clunking noise in rear diff 99OBW

[lizardbrain]

I've got a clunkclunkclunk noise coming for the back of my well beat 5 speed 99OBW with 125,000 miles. It does increase in frequency the faster I go, and goes away when the clutch is pushed in. No sound when not moving

 

I've just started driving this car, so I don't know how long it's been making the noise.

 

I put it on stands and let it idle in 1st gear, and put a piece of steel tubing up to the the rear hubs and diff, and it seems to be coming from the diff. No clunking coming from the rear hubs, and I can hear the clunking from the carrier bearing and the rear of the trans, but much softer. Seems loudest at the left side of the diff.

 

I haven't opened the drain plugs to see if there's any oil in the diff, but there isn't any traces of leaks that I've seen yet. I'll check that in the morning.

 

Anybody have any ideas? Bearing in the diff? Bad axle? ??

 

Thanks in advance,

 

Pat

[nipper]

Clunking is either a bad bushing or a bad Universal joint. If its a clunking joint you will notice it rather quickly by turning the shaft by hand.

 

Now if the clunk matches road speed (not there when you change directions) its possible you may have a broken tooth in the diff. Does the noise match tire speed, or does it seem to be three tires turn to one clunk?

 

 

 

 

nipper

[lizardbrain]

I'll run it on the stands again, and see if I can count clunks while watching the tires to see if the noise is in time with the drive line or the tires. I have to straighten out the heat shield under there anyway, so I may as well take it off, and really look at the drive line. Which bushing should I look at, all of them that holds the diff in place?

 

Thanks for the response,

 

Pat

[nipper]

Having the driveline up in the air is going to confuse you to hear the noise.

 

For instance (im going to do simple numbers here). It takes three turns of the driveshaft to make the ring gear turn once. The power from the ring gear goes into a mechanical splitter, that avgs the driveshaft rotation between the speed of the left wheel and the right wheel (this is how you can make turns). If one wheel is turning 0 times and the outer is turning six times, the avg is three (hence the driveshaft speed). Thats why i was asking for the pattern of the noise.

 

This is assuming is is a hollow sounding knock of some kind. If it is a scrape kind of noise it may be something in the brakes. Inspect the rear CV's too (though they tend to last forever).

 

You may also wish to drian the rear diff fluid and have it drain through a cheese cloth to see what comes out of it.

 

Chrysler rear diffs used to thunk as they got older, when you went from forward to reverse. This was just play developing in the diff, and the cars went thier entire lives like this.

[lizardbrain]

Thanks for the help, nipper.

 

Just to be clear on the noise, I don't get any when stopping or starting, or when going forward to reverse, but it is there in reverse. Now that I've decided it wasn't going to grenade any second on me, I drove it at about 55 (speedo doesn't work yet,) and the sound does get to be a roar. Sometimes it goes away for a couple of seconds at steady speed, but it's always there on accel or decel.

 

I did take off the heat shield and took the drive line out, it's fine, or at least it's not loose or crunchy feeling. I drove the car around in tight circles, forward and reverse, and there was no tires scuffing or other bad things. I tried to count the clunking, and it's between 4 and 5 per second at 1500 rpm in first, which by my very not precise calculations, could be tire speed. I'm going to tie a piece of rope around the wheel, cross ways, to see if the thump of the rope has the same frequency as the sound. I still have not drained the diff oil to see it there's chunks in it, but I guess I had better.

 

The front bushing on the left rear control arm is toast, so that may be why it sounds so bad in the car. The girl friend says she didn't hear the sound as I drove away.

 

Another question: does anybody know if a control arm from a 95 brighton will fit the 99OBW? And do the control arm bolts come loose with a long enough cheater?

 

Thanks again,

 

Pat

[nipper]

Sounds like your rear diff is tired. That raor is an unmistakable noise, esppecially if ti comes and goes with thorttle, or incline of the road.

 

Yes this wont blow up on you any time soon. you will probably replace it out of annoyance more then any other reason.

 

 

nipper

[forester2002s]

I would check the oil level in the diff, ASAP.

If the oil-level is OK, I agree that the diff is unlikely to fail suddenly.

However if the diff is low on oil (or no oil), then it could seize-up at any time.

[lizardbrain]

Yes, I checked the oil level, and it was up to the overflow hole. I'm sure it needs to be changed, along with all of the other fluids.

 

I wrapped a 1/4 rope around the tire, and while the roads are so bad I couldn't hear the rope (without driving a couple of mile to get on smooth pavement), I was able to look out the window and see it going around, and the noise is NOT in time with the tire speed, so it must be at drive line speed. At this point, I hate the noise, but I'll live with it until I get to the states later this summer to go to a real junk yard.

 

Thanks for all the advice, I really appreciate it.

 

Pat

[nipper]

is the noise in a 3 to one ratio or there abouts?

 

 

nipper

[lizardbrain]

Yes, somewhere around there. Wouldn't bet much on it, but that's close. I'm going to spending a bit time with/on this car, so if you have any ideas, I'm willing to try.

[Murthius]

I'm not a pro or anything but, my rear diff made the same exact sound. However I stupidly did not check the oil level and just drove it like that for a couple hundred miles not knowing if it was dry or what. The sound got progressively worse, and the clunk became a grind which I could feel holding the car back everytime it made the sound and if I was at a stop light I had to really give it gas to go from the dead stop, as it felt like there was something holding the car back from behind and on the way to get a quart of oil for it (yeah, I'm about to check it a day late and a dollar short) BAM it literally popped. went from ~25mph to 0 in 0.001 seconds. Wheels were all locked up, and there was a golf ball sized hole in the back of the diff. So yeah, based on my experience I would say you should get it taken care of asap.