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Looking to drain and refill my rear diff, and transfer and front this weekend. I have owned the truck for 20,000 miles, and now has 90,000 on it. I Don't know if it has been done or not before, but it was a certified pre-owned. (yeah I know that don't mean anything). What I am asking is, lets say I start to drain the fluid, and notice it is really bad looking but no metal hunks or anything like that, would it be wise to put in some cheaper fluid in, and run it for xxx number of miles and then drain and replace with the Royal Purple that I want to.

It is a LS rear diff, not sure if that would matter in your suggestions or not. And then asking for the same advice for the Front Diff, and Transfer Case.

On a cost saving side of my project, would Mobil 1 synthetic be fine for the front diff, and transfer case as they are not LS. (and yes I know that some use the Mobil 1 fluids in their LS Diffs and don't have a problem, but read some last night that were--with the LS Mobil1 formula.)

Thanks for your comments.
 

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Or is there a treatment I can add to them that will help cleanse them out, and be fine with the drain and refill?
 

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you mean sort of to flush it out? if you have the cash to burn, it cant hurt. havent looked into fluid prices recently but even if you filled it and ran it once around the block and then drained it im sure it would help a bit

but i reality, i doubt it would hurt you to give it a good long drain (jacking up one side to get everything out) and just filling it with royal purple. whatever is left will be in such a low concentration anyways
 

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Looking to drain and refill my rear diff, and transfer and front this weekend. I have owned the truck for 20,000 miles, and now has 90,000 on it. I Don't know if it has been done or not before, but it was a certified pre-owned. (yeah I know that don't mean anything). What I am asking is, lets say I start to drain the fluid, and notice it is really bad looking but no metal hunks or anything like that, would it be wise to put in some cheaper fluid in, and run it for xxx number of miles and then drain and replace with the Royal Purple that I want to.

It is a LS rear diff, not sure if that would matter in your suggestions or not. And then asking for the same advice for the Front Diff, and Transfer Case.

On a cost saving side of my project, would Mobil 1 synthetic be fine for the front diff, and transfer case as they are not LS. (and yes I know that some use the Mobil 1 fluids in their LS Diffs and don't have a problem, but read some last night that were--with the LS Mobil1 formula.)

Thanks for your comments.
If you are concerned about sludge in your differential I would run a cleaner compatible with LSD prior to draining it. I see nothing wrong with running a cheaper LSD compatible gear oil for a thousand miles and then draining and refilling with Royal Purple.

My first drain and refill of the differentials and transfer case yielded this from the rear which turned out to be missing the breather.

Water Bucket

I filled with cheap gear oil and drained a thousand miles later and then refilled with Royal Purple. Did the breather modification and have not had any problems with blowing seals since.
 

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For the LSD rear diff's standard gear oil is recommended by the manufacturer so i'd stick with what they recommend and add a friction modifier. Plus it's cheap so if you run it for 5-10k then drain it out it'll only cost you about $20-30. I was in the same boat as you with my '06 and went with regular dino 75w-90 gear oil w/friction modifier.
 

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Good advice from Lizard.

I just changed out my differential fluid about a week ago. This is the fourth drain and refill I've done. The fluid that drained out (Mobil1 synthetic) was very clean. Looked like fresh motor oil. There was the usual small deposit of gray powder like substance on the drain plug. About the volume of an aspirin but no other particulates were evident. I bit the bullet and replaced with Royal Purple 75W-90. My '01 doesn't have LSD so special fluid was not a consideration.

Your truck will thank you and it's an easy service. As mentioned by many before remove the fill plug first.
 

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yep! just drain and fill it with purple. i used lucas and the additive and the shudder returned in 5k miles. i then tried purple and bought a tube of the additive to add, just in case. 15k miles later i still have the tube of additive and no shudder, yet.

if there are not chunks and only slimy silver crud on the plug, save your time and money and just put in the purple stuff.
 

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I had green swamp muck like oil in mine. Just refilled with syntetic M1 front/t-case/rear, been worry free for 10,000 miles. As far as washing out there is no need, unless you went swimming with the truck (aka water in diff oil) then flush with el cheapo oil for whatever miles and put good stuff in later.
 
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