what makes one 722.3 different from another? - PeachParts Mercedes-Benz Forum

Stretch · #5 01-31-2012, 04:02 AM

Quote:

Originally Posted by sixto

What are the differences between 722.3s for different applications? Obvious to me are the bell housing bolt pattern and tail housing speedo drive. What other characteristics are or can be different?

1) Torque converter stall rpm. Any other TC differences within 722.3s? Multiplier ratios?

2) Vacuum modulator. What differs besides the color of the plastic case?

3) Valve body. Gear selection and shift timing based on selector position, modulator vacuum, control pressure input from engine throttle, centrifugal governor signal, kickdown switch signal, instantaneous gear setting. Oh, inane second gear start. Anything else?

4) Centrifugal governor. Is this what tells the transmission how high the engine can rev safely; i.e., when to downshift or else?

5) Secondary pump. Doesn't affect behavior.

Aside from interfaces and possibly beefier components, what is different between, say, a 722.370 (S500) and a 722.315 (123 300D)? Why can't Brian just swap a 722.321 (87 SDL) valve body into his 722.351 (300SEL) to have first gear start?

Thanks,
Sixto
87 300D

If you look in the ATSG manual (722.3 / 4) you can see that the vacuum modulators changed after 1981 - version A and B are shown. You are meant to upgrade to the latest version...

...on the same page (5) you can see that 722.310 transmission can have all of the colours available! .312 can have all but one colour (white) most transmission types listed by ATSG are either green or red - and many of them have been fitted with both green and red...

I get the impression from the ATSG manual that the colour of the vacuum dashpot is of little importance even though they have gone through to the trouble of listing virtually every type of transmission with virtually every colour produced. It is all very confusing.

Note also at the end of the ATSG manual the modulator brackets are different for the two types => page 107. Additional information concerning the modulators is conveniently hidden on page 119...

As for the governor I think this is the most important part of the transmission when it comes to shifting up or down. The governor is the mechanical / hydraulic brain that controls or manages the when to shift points in these transmissions - it is all calculated from road speed. (Thanks to Govert for sending me information about this - sorry it is in Dutch so it is of little use to most readers here)

The valve bodies are indeed complicated and the springs used within seem to have been changed quite a bit - see page 120 in the ATSG manual for example. Dieselkraut23 and whunter have been searching for part numbers - see

K2 part number for 722.3?

K2 spring kit MB part numbers needed

Differences highlighted in the ATSG manual include the TV plunger (whatever that is) see page 108; separator plate page 115; B1 piston page 116; and the lower valve body update information on page 120.

I have a gut feeling - and it is only a gut feeling that rather than changing the valve bodies more of a correct shifting effect would be gained by changing the governor. However, to be on the safe side matching both the governor and the valve body in the swap would probably be best.

EDIT:-

As far as I can tell from the ATSG manual, the gear ratios stayed constant between each type. I don't know for sure if that is the case - but I understand for top gear the output is usually 1:1 and only the final drive at the differential was changed for say a diesel powered vehicle and one with a big fat V8.