2-3 shift nonexistent
 

My brother's 85 300d will not shift into 3rd. Once it releases the pressure from 2nd the engine just revs. Even letting off the go peddle does not allow it to shift. It does nothing until you slow down enough to get it back into 2nd... Is the tranny toast, or is there hope of an adjustment? I have a replacement out of an earlier model, but thought the 85 model was supposed to be the berries.
BB

Sounds like toast to me. Better than sticking in low gear like mine did though!
Besides shifting mroe smoothly, the '85 is known for being less robust than earlier trans. And less common in wrecking yards.

You ought to find an '85 trans to swap o/w you may have to deal with the vac shift levels, they are modulated by the blue flying saucer thing on the fenderwell and are intended to work with the '85 transmission.
I've never heard of a swap in an '85 diesel to use an earlier trans but its possible I'm sure because I have a '79 300TD with an '85 turbo engine in it hooked to a 6 bolt trans out of a 116 chassis car. It required a different driveshaft and the trans tailpiece had to be modified to fit. There are lots of things that can be swapped in Mercedes as long as you have all the bits and pieces and some knowledge of what will fit and what won't. Hopefully someone here will know for certain what will work in your '85.
Shopforum member l3ushwig is just parting out a wagon BTW, an '85 I believe, maybe the trans is available? Search the Parts section and see.

What you could do is the standard trans-x treatment followed by a fluid & filter replacement and pray routine. It has worked for a few people. Could be a B2 piston or something like that, or a K1 spring. What I'm trying to say is if it happened suddenly then try and see if there isn't a more peaceable solution before you go trying to find another tranny, involving a procedure performed while the tranny is still in the car. You might get lucky.

what is the 1-2 shift like? Is it normal like always or is it delayed. Also does it go into neutral when it tries to shift or does it just not shift out of second?

Well...
 

It has been a while since I drove it... but I think that 1-2 shift is normal, then it goes into neutral (I guess). You can rev it up to redline with nothing happening, untill you slow back down and it shifts back into 1st.

The k-1 spring kit is cheap and easy to change. K-1 handles the 2 - 3 shift.
I'd change that and add Trans x to see if it helps before changing the transmission. Parts would cost less than $25 so if it doesn't help your not out much. I'm assuming that trans uses a K-1.