and pinion seals. You simply put a specific amount of lube back in after draining. With the original fill plug, this should be to the level where it just comes out of the hole. With aftermarket covers with drain plug, put the specified amount in and then determine where this is on the cover for future reference (stick your finger in the hole and see where the level is).

Keep looking elsewhere you can find an inexpensive cover with fill plug for the 7.5/7.625 rears. I would have it in hand before taking the old cover off.

Not sure what you are asking about the shop replacing a bolt. But If it's an experienced shop in Michigan, I'm sure they have dealt with rusty frozen stripped drain plugs before.

Good luck and best wishes for a successful repair.

What I met by the shop question is a lot of shops use air tools and therefore can use a lot of torque. In my limited experience these said shops would do an oil change and put the oil plug in so darn tight that it is near impossible to remove without an air tool.

I'll take a look at the tabs tonight, crossing my fingers that it is the 8.5" since I know my local parts store sell them with a life time warranty.

Any chance you know where to find the 7.5" with a fill plug. Not finding any online yet. And what is with some of them costing well over $100 and even $200.

Going to a friends house tonight with one of my cheap socket extensions to grind it down flat on the tip. Then whack it in with a hammer :icon_smash:. If this fails I'll have to get a cover with a fill plug. Still can not find a cover with a built in plug for the 7.5, plenty of 8.5.

try heating it up with torch

Just when I thought I had enough grip and the filed down socket starts to turn... it lurches and makes a perfect circle :icon_rant:.

Biting the bullet and paying the additional $70 to have a shop replace the cover:icon_sad:.

The shop does know about the now-damaged fill plug and plans to get it out? Not a criticism, I've done exactly the same to a fill plug before myself. A shop WILL charge you extra if the fill plug is damaged.

Ya they said if it was undamaged $28 damaged $38 max. Then I asked how much just to do the whole job cover and all and they said $40 if I supply parts. Worse case I have to pay $80. Boy are they going to have fun :icon_razz:.

Excellent!! You made a good choice. Best wishes!

I'll know for sure Friday. I bet I could whack in a new larger drive, or borrow a friend's welder and weld on a socket... but I'm done with this and frankly don't have the time.

I was at a ring and pinion shop and the mechanic used an air chisel on the corner of the square opening and backed the plug out. I've gotten the same results with a chisel and a hammer. Replace the now ruined plug with a stainless plug and coat the threads with anti-seize. Tighten only to past snug.

I am assuming you have the stock recessed 3/8" plug?

Speaking from experience, you can use an impact gun on it's lowest setting to get the plug out. Use a 3/8" impact extension, push hard and keep the gun square. Use a good penetrating oil like liquid wrench and let it soak if you can. Wear safety glasses.

Do yourself a favor and don't put that darn plug back on. Go to the hardware store and get a heat rated cast iron plumbing plug with a square head. You'll actually be able to get a socket on it. Prior to re-installation, dab some anti seize on it.

$63 (student discount:D) + parts and the new cover is in. Glad I didn't have to do it, the plug was a perfect circle, six of the cover bolts head's snapped off, and it took forever for them to clean off the old gasket with a chisel! A hell I'm glad I didn't go through.

On the plus side, I asked if he noticed any damage to the differential and he said it was in great shape, no discoloration or anything:icon_special:.

What a PIA that cover was. Sometimes it is better to let someone with a lift, the tools and the tenacity to get job done and in a very timely manner. With a stripped out plug broken bolts to deal with, it was worth the money.

Went out to look over the work today and there was still a small puddle (few drips, enough to stain the concrete) under the differential:icon_rant:! The thing was soaked in oil and gunk before, and this is the first time I took a close look. Could the differential just be slowly drying out?

I'm parked in the same spot I have since before this, so it is likely the dark spot is just a stain in the cement. I went under to clean the differential a bit, and after some rubbing along the lower edge the towel had a good amount of black gunk, not really oily, just nasty black gunk.

The amount is certainly less then before the cover was changed, and the cover itself is dry. The entire bottom of the diff (minus the cover) was coated in it. What kinda worried me is it was slightly (stress on slightly) more concentrated by the drivers side axle, though no oil on the axle itself. However the gunk was pretty thick on the drivers side of the cover, I suspect that was the point where it was leaking through the cover/gasket. and therefore I think it is why the axle area was more concentrated in gunk.

This cover was allowed to leak for a VERY long time. The entire bottom 3/4 of my diff was soaked in oil and thick gunk before the cover was changed. I'm thinking they just didn't clean it since the new cover is dry and clean.

I recently installed a Ring & Pinion Gear and debated to use sealant or not on the gasket. I decided not to use any sealant but to just make sure all mating surfaces were cleaned very well and torqued all bolts equally. Not a drop has leaked from the cover and I had to change the diff fluid at 500 miles and I just finished a rear disc brake conversion where I had to pull the axles again. At the fluid change I re-used the same gasket and again no leaks. The last time I used a new gasket without sealant and not a drop has leaked from the cover.

Went at it with some brake cleaner to try to clean it up, lots of build up of just dark black mud. Got what I could off, still quiet a bit remains. Asked a mechanic friend and he said that it may never truly look "dry" again.

I noticed that the passenger side of the diff about where it meets the axle there is what looks to be a plastic ring, but there isn't one on the driver's side. What is this? Should there be one on the driver's side?

My 2000 has a black plastic ring in that location that holds the parking brake cable.

Should there be one on the other side? I ask since the divers side is darker then the passenger side, thought maybe it was related somehow.

After cleaning it my guess is it just got more dirt on it somehow since what came off on the towel seemed like a thick black mud which was more concentrated on the drivers side of the diff.

Here is an image on what the diff looks like on the drivers side. Is it normal? Should it still be this dark? I cleaned off as much as I could with brake cleaner but it just keeps making the paper towel black with very little visible progress.


https://s1.postimg.org/rjroi6zxb/rsz...801_204722.jpg

This is what the passenger side looks like.

https://s4.postimg.org/7b2frpufx/rsz...801_204726.jpg

It's fine. I wouldn't give it another thought unless you notice it start to drip on your driveway. They did put a new plug in for you, right?

I honestly didn't check for a new plug. I kinda just assumed. They did put in new bolts (all of them) and they guy said he had a box of plugs and would just put in a new one.