w123 transmission question
 

I need a new transmission soonish for my 1982 300TD. I've got a friend who has one he'll sell me for $100, he says it needs a new B-1 piston, which is about $150 for the kit, according to him. It's sitting on his garage floor.

Is the B-1 piston something not to terrible to replace on my own, and is it worth the risk? My transmission flares from 2-3rd gears, even with no vacuum, which according to the Monster Thread means that it's near the end of it's service life.

Is this kind of repair covered in the factory manual CD that I will be buying shortly?

The Factory CD manual has no Transmission repair info.

I would not count on what someone selling something has to say unless you have know them for a long time and know they have some mechanical expertness.

Look in the links below and see if there is info on the B1 piston.
On the other side of the Transmission is the B2 Piston. That Piston frequently binds up or breaks apart (this happen to me and it is on the passanger side of the Transmission, US models).
I was able to replace it myself.

The fact that the B2 Piston is the frequent cause of a problem makes me suspect that the Seller may not know what is wrong.
Ask the Seller what the symptoms were he was haveing. If it was not going into first Gear that is a typical B2 Piston symptom.

DIY Repair Links
http://www.peachparts.com/shopforum/diy-links-parts-category/

http://www.peachparts.com/Wikka/DoItYourSelf

Here is an article on adjusting the Transmission
http://www.continentalimports.com/ser_ic20242.html

There are also shift kits desgined to remove 1-2 flare. Search on Superior Shift kit.

He's a friend of a friend who loves these old Mercs, has quite a few of them that he wrenches on himself. The transmission worked when removed from the car that he converted to a manual gearbox, I'm going to chat with him tomorrow to find out how it behaved when it was removed, and to see what kind of condition the fluid is in. For $100 I'm thinking it might almost be worth the risk.

The thought is thus: my transmission works. It takes 2 seconds to shift into reverse, almost the same amount of time to shift into drive, it feels like it's either skipping 1st or in it for the briefest period of time. With no vacuum it only flares between 2-3, no problems going into fourth, and then clunks pretty loud on the downshift. With vacuum it flares 2-3 and 3-4 gears with the modulator going from 15-0, no leaks. I haven't done the k-1 spring kit yet or the b-2 kit on my own transmission which might fix the issue, and I haven't touched the vacuum adjustment on the transmission side yet either. The Monster Transmission thread consensus is that my transmission is nearing the end of it's service life, which is why I'm looking into a replacement before it fails. If I buy this one I can do the pistons and springs easily while it's out of the car before putting it in.

Am I a fool?

I had the below in my Notes:
Replacing the b1 piston
http://www.peachparts.com/shopforum/tech-help/131810-replacing-b1-piston.html#post962646