My 85 300SD that I bought a few weeks back suddenly does not
want to upshift from 3rd to 4th. The only way for me to have the
transmission shift into 4th is at highway speed drop the transmission into N and then drop into D and this drop it into 4th.

The shifts from 1 to 2 to 3 seem to be a lot more jerky then before
and the shift points are lot higher in RPM.

I look forword to your suggestion and comments.

Thanks
Venkat

my car used to do that too. I had to just go out onto the highway and I opened it up as much as i could a while. I think this might be a problem with driving these cars around the city too much at low speed. Anyways maybe I'm wrong but this seems to have worked for me. Also try and do this going downhill.

__________________
W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.

Change the tranny fluid and filter immideately.

On my 1983 240D when the vacuum line going to the transmission came off the first shift was real hard and it would NEVER go into high gear. Re-connected the vacuum line to the tranny and now everything is fine.

__________________
Jim

I had exactly the same problem that you describe (1984, 123 turbo). My temporary solution was the same, run it up in 3rd, slip it into neutral and then back into drive. THis can't be good for the transmission. My mechanic found that the bowden cable had rust in it and had to some extent seized. Fortunately all it needed was to be cleaned out and lubricated, about a 1hr job. This may not solve your problem but it may be a cheap fix that should be entertained before more expensive alternates are considered. Good Luck.

Greetings VenKat,

If you are experiencing high RPM's before the shift takes place, high being 3000 rpm then try screwing in your bowden cable adjustment a turn or two and test drive the car again. This should lower your shift point rpm's and also allow fourth gear to kick in. Screwing the adjuster out will raise the rpm before shifts and if to extreme will not allow the shift from third to fourth take place. Proper adjustment should have you shifting into fourth gear with moderate pedal pressure around 2800 to 3000 rpm.

Just a thought to look into,

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Thanks everyone for all your suggestions. I does up shift into 4th
eventually at around 3500 rpm. I took it to the shop and had the
modulator adjusted to no avail. The shop is going to replace my
modulator tomorrow as they think it is suspect. I will let you guys know the results. Thanks once again.

Venkat

Guys,

Changed the modulator and replaced the transmission fluid
the upshifts are happening a little earlyer on the RPM range then
before. Any suggestions.

Thanks
Venkat

Greetings,

You can adjust the shifting rpm of your tranny by screwing in the bowden cable adjuster on the valve cover for a quicker shift, or thread out the adjuster for a drawn out higher rpm shift. Look at the following site for adjustments to suit your needs.


http://www.mercedesdismantlers.com/


Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Guys,


It is strange but my car has started shifting normaly since yesterday.

Venkat

There was probably a foriegn peice of something that got into one of the checkvalves or something that finally dislodged itself. You should still change the fluid and filter ASAP.

Had this happen with an old Buick Century with vacuum powered shift points (non-electronic trans) Had to floor it till the engine almost exploded to get it to go into 3rd..turns out it was a 1 inch vacuum hose that fell off...

Turbodiesel,

I am guessing one of the many passages in the
valve body was probebly lodged with something which caused the problem and once it dislodged everything is fine. I had the transmission fluid changed when the modulator valve was changed but not the filter as I did not have one on hand. I will
do asap.

Tx
Venkat