Rear Differential Oil
 

Going to put a new gasket on my rear diff on my 71 C10 307 V8 Automatic. Leaking pretty bad and I don't know the history so I figured I'd fresh'n it up. What are the specs on the gear oil, 75W-90, ... etc? Non synthetic I assume.

Service manual says GL5, not sure what that translates to in a 75w, 80w, .... Also, how many quarts? Any special additives?

Example: Ok to use this?
https://shop.advanceautoparts.com/p/...lvoline+80w-90

Thanks in advance!

Re: Rear Differential Oil
 

Get the gear oil gasket maker for sure to have no leaks. This stuff works great and is much better than the normal stuff. I use the Valvoline 80-90 gear lube in all of mine.:chevy:

https://www.autoserviceprofessional....desktop-view=1

https://images.autoserviceprofession...-Oil-RTV-1.jpg

Re: Rear Differential Oil
 

^^ Andy beat me to the punch with that Permatex. It's called Gasket Maker but I smear a thin coating on both sides of a gasket. No leaks, great stuff, made to use with gear oil.

I typically use Mobil-1 75W-90 synthetic, but any good gear oil will work fine. If you have an open diff you don't need any additives.

I'd get 3 quarts and you'll probably have some left over.

Re: Rear Differential Oil
 

Thanks for the responses, just what I was looking for!

Not sure if open diff or not. It is a 12 bolt though.

The brake line is attached to one of the bolts. It appears to be very rigid. I assume it will easily move out of the way once I remove the bolt that attaches it to the diff cover. Not much space with the panhard bar being close also, but I assume just enough room to get cover off and back on. Thanks again!

Re: Rear Differential Oil
 

There will be enough room once you take the bolts out.

I agree with the recommendations so far, but if you discover it's a positraction, I like to use Royal Purple in those. No friction modifiers are needed with Royal Purple.

While you're in there, snap a pic of the numbers on the ring gear. At some point you might want to know for sure what your rear ratio is, and that will tell you.

Re: Rear Differential Oil
 

The GL 5 is not the viscosity. It is a anti friction rating. You must use gl5 in differentials.
Practically all gear lubes are rated for GL 5. If your seals are old you might use 85w140 in the rear end unless you are using it in extreme cold.
If it is a Posi-trac you need to put an additive in it.
George

Re: Rear Differential Oil
 

I put 'Lubelocker' gaskets on mine. No sealant needed and you can reuse them if you have to pull the cover again. No leaks ever.

Re: Rear Differential Oil
 

I used LubeLocker for both my front Dana 44 and the rear 12 bolt and NO LEAKS ! Quite honestly it's my first time not using the typical gasket / sealer and after doing so I don't know why anyone would mess with smearing it all on equally and dealing with the mess. Sure the Lubelockers are more, but remember you don't have to buy the sealer.

Take pics of your ring gear so you'll know what ratio you have FOR SURE.

I used Mobil1 75W-90 Synthetic Gear Lubricant LS which will work for BOTH limited slip and non limited slip rear ends.

Re: Rear Differential Oil
 

I used the Right Stuff by Permatex on my rear diff on my Ram....no gasket...worked great!!
I learned about it from this site....surprised no one has mentioned it yet....

https://www.amazon.com/Permatex-3369...a-448741432246

Re: Rear Differential Oil
 

Lubelockers are new to me but sound intriguing. Summit lists 43 different gaskets, unfortunately none to fit my K20's rear diff.

Re: Rear Differential Oil
 

Same here I get the big aerosol can of the right stuff for jobs like this. Never had a leak using it and it cleans up pretty easily when it’s time to change the oil again. In use 80w90 for oil.

Re: Rear Differential Oil
 

I use Purple Power, too. I have a posi rear and also use it up front w/o posi. No harm in using better than called for.

Re: Rear Differential Oil
 

Just for clarity, GL5 is a SAE test sequence that certifies a fluid to meet a standard.
It is normal for an older standard be replaced by a newer standard.

But there is nothing to prevent an oil blender from marketing an lubricant without pursuing the expense of certification.

Re: Rear Differential Oil
 

Make sure to use a thread sealer on the bolts that pass thru the housing into the oil or it will
leak in those areas. I forget which two they are but you can look at them and tell.

Re: Rear Differential Oil
 

If you have a posi and you want to use Royal Purple there is one that end in LS, that means limited slip. I use that in my ZL1 Camaro and rear is nice and quiet.