80w90 in rear diff? | Ford Explorer Forums - Serious Explorations

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80w90 in rear diff?

myersc

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2002 XLT
I have a 2002 Explorer with the 3.73 limited slip rear-end and my Ford dealer said I could put 80w90 weight in it instead of the 75w140 synthetic. They also said I had to add the limited slip additive. Has anyone ever put 80w90 in the rear? Am i cutting corners to save money by putting in 80w90? The reason I'm doing this is because my clutch pack is sticking and I'm hoping that the additive will help the clutches slip when making slow speed turns. Thanks.
 



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75W140 is what you want. At some point Ford recommended upgrading to this from 80W90 because of the noises. If you get one like Mobil 1 75W140 Synthetic LS I believe it does not need a friction modifier added due to the fact it already has one included in the formulation.
 






yeah most synthetics already have the friction modifier in the bottle, i know royal purple has it
 






I spoke with my Ford dealer and they said I would be fine putting 80w90 in it. So I went ahead and installed 80w90 and two bottles of Ford anti-friction fluid. To my surprise my vibration from the rear-end no longer exists. But my concern/wonder-about is should I have put in 75w140 synthetic instead of the 80w90. I thought as Ford said I was fine with 80w90 that I would be ok. Though every post I read on the forum states I should be using 75w140.

I have a leaky rear seal that I'm going to have to change and will do this on my own. Maybe at this point I will replace the 80w90 with 75w140. When I pull the axle will the fluid leak out???
 






80w90 isn't going to hurt anything....that's what the diff was originally spec'd for. However, I said before, Ford recommends going to 75w140 (read the last bullet in the TSB in the right hand column):


http://mygtcs.com/mustang/documents/tsb/tsb04-24-20.pdf

This was to solve some noise and other issues that some people were having. 75W140 also offers better protection to the gears and has better heat resistance properties so it should last longer before changing under normal circumstances. Probably even more important if you tow things or offroad with your truck.

Also as I said and gamecocks confirmed, the good synthetic 75w140's contain a friction modifier already so you can forgo the separate bottle.

Glad your problem went away. If it comes back try a good synthetic 75w140.

As far as leaking fluid when you pull the axles, you might lose some...depends on how much gear oil/friction mod you put in there. If it's just up to the bottom edge of the fill hole then you should be all right.

I spoke with my Ford dealer and they said I would be fine putting 80w90 in it. So I went ahead and installed 80w90 and two bottles of Ford anti-friction fluid. To my surprise my vibration from the rear-end no longer exists. But my concern/wonder-about is should I have put in 75w140 synthetic instead of the 80w90. I thought as Ford said I was fine with 80w90 that I would be ok. Though every post I read on the forum states I should be using 75w140.

I have a leaky rear seal that I'm going to have to change and will do this on my own. Maybe at this point I will replace the 80w90 with 75w140. When I pull the axle will the fluid leak out???
 






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