1979 300D won't shift down to 1st gear - PeachParts Mercedes-Benz Forum

waldos313 · #1 08-09-2008, 10:37 AM

Our 1979 300D runs great at speed. We just installed a fuel boost pump kit and it really does help starting and idling and did help a little on power too. I was hoping it would also solve our shifting problem as well but it did not. From a dead stop, the car will always start rolling in second gear (which as everyone knows makes it painfully slow) even if I mash the pedal down. It will do this even if I shift into neutral while stopped then shift to drive just before moving.
We've already done the following to this car: recent valve adjustment, timing chain replaced (has good timing now), recent diesel purge, new filters, fuel lines and fuel strainer, adjusted kickdown rod from throttle to transmission (which did improve the shifting above 20mph to earlier shifts for more power).
The car runs excellent on the highway and has passing power even at 70 mph. Its just the starting out that scares me. It will shift down to first gear if I'm already rolling at about 5-10 mph however which is what mystifies me.
Anyone have some valuable 2 cents?
Thanks,
Brandon and Megan Oswald
Pensacola, FL
1979 300D
1985 300D Turbo

tobybul · #2 08-09-2008, 11:39 AM

Quote:

Originally Posted by waldos313

Our 1979 300D runs great at speed. We just installed a fuel boost pump kit and it really does help starting and idling and did help a little on power too. I was hoping it would also solve our shifting problem as well but it did not. From a dead stop, the car will always start rolling in second gear (which as everyone knows makes it painfully slow) even if I mash the pedal down. It will do this even if I shift into neutral while stopped then shift to drive just before moving.
We've already done the following to this car: recent valve adjustment, timing chain replaced (has good timing now), recent diesel purge, new filters, fuel lines and fuel strainer, adjusted kickdown rod from throttle to transmission (which did improve the shifting above 20mph to earlier shifts for more power).
The car runs excellent on the highway and has passing power even at 70 mph. Its just the starting out that scares me. It will shift down to first gear if I'm already rolling at about 5-10 mph however which is what mystifies me.
Anyone have some valuable 2 cents?
Thanks,
Brandon and Megan Oswald
Pensacola, FL
1979 300D
1985 300D Turbo

You should post this in the Diesel Discussion section.

Have you played with the tranny modulator valve?

waldos313 · #3 08-10-2008, 02:15 PM

Not sure which valve that is...

duxthe1 · #4 08-10-2008, 03:29 PM

There is a kickdown switch on the floorboard that the pedal pushes when you mash it to the floor. The switch could be bad or the fuse that powers it could be blown. If the fuse is blown check for a frayed wire underneath near the trans mount.

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