I am having trouble with my '81 300D 722.118 tranny that is peculiar. It works fine when cold, and for as long as I leave it in D while hot/running. But when hot, if I shift out of D or shut the car off I have major slipping in 1,2,3 (reverse works perfectly). I've found that when this occurs if I nurse it up to speed, as soon as it shifts into 4, all is well again. I can speed up and slow down with no slippage in any gear. Alternatively, if I let the car cool for an hour or so, all is well.

From the ATSG manual I know the B2 piston is 'engaged' for 1,2,3 and released for 4. I also know that the B2 piston has some sort of valve built in (but don't know what it's purpose is, or how to test it).

I removed the valve body and used compressed air to measure the B2 band free play. It was out of spec, so I purchased and installed a larger pressure pin (26mm ~$13). Now the free play is in spec. In order to install the pin, I had to partially remove the B2 piston. The B2 piston did not appear to be broken --- no metal pieces or broken plastic on valve.

I did notice something odd when I applied air pressure to engage B2 --- occasionally it would only partially engage, and air would come sputtering out through the hole used to dis-engage B2! This never happened when I used air pressure to dis-engage B2.

It didn't say in the manual what PSI should be used to engage and dis-engage, so I used several pressures between 60-80psi. It didn't seem to make any difference. Unsure of what was normal behavior for B2 piston/valve
I reinstalled the valve body, etc. and test drove the car. The problem still exists.

Now I'm suspicious that there is something wrong with the B2 piston and/or it's valve. Before I remove, inspect, repair/replace it I'd really like to know if I'm on the right track. I'm sure a new B2 piston is pricey, and I'd hate to replace it and still have the same problem.

David Howard