Why does it shift-up so rough ?

[TheEngineer]

On this 1969 280SL of mine, the automatic shifts very smooth when the car is cold i.e. when it has not been driven for 8 hours or more. After a few miles, after the car has warmed up, the transmission begins to shift with a pronounced jerk, especially from 2nd to 3rd gear. Much more pronounced when I’m easy on the throttle. When I wind the car up in 2nd gear, to about 3’500 rpm, it shifts pretty smooth, even when warm. It always shifts down nicely. I thought at first, that when cold, the hydraulic clutch has not filled completely with transmission fluid and has more slip, but I have made stall tests, both cold and warm, and found no difference. The hydraulic clutch has very little slip compared to the torque converter used in later MB models. Perhaps as a result, later transmissions shift much more smoothly. I’m very much puzzled by the fact that it shifts so nice when cold and I wish, I could obtain that during all of my driving. My friendly MB dealer tells me, the transmission is fine, and what I experience is normal for the car. Any comments or advice?

1969 Signal Red 280SL, Automatic, P/S, A/C. Mechanical engineer-ret.

[peterm]

Likely not the cause but in the not too distant past I had a problem with the tranny acting up which was cured by checking the fluid level (as suggested on the board) and adding the appropriate Dextron, which cured the "roughness"

[Cees Klumper]

My automatic ('69 car) shifts very smooth cold or warm, hardly ever any 'jerkiness' (although sometimes you feel the up- or downshift).

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[TheEngineer]

Dear Cees Klumper :
Happy Birthday (a little late). Thank you for your comments. It looks like our vehicles are about the same age: My Chassis number (i.e. the chassis number of my MB) is 113044-12-007537, it was built Jan. 1969 The transmission is K4A025. K stands for “Kupplung” “A” is the revision, “025” is the rated torque capacity in mkg. S/N is 033550. Please tell me your vehicle Chassis number for comparison.  If I can get this transmission to shift smoothly, I’ll keep it; otherwise, I already have a “W” transmission ready. “W” stands for “Wandler” It came from a 1979 280CE. It is 3 inches longer and I have to do some cutting on the driveshaft and support plate. I’m not looking forward to that. After all the comments received, I may be motivated to change the transmission fluid. I’m not looking forward to that either: It’ll run down my arms, into my armpits and then I have to wash myself. As far as I can tell from the records dating back only to 1991, the transmission fluid has not been changed. I thought, Oil lasts almost forever. It has been in the earth for millions of years, and, around here, they still pump it out and use it.


1969 Signal Red 280SL, Automatic, P/S, A/C. Mechanical engineer-ret.

[Tom]

Frequently a rough shift as you describe, especially when coming to a stop, is an indicator that either your idle throttle swithc on the intake mainfold needs adjustment/replacement or the 3 way solenoid on the transmission is bad.  Check the posts from Joe Alexander on this matter on this site and the old Yahoo site.

Best,

Tom

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1971 280sl Tunis Beige Metallic (restored & enhanced)
1971 280sl Tobacco Brown (low mileage stock)
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[ja17]

Hello theengineer,
Somethings you may wish to know about if you attempt a conversion. As mentioned the transmission length is longer. The shift pattern is opposit. So you will have to change the shifter and its base also. The nose on the  torque converter is smaller on the later transmissions so it will not center up in the crankshaft.If you use the earlier converter it will not fit the front pump on the late transmission. You will have to intigrate a linkage rod from the accelerator linkage to the tranmission. Some minor modifications to the transmission lines would be needed. Most but not all of the transmission/engine bolts will line up.

These problems are not insurmountable. I always thought this could be an interesting project. Keep us informed.



Joe Alexander
Blacklick, Ohio

[hands_aus]

I think too much fluid is as bad as too little fluid. You need to check the fluid level when the engine is hot. Also change the filter at the same time as changing the fluid.

If you have the Service manual on CD there is a section on these transmissions including diagnosis of faults.

There are two pressure switches on the transmission and also there is a modulating pressure valve which affect the smooth changing. If they are not working then you could have problems.

The Haynes manual has procedures to test these components of your transmission.

My auto was really hard shifting up but smooth shifting down.
I made sure the idle switch on the inlet manifold and the 3 position solenoid on the top of the transmission were working.
From there because I don't have the pressure gauge needed, I took it to the local MB service group and they adjusted the modulating pressure.
Now the transmission changes are hardly noticeable.

Bob (Brisbane,Australia)
RHD,1967 early 250 SL, auto