Diff grinding after fluid change.

blistovmhz · Mar 6, 2012

98 XJ, AX15, NP231 (SYE), D30HP front, Chrysler 8.25 (LSD) rear.

Pulled the rear diff cover for inspection. Everything looked clean and no chips/play. Threw the cover back on, poured in a few bottles of 75w90 gear oil with built in friction modifier (whatever the shop had listed for this diff with the LSD).

A few days later I was parked on a hill and let the Jeep roll back (with wheels turned slightly) and heard some noise coming out of the rear. Thought it sounded like the tire lugs grabbing onto the brake line or something. Inspected, couldn't find anything, crossed fingers and drove home. Problem seemed to go away, so I figured it was just break-in for the new oil.

Noise came back last night, again while slowly rolling backwards down a hill while turned slightly. Got home and parked with wheels turned, threw in neutral and laid under the truck and just pulled the Jeep backwards while I listened to the diff. Sound is definitely coming from the diff.

So... wtf? Is all 75w90 GL5 with friction modifier not made equal? Should I just add some regular fiction modifier or is it time to flush and start again with better oil?

2X_01_Jeeps · Mar 7, 2012

LSD without modifier in the oil makes the rear end sound like it's coming apart - on turns.

Straight motion where the wheels turn together at exactly the same rate wouldn't cause the LSD clutch to try to move so shouldn't make noise. Lift the vehicle and roll the driveshaft by hand and see if you can hear the same thing.

The simple solution is to try again. Change out the oil and use separate friction modifier and gear oil and mix to spec for yourself.

You didn't say how you checked for chips. I drain the fluid into a clean pan (have to remove the diff cover) . Then I wipe the inside of the housing with my hand (in nitrile glove) to move the remaining oil and any chips to the pan. If there are recesses, I work them out as well. I want the housing as clean as I can get it without resorting to solvent flushes.

Then I use a magnet to dip and swish thru the oil to pick up metal.

That trick found the failing carrier bearing on the gray jeep at 34k leading to a warranty repair.

The same trick found metal at 53k in the white jeep from a failing carrier bearing - paid for by yours truly. (out of warranty but undoubtedly the same lousy bath of bearings. It waited to 46k to start making noise.)

blistovmhz · Jul 30, 2013

2X_01_Jeeps said:
LSD without modifier in the oil makes the rear end sound like it's coming apart - on turns.

Straight motion where the wheels turn together at exactly the same rate wouldn't cause the LSD clutch to try to move so shouldn't make noise. Lift the vehicle and roll the driveshaft by hand and see if you can hear the same thing.

The simple solution is to try again. Change out the oil and use separate friction modifier and gear oil and mix to spec for yourself.

You didn't say how you checked for chips. I drain the fluid into a clean pan (have to remove the diff cover) . Then I wipe the inside of the housing with my hand (in nitrile glove) to move the remaining oil and any chips to the pan. If there are recesses, I work them out as well. I want the housing as clean as I can get it without resorting to solvent flushes.

Then I use a magnet to dip and swish thru the oil to pick up metal.

That trick found the failing carrier bearing on the gray jeep at 34k leading to a warranty repair.

The same trick found metal at 53k in the white jeep from a failing carrier bearing - paid for by yours truly. (out of warranty but undoubtedly the same lousy bath of bearings. It waited to 46k to start making noise.)

Heh. Resurrecting an old thread to mention that I didn't listen to you, and probably should have

Changed the oil out again long ago, but the sound came back, then disappeared, then came back. Changed out again when I swapped in my disc brakes, and foolishly used the same goddamn shitty gear oil I'd used the last two times. Last night on a trip back from the US, my diff started gettin' warm and the grinding came back. When I got home and turned to park in my spot, it sounded like it was tearing itself apart.
Opened up the diff again and gear oil definitely didn't look right. Wrong colour, smell was off, but still no chips or anything. Going to do a more thorough inspection for any metal shavings right now, but I suspect the gear oil is just shitty and will try a better oil and separate friction modifier tonight.

Thanks dude.

Johnnie Walker · Jul 31, 2013

Maybe bearings are failing. I run Amsoil 75w-110 front and rear. No LSD/locker, but it is a full syn and no additional friction modifier required.

Tim_MN · Jul 31, 2013

As commonly happens, gear lubes that claim to include friction modifier for Limited Slips often cause the LS to make noises until the owner adds 2-4 ounces of friction modifier.

WB9YZU · Jul 31, 2013

http://www.naxja.org/forum/showthread.php?t=1103214

Diff grinding after fluid change.

blistovmhz

NAXJA Forum User

2X_01_Jeeps

NAXJA Forum User

blistovmhz

NAXJA Forum User

Johnnie Walker

Piece of Fish!

Tim_MN

Freakish Hand Strength

WB9YZU

NAXJA Forum User

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