Originally Posted by C32AMG

04-17-2004, 08:15 PM
C32AMG
Registered User Join Date: Mar 2004
Location: new york
Posts: 183

The primary pump, supplies pressurized fluid to the hydraulic circuit. This pressure applies bands, clutches and lubrication for all moving parts. The most hydraulic circuits are found in the valve body. As the fluid moves into the valve body it has the potential to actuate every single valve. When the valves move they redirect the pumps pressure to control the application of bands and clutches thus providing up and down shifts and different ratios through the planetary system. The pumps working pressure is always the highest pressure in the hydraulic system.

All other pressures are derived from this maximum pressure and is reduced and controlled by regulating valves. The primary control valve is the pressure regulator valve. Mercedes calls this valve the control valve working pressure. It controls and regulates the amount of working pressure in the transmission. This pressure varies depending on which way the valve moves. If the valve moves towards the spring, which sometimes breaks, we have low working pressure. If it does not move, or moves a little, we have high working pressure. There are other pressures that balance and regulate the pressure regulator but when we have 210 pounds of working pressure in a vehicle in drive, the problem is usually the pressure regulator.

The governor is the road speed input from the transmission. It has no regulating pressure from a stop and does not control a first gear start in any valve body. In a Mercedes first gear start valve body, the 1-2 command valve is stroked in the first gear start position; by design once the car is started, commanding the B2 band on and the F, one way clutch locked. If the valve body were a second gear start, then the one two command valve would be stroked in the 2nd gear start position commanding the B1 and B2 bands on.

The description of operation in that PDF is for a 1996 C22, which Is a 722.4 transmission that starts in second gear.

What they are referring to by the engagement dampening circuit, is the accumulator cutting in oil circuit wish is a dampening system designed to soften shift engagements from a dead stop (not at road speed):

The dampening circuit just cushions the selected gear engagement.

N to D = B1 and B2 = 2nd Gear
N to 3 = B1 and B2 = 2nd gear
N to 2 = K1 and b2 and f is locked = 1st gear
N to R = K2 and B3 = Reverse




In the neutral position there is no power flow between the engine and transmission, no bands or clutches are applied. This is also the towing and push start feature of the car.

By moving the transmission lever from neutral to drive at road speeds, you are going from a pressure less system (neutral) to a high pressure system (drive). At that high pressure you are probably freeing up whatever is stuck in the valve body.

I think the problem is in the valve body. If that car was at my shop I would change it.


In any 722.3-4-5 MB or Porsche 928 if you move the selector lever manually to second, the transmission will start in first gear. This is engine breaking. Try that as a test.




This is a foot note to my above post.


How a transmission shifts is based/ derived from a balance /unbalance of pressures


The main plays are

Governor, road speed input oil.
TV Bowden cable / rod, load input
Modulator pressure load and speed dependent.
Working pressure, pump

Shifts happen when governor pressure moves the shift / command valves in the valve body (control center) in opposition of TV, Bowden cable/ rod, control pressure, making the connection between main pressure and the appropriate band and clutch drums