Switching to synthetic differential fluid

iwannadie

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Jul 28, 2006
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gilbert, az
I tried searching and couldn't come up with anything, not sure if its just my terms or not.

I'm planning on changing my Diff.(LSD) fluid out with redline 75w90 but not sure if I need to flush it with anything. I didn't think going from unknown fluid right to synthetic would be ok. I don't mind running something else through the diff. if it matters, I'd like to do it right the first time.

Should I just get 3qts, change it then put some miles on it and change it again to get all the old fluid out? Or, just simple drain and refill?
 

iwannadie

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Jul 28, 2006
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gilbert, az
I searched in the oil section and only came up with 8 threads with just "differential" in them. I read the Kendall 75W-90 full synthetic gear oil thread also, didn't see anything about going right to synthetic fluids...
 

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
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Feb 10, 2006
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You can use Red Line 75W-90, but I'll warn you, Red Line can make some high mileage LSDs chatter. It's going to depend on how worn the clutch plates are. Ford 75W-90 Gear oil and LSD additive usually works better on a LSD with a lot of miles on it...start with about 1 oz of the additive to a fill.

You will need 2 quarts of whichever you choose.

And, yes this info was already in the Lube Section ;)
 

iwannadie

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Jul 28, 2006
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gilbert, az
jdub;1325754 said:
You can use Red Line 75W-90, but I'll warn you, Red Line can make some high mileage LSDs chatter. It's going to depend on how worn the clutch plates are. Ford 75W-90 Gear oil and LSD additive usually works better on a LSD with a lot of miles on it...start with about 1 oz of the additive to a fill.

You will need 2 quarts of whichever you choose.

And, yes this info was already in the Lube Section ;)

I did read about the ford gear oil and thought about it. I figured I would try the redline and see how it acts, if it chatters I'm going to look at a rebuild(or switch to ford oil in the short term).

I swear I read so much and did not see anything along the lines of "its ok to switch to synthetic just drain/fill, no need to flush the old fluid". Oh well though, I did try maybe I glazed over it. I really so love the oil section after all.

On a side note, If anyone has a hard time with the Fill plug, like I did. I got my breaker bar lined up and slid my floor jack under it. I gave it a pump and was in shock when it didn't budge! The jack is like a 3 1/4th ton jack and lifts my cherokee a few inches with a single pump. I kept pumping and eventually the sucker turned. I can't imagine how tight it was on there, no rust or any signs of loctite. I did lower the supra back off jack stands and a few ounces of old fluid came out too. I also pumped a bit of fresh valvoline 75w90 fluid that I had laying around though just to push as much as the old stuff out as I could.