Will 75w-140 quiet bad bearings in a rear end?

[Sparkman]

I bought an '01 Cherokee Sport recently. It has the 4.0, 4WD, and a 4 speed automatic. 38k miles. It has about 2k miles left of the 4k mile NY lemon law warranty.

It has been making a loud noise in the rear end at 50-55 MPH at certain throttle settings. I took it to the dealer's shop in a nearby town (happens to be a ford shop) and they said the side and carrier bearings were bad. They had to order the parts, so it didn't get done that day. In the mean time, I had to take it to another shop in the same dealer chain for something Jeep specific, and they were going to look at the rear end. I just picked it up, and boy am I steaming. They said that nothing was wrong, they couldn't hear a thing. They took the cover off and looked around, but no problems. Funny thing is, now it doesn't make the noise nearly as bad. Almost can't hear it. The only possible explanation in my mind is that they put 75w-140 or some other thick lubricant in it to quiet it.

I am considering taking some 75w-90 with me and insisting that they put it in, then I will go for a ride with the GM.

 

[mountravlr]

Rear ends do get noisy when low on lube, the change in the noise may be from topping off the lube.

 

[Pablo]

If you have a loud rear end, adding 75W-140 will not quiet it. Well it will if the situation was as mountravlr says...low to none.........

 

[Sparkman]

Thanks for the replies...

It seems to me that the first shop must have had the cover off to determine that the carrier and side bearings were bad. I could be wrong, but I would think the lube level would have been correct when it left that shop. It seems very odd that the noise suddenly got much quieter, unless like you said the level was low, or they added some lubricant that would quiet it long enough for the warranty to end.

I need to make some phone calls tomorrow and do a little detective work. I got the run around today and that doesn't sit very well with me.

 

[MolaKule]

quote:

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It seems to me that the first shop must have had the cover off to determine that the carrier and side bearings were bad.

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They most likely were going by the noise it made. It is very difficult to observe the bearing(s) directly. Normally, the differential carrier has to be removed, the drive pinion removed, and the axles taken out to really assess the damage.

Pinion drive bearings will start to fail if the fluid level has been low for some time or if the fluid was contaminated somehow. The new fluid probably gave some temporary life to the bearings. The wheel (axle) bearings may need replacement as well if the fluid level was low or the fluid's life was at its end.

Have you ever replaced the fluid in the diffy(s)?

I would let the first shop go ahead and replace the bearings and the shim packs. Make sure they also inspect the wheel bearings for possible inadequate lubrication and damage.

 

[Sparkman]

You're right Molakule. I called the shop yesterday and they said that one of their techs used to work at a jeep dealer, and this noise is usually the carrier and side bearings. They hadn't removed the cover. They are going to replace them for me. I haven't changed the gear lube as I just got it, and I have been hammering on the dealer to do everything during the warranty period. I have four quarts of Mobil 1 75w-90 waiting to go in it, but I wanted to wait until I was sure they weren't going to drain it.

The noise was quiet at first, but after a couple of hundred miles it is much more noticable. I am glad it's getting fixed.

 

[cousincletus]

Some rears have the outer bearings separate from the gear lube...they are packed in grease. Before you take it in, check the pinion nut and see if it's loose. Had one come loose on a Chevy p/u truck and I was sure the rear was going bad. Found the loose nut, tightened it and to this day that old truck is still going with the same rear end in it. Just make sure you check the oil in the rear every six months or so. Did you see any signs of leakage anywhere? Check the pinion shaft seal, the pan gasket seal and the brakeplates for signs of leaks.

 

[MolaKule]

Cousin cletus,

I hear you and that's a good point. Wouldn't Sparkman have to drop the driveshaft to tighten up the pinion nut?

But look at Sparkmans's mileage, 38,000 miles.

I have never had a diferential even make the slightest noise until way after 180,000 miles.

I wonder if prevous owner went through a flooded area or had it out on Chappaquidick?

[ May 22, 2004, 12:11 PM: Message edited by: MolaKule ]

 

[Robert R. Wilson]

My wife's 99 grand cherikee (bought new) has had the rear diff bearings replaced 3 times under warranty. Now the warranty ia expired and it is noisier than it ever was. Maybe this is a generic problem with Jeeps?

Bob

 

[MolaKule]

Again, a good heavy duty gear lube for problem differentials is Schaeffer's #267.

Now would be good time to put the fluid in since it's becoming warmer outside.

[ May 27, 2004, 12:46 PM: Message edited by: MolaKule ]

 

[Sparkman]

They replaced the carrier bearings and it actually got louder. They ordered a bunch of parts, supposedly including a new ring and pinion, and they are rebuilding it day after tomorrow.

 

[Ken2]

Adding a heavy lube may quiet noisy bearings or gears for a short time. It certainly isn't a fix.


Ken

 

[Sparkman]

They completely rebuilt the rear-end. New bearings, seals, ring, pinion, differential gears, differential case, etc. It was quiet at first, for about the first 100 miles or so, now it still does it a little bit

, but it's much better.

The front differential had what I described to them as a pinion bearing noise, they thought it was the brakes so they put new pads and rotors on it. Didn't fix it, so they replaced the pinion bearing(s), now it is quiet.

Luckily this was all on their dime under the NYS lemon law warranty, which will probably expire this weekend (90 days, 4k miles).

Their invoice lists both
" 3 XY*80W90* QL LUBRICANT-HYPOID THERMALLY STA"
and
" 3 XY*75W140* QL OIL - RR AX LUB" twice. Can I assume the 75w-140 is synthetic? Can I assume they used the 80w-90 for the front? Is hypoid something I want to be using? Should I leave these lubricants in there for a while? At least for a break in period? I have four quarts of Mobil 1 75w-90 waiting to go in if need be, but I hate to be wasteful.

 

[MolaKule]

quote:

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3 XY*75W140* QL OIL - RR AX LUB" twice. Can I assume the 75w-140 is synthetic? Can I assume they used the 80w-90 for the front? Is hypoid something I want to be using?

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Most differentials are of the hypoid design so yes you want that.

Most front differentials are filled with 80W90 since they are coasting most of the time, and some rear differentials are filled with 75W140.

I recommend changing differential fluid at 5 - 7.5 k miles after a differential rebuild.

Do not assume they used synthetic fluids. It appears from the cryptic message that they used Quacker State dino.

 

[Sparkman]

quote:

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Originally posted by MolaKule:

I recommend changing differential fluid at 5 - 7.5 k miles after a differential rebuild.

Do not assume they used synthetic fluids. It appears from the cryptic message that they used Quacker State dino.

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I will change them in 5k miles then, good to know.

I wasn't sure if a dino base oil could get the spread of a 75w-140, that's why I asked.

Thanks Molakule!