Delete Secondary Pump?
#1
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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.
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.
#3
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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.
![](http://www.benzworld.org/forums/attachments/w126-s-se-sec-sel-sd/226458d1236481193-replacing-transmission-secondary-pump-seal-722.3xx-secondary-pump-removal.jpg)
#4
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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.
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.
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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 .
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#6
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Apparently 30mph gets it done, from what I can figure out.
#7
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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.
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Greg... best I could find but no mention of a kit. Maybe other Mercedes forums?
http://www.peachparts.com/shopforum/...agnosis-2.html
http://www.peachparts.com/shopforum/...agnosis-2.html
A pumpendectomy.
#11
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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?
#12
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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
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They won't shift into 3rd or 4th gears without the governor.
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Greg, I didn't find the kit but check this for valve body adjustments:
https://rennlist.com/forums/928-foru...eed-928-a.html
https://rennlist.com/forums/928-foru...eed-928-a.html