differential play/backlash

[240Joe]

1983 300D 132kmiles

The car has a clunking sound when you move the selector lever from drive to reverse with foot on brake. Also clunks when you apply power and release it when running at a constant speed.

With this mileage I would think it would be front flex disk. However, both flex disks and the center support bearing look good. I jacked up one rear wheel and I get about 3.5 inches of travel at the circumference of the tire. This translates to about 16 degrees of free travel. My 1980 240 has about 0.75 inch of travel measured at the same point.

By watching the drive shaft and the axles when I move the wheel, it looks like about 80% of the travel is in the differential.

Everything looks like the differential is worn, but the mileage (which is correct) doesn't seem correct for this type of wear. Any ideas?

thanks
Joe

[84300DT]

sorry to tell you but your symptoms are Exactly the same as mine
were- I hope your result is not though..
anyhow i did the same test as you with the same result about
3.5 inches of play.puzzler - need help!

[240Joe]

After you replaced the diff, and the half shafts, did you finally get rid of the clunking?

I've started the teardown, and have a used diff on order. I should have more info by the weekend.

Joe

thanks for the reply.

[Ken300D]

Its hard to gauge degrees of "clunk" on a message board, but my 1982 300D with 325K also has a clunk to it that is almost certainly caused by looseness in the differential.

One symptom that is a little tricky getting used to is that when I put the car in Park, it may continue to roll for a few inches. That can be disturbing when parked in close quarters!

I've had the cover off my differential due to replacing the half-shaft axles. The insides looked to be in good shape. From what I could see, the "slop" or "looseness" appeared to be part of the design, and not from wear. There is a shaft in the center of the insides of the gears that holds one or two smaller gears in place. Well, that shaft is fitted into a slot, which allows it to move back and forth to some extent.

I don't understand the design or the reason for the slot, but the car is doing fine and I can stand a bit of a "clunk" under the circumstances you describe.

Maybe other W123 owners will chip in with their observations.

Ken300D

[240Joe]

ken300D

I could easily put up with a bit of roll after putting it in park, but my clunk is so bad that it makes a pretty loud clunk when just applying power and releasing it while running at a steady speed. It is definitely not correct.

It might be interesting to know how much travel you have at the tread of the tire if you raise one rear wheel and turn it back and forth. I've got 3.5 inches on my 300d, and about 0.75 on my 240D, which I believe is nominal, or better, for a car with 250 kmiles. I found somewhere on the net where a guy said a quick check is to have less than 2 inches of slop at the tread, with 1 inch closer to nominal. He said that anything over 2 inches indicates a problem.

All of this assumes good flex disks, support bearing, etc.

Thanks
Joe

[84300DT]

joe-
after replacing the diff and 1/2 shafts - no clunking - or really any sounds whatsoever coming from the rear end - the flex discs and bearings were ok. It does still have a little 'play' when putting into park
btw-
also put up another post to do with the 1/2 shafts


1/2 shafts

good luck-
bob

[123 300D driver]

My 79 300D also makes a clunking sound when rocking it forward and backward on flat ground. The sound comes from too much play between the spider gear shaft (in the diff) and the drilled hole that the shaft fits into. I would say about 1/64" play on both ends.

The clunk only occurs when there is NO load on the drive train while upshifting, particularly between 2nd and 3rd at about 40 kph (25mph). As long as there is a load (accelerating even slightly) the clunk is decreased or eliminated. I decreased the noise level of the clunking sound somewhat by switching to 85W-140 gear oil.

Some history on the car: The PO was a complete dingbat that didn't maintain the car. When I bought it from him, the tranny shifted from 2nd to 3rd with a "bang" at about 50kph (30mph). It would not shift until that speed threshold was reached, and then it would "bang" into the next gear. Only a dingbat would put up with this for any length of time without getting it fixed. Could be, years and years of this caused the spider gear shafts to deform

I have since adjusted the shift points and added some tranny conditioner, so now the tranny shifts OK and the clunk is not getting any worse. The clunk can be minimized by keeping a load on the drivetrain at the shift points. The diesel is only 75 hp, so I think the problem is gone!

Why did I even buy a car shifting with a "bang"? I got it for a good price and I figured I could fix the problem.

[240Joe]

I got the diff cover off, and the same hole that 84300DT indicated was elongated on his is elongated on mine. Massive amount of slop. The gears themselves don't look too bad.

Now the problem is that one of the axles is stuck in the differential. I'm not sure why but can't easily see how to unstuck it. I suppose I'll just drop the diff with the axle inside, and then figure out how to extract it.

I thought the fuel line looked like it was starting to leak yesterday, and of course it started to pour today. So I got covered in diesel while I tried to clamp off the line with vise grips.

I'm also having a bit of trouble figuring out how to get the front differential mounting nuts loose. There is not much room to work, and the nuts/bolts are rusted. I soaked them in liquid wrench so maybe that will make it a bit easier.

I need to rest for a day or so before I resume my quest...my arms pretty much gave out towards the end of another 3 hours session. The differential won't be here until Friday, and most likely monday anyway.

Now to fastlane for hoses, and the tank filter, and maybe a flex disk for the front.

Joe