I have been struggling with the gearbox on my 928 GTS -93. The gear doesn't always change to a bigger one, but it feels like it stays in 2nd gear. Isn't that the normal starting gear? After a short stop, the gearbox returns to normal activities. I've tried to find out the amount of oil in the gearbox, but the oil level in that little jar varies illogically. Sometimes full, sometimes almost empty. Any help here? How to fix?

 

To figure out the trans fluid level run the engine for about 5 mins then check the level

lay on the ground and use a flashlight to see where the level is with the engine running
If it needs fluid then lift the car so it’s level and fill the tank with the engine running

 

The auto tranny requires a rather specific amount of ATF in the system to operate correctly. Too much in there and it will vent out of the breather in the top of the tanny casing and deposit ATF on the windscreen of the car behind. Too little ATF and at some point of depravation it will cease to operate correctly - If left long enough like that logically it will cause damage to the tranny.

The problem you experienced with the level is quite normal- The problem is that the torque converter is filled with ATF and sits at an invert level higher than the main body of the tranny. The system is configured such that the correct level is only seen in the reservoir when the car is is level, the ATF is fully warmed up and the engine is running. Then and only then can one be sure the level is correct and even evaluating that can be a bit tricky as visibility with the car on jack stands is not great- better to do this on an elevated platform if possible. When the ATF heats up its volume expands- there is a lower level marker on the reservoir that guides the approximate fill point when the tranny is cold but the upper mark when fuly warmed up is the reliable marker. When the egnine stops running the ATF contained in the torque converter flows back into the main body of the tranny and then one cannot see as level as the reservoir is fully flooded. Although the reservoir has what looks like a filling cap do not touch that thing or you may end up with ATF al over the deck when hot.

The return line from the ATF cooler has on the right hand side of the tranny, a filling device. This has a cap over it that has to be removed and then there is a quick fit connector that should be used to transfer ATF from a filling device. I canot rfemember the name for this type of connector but it is also easy enough to slip a piece of hose over it. I used a 10 litre pressurised garden spray bottle to transfer ATF via this connection. When adding ATF I know the cold amount my tranny needs, I simply add that amount and then run the motor for 5 minutes or so to warm up the ATF and then check the fully warmed level mark.

Generally speaking the MB 722.3 tranny is pretty good at holding its inventory but these things are now 30 plus years old and seals [both static and dynamic] eventually start to weep and ultimately fail. My 93 tranny was bone dry when checked a few weeks ago but doubtless something will start to leak sooner or later..

 

“ I can not remember the name for this type of connector but it is also easy enough to slip a piece of hose over it.”

 

The bowden cable may need adjustment (not sure if that is correct name) if fluid is good.

 

Could be insufficient vacuum to the vacuum modulator at the transmission? IE. broken or split hose from the engine.

 

Thank you for the comments. My conclusion is that there is too little ATF and too much does not cause problems to the car. So I drove to my man gave and lifted the car. The jar was totally empty! I added 1 liter to reach the max line. Started the engine for some 5 min and went through all gears. Now the ATF in the jar reached only to the 20C line, not more. I added another liter to reach the max again. Started the engine and went through the same procedure with the gears and now the ATF is between min&max. Now the gears change more smoothly while driving. I will do some more testing and possibly still add more. I have to find the courage to leave the engine running and make sure that there is ATF up to the max line.

This is my setup. I have a small 12V oil pump that pushed the ATF through the valve. The car behind is just a decoration here

 

Not familiar with that trans fluid-
It’s listed as Dextron II
I have always used Dextron III

 

A small update here. After filling that 2 liters of ATF, the gearbox has worked normally. The fluid level has also been checked after the engine has warmed up, and now it stays between min & max. It also seems that I got the radiator joint leak fixed, so the oil level in the system is better maintained.

 

Based on your response, you may not fully appreciate the nuance of this trans fluid level system for filling and checking.

NOTE to fill or top off the trans, you need the engine to be running as the filling process is being carried out.

NOTE from an empty system refill the pan via the tank or the fill port watching to when the tank is full,
then start the engine and run it till the tank is low, this will be the pump filling the system.
Then turn off the engine, this takes about 30 seconds.
Then go add more fluid.

Repeat this process till the tank level stays constant ,
you dont want to run the trans without fluid any longer than necessary,
as internal bushings and seals could be damaged.

Its OK to be afraid of the engine running while working under the car,
as the exhaust will be hot ,
so you have to be aware of that,
wear long sleeves and gloves.

NOTE shutting off the engine with the fill cap removed,
could cause the fluid to start overflowing the cap edge.
as the fluid will begin to drain back to the pan.

NOTE this can take a few minutes to start being evident.

 

Thanks for posting the picture of the Mobil ATF 220, I didn't know they made a Dexron II D formula. I try to use original manufacturer recommended stuff rather than the new and improved "one formula works for all" stuff. Mobil ATF 220 seems perfect.