no 4th gear, 300D, fluid is fine - PeachParts Mercedes-Benz Forum

odie · #1 12-13-2007, 03:11 PM

Is there anything external that would cause the 4th gear to be gone? It's just not there.

Modulator, no vacuum, throttle cable adjustment, etc?

It's a 1992 2.5 300D. I did a complete filter and fuild change.

the other three gears are fine. It's just there is no 4th gear. The transmission shifts into 4th normally but it's as though there are no gears or anything. Zero engagement. It acts like neutral when it shifts to 4th.

I'm about to toss in the towel and sell the car for the value of the engine & parts. It drives around fine in 3rd but I can't use the car like that. Maybe if I have a good used tranny?

rrgrassi · #2 12-13-2007, 05:56 PM

Could be anything, worn clutches to some check valve not closing, kick down switch or solenoid not working. What happens when you disconnect the kickdown switch?

odie · #3 12-14-2007, 09:16 AM

where is the kick down switch? under the pedal? linked to the throttle linkage on the engine? Switch mounted on the transmission housing? ......I don't have any shop manual for this model. There is some kinda device mounted on the trans on the driver's side with a wiring harness going to it. Any idea what it is?

pawoSD · #4 12-14-2007, 10:55 AM

Yes the kickdown switch should be under your pedal on the floor. With a cord/connector going into it. Unplug it and take it for a drive. Its very common for it to jam and prevent 4th gear. Hopefully that helps!

odie · #5 12-14-2007, 01:31 PM

Hmmm, kick down switch does not sounds like the problem to me. It's not preventing shifting into 4th. The trans appears to shift very smoothly into 4th no problem, just there is no engagment once it shifts to 4th. It's like the gears are just missing.

it shifts 1-2-3 normal. As soon as I feel the car/engine/speed is right for when I think the shift to 4th should happen....the RPMs suddenly increase as though the trans is in neutral and no matter how much I rev the engine the car is just coasting. Eventually it will shift back into 3rd as the RPM increase and car slows down and away we go again normally until it's time for 4th again.

It's like someone just removed the gear or belt for 4th but left everything else there.

If the kick-down was stuck, would it not just keep me in 3rd all the time? Or am I wrong on how this kickdown switch works?

pawoSD · #6 12-14-2007, 03:54 PM

If you let off the throttle in this "4th zone" does it rev up again if you go back on the throttle?

If so....and the kickdown issue has been tested....I'd say last ditch effort is to change filter/fluid and check the pan for anything odd, such as metal fragments or clutch pack material. If nothing reveals an answer or fix....the 4th gear clutch is probably dead.

These trannies are not all that expensive to have rebuilt if you can pull/install it yourself.

odie · #7 12-14-2007, 04:42 PM

it just revs freely in 4th. I can play with the gas pedal but the RPMs just go up & down with no apparent affect on the driveline.

I replaced the filter. already. It was being driven around on very low fluid by a teenager and basically stopped going anymore when the fluid got too low. They just parked it and "daddy" decided it was time to get rid of it.

But if the fluid was that low, I would think it would have not even been able to shift into 4th so how does the 4th gear clutch go bad? 1-2-3 are perfect.

kerry · #8 12-14-2007, 05:00 PM

Nothing wrong with a 3spd.

pawoSD · #9 12-14-2007, 06:58 PM

Quote:

Originally Posted by kerry

Nothing wrong with a 3spd.

Except for a top speed of about 55 if you don't want to blow up the engine....

I'd just get the tranny rebuilt. Those are fairly rare cars. Especially if the car is nice overall.

odie · #10 12-16-2007, 03:15 AM

the car is not great. just a good daily driver candidate, if the 4th worked. considering thse cars sell for several thousand, it might have potential...however i already have an 87 TD wagon and 84 190D.

what do you think a good used tranny should cost?