Rear differential Lubrication ????

[Booie]

I am going to change the Rear differential oil does anyone no the correct weight of Lubrication to use and do I need posi traction addditive and how much is needed in a 79. I was also told only use the GM Brand products.

 

[GTR1999]

You will need a good suction gun. When I rebuild diff's I add a drain plug but this won't help you now.
I use Lucas 85-140 gear oil and GM additive. I like the lucas better then any other.
I couple of things on the 79 you have to be aware of and to check.
They had bad side yokes, posi clutches and ring gear bolts. check for endplay in the yokes if you have more then 050" then watch them. If you have more then .125 replace them, if left to go too long the yoke will hit and grind the housing and then you'll lose it.
good luck
Gary

 

[Booie]

Thanks Gary I appreciate the help and you insight. Bruce

 

[GTR1999]

No problem Bruce.
If you want to see what these unit are about, check my link. It will go over the areas of concern.

http://www.vettemod.com/forum/showthread.php?t=167

 

[LanceB]

Gary,

Excellent post on how to rebuild a differential. If I ever have problems I would love to get it to you rather than someone here local (or make the huge mistake of trying it myself). Too bad you are so far away. My brothers 77 made awful sounds that all went away once we siphoned out the old differential oil and put in GM gear and the additive. I just hope they don't come back.

Lance

 

[bgall2]

Changes oil in my 78 couple months ago. You should use the posi trac oil, 4 oz you can get from NAPA outo parts. I used 80-90 wt oil to full. My rear end was making lots of noise but none since the change. I think the posi trac oil is the key. Get all you can out with a good suction gun.

 

[6880 Mike]

My advice is to use only genuine GM posi fluid and additive.

 

[muddywaters]

Yeah Mike, I'm with you on that one, I've used other gearlubes with the additive and once in a while a problem occurs (Chatter), I only use the GM Lube/Additive in the rear ends, they'll usually let you know right away that you should have.......