Differential Flush ?
Thread Starter
Pro
Joined: Nov 2011
Posts: 517
Likes: 20
From: Scroggins Tx
Differential Flush ?
As I have removed all my rear suspension and related items I removed the differential cover and drained it. What came out was very black and very thick. It looked like East Texas heavy crude oil. Would flushing it with something like naphtha be OK or could this be harmful? The diff seems to be in good condition,very tight and no metal in bottom. I don't plan to tear it apart. Thanks Dave.
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
Curious on why the fluid would be so dark, as not exactly like you're getting engine oil combustion blow by. Bettin' you've got lots of posi clutch pack particles, and good time to change the pack out while everything's drained. Some put in the GM posi friction additive, but I don't, and just use fluid rated for this. I used the additive once to quiet thing things down around turns, but took away most of the strait line lock up too. Not doing that again.
Melting Slicks
Joined: Feb 2006
Posts: 3,428
Likes: 5
From: Japan
When I took mine apart years ago I sprayed out the housing with brake cleaner just to get as much of the sludge and slime out of there as I could, then refilled it with 85W90 gear oil and a bottle of the posi additive....no problems.
Burning Brakes
Joined: Jan 2006
Posts: 1,223
Likes: 174
From: Fort Wayne IN
Drifting
Joined: Dec 2004
Posts: 1,714
Likes: 42
From: Austin Texas
I blew through 3 cans of brake cleaner until the run-off was clear. I wouldnt think you could get it too clean as long as you refill with the proper oil and additive.
Since you have the cover off, take this time to inspect inside and verify that the ring clips are still on the yokes. It is not unusual for the shafts to wear down past the clip and find pieces of clip laying around.
I vote for clean and inspect.
Since you have the cover off, take this time to inspect inside and verify that the ring clips are still on the yokes. It is not unusual for the shafts to wear down past the clip and find pieces of clip laying around.
I vote for clean and inspect.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Anything inside a cast iron component will turn black after a period of time. The 'loose' carbon in the cast iron just mixes in with the fluid.
I would not recommend putting a volatile cleaner, solvent in a Posi-traction differential. The clutch plates could absorb it and cause the friction material to break down or maybe just change frictional characteristics. I agree with the above suggestion to put the required amount of fresh gear oil and posi additive in and close it up.
If you feel you really must flush it, stick some low-dollar gear oil in there and run it a bit; then suck that out and throw it away. Then, refill with the 'good stuff' and the posi additive. (But, I don't believe all that is necessary.)
I would not recommend putting a volatile cleaner, solvent in a Posi-traction differential. The clutch plates could absorb it and cause the friction material to break down or maybe just change frictional characteristics. I agree with the above suggestion to put the required amount of fresh gear oil and posi additive in and close it up.
If you feel you really must flush it, stick some low-dollar gear oil in there and run it a bit; then suck that out and throw it away. Then, refill with the 'good stuff' and the posi additive. (But, I don't believe all that is necessary.)
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Burning Brakes
Joined: Sep 2008
Posts: 805
Likes: 5
From: Naperville Illinois
When I rebuilt my diff I cleaned the case and all the individual parts--including the (steel) clutches--with brake cleaner and then again in the parts washer before re-assembly. Used Lucas HD gear oil and the additive...turns are silent and launches are loud 
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Since the cover is off I would use a lint free cloth and wipe everything down as good as possible getting into all the nooks and cranies, put a quart of fluid in it with the cover opening up. Rotate it a few times and dump it out. Wipe everything down again. Install cover and new fluid and additive. I used Amsoil gear lube in two of my freshly built differentials and did not need the additive. It supposed to already have the needed ingredients for use in a posi. Never an issue.
Pro
Joined: Nov 2007
Posts: 710
Likes: 0
From: Northern Florida
As I have removed all my rear suspension and related items I removed the differential cover and drained it. What came out was very black and very thick. It looked like East Texas heavy crude oil. Would flushing it with something like naphtha be OK or could this be harmful? The diff seems to be in good condition,very tight and no metal in bottom. I don't plan to tear it apart. Thanks Dave.
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
Since the cover is off I would use a lint free cloth and wipe everything down as good as possible getting into all the nooks and cranies, put a quart of fluid in it with the cover opening up. Rotate it a few times and dump it out. Wipe everything down again. Install cover and new fluid and additive.
I wouldn't put anything but gear lube in for a (probably unnecessary) flush. It is a "how much do you have to win versus how much do you have to lose" situation, IMO. I use the GM lube and 2x additive. After sitting for a month or more, it will chirp on the first 2 slow corners until the clutch pack frees-up (it is set with a lot of spring pressure) and never breaks one wheel free.
By the way, diff "oil" is NOT a normal petroleum product / oil. It a synthetic fluid (poly butyl sulfide) which is why it smells of sulfur. IMO, the sea foam guy is playing fast and loose with your diff / money.
Last edited by Rich's'78; Feb 2, 2012 at 05:03 PM.
