Transmission 300E 2.8 - PeachParts Mercedes-Benz Forum

radunegru · #1 07-28-2004, 12:59 PM

Transmission is shifting hard 1 to 2 gear and 3 to 4 and also when I shift it in to drive from P or R.
The reverse is working perfect no delays no hard shift.
I did change the differential bushings, the flex disks are new, rebuid valve body, new filter and oil (Bilstein Made in Germany),adjust the modulator to lower the presure. Nothing helped. I gus the only choice is to rebuild it?
Does any one has any idea?

Hirnbeiss2 · #2 07-28-2004, 02:03 PM

How's your vacuum? Low vacuum or a bad diaphragm causes hard shifts.

radunegru · #3 07-29-2004, 09:28 AM

vacum is ok as long as shifts right from 2-3

stevebfl · #4 07-29-2004, 09:37 AM

Low modulator pressure will cause that trans to slip. Somewhere between where you are at and slipping is a modulator pressure that gives good shifts. It will not vary from shift to shift so its only usefull for general conditions such as yours.

To do it right modulator pressure should be measured against a standard and if right and shifting is wrong, there is another issue. When testing mod pressure the value is for zero vacuum, but once that is established the value at idle vacuum should also be noted and it should be way different. If vacuum were applied to the modulator with a mitivac while the gauges were measuring mod press, a steady change in pressure should occur between zero and idle vacuum.

These cars will shift much harder if the power (and thus manifold vacuum) is reduced for any reason. Thus a smooth powerfull motor is often part of the cure.

toofast45 · #5 02-07-2008, 02:00 PM

Quote:

Originally Posted by stevebfl

Low modulator pressure will cause that trans to slip. Somewhere between where you are at and slipping is a modulator pressure that gives good shifts. It will not vary from shift to shift so its only usefull for general conditions such as yours.

To do it right modulator pressure should be measured against a standard and if right and shifting is wrong, there is another issue. When testing mod pressure the value is for zero vacuum, but once that is established the value at idle vacuum should also be noted and it should be way different. If vacuum were applied to the modulator with a mitivac while the gauges were measuring mod press, a steady change in pressure should occur between zero and idle vacuum.

These cars will shift much harder if the power (and thus manifold vacuum) is reduced for any reason. Thus a smooth powerfull motor is often part of the cure.

Steve,
I am quoting an old thread of yours regarding transmissions. I hope you can advise me.

I just had my transmission re-built and picked it up yesterday. My car is a 1993 300E 2.8

Now the car starts on 1st gear all the time and shifts hard to 2nd. I told the tranny shop about this and the guy insists that this model always starts on 1st. As far as I know, this car starts on 1st only when you press aggressively on the gas pedal to get it to start on 1st. Otherwise, under normal driving conditions, it should start on 2nd. Am I right?
I've been looking for any material about this, but could not find any. I'm still looking, but if you can lead me to the right web site or thread, it will be highly appreciated.
If this starting on 1st is resolved, will it fix the hard shift fromm 1st to 2nd? or will I need to adjust the modulator (or adjust somehting else?)
Thanks for any advise.
Rico

jcyuhn · #6 02-07-2008, 03:16 PM

You are incorrect. The 124.028 (ie your car) always starts from rest in 1st gear. That is normal and correct operation. Earlier model year 300Es had 2nd gear start, but by the time the M104 engine was introduced (in the USA) 1st gear start had been adopted.

I have one of these cars as well. The transmission shifts a bit firmly when cold, but shifts are very quick and smooth when fully warmed up. Of course this is all subjective; it depends on your definition of "firm", ambient temperature, synthetic vs. conventional ATF, etc.

If you have firm shifts the first thing is to find and fix any vacuum leaks on the engine or vacuum lines. Even surprisingly small leaks affect shift quality. The electronic engine management on this car is surprisingly good at adjusting to and hiding vacuum leaks, so you can't assume there are none just because the engine still idles smoothly at the correct RPM.

- JimY

toofast45 · #7 02-12-2008, 08:25 PM

Jim Y,

Thanks for your input. The hard shifting from 1st to 2nd resolved itself. It is now shifting smoothly.
The new issue is the shift from 2nd to 3rd which is slipping especially in the morning. Do these things always happen after a tranny rebuild?