1981 240D won't shift out of 2nd ! - PeachParts Mercedes-Benz Forum

wilburtual · #1 11-12-2013, 07:40 AM

my 1981 240D has been having transmission issues lately... for a couple of months it has been flaring pretty bad going from 2nd to 3rd, to get it to shift I'd let off on the pedal untill it shifts then ease it into 3rd...then also needed to east into 4th. i changed the fluid and filter hoping to help and it did help a little, didn't flare as much, but not great.

A couple days ago it started to not shift from 2nd at all. it will start in 1st and go to second, but then no matter what speed you try to get to, doesn't even try to go to third, no flaring just keeps on increasing RPM in second.

about a year ago, i had this same issue, stuck in second, and i found that the hard vacuum line that goes from the valve cover to the transmission was unplugged, once i plugged it back in, it started to shift as usual. so, this time i am hoping it is a vacuum issue again.. ??

I've check that all lines are plugged in and I ordered some replacements parts from pelicanparts. I replaced the little white plastic vacuum valve that is on the valve cover hoping it was that, since the little plunger flap was almost completely worn off. but, replaced it, no change. i also replaced all the rubber vacuum connections and junctions under the hood to try and find a leak. oh, and also changed the green vacuum damper dashpot thingy.

so,,, now I am wondering where to go next - does it still seem like a possible vacuum issue? how about the valve that is on the Injection pump, can that be a culprit? anything on the transmission itself? i read on another thread about a little cap on the transmission modulator can leak?

help!! thanks

Zacharias · #2 11-12-2013, 03:57 PM

To ensure meaningful replies, it would be best to confirm what model of transmission your car has. The number is stamped on the transmission body, the lip just above the pan, on the passenger side. It will likely be crusted over with grease and oil. If it's impractical for you to look, perhaps someone else will confirm....

I am going to go ahead and answer, as I am pretty sure it will be like the one in my wagon (which was originally in a 240d), a 722.117 or .118 -- in which case it's a vacuum-only controlled transmission (no lever to the transmission from the linkages).

To do what I suggest you will need a vacuum gauge and a vacuum tester, such as a Mityvac.

I suggest you proceed by:

1 - undo the main vacuum line running to the brake booster and measure the vacuum output of your vacuum pump with a vacuum gauge. Sorry I am not sure I remember the correct figure, I think it's anywhere between 18-22 hg? If it's low or jumping (gauge wavers really erratically), you need to replace the diaphragm in your injection pump.

2 - Apply vacuum through the vacuum line running down to the transmission to see if the vacuum modulator holds vacuum. If not, the cap may be leaking.

3 - if all seems good here, move to the whitish/yellow vacuum control valve bolted to the injection pump. This has a spring inside that acts on a bleed valve. Some of these get very tired and the spring needs to be retensioned. Link to DIY: http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1261744-transmission-flaring-clunking-vcv-diy.html (unfortunately some of these valves are not servicable, have a lock ring instead of the nut shown in the DIY... in this case you will have to get hold of a used valve that is adjustable).

I suspect your issue is lurking in one of these areas.

cooljjay · #3 11-12-2013, 08:02 PM

You have a kickdown switch behind the accelerator....if this gets stuck it can also cause your issue.... Does it work? To rule out that as a problem....simply unplug it....and see if there is a change...

wilburtual · #4 11-13-2013, 06:40 PM

thanks for the suggestions.
I have unplugged the kickdown switch, it was not working anyhow. unfortunately, no change, still stuck in 2nd.

I will try the vacuum related tests and report back with my findings.

wilburtual · #5 11-24-2013, 08:56 PM

I have tested the vacuum to the modulator with my Mityvac and it seems that is the issue... the plastic end cap piece on the modulator freely rotates around 360degrees.. at some positions it holds full vacuum, but when turned a little bit, it loses all vacuum.
When searching around the forum as well as looking at pelican parts for replacements, it seems most modulators are a type that has a black rubber cap on the end and the vac hose plugs into the body of the modulator. However, mine seems different. it has no rubber cap, instead a plastic cap piece on the end, that freely rotates around, and the vac hose plugs right onto the cap... anyone have any experience with this type of cap? I can't find any info on this type, or how to replace this cap- hopefully it is just the cap leaking and it can be swapped. I found a photo online of this sort of cap, I've attached for reference. But, I can't find anywhere that sells this type of replacement cap.. any ideas?

wilburtual · #6 11-24-2013, 09:26 PM

I just found this link to a replacement modulator... it seems this might be what my 81 240D has?

https:// m e r c e d e s s o u r c e .com/store/7221x-red-body-diesel-automatic-transmission-vacuum-modulator-instructions

ROLLGUY · #7 11-24-2013, 11:51 PM

Before buying a new modulator, try cleaning the cap and mounting surface, and replacing the Oring. I have had success with this, and have saved the expense of a modulator with a 25 cent Oring and some cleaning....Rich

wilburtual · #8 11-25-2013, 12:33 AM

thanks for the tip, rollguy, i'll try replacing that o-ring.
does the cap just pop off? I see some sort of retaining ring, maybe I just squeeze that with pliers to get the cap loose?

thanks!

wilburtual · #9 11-29-2013, 02:27 AM

I changed the O-ring on the modulator under the cap and it now holds vacuum ! BUT... the car still doesn't shift

(
so, I am thinking maybe I try changing the whole modulator ... when I had the cap off to change O-ring, there was fluid under the cap. I think I read somewhere that there shouldn't be any sort of fluid in the modulator, and if there is its probably bad. anyone have experience with this?
anyone changed one of these before, does it just screw out?

ROLLGUY · #10 11-29-2013, 11:38 AM

Quote:

Originally Posted by wilburtual

I changed the O-ring on the modulator under the cap and it now holds vacuum ! BUT... the car still doesn't shift

(
so, I am thinking maybe I try changing the whole modulator ... when I had the cap off to change O-ring, there was fluid under the cap. I think I read somewhere that there shouldn't be any sort of fluid in the modulator, and if there is its probably bad. anyone have experience with this?
anyone changed one of these before, does it just screw out?

I have changed one, and the fluid will run out if not drained below the level of the modulator. You will then have to adjust the pressure with the "T" under the cap. You can do it with a gauge (hooking the pressure gauge up to a test port) if you have one. I did not have a gauge, so I just adjusted it by feel (driving the car, feeling how it shifted). If it shifts late and hard, there is too much pressure. Turn the "T" counter-clockwise a couple turns. If it shifts early an/or soft, turn the "T" clockwise. I have had satisfactory results doing it this way. You have to remove the cap each time to adjust the "T". As others have said, it could also be the kick-down solenoid or switch.......Rich

EDIT: the solenoid could be stuck or clogged internally, and that would not matter if the switch was hooked up or not.

wilburtual · #11 11-29-2013, 04:45 PM

thanks Rich,
I'll check into the kickdown solenoid, I didn't know there was more to it than just the switch, so I figured just unplugging the switch took that piece of the puzzle out of the equation..

wilburtual · #12 04-13-2014, 11:26 PM

I have tried the vacuum tests and the vac pump seems to be OK, I disconnected the vac line to the transmission and it holds vac with the mityvac, I tried driving while applying vac to that line and still no shift. although now that I changed all of the vac lines and junctions under the hood I do seem to get 1st gear every once and a while, while in the past it always started in 2nd and stayed there, it never went to first (so it was always soooo slow!)

not sure what to try next, I can't find the modulator style that it has anywhere to try and replace it.. no parts stores seem to have it, tried a bunch of CL parts cars, no one has the style with the red housing and cream colored cap! I am assuming it is not possible to swap in a different modulator style..?
this is the style my transmission has:

I found this photo online ,but can't find an actual part for the life of me!

anything else I might try? IF the modulator was bad, would / could it cause my stuck in 2nd issue? or is my transmission just toast?

Can the kickdown solenoid get stuck "on"? i've disconnected the switch, but can it physically get stuck? how would I diagnose to take the kickdown solenoid out of the equation?

thank you!!!

pj67coll · #13 04-14-2014, 12:03 AM

I'm afraid I can't answer your solenoid question but I do have a question of my own. Have you tried shifting thru all the gears manually? And is it still stuck in 2nd when you do that?

- Peter.

wilburtual · #14 04-14-2014, 12:06 AM

yes i have tried shifting through the gears while driving, it stays in 2nd no matter which gear the shifter lever is in. (except n, r and park!) it still reverses fine.

cooljjay · #15 04-14-2014, 12:36 AM

The kick down solenoid can get stuck, mine did....it was bad....you can check it on the transmission by simply jumping the plug that goes into the switch....go under the car and touch the wire to the solenoid you should hear a click...no click its bad....it can also be removed and tested with the battery....positive line on the screw and negative on the bolt that goes into the transmission.