rob_engineer

Changed my front and rear diff fluids today so I could get the higher viscosity synthetic fluid for towing. My jeep is only a few months old with 4500 miles. The rear fluid looked dirty compared to the front. Both magnetic plugs had "stuff" on it. I suppose microscopic bits of metal from break in. The rear had more than the front. I'm talking about 1/8" build up of stuff on the rear plug.

dlincoln91

thats just normal break in and wear. i wouldnt worry about it. the rear fluid shouldnt look any worse than the front unless it looks milky which means water is in it

rob_engineer

I'm not worried. I assumed some break in wear was normal, hence the reason for the magnet. Rear fluid was just s little darker in color and less see through. Glad I changed it.

carolinajk

if you change it again in another 4500 it will look the same nothing to worry about unless you see obvious flecks and specks of shiney metal

Sargeant

Don't beat me up here, cause I'm new to this field of science, but I would venture to say the reason for the darker color in the rear diff would be to the greater work load it has had compared with the front. I'm assuming that the majority of the 4,500 miles were driven in 2H and not 4H.

rob_engineer

True, but I just didn't think I would see a difference in fluid color on a 3 month old jeep with only 4500 miles on it. Because I will occasionally tow, I think I will plan on changing the diff fluid every other oil change. So if I do 5000 miles changes the diff fluid will get changed every 10,000 miles. It's so easy to do.

AJMBLAZER

What he said.

When you have new gear sets installed it's important, but not commonly done, to break in the front gears as well as the rear. I had a truck regeared and I pulled the rear driveshaft and drove it around in 4hi for an hour. Comprehensive? No. Probably better than most though. Got a couple heat cycles into it like recommended.

Theoretically since that front is always spinning now it's sort of breaking in as you drive around but as he said far more load is going on the rear axle. The factory recommended break in procedure works for everything in the drivetrain, not just the engine, but since the front axle isn't always under load it won't see the same wear.

isolated1523

I had so much gunk after my re-gear that when comined with the heat of the gears breaking in, it gummed up both locker plungers in the diffs. Had to get them replaced at my 500-mile fluid change.

-Adam