what is the b-2 piston in the trans?
 

I have a trans leak in my '88 300E (160K miles). I did a SEARCH here and I read alot of people talking about the b-2 piston in the trans.

My mechanic thought my leak was the pan leaking but he later found out it was coming from somewhere else. He told me that there is a little piston behind the neutral safety switch that has an O-ring on it. He says the o-ring is worn and is leaking. He told me the only way to replace it is to drop the trans. He says it has to be done from the inside. I've only had the car for about 4 months and he told me that the P.O. must have had the leak and someone had tried to fix by "epoxying the crap out of it".

He called the local MB stealership and they said $2400 for a reman trans.

What are your comments on this? Is the piston he refers to, the B-2 piston? Sorry for my ignorance but I am learning quite a bit from you guys.

Thanks, fellas.

Sounds like the "reaction" valve o-ring. The B2 piston is on the other side of the transmission.

Your mechanic is right the only way to remove the B2 reaction valve is to remove the transmission, if it’s working properly then just seal it from the outside. Change the transmission when it really needs one

thanks again fellas.
 

This website is the greatest.

Trans. question for 84 300sd. Trans will not go into 4th gear.
 

84 300 sd with 180,000 miles, the trans will not shift into 4th gear. the trans has hard shifting the normal stuff with these old used cars. do you think i need a new trans or replace some thing like the b2 pistion? i am pretty mecanicaly inclined and could probally do a parts swap with little problems. any info on this problem would be appreicated greatly. WAH.