Harsh shifting - 280SE

[Nitz240D]

Hello All,

I haven't brought the 280SE (just recently purchased) down to my Mercedes Mechanic yet but I wanted to see if you guys had any input towards this problem. The car is beautiful, has 128K miles and is pretty much all original. The car drives nice, starts fine, etc. However the Trans. is a bit wierd. I have never owned a W108 chassis so I don't know if this is a common problem, just the way the trannys are or what.

The car drives almost like it's in L or S instead of D(rive). It holds the gears for what seems to me an abnormaly long time. I have the throttle down say 35% and it won't shift to 3rd gear untill like redline. 1-2nd shift is pretty good that shifts early, but the 2-3rd shift is delayed. Also it shifts quite hard. When I was driving in traffic, the car jerked pretty good when shifting up. And it would also downshift to 2nd at like 30-35mph out of nowhere - even when I was totaly off the throttle.

When I got the car home I checked the trans. fluid level but I am not sure if I am doing it right because there are like 4 different marks on the dipstick for different temps and the like. When I checked it, it looked like there might be too much fluid which I know is a bad thing, but I am not sure.

Any suggestions? Cables to adjust? Switches to check? Thanks in advance!

[Tom Hanson]

What year is the car? The early W108 280SE used the K4A025, which was a very rough shifting unit. The later version, K4C025 was somewhat smoother, but a dinosaur by today's standards.

[vickersw]

I am not sure about that transmission in specific, but most transmissions of that vintage had a modulator mounted on the side of the transmission. Its job was among other things to control the point where the transmission shifts. You should check the vacuum line leading to it on both ends of the line to make sure it is properly connected. Then, pull the vacuum line off from the modulator and see if any transmission fluid leaks out of the hole. If you see any anomaly, it's a quick replacement fix!

[ja17]

Hello,
If the transmission has a four bolt oil pan it is the later version. On this version vacuume to the modulator and a linkage rod control the shiftting points. As mentioned make sure that there are no vacuume leaks. The position of the linkage rod going to the transmission can will change the shift points. This is the easiest thing to check or adjust first. In addition the vacuume modulator unit itself could be defective or incorrectly adjusted. The modulator can be adjusted but normally is just replaced (fairly inexpensive). I would check the linkage first!

If the transmission pan has a sixteen bolt pan it is the early four speed automatic. This version has D 3 2 1 on the shift gate instead of D S L on the later three speed automatics (above). On this version there is no mechanical accelerator linkage going to the transmission, but rather a linkage rod controled electronically, by a three position solenoid on the transmission itself. This solenoid is activated by a switch on the intake venturi. If thethree position solenoid or its linkage rod is stuck the transmission will not shift properly. In addition if the venturi switch is not set up properly the downshifting will be very abrupt. These early automatics do have a vacuume modulator also, however the problem is usually at the three position solenoid or the venturi switch.
Find out what version you have first, so we can advise. The change was made in early 1969.

Joe Alexander

[wjaycox]

Your problem is most likely that you are not getting sufficent vacuum to the modulator pressure cell located on the right rear of your transmission. Check the connection point located on the rear of the intake manifold next to the firewall. This also supplies vacuum to door locks.Make sure that all hoses are on.
Without proper vacuum the trans will wind gears until the governor performs the shift. The modulator pressure softens and lowers the shift points and is regulated by vacuum resulting from throttle position. So you either have a leak or need a modulator adjustment.