Crisis

The original 1990 tranny with PSD has had its pump explode. I have obtained a used 87 tranny with LSD. The original plan was to salvage the required parts from the 87 tranny to repair the 1990 one. However, this will be significantly more expensive than to simply swap out the 1990 tranny and replace it with the 87 tranny ( I am paying to have the work done). So my question is that, other than losing the advantage of PSD and living with LSD, is there any reason that I can't replace the PSD tranny with the LSD tranny? I just want to get the car back on the road again for summer, preferably at a reasonable cost.

Tails

My first impression is that this should be acceptable. The PSD is nearly totally independent, however it does take an input from the ABS and the "G" force box under the passenger seat. The indication of the PSD activation in the Digital Cluster is easily fixed by removal of the "light globe" and putting a circular sticker over the hole. All digital PCBs are built to take all the indication lights from the PSD, air bags etc., it is just that there is different models of the boards and they should be backwards compatible, so your K26 digital cluster PCBs should work satisfactorily.

If you have the electrical drawings for the MY87 and the MY90 you will be able to recognise the changes in the electrical circuitry.

The safety switch, gear indication, bowden cable and the vacuum line are the same IIRC. These auto boxes are 722-3 large pan boxes.

Before installation of the 87 box, it would be a good idea to check the adjustment of the brake bands and determine whether different length pins need to be fitted and the the box internals are in good condition.

I would also recommend that a filter, ATF and the pan gasket is renewed with the latest version. These parts are also available from Mercedes Benz.

After installation, the modulation valve will need to be adjusted, the gear selection matched up between the gear selection lever and the box lever/ safety switch and all the throttle cables, cruse control cables etc are adjusted to specifications.

Herman K

You have a PM

ammonman

If you remove the PSD pump system completely you will need to install a resistance jumper at the PSD lock solenoid connection to trick the PSD/ABS computer into thinking the PSD is still there if you want the ABS to work. The combined computer will see the lack of a PSD lock solenoid valve as a fault and disable the ABS system. A search will reveal the proper resistor rating.

Mike