1968 GMC Rear End

[68gmcdude]

Hello...

I am going to be pulling the cover on my rear end to replace the gasket and fluid and have a few questions.

1. What weight gear oil is recommended?
2. What brand gear oil does everyone recommend?
3. How do I determine what gears I have?

Thank you!

[Getter-Done]

GL-5 90 weight oil is okay for the older stuff.

Amsoil has good products.

And the ratio is stamped in the ring gear.

[cwcarpenter98]

That being a Dana 44, there's a good chance you could have some 3.54 gears.

I've been using 80w-90 in my old axles and haven't noticed any issues. If you've got a limited slip, make sure you have either some additive on hand or use a gear oil that comes with the limited slip additive already mixed in

[68gmcdude]

Finally got some time. Open rear end with 3.54 gears. New gasket and fluid in.

[Mike C]

Always my recommendation to take it apart and look and change fluid. But I believe I see the Dana tag under the cover bolt at 11 o’clock? That would tell you as well. But you can’t always believe it… I have an 86 K30 with Dana 60 in front and it had the 3.73 tag under the bolt but a set of 4.10’s inside!

[68gmcdude]

I have a leak at the rear end after putting on the new cover gasket. The leak is not coming from the cover. I believe it is leaking where the driveshaft enters the rear end so I am going to replace the pinion seal. Any tips on doing this? Do I need a special tool to insert the new seal? Thanks ..

[Mike C]

The Dana axle doesn’t use a crush sleeve, so it is easier to get it exact when you put it back together since you can torque to spec. I would get a new pinion nut. You cannot use a seal installer because of the pinion (maybe a ball joint boot installer?) I just use a wide, flat hammer to go around the seal tapping it in.

[68gmcdude]

Ok. What is the truck to getting pinion nut off? I don't have an impact. I tried using an 18 inch breaker bar with a 2 foot pipe added to it for leverage. It's not budging.

[jumpsoffrock]

Originally Posted by 68gmcdude

Ok. What is the truck to getting pinion nut off? I don't have an impact. I tried using an 18 inch breaker bar with a 2 foot pipe added to it for leverage. It's not budging.

Lots and lots of torque.
I have a Dana 44 in my '56 Ford and I wanted to replace the pinion seal during some other resto work I was doing. I made a "pinion holding tool" that prevents the pinion from turning when applying torque. I'll post a pic. I made it myself with scrap I had laying around.

After that I put a good 18" breaker bar(Proto) and used a hydraulic car jack to "lift/turn" the end of the breaker bar but the socket kept slowly coming off.

So I had to jury rig a weird thing that basically bolted the socket to the bolt.


I applied so much torque that the breaker bar looked like a banana. It was EXTREMELY tight. I've never experienced anything that tight before, other than maybe 50 year old lugs on a 2-ton truck.

[68gmcdude]

When removing the pinion nut, should the transmission be in neutral? Should parking brake be on?

[jumpsoffrock]

Originally Posted by 68gmcdude

When removing the pinion nut, should the transmission be in neutral? Should parking brake be on?

Trans doesn't matter, I left brake off, tires were blocked anyways.