CHECK YOUR DIFFS...

Pryme · March 29, 2023

10 minutes ago, 64BAwagon said:

I did my 2021 3500 rear diff and the cover gasket is definitely reusable. When I serviced it I pulled the cover plate off and painted it also.

The first change I always pull the cover so I can wipe the inside of the case out. I dont spray the gears down with cleaner because I have always felt that the residue from the cleaner would have an effect on the new fluid. I cant prove it but I just avoid it in case. For me, cleaning the magnet and wiping out the bottom of the case is enough.

I caught a sale at Auto Zone over a year ago that had Delo full syn 75W90 gear oil for less than $9 a qt so I stocked up. Rural king also has Mystik full syn for a good price.

What’s the gasket made out of? Did you also reuse your fill plug gasket without issue?

looks like the cover bolts are 30lbs is that what you did?

XY74 · March 29, 2023

My 2020 rear diff has a drain plug. Changed the oil in it last month.

Pryme · March 29, 2023

5 hours ago, XY74 said:

My 2020 rear diff has a drain plug. Changed the oil in it last month.

Well gat dabnit why did they decide to take it away? My 22 has a fat spot on the bottom the right size for one to be tapped in but they never did. What a joke. Well I received this on my doorstep today so the diff fluid will be my first of many uses for this thing.

I could see this doing a great job of swapping out trans fluid on this truck in the future too once a dipstick is installed.

Edited March 29, 2023 by Pryme

64BAwagon · March 29, 2023

The gasket is a metal core encased in rubber, similar to many of the newer transmission pan gaskets. The fill plug worked fine, no need to replace the seal. I would estimate that one would last quite a while. Like many other items such as the oil pan plug gasket, I have a spare on hand but only replace them after 3 or 4 times.

As for the drain hole, my guess would be that it probably costs GM a few bucks to have the holes drilled and tapped in the diffs and a plug placed there. Most of the time these things are all about money.

I thought about drilling mine out but the case is really thick and my luck would be that I would mess it up. I have a 1/8 pipe tap so it wouldnt cost me anything but I figured for a quick spill and fill I would just loosen the screws on the cover and pry the lower portion away and let it drain that way.

Edited March 29, 2023 by 64BAwagon

Pryme · March 29, 2023

34 minutes ago, 64BAwagon said:

The gasket is a metal core encased in rubber, similar to many of the newer transmission pan gaskets. The fill plug worked fine, no need to replace the seal. I would estimate that one would last quite a while. Like many other items such as the oil pan plug gasket, I have a spare on hand but only replace them after 3 or 4 times.

As for the drain hole, my guess would be that it probably costs GM a few bucks to have the holes drilled and tapped in the diffs and a plug placed there. Most of the time these things are all about money.

I thought about drilling mine out but the case is really thick and my luck would be that I would mess it up. I have a 1/8 pipe tap so it wouldnt cost me anything but I figured for a quick spill and fill I would just loosen the screws on the cover and pry the lower portion away and let it drain that way.

With my new super sucker I plan on just doing the diff every 20-25k miles because it should be very easy. That will equal 4yrs for this truck.

I figure that’s way ahead of the game considering most of these trucks run 100k miles on the factory fill before maybe getting around to it haha.

Grumpy Bear · March 30, 2023

5 hours ago, Pryme said:

I figure that’s way ahead of the game considering most of these trucks run 100k miles on the factory fill before maybe getting around to it haha.

I've done three since new. About every 50K.

64BAwagon · March 30, 2023

It used to be in the manual on full size trucks to change the rear diff around 5k miles to get the break in sludge out of it and keep the clutch packs freed up. I had 2 trucks that had issues with the G80 lockers sticking. My 03 Avalanche was so bad that it rolled up a 6 inch pile of asphalt while parked on a warm day just from the tension caused by the locker not releasing. Of course I took it to the dealer and all I got for my trouble was a new door ding and them telling me I had used the wrong fluid when I changed it 6 months before. This was before GM figured out they needed a small amount of friction modifier in the fluid. Once I added that I never had another issue with it. I was always nervous about that axle and rear diff after that. It must have been under a great deal of tension.

Pryme · March 30, 2023

2 minutes ago, 64BAwagon said:

It used to be in the manual on full size trucks to change the rear diff around 5k miles to get the break in sludge out of it and keep the clutch packs freed up. I had 2 trucks that had issues with the G80 lockers sticking. My 03 Avalanche was so bad that it rolled up a 6 inch pile of asphalt while parked on a warm day just from the tension caused by the locker not releasing. Of course I took it to the dealer and all I got for my trouble was a new door ding and them telling me I had used the wrong fluid when I changed it 6 months before. This was before GM figured out they needed a small amount of friction modifier in the fluid. Once I added that I never had another issue with it. I was always nervous about that axle and rear diff after that. It must have been under a great deal of tension.

What fluid do you use now?

I’ve seen plenty of ppl use the amsoil severe gear without issue so that should be good.

64BAwagon · March 30, 2023

I have always used a 75W90 GL5 full synthetic. I buy whatever brand is on sale. When I was working I used Mobil 1 since thats what we used on our trucks and we went through a couple of kegs a year. I have some Mystik and some Delo400 currently. My understanding is that the new formulas have a small amount of friction modifier now so its not needed. There is a point where too much of it is bad.

Pryme · March 30, 2023

So my differential was indeed low from factory specs of 3.17qts.

I removed 2.5qts with the super sucker 1,000.

so it wasn’t horrendously low but still, that is very poor quality control at the factory. I can’t imagine they don’t have a machine that is computer controlled to squirt exactly 3.17qts in, so why the discrepancy between different trucks on this very elementary thing??

You may ask how do I know I got it all out. Well this process took longer than I anticipated. And also I let the truck sit for an additional 30 min or so and brought the super sucker 2000 back over and nothing else came out. So I ran a small flexible magnet down into the diff because I’m super ****** and had the time to see if any magnetic material appeared on the magnet. None did and it was also dry.

The fill plug was also clean without any magnetic fuzz.

it makes sense considering when I checked the factory fill, it was about .9” from the top.

I put in the 3.17qts and it is now roughly 1/4” from the top.

So how did the super sucker 3000 do? Well the machine itself is a beast. It sucks like crazy. (Hey now) and seems well built. The problems are as follows:

The hoses that come with it are hard cheap plastic and they prefer to stay coiled up. Even when room temperature, they don’t lay out. So they don’t like to stay where you put them.

The main hose is like 5/16 so it’s decent. The others are very small, like 1/4” which you need to reach the diff so even with the fluid warm from a drive it took forever due to that small hose.

For an oil change or anything top side that isn’t doing a diff, it wouldn’t matter.

I will get some more large hose that is softer.

Edited March 30, 2023 by Pryme

64BAwagon · March 30, 2023

I have been thinking about getting an extractor, what did that one cost you ?

The rear diffs come from American axle as a complete assembly with fluid installed. You might want to send them a message including your VIN to let them know. Major components like a rear diff are serialized but I couldnt tell you where its at.

Like so many other DIY projects you now have the satisfaction of knowing the job was not only done but done correctly.

Pryme · March 30, 2023

48 minutes ago, 64BAwagon said:

I have been thinking about getting an extractor, what did that one cost you ?

The rear diffs come from American axle as a complete assembly with fluid installed. You might want to send them a message including your VIN to let them know. Major components like a rear diff are serialized but I couldnt tell you where its at.

Like so many other DIY projects you now have the satisfaction of knowing the job was not only done but done correctly.

Yeah I should give them my best Karen and call them up. But yes, I feel good about it being to spec with nice fresh fluid after 4,400mi of break in.

It was 116.00 on Amazon sold and shipped directly from mityvac.

I will for sure use this for small engine oil changes especially my super annoying push mower that Ariens designed so the crankcase drain plug is literally on the deck. So there is zero you can do but have the oil drain onto the deck and hope to tip it towards a container. It’s a joke. No room for a tube either.

so I will be using super sucker on it.

But this thing would be great to pull transmission fluid out of these trucks because you would know exactly how much you pulled and simply add that amount back in.

shadow gray 2020 hd · April 9, 2023

My front diff is fine, but back is low enough that I couldn't even touch it with my pinky. Pretty ridiculous on a truck bought brand new with only 20,000 miles on it to be low. I am sure it was low from the factory because it sure hasn't leaked. Yet another GM failure on the truck I bought brand new. Very disappointing. Guess I will be driving into town tomorrow morning and buying a couple quarts of gear oil, or should I take it to the dealer? With it being under warranty still, the dealer has done all the service work and oil changes, don't guess they check diffs when they do their multipoint inspection?

No idea how low it is, after reading another thread in here, hoping no damage has been done to it.

Edited April 9, 2023 by shadow gray 2020 hd

DuckBoi · April 10, 2023

On 3/29/2023 at 1:50 PM, Pryme said:

Well gat dabnit why did they decide to take it away? My 22 has a fat spot on the bottom the right size for one to be tapped in but they never did. What a joke. Well I received this on my doorstep today so the diff fluid will be my first of many uses for this thing.

I could see this doing a great job of swapping out trans fluid on this truck in the future too once a dipstick is installed.

My 23 has a drainplug for the rear diff. Perhaps you got a defective diff cover?

shadow gray 2020 hd · April 10, 2023

3 hours ago, DuckBoi said:

My 23 has a drainplug for the rear diff. Perhaps you got a defective diff cover?

No drain plug on my differential cover, there isn't even a place on the cover for a drain, mine is a 2020 though.

20 hours ago, shadow gray 2020 hd said:

My front diff is fine, but back is low enough that I couldn't even touch it with my pinky. Pretty ridiculous on a truck bought brand new with only 20,000 miles on it to be low. I am sure it was low from the factory because it sure hasn't leaked. Yet another GM failure on the truck I bought brand new. Very disappointing. Guess I will be driving into town tomorrow morning and buying a couple quarts of gear oil, or should I take it to the dealer? With it being under warranty still, the dealer has done all the service work and oil changes, don't guess they check diffs when they do their multipoint inspection?

No idea how low it is, after reading another thread in here, hoping no damage has been done to it.

Ended up being just over a quart low. With 20,000 miles run on it that low, what are the chances of damage?