'81 240D 3rd to 4th shift issue
 

I did a search and could not find what was a definitive answer to my question.

I have an '81 240D auto and it shifts 1st and 2nd normally. Then at the proper time shifts to 3rd, stays for a second, and on to 4th.

The bowden cable seems like it adjusts the shifting on all gears, I'm having problems only with 3rd to 4th. Would adjusting the bowden cable then change 1st to 2nd as well?

The K-1 spring - I read some posts that said it fixed similar problems others were having and some said it had no effect at all.

Am I missing something in thse posts that the more experienced can extract?

my wifes 240 has the same problem. the indy wants to replace the vacuum valve(the white thing on the left side, rear of the engine) and the two(or is it one ?) three way vacuum valves on the valve cover. we already have replaced the modulator on the trans.

K-1 spring kit cures a sluggish 2-3 shift....the 3-4 shift is a B-2 piston issue...if it does it every gear you have way too much vacuum at the modulator...

BHD - I only get the quick shift from 3rd to 4th. Is the B-2 pison a major fix that Indy needs to do or is it something I can easly do in the driveway?

is it a quick shift or a sluggish shift? quick hard shift is too little vacuum at the modulator.. The K-1 springs kit fixes a slow 2-3 shift...the B-2 cures a slow or non-existant 3-4 shift...

BHD - The shift is quick, but suttle. I can tell the shift occured by listening to the RPM and resulting loss of pick up from being in 4th too soon.

thats not a B-2 problem then....when they start to fail it flares and when it breaks it won't go into 4th at all...


I'n not sure whats casuing the early 4th shift.....I misread your original post.....

this must be the 722.1, right? how does this unit vary from the 722.3? In that unit, the 3-4 shift occurs when the B2 band disengages and the K2 applies while K2 remains applied and B1 remains disengaged.

you got me...I have no crystal ball on this trans....I have been reading the Mercedes trans manual but havent got it memorized yet...I know others here know this trans far better than I do that will offer up some of their knowledge. I'll leaf through it some later tonight when I get home...

At the risk of disseminating false or inaccurate information, I will let you know what I found with my 240.

My shift points were all messed up after an engine change from a Euro injection pump to a NA one. To get my shift points back, I needed to adjust the screw in the modulator and all was fine again. My transmission is a 722.118 in a 1982 Euro and yours might be different, but mine doesn't have a Bowden cable and works by the shift points controlled by the modulator on the transmission and the harshness of the shift controlled by vacuum through the 3 way valve on the valve cover and the vacuum valve on the injection pump. Yours may be different.

You might want to do the search for shift problems on this board and study up for a night or two because this is quite a topic, but I would check the easy stuff first and check the vacuum lines and connections. Next I would buy or borrow a Mit-T-Vac tester and check the numbers working from the vacuum modulator back through the 3-way valve to the vacuum valve on the IP. You can pick up some of the values here on the board. The vacuum from the valve on the IP should vary from high to low as you advance the throttle. The 3-way valve likewise adjusts the vacuum dependant on the linkage position. These valves frequently leak or fail causing quirky shifting. Good news is that they are cheap.

If your problem is internal to the transmission, disregard everything I say because that is above my pay grade. Good Luck, Jim

Thanks for all the replies and information. I will do more searching, I had initially just searched on SHIFT 3rd 4th.

Friday when I was driving home(lots of stop and go traffic), I made note of exactly how the shifting was acting. Shift from 1st to 2nd was harsh, whether I was on the throttle hard or easy. 2nd to 3rd was normal for the second that it remained in 3rd and easily went into 4th. When I pressed hard on the throttle, sometimes it would downshift on its own and remain in 3rd until I'd back off the throttle a little then a smooth shift into 4th.

I'm embarrassed to say, I just checked the ATF after a 20 min drive. The fluid looked and smelled OK. It was about 1/2 inch over full on the stick. I checked in Park and neutral. I'm not sure what to use to pump out some of the fluid through the dipstick.