GregBBRD

Steve Cattaneo referenced a kit made by Mercedes to eliminate the secondary pump on the early 928 automatic transmissions, a couple of times.

Anyone have any idea what the part number for this kit is? Any further reference information? Instructions?

Mercedes parts guys look at me with a blank stare when I ask them about this.

Mongo

Greg... best I could find but no mention of a kit. Maybe other Mercedes forums?

http://www.peachparts.com/shopforum/...agnosis-2.html

Mongo

Here is an image to support it, but this is a reseal. At least it gives us an idea of what we would be looking at. I am not sure if this is the same transmission as the 928's though or if the 928 is a 722.3 derivative.

GregBBRD

More information:

The pump is present only so that the vehicle can be push started....not a super common thing with the 928 crowd.

The pump puts a tremendous additional load on the governor gear set (which is what drives the pump) and failures do occur.

Interestingly enough, the early 4 speeds had a spray tube to continuously spray transmission fluid onto this gear set, which got removed, at some point in time.

I had a failure of this gear set on a 1989 transmission (does not have the spray tube), with no obvious reason and desire to eliminate the secondary pump, completely.

Steve Cattaneo referenced the existence of a kit from Mercedes to accomplish this. I can find no other reference anywhere.

James Bailey

I thought that was the function...."push starting" recall it had to be pretty high speed to work. Quite a picture in my mind of an old ford truck rubbing up against the 928 rear bumper cover I could see pushing an old Mercedes Taxi .

GregBBRD

Very essential extra, in a 928, like I said.

Apparently 30mph gets it done, from what I can figure out.

Mongo

Just out of curiousity Greg, do you even know what happened to Steve Cattaneo? I remember him from a decade ago on here, and that's it.

Speedtoys

This must free up at least 40Hp.

Or add an inch to rear tyre contact patch too.

James Bailey

Much like our appendix ....... no useful purpose !

Speedtoys

That thread is pretty simple..just...remove gears and stuff, reseal.


A pumpendectomy.

Mongo

What is the whole purpose of this governor on the auto transmission? There is no speed limit on these cars to my knowledge. Does it have to do with protecting the transmission during shifts, like the transmission protection switch aside from push starts?

ammonman

From the "Automatic Transmission A28 Description of Operation" booklet: "Centrifugal Governor delivers hydraulic pressure, which has influence on up-shifts and downshifts in the valve body, in accordance with road speed." So it modulates a hydraulic pressure to the valve body that is proportional to the transmission output shaft RPM, thus inferring road speed in each gear. The valve body uses this signal along with the signal from the throttle pressure cable to determine when to shift up or down.

Mike

GregBBRD

They won't shift into 3rd or 4th gears without the governor.

GregBBRD

I think there are some changes that need to be made to the pressure section of the valve body, too.

Avar928

Greg, I didn't find the kit but check this for valve body adjustments:

https://rennlist.com/forums/928-foru...eed-928-a.html