I am replacing the two pinion seals next weekend on my Jeep because they are leaking. I have a Dana 30 and Chrysler 8.25 and I am curious as to what fluids I should fill the diffs with afterwards? Should I use a friction modifier?

 

75w90 in front, 75w90 in rear for "normal" use, 75w140 synthetic in rear for towing (or oversized tires and "hardcore" off-roading). You only need friction modifier if you have an LSD (limited-slip differential).

 

"Hardcore" offroading? I am building my Jeep to be a weekend warrior maybe once a month. Should I just use the 75w90 in both front and rear?

 

Yep, you're fine with 75w90.

If you like synthetics they're fine for use. If your plans for offroading include frequent trips through water don't bother as it will get really expensive. Gear oil should be changed any time your axles go for a swim... the seals keep oil in, not water out.

 

Yeah if you're going through water & draining your oil often just use cheap stuff.

If you are in a dry area & doing steep stuff etc I'd say maybe do the 140. One thing you could do is get out 1/2 way through a trip and check the heat of your differential covers front vs back and if the rear is super hot, you could do the 140. Essentially you don't want the oil to thin out too much from overheating. I imagine that's what they are anticipating from towing & offroad use. I just put cheap 75W90 in there since I'm not doing much crazy ****.

Do heavy rock crawler guys run anything super fancy?

I love oil nerd stuff. Maybe its my time working with shocks

 

Really? I used to have a Tacoma that we would use to haul deer across a creek on our hunting property. I extended the diff breather lines up into the engine bay on the front and gas filler neck on the rear. I changed the fluids a couple times when making repairs or upgrading parts and never had any signs of water in the housings. Is this a common problem with the XJ?

 

How deep did you go? Might've been luck. Age of seals will also play a huge factor.

Some guys just check for water and everything's fine, but I wouldn't risk trashing the gears and bearings to save $10 on gear oil.

 

Depended on how much rain we had, but at times it was almost to the tops of the tires. I agree that I would rather change the oil than rebuild the axle that's why I'm asking.

 

I got ta believe that somebody out there researched and found a double lip seal that fits this aplication... I mean, after all don't outboard motors have a spinning shaft with water on one side of a seal and oil on the other ???

 

Sure do... No idea if such an animal exists in an automotive application. Some military vehicles use air to slightly pressurize the axle, enough to keep water out

 

It's a simple matter of finding out the OD, ID, and width measurements and then looking up in a seal manufacturers catalog for a good fit with double lip seal... They likely will have several to choose from that are made of differeing materials.... I'm thinking Viton would be a good choice...

 

they are seals... the keep oil in and outside elements out..

they aren't a check valve. water comes in the breather vent or bad seals.

 

Seals don't take that long to become 'bad' lol. Jeep axle seals aren't designed to stop water. There's a significant difference in viscosity and molecular size between H2O and 75w90

 

Yep. Water get in seals a lot faster