Best gear oil for the differential
 

Hey fellas,

I am thinking of doing a differential service this weekend and I would like to know three things.
Firstly, what is the best gear oil I can put in my differential? I want the best because I don't plan on doing the diff again for a while.
Secondly, the guy at O'reilly's sold me gray RTV sealant (high temp) for my differential seal. Is this what I should use?
Lastly, What should I torque the bolts to in order to be in spec? I can buy a new 20-100lb/ft wrench for about 75 bones.

Thanks.

I don't know what diff you are working with on torque specs. Use the Synthetic gear oil that Ford calls for. It is like a 75/140. Big rear ends in tractors use 75/90 which would work fine but you may not find it at regular parts stores. Use Perm. Ultra Grey. Synthetic gears oils do not hurt it. Permatex has came out with a sealant for diffs. It is made for synthetic gear oils. Don't use the regular black rtv. The Ultra Grey is what was recommended by Eaton and Rockwell for years. Doesn't take much and works good.

grey will work fine, black is better, i usually just buy the gasket though. a full synthetic is the best, but in an old axle id stick to a good conventional gear oil, otherwise youll end up with seal leaks. i dont usually i use the German torque spec on the gover bolts...tighten them untill there gutantight..lol just snug them up good,

well the book says to use sae 80 or 90 gear oil for front and rear diff as far as tourque order of bolt sequence i would go arcross from each other the same way you do a tire.... as for as torqe spec i couldnt find anything some diff come with a gasket but for most part RTV Red color is all i use

if you have a limited slip rear diff make sure you add the limited slip additive so you don't destoy your rear end

I used a gasket when I did mine. I used RTV at first but the oil was leaking through the cover and not the gasket so I just got a new cover/gasket. I put full synthetic 80w-90 in and tightened the bolts with a 3/8 impact gun - hasn't leaked since. Make sure you clean the metal shavings off the magnetic fill plug.

I didn't use a additive, I'm gonna mess up my limited-slip?

i use valvoline 80-90w with the limited slip additive already in it

I used valvoline too so I hope there was a additive in mine too, lol.

Snapon, make sure the lube had the hyploid gear modifyer, not sure what it does but is for the disks in it. only some synthetics have it. Look on a bottle of yours and make sure. If not it comes in 4oz bottles, smells bad, and i know the ford stealer has it id assume auto parts stores would

if you really wanna torque the bolts the spec is 35 ft lbs

My diff oil smelled bad but I'll check the bottle, lol.

Don't use the Regular black Permatex rtv. Synthetic gear oil eats it. The Right Stuff that you see is junk also for these oils. I just had to fix a powerdivider on a Rockwell diff because of the right stuff. It turned to jelly and clogged the oil pump. Lost the bearing in the divider. Yeh. The guy used way to much. You don't want to see any hanging out anywhere when you clamp it down. This is an issue to too much is TOO much. Maybe fine on valve covers and oil pans but synthetic gear oils eat most RTV sealants. Thats why Permatex came out with sealant for this. Two reasons. To make money and to stop the confusion on which sealant to use. Not knocking anybody but I have allot of experience with this. I don't want to see you have to do it again a year from now. I don't use RTVs on many things. I can guarantee the Ultra Grey will work. I have been told that all of the "Ultras" will work for these oils but I can't say. I haven't tried the others.

Checked my fluid and it was valvoline synthetic 80W 90 limited slip oil, I'm guessing its the right stuff.

Sounds like you are good to go!:-X22

Here's another low-level question. How much oil should I buy? I think a gallon would do it.

I'll have to look in my owner's manual and see if I have a LSD. I will get the synthetic stuff and the Ultra Grey. Any negative effects if I don't have a LSD but the additive is in the oil?