Diffrential Oil & Friction additive

kenewagner

Registered User
What is everyone using for brands and weight on diffrential oil. I have access to Lucas Brands. There is Synthetic 75W90 or 75W140 there are non synthetics as well in about the same vicosity. What kind of friction additive and how much to do a rebuild on the rear end? Right now I am just getting my Ducks in a row. Thanks


Ken
 
I use the 75-80w90 with 2 bottles of ford friction modifier to break in the rear end then change to 75w-140 synthetic afterwards.
Alan
 
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1.5 quarts of Royal Purple 75w-90 with no added friction modifier is what I have been running after a clutch pack rebuild, and I know of one other person with a turblow running the same for quite some time.
 
1.5 quarts of Royal Purple 75w-90 with no added friction modifier is what I have been running after a clutch pack rebuild, and I know of one other person with a turblow running the same for quite some time.

Why no friction additive?

Ken
 
So if the diffrential is broke in run the 75W140 How about diffrent materials on the friction material (stock friction plates vs carbon) and diffrence?? Synthetic superior to organic??

Ken
 
Why no friction additive?

Ken

Just what Corey said, with Royal Purple, Amsoil, and most likely others, read the bottle its maybe in there. You can always add a bottle of friction modifier if you feel the plates are sticking to much for your liking going around corners. As for the weight 75w-140 is the way to go for longevity on the diff, but I figured the ~4000 miles I drive a year the lighter weight would suffice.
 
Is the Redline 75w90NS (no-slip) something to use? And also use additive from Redline with LS included?
 
I have done a boat load of 8.8's and if using synthetic fluid, friction modifier is not necessary. I use Mobil 1 75w140 and no modifier at all. There have been no failures in clutch packs in 18 years over approximately 50+ differentials. The most important part of setting up a differential is lash, pre-load and pinion depth. If you have that correct, you will have a happy differential. Personally I run about 26 in/lbs. of pinion preload if the bearings are new (about 19 in/lbs. if the pinion bearing is slightly used) and I like running about .008 of lash according to the dial indicator. All differentials have been happy. The Ford Racing Gears are best to use IMO. They use a base .030 shim and the pinion is marked to let you know how far up or down to go from the base .030. If the pinion is marked with a -1 then run a .029 shim, +2 then run a .032 shim, and so on. Everytime I have used this method the pinion depth was right on to +-.001. Oh and if the pinion isn't marked at all then start with a .030 shim. :)
 
Pinion depth is determined more by flaws in the casting of the housing than the thickness of the pinion gear. I've never found that one pinion gear will use the same size shim if used in different cases
 
Pinion depth is determined more by flaws in the casting of the housing than the thickness of the pinion gear. I've never found that one pinion gear will use the same size shim if used in different cases

I never said it would use the same size shim. There is some deviation in the carrier housing however the manufacturing processes have gotten so good that the housings since the mid to late 80's are almost all dead on. The largest deviation is now found in the machining of the pinion. This is why the Ford Racing now marks the pinion gear. It used to be that the differential housings were poorly manufactured. This has changed to aid in the speed of the manufacturing process. This way the factory doesn't have to fool around setting pinion depth on every differential that gets assembled.
 
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