Play in Powertrain - First Time 240D Owner!

[Luftmensch]

Hello dieselfans,
I've just gotten myself into an '83 manual 240D, 250K or so, the first car I've ever owned. I read a lot of the peachparts forum before I bought it - you all sold me. I figured it would be a good car to learn on.
I'm stuck on a problem and looking for help with diagnosis and repair. There seems to be some play or worn part somewhere in the powertrain. When I'm accelerating in any gear, the car runs great, but when I let off the accelerator a bit, I get this clunk or knock somewhere. Then when I go to accelerate, I hear it again. It seems as if there's some worn element of the powertrain somewhere that doesn't interlock snugly against the subsequent element of the powertrain.
I got under the car with the transmission in first gear and noticed that the driveshaft seems to give me about 20 degrees of rotation. I've already checked the front and rear flex plates, the center bearing, the U joints, and the differential. All of them seem to have almost no play and be in good shape. The only place I've noticed anything is in the transmission. I can hear a soft tap sound when I turn the driveshaft from one extreme to the other.
Any thoughts? Does it sound like a worn part in the transmission, or is there some other part I should check? Before I start tinkering with the transmission, I'd like to have an idea of what I might be looking for and if I'll be able to handle the repair. The most complicated thing I've done to a car is replace an alternator.

Thanks for any help! You all have already helped me diagnose a worn steering gear

[charmalu]

Welcome to the forum.

I assume you have a manual transmission from the way I read it. there is a nut at the rear of the trans that holds the Flange on. If this has loosened up over time and caused the Flange to work back and fourth it wears on the Flange Splines, and they will wear to a point and cause the slop. the trans shaft being a harder steel won`t have the wear.

I had this problem with our 240 a couple years ago. swapped in a good used one and the nut from the donor trans. the nut will have to be staked to the shaft, and the used one lined up in a different position.

As long as you didn`t get a lot of deferred maintenance and abuse from the previous owners. your 240 should last you a long time. they are a pretty basic vehicle to work on, and dependable.

Charlie

[barry12345]

Try rocking the engine by hand. Exhaust may be hitting for example as you take the the load off of the engine. What shape are your motor mounts and transmission mount in? They can get pretty bad with age.

[Luftmensch]

Thank you both for your help!

Charlie, any ideas where I could get a transmission flange and nut? Could I pull them from an automatic transmission, or will I need to find a donor manual trans? And what did you mean about staking the nut to the shaft?

barry12345, the engine and transmission mounts were replaced at some point, but I'll take a closer look at them and any engine rock.

We got some golfball sized hail yesterday…ruined a bunch of tomatoes, but the 240 was in the garage!

[cooljjay]

Sounds like bad axle shafts....boots crack....oil leaks out....starts clucking pretty bad...

[Alastair]

20 deg play in gearbox --with the car in 1st gear isnt a lot.....

There are two gears in the box that transmit the power in 1st gear (Input shaft to layshaft, and layshaft to mainshaft)--that have to have clearances and will show up as movement relatively.

Try same test with car in 4th gear, there'll be less slop (as mainshaft is coupled to input-shaft, by splined sliding sleeve) and maybe you'll see where it is...

My bet is with centre-bearing,--the bush wears and the bearing clunks round in its now worn frame...

[charmalu]

I don`t know if an automatic trans flange will work or not, the one I used was off a spare manual trans I have.

To stake the nut, is using a special nut that has a shoulder. using a hammer and punch the shoulder is hit and crimped into a slot in the shaft to keep the nut from backing out or loosening.

This picture will give you an idea of what it is.

Castlated Transmission Sockets

Charlie

[Stretch]

I think the output flange nuts are different on the manual transmissions - so I don't think you'll get any joy with the automatic transmission version. Perhaps it is worth getting in touch with the site's sponsors to see if they can confirm this?

As for the clunk sound - I think it is very difficult to check the axles without removing them from the vehicle... but that's my number one suspicion.

[Skid Row Joe]

Best way to see and hear what's going on under there is to put the car in 1st gear on a flat surface with the engine off, and have someone rock the car for and aft, all the while you watch, look and listen to the bottom drivetrain.

We found a couple loose bolts and nuts on a Pontiac Sunbird's AT drivetrain assy 35 years ago that way.

Counld be axle shaft(s) as jjaycool said, or another thing - it may be a worn differential mount??

I may be wrong, but I didn't know that MB cars had "U-Joints" incorporated into their driveshaft assemblies?? Do you have any pictures of these U-Joints and their associated grease fittings??

[charmalu]

Originally Posted by Skid Row Joe

Best way to see and hear what's going on under there is to put the car in 1st gear on a flat surface with the engine off, and have someone rock the car for and aft, all the while you watch, look and listen to the bottom drivetrain.

We found a couple loose bolts and nuts on a Pontiac Sunbird's AT drivetrain assy 35 years ago that way.

Counld be axle shaft(s) as jjaycool said, or another thing - it may be a worn differential mount??

I may be wrong, but I didn't know that MB cars had "U-Joints" incorporated into their driveshaft assemblies?? Do you have any pictures of these U-Joints and their associated grease fittings??

Here is a picture of a MB Drive Line. There is no grease fitting on the MB U-Joint.
W123 euro 5-speed driveshaft

Yo Joe, time to crawl under your ride.

Charlie

[Skid Row Joe]

Originally Posted by charmalu

Here is a picture of a MB Drive Line. There is no grease fitting on the MB U-Joint.
W123 euro 5-speed driveshaft

Yo Joe, time to crawl under your ride.

Charlie

Once they lowered the late '90s sedans and attached with screws, the three-piece diaper systems under them, well, I cannot comfortably slide under enough to do an oil change & remove the larger diaper section - I had to go to jackstands.

Well, back to drive-lines......I need to take a long look under my old E300 before it's gone here in a few weeks. See what I've been missing for 14 years under there. One of the best things about MBs is their sealed n greased for life joints. -As per maintenance time. The double-wishbone front suspension to me is a thing of beauty. Now some of the lower end ones have thoise cheesy McPherson strut suspensions.

[Air&Road]

There is one u-joint in the center of the driveshaft. It RARELY wears to a point of making slack in the driveshaft. It's wear will sometimes cause vibration problems.

If you can safely get the car in the air with the rear wheels suspended, you can get underneath and locate the problem pretty quickly. If you don't find a broken flex disk or some other obvious thing, use a jack underneath the front of the differential to check the diff mounts.

Hope this helps.

[Luftmensch]

Thanks for all your help! I'll keep you all posted the next time I get into the shop - finishing up a gardening project now.