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Rear axle oil breaking down

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Sorry I didn't take any pictures for you guys but, I dropped the cover off the rear of my 600 this weekend. I did so because I was getting a bearing whine and I couldn't explain it with bad u-joints, I checked them first. When I opened the rear end up, the oil was foaming like it either had water in it or it was breaking down. Since this truck has never seen anything that would submerge the rear axle, I can't imagine it was water. The truck had 18,060 miles on it when I dropped the cover to find that. I refilled the axle with Royal Purple full-syn 75W-90 and after a few miles of driving, the noise went away completely. For those that haven't changed their rear axle oil, you might want to think about it. I was getting a loud bearing hum at about 19 mph on the speedo and it didn't matter if I was on the coast or drive side of the gear. The gear tooth wear pattern looked good and everything else checked out in there so, all I can figure is the pinion bearings were not happy about the foamy oil.



For what its worth, my next door neighbor, who also owns a 3rd gen truck, is getting the noise at 21 mph on his speedo but, figured it was his wife just not understanding the truck sounds. :-laf Once he road around the block in mine and listened to it, he took his out and heard the same thing. I believe he has around 34,000 miles.
 
I have a whine at about 20mph too. Mine showed up when I put the on the Michelins/Rickson's. They're really noisey and I figured it was just a peculiarity of the tires. I've been thinking about dropping a little LSD additive in the rear and seeing what happens. I know the 3rd Gens don't need it, but I've read here that it has helped out a few with rear end noise.
 
3rd generations. In fact went 90k on every fliud but oil of course. One 6 speed 4x4 towing 90% of the time the other is a 2wd auto towing about 90% of the time. Really wasn't a nasty looking fliud in them so says the owners. (2 friends of mine. )Heck they were waiting to change at 100k but I kept saying something about maintance. The 2 wd has only done his fuel filter 3 times. Once every 30k or so. Said only the first one looked a little funky. He complained that a trans filter and flush at the same time was around $160 bucks! He's a ex airline captain.
 
I changed the lube in both the diffs a couple weeks ago. The fluid out of both diffs was a little darkened, but still had a golden honey color. I've had both diffs completely under water at least twice now - got 40K on the odometer.
 
Hope you cured your problem. If it had water the fluid would have been gray/white like a milk shake. Did you check the level of the fluid before you took the cover off? Should be 3/4 in BELOW the hole. No way that your dealer"s lot boy check the rear and added some non synthic fluid?? I checked mine at 2000miles was fine.
 
DPKetchum said:
I know folkes that have run factory fill till 90k whith no problems and oil in diffs looked good.

DP, are you talking about 3rd gen trucks or 2nd gen's that had tha Dana axles under them ? :confused:
 
fluid level

As I understand the tsb on fluid level, it states for the 11. 5" rear end,

the fluid level should be 1/4" below the fill plug + or - 1/4" so anywhere

from 1/2" below to level with the fill hole is ok.
 
I didn't think to check the level before I dropped it. Just taking a guess at it, I would say the level was at least close considering the amount I got out of it. So far, I believe the problem has gone away. I have not heard the noise since changing the fluid. I do not believe there was water in the fluid because it did not look the least bit milky. The fluid looked very gray and had a significant amount of foaming/bubbles in it.
 
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