I have a 722.3 transmission which I just installed into a 300SD. Won't go into all the details, but basically it doesn't shift into 4rth gear. This could be a modulator or a pressure issue within the trans. Yes I know that the correct vacuum needs to be present at the modulator valve and the vacuum pod needs to be set correctly, but to do this there needs to be some test equipment set up. I wondering if anybody on this forum has setup to test working pressure, and modulating pressure and what size banjo fittings where used ?

Yes, the topic has been covered extensively, even this month.
https://jenniskens.livedsl.nl/Technical/Tips/Files/Mercedes%20722.4%20adjustment%20guide.pdf

Vacuum doesn't affect shift timing
Bowden cable does, so adjust it first.
Check all pressures with harbor freight oil pressure kit ($30), car on jack stands, in drive, idling

1985 mercedes 300sd 722.3 transmission shifting problems

Did you check the kickdown switch under the accelerator pedal? They can go bad or get stuck preventing shift into 4th.

__________________
'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.

Thankyou Filp. I'm still researching the links you provided. WDBCB20 yes the kickdown switch was checked and appears to be operational.

Currently we checked first the vacuum. We found that both the vacuum amplifier/transducer on the driver side fender and another vacuum module secured to the radiator reservoir responsible for EGR operation where both leaking vacuum. These leaks where audible. Vacuum to the transmission module coming off the vacuum transducer was around 8 hg. Car was sluggish. Both parts where replaced with units from a donor at a junk yard. Both hold vacuum without much of a leak and there is now 15 hg of vacuum going to the transmission. Going on a test ride, the car takes off like a bat out of hell. Great pickup. Problem is it won't shift to 4rth.
Accelerated car to about 55 mph and was still in 3rd. When you let off the go pedal, it slows down (engine braking) just like that of a manual trans. This points to the K1 & K2 piston. Have a replacement piston kit on order and should be in shortly.
Thanks for the help so far. Will keep you posted and also to what the fix is.

Why not just put a couple of golf tees in the line to cut off the EGR? It is not needed and could help with your vac leak problem. Although I am really a purist and try to keep my '81 SD completely stock, I did this years ago and have never seen a problem from having no EGR.

Pic of mine showing one of two (as I remember) golf tees. The white one is easy to see; I think another is very dark at the bottom of the pic.

Attached Thumbnails

 

If it takes off like crazy it can also mean two things
1) Bowden cable too tight
2) Low ATF level

Check both

Please explain how either of these would affect acceleration.


"Takes off like crazy" sounds like a good thing, indicating that the engine is making good power. The transmission is designed to expect normal power from the engine, and when engine power is down, this can manifest as poor shifting, which causes the mechanic to try to diagnose a transmission problem when the real problem is with the engine.


Low ATF can cause problems with shifting into high gear, and may be part of the OPs problem, but I'd like to know why this would affect acceleration.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Are you serious?
Shifting to 3rd below 30mph would certainly affect acceleration

Maxbumpo (and I) are wondering how a tight Bowden cable or low ATF correlate to the car taking off quicker than before. Can you explain your reasoning?

+++

What does shifting into 3rd below 30 mph have to do with the OP’s post? Of course that would affect acceleration, but the OP describes the transmission as failing to shift up into 4th.

__________________
1983 300D Midnight Blue
4 speed, W115 intake mani, non-EGR exhaust mani, KKK K26, 3 pc Euro bumpers, Lo-spec Euro headlights, AL129X, hubcaps, custom A/C

1987 300TD Smoke Silver
Euro headlights, thermostat relocation, coolant bypass mod, rebuilt Becker + Jehnert + Helix audio, OEM Oris roof boxes and surfboard racks, Euro towbar

1983 300TD Reed (Moss) Green / Dark Olive MB Tex Euro spec

1983 300TD Silver Blue / Blue cloth Euro spec, OM648 and 722.6, 15" hubcaps, W126 S2 brakes

What would happen if the kick-down solenoid were to stick open or partly open ?

My experience is the reasoning, with two transmissions...with very low ATF they had erratic behavior as described, super quick acceleration, only 3 gears. I don't have the expertise to comment on inner workings of those. You can test my hypothesis the next time you change the fluids. Maybe my transmissions are worn. I'm no expert, just use my experience and the forum knowledge + ATSG

Ok fluid levels are fine to a-little above full line. So starvation is not an issue. Research indicates that this is probably a K1/K2 spring issue in the valve body. There is a very good write-up on the forum about this and locations for replacing these unit. I've ordered a kit from ebay and will be installing this in the next few days.
If that does not correct the problem, then I have a valve body from another 772.3 that came out of a completely working trans.
The reason for replacing these spring assemblies is that I want to know what is going on rather than just replacing parts (valve body) and not knowing why it's not up-shifting to 4rth gear.
Also I've got a gauge set on order and will post results after the kit arrives.

The K2 spring in the valve body just adjusts the smoothness of the shift, it is not what is actually shifting the trans.

Bad k2 clutch or dirty clogged valve body is what I would say is the more likely problem

__________________