240D: Hard to describe effect, getting underway smoothly in 1st gear.
 

Even harder to search for.

Hello Folks,

My son is now the recent new owner of a nice 1981 240D with manual gearbox. We think the car has 141,000 miles as a best guess.


We notice it’s hard to start off smoothly in 1st or for that matter, backing up in reverse.

As you rev up the engine and let out the clutch, some of the engine’s energy
seems to go into the body or suspension as sort of a twisting or wind up motion.
Sort of like the body/suspension absorbs what should be forward motion and releases it a bit later which makes for a sensation of slightly lurching or galloping forward.

It makes it hard to start off smoothly and its enough of an effect that I’m thinking that if fixed, the car’s acceleration (ha –ha) off the line would be more brisk.

The car has brand new motor mounts and brand new rubber donuts (guibo’s?) at the front and rear of the driveshaft. The driveshaft itself was replaced not too long ago by the previous owner though I don’t know why.

The mechanic who installed the donuts for me when we first got the car a few months ago thought the center driveshaft bearing was fine, same for the transmission mount.
I believe he also thought the rear diff mount and subframe mounts were OK. But I’m not absolutely certain about those last two.

So what do you think? Is this a common complaint?

Is it likely to be some rubber part?

Could it be a weak clutch/pressure plate?

Anyone heard of this before?

Many thanks

Curt

Just a thought, but are the calipers or parking brake sticking? Easy to check and rule out :)

I supposed you could open the hood and watch to see if the engine is flopping about when the car begins to go forward or backward. Maybe one of those new mounts isn't installed right.

It sounds like a weak lower engine mount and transmission mount to me. Have you checked those? I know there is a procedure to properly adjust that lower engine mount.

Mine felt like that for a long time, turns out the rear brakes were sticking. Then it suddenly got worse (and obvious) about two weeks ago. Two new calipers and some pads has me rolling free.

Hi Everyone

OP here. Thanks for the responses and so to followup,

The mechanic (an independant mercedes specialist) rebuilt the entire rear brakes assemblies about two weeks ago.
The rear psitons were frozen in the calipers and the parking brake assembly was not working too well.
The problem I described above was there before and after the brake job, so Im pretty sure its not brake related.

Regarding the engine mounts, I had no idea there was an adjustment for the engine mount. Cant imagine what could be adjusted.
I put those in myself and its all torqued down and then double and triple checked.
I will try to see if one of the new mounts is defective by seeing if I can get the engine to move around under load.


Still wondering if it can somehow be the rear diff mount or the subframe rubber peices. I dont know how to test for that.

Thanks for the ideas so far.

Curt

Are you sure it isn't clutch judder? This can be caused by a worn or poorly resurfaced clutch disc, or oil leaking from the rear seal onto the clutch.

There is a rubber mount under the engine between the cross member and the oil pan. It is called the T-mount. That is the mount that is adjustable. I am not referring to the ones on either side of the engine under the arms.

I remember with mine, I had to adjust it back and forth until I got it where i wanted it. One way got smoother 1st gear starts the other way got what you are experiencing. There is actually a tool you can make to use as a referencing when adjusting that mount, but i didn't find it was necessary.

Ohhhhh... that mount, the one near the union of the engine and trans.

I had to loosen that one up to raise the engine to do the motor mounts.

I put it back where it was roughly and tightened it back down.

I guess I should take another look at that one.

Actually, maybe I should just replace it as it being way down near the road, it was pretty beat up and an oily mess.

I wonder if they are available without going to the mercedes dealer?

Thanks much, I would have never thought of that one.

Curt

Replace it, they are cheap and very easy to change.

SPECIAL ORDER SIP Engine T-Mount, Front,1232400365 - PeachParts

I second "clutch judder". It is common with a worn or baddly surfaced pressure plate. It can also be made worse by improper or inexperienced clutch application. When starting out the engine should only be reved up just enough to prevent the car from stalling. Some people rev the car way too high and slip the clutch. Think about it, when you shift into any other gear but 1st, you just effectivley dump the clutch. You don't feather it at all.

The mercedes is designed with a lot of rubber in the suspension and drivetrain mounting points to isolate the rough diesel vibrations from the passengers. I suspect you are accustomed to other cars with less rubber in them. I would have someone who is familiar with stick mercedes diesels drive it before getting too excited about it.

If it's not the rear mount, then another possibility is the accelerator linkage damper (little tiny shock absorber, should be mounted near the injection pump). When this damper goes bad, the movement of the engine and the throttle linkage introduces what you describe.

If that is not the cause, then I fear you need to have the clutch overhauled, be SURE to get OE parts from a dealer that are ordered using your VIN to get the correct disk.

Wow guys, thanks so much for the great replies and insight.

I guess Im going to have to consider the clutch, but first, I will replace the T mount trans mount.

Then I will learn how to drive the car taking into account all the rubber.

That thought did occur to me just for a brief moment when I got under it last week and looked at all the rubber in the drive system and rear suspension.

But what is this tiny shock at or near the injector pump thats part of the throttle linkage? Have not seen anythng that looks like that.

I had an old Fiat Coupe that had severely worn motor mounts and the early all mechanical throttle linkage (no cables in the system, all hard links).
Upon taking off in first, the engine would move in a driection that increased the throttle, then it would whip the other way, then back and so on.
Major lurching at every stop sign and light. Embarrassing to say the least. Just about impossible to drive.
Fixed the mounts (and other stuff) drove it for almost 200,000 miles. It was a fixtuire at our house till the rust finally killed it.

Again, thanks for all the help.

Curt

another possible issue is also with the clutch, if you have a broken spring or fork finger the clutch will partially disengage, and cause the feeling you have also.