1979 300d NA

Okay now I know it's not a fast accelerating car.

But I think I may have an issue with throttle pedal / linkage.

50-80 mph acceleration when the pedal is pressed to the floor
(but not engaging the kickdown) takes a while to get to 80 and
the speed climbs very slow but steady and
eventually you get there.

some would say it's typical for a non turbo.

however if I engage the cruise, the speed increases from
50-80 at a much faster rate.

obviously I have some sort of pedal linkage issue.

I've removed the pedal and am just using the steel rod as a test
but for the first 1/3 -1/2 of travel there is no increase in revs.

If I use the linkage on top of the valve cover. the revs increase without
any slack being taken up.

Any ideas?

It sounds like you are on the right track looking at the linkage. There is large rubber piece in there that wears and falls apart. Without that you will never get the full travel of the lever on the side of the injection pump. If you have someone push the pedal while you look at the lever, the lever should go all the way to the stop.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Well you could have someone press the pedal a little. While observing where the slack or lack of movement is in the linkage system. Repeating it slowly should reveal the problem area or areas.


As mentioned there is a ball assembly on the firewall that is a common failure item with age and use. When you have found and repaired the problem the arm on the injection pump should reach the stop. On the injection pump.

Very very common problem on 240ds. I once repaired one the owner had driven for five years with the problem he claimed.

Yea I don't have the linkage as pictured below



I have a rod that runs along the firewall from the DS to the PS

There is a plastic piece there but it looks to be in good shape.

You may want to check your accelerator pivot mount and see if the rubber is cracked and/or deteriorating. It may cause the issues you are mentioning. See pic here:



Dkr.

Yea, my particular model does NOT contain that particular linkage assembly.

Mine has the shaft that runs from the DS to the PS of the engine bay.

They do use different style linkages. Again observation of movement or not should indicate the issue. If everything is tight rod lengths may need attention.

Some models have a type of universal in line. There are two rubbers on those forks in the universal. They can rot off with age and if you did not know they should be there. You could miss that. I do not think you have that setup though as there is no ball assembly on the firewall to transfer motion from lateral to rotational.

The 240ds in 1983 had that setup. The little rubber sleeves are the cheapest part Mercedes probably sells.

Still if you find the universal is in your set up. Twisting one half against the other should reveal a lot of slop. If they are missing. It deals with radial motion. Usually located alongside the engine if you have that particular setup.

Do not make this harder than it has to be. It may take two people to locate the slop. Remember you could have more wear than just in one place as well. No slop anywhere? Remote possibility someone had the system apart and there is a wrong length rod somewhere.

Interesting thread. I took my car from a body shop and noticed the same thing.
It's fine up to 30-40mph. Then if you slam it, it just smokes.
But mine is w124 with om603 turbo.

Not a linkage problem I suspect. Was it doing this before it went to the shop? If not I was wondering what happened.

Definitely check this, mine failed a few months ago requiring a tow truck ride home.

Maybe post a picture of your linkage set up ? .

It's been so long since I sold my last '79 300CD I've forgotten, maybe looking at what you have will allow someone to spot the problem .

My first Mercedes diesel was my '82 240D and it was incredibly slow and worse on hills / freeway so I got it dirt cheap, turned out the throttle linkage was incorrectly assembled by who knows who, once I realized the IP wasn't going to full stop with the pedal floored I at least knew where to look, it still took me a while to figure it out .

FWIW, no, NA 5 cylinder engines are not terribly slow .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I love these threads on here, nobody ever reads...

These linkages in general can be a pain. You really have to take each piece and check that there's no play and then move to the next one. I still haven't gotten mine worked out 100%. I found that the "precise measurements" given in the manual for each rod are worthless once enough time goes by and things get worn, so it's trial and error if that's the case with yours. I had mine all set good where it would actually hit the kickdown switch finally, but for some reason it has always gotten in a bind if I went over a dip while pressing the pedal, and one day I was pressing hard and hit an unexpected dip and it got bent somewhere so if I floor it it just pops one of the ball sockets off. Oh what fun!

I'm sure when they're pretty and brand new these contraptions are great but I do wish it just had a cable like a normal car at this point.

Sounds like bad engine mounts Rog.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Nay, it's always done it and the ones I have in there now are solid urethane. My only theory is that the sway bar is interacting with the linkage somehow. It's the only thing in the area. However, it still does it even after having changed the bushings. I would love to stick a GoPro under there and see exactly what it's doing...

? Urethane motor mounts in a Diesel ? . I bet it vibrates a lot .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better