Slack in Drivetrain

My manual transmission 300E seems to be getting much more "slack" in the drivetrain these days.

I have checked all components individually with the shake and wiggle test. Nothing individually seems to be bad. The flexdisks are tight and the half shafts seem tight, as does the universal joint in the center of the driveshaft. The only thing I can lay this off on, is possibly too much slack in the gear and pinion, and/or the differential unit.

Has anyone experienced this? This is beginning to take away the fun of driving my stick shift car.

Additionally, if I end up rebuilding the rear axle, what gear ratios are available and how much trouble is it to recalibrate the speedometer?

The car currently has a 3.08 and seems too "long legged" for me. This cars M103 engine has a more peaky power band than my C240. I believe the 300E needs the six speed more than the C.

Comments and experiences appreciated,

[Glen]

Larry,
When I had my 300E, replacing the rear differential support bushings fixed some slack issues I was having. You might take a look and see if the bushings are worn.

I agree, the gearing is too long legged. The space between 2 - 3 is especially huge in my opinion. You might consider a 3.27:1 LSD from a 16V...

[Ron Brooks]

While not MB experienced, you are describing exactly what I experienced in my 944. Ring and pinion is the weakest link in those cars and it had some when I bought it with 43,000 on it. By 150,000 the slack got to the point where it was almost like an on/off switch when applying the power. It did teach me excellent rpm matching when changing gears though. The problem did take away a lot of the fun towards the end. Good thing my next door neighbor, the factory trained Porsche mechanic messed up a timing belt change and blew 7 of the 8 valves when they greeted their repsective pistons. So, I'll never know the joy of driving the rebuilt rear end.

Glen,

Thanks very much for the response. I got under and sure enough the rear, top two bushings are indeed loose. I pull and pry around and can't move the differential much, but if torque is applied from the driveshaft, it may very well move it much further.

I also felt the ring and pinion slack and it just doesn't seem to be excessive.

Did you have to drop the whole differential down to replace the differential mount bushings?

Thanks for the responses everyone,

[md21722]

Larry my mechanic says you don't.

If I was doing it, I'd support the differential with a tranny jack and remove the two rear bolts and the front top bolt and let it donw slightly so you can get at the bushings. The axles and driveshaft should move to allow you to do this. When I rebuilt my rear suspension, I swapped differentials, so I don't have direct experience with your problem.

[Glen]

Larry,
With the right tool, I don't think you have to completely drop the diff. Unfortunately, I didn't have the right tool I changed them at the same time I redid the whole rear suspension. I had the cross member out of the car completely and used a 12-ton shop press to R&R the bushings.

[Ken300D]

I have a tremendous amount of slack in my 1982 300D differential, and a fair amount of whine. The whine is not as loud now with Mobil 1 synthetic gear oil in the case.

While having the driveshaft down to replace flex disks, I made an effort to look at and measure the differential slack. With the rear wheels firmly in place (and thus the axle shafts not moving), the driveshaft slack is 60 degrees of movement (360 degrees being one complete revolution).

Now THAT is what I call slack!

Although a lot easier to estimate the measurement with the driveshaft off, you should be able to get close on measuring how much differential slack you have by engaging the parking brake and putting the transmission in neutral. Then, get under there and turn the driveshaft by hand back and forth.

Do I have the record for the most differential slack?



Ken300D