Transmission problem - '78 450SL - PeachParts Mercedes-Benz Forum

lrsharr · #1 04-20-2011, 12:24 PM

I have a problem with my 1978 450SL transmission. When cold, it won't go into reverse. Actually, I can feel it shifting into reverse, but the clutch/bands (?) won't engage. After the transmission warms up for 10-15 minutes idling or driving for 5-10 minutes, it will shift normally.
After going through the archives and reading prior posts, I'm assuming the problem is in the valve body (it's been parked winters for several years). It has acted this way for the 3 years since I bought it.
I have changed oil & filter and done the SeaFoam thing, also, after warming up the transmission, sat in the driveway exercising the shifter in an effort to flush the presumably stuck valve - all to no avail.
So, the questions are:
a. Is the valve body the likely culprit?
b. Is this accessible without removing the transmission?
c. Where the heck can I find a manual for this 722.1 transmission? I've hunted all over the internet, but to no avail.
Would appreciate any insights anyone might want to offer.
Thanks.
Larry Sharratt

loepke72 · #2 04-20-2011, 12:47 PM

I'm fairly certain you have the 722.0 transmission, not the 722.1. Either way, the only thing that applies in reverse is the reverse band, so about the only thing that can go wrong here is the reverse servo. Probably a hardened seal since it seems to work better when the transmission is hot. If that seal is hardened, count on all the other internal seals going bad soon if they haven't already. If that's the only thing you want to replace, I think it can be done without transmission removal. The reverse servo is the one closest to the front of the transmission.

As far as repair manuals, the only manual available for the 722.0 is the one published by MBUSA a long time ago. The 722.1/.2 had a manual published by ATSG, but it has been out of print for some time, but that is a different transmission because it is a four-speed unit whereas yours is a 3-speed. There is, however, a fair amount of parts interchange between the two units, but the gearset, clutch, and band applications are different. Search the vintage Mercedes forum; I had a thread about 722.0 overhaul about a year and a half ago. I never did the write-up since I didn't get the tramsmission working properly at the time. That transmission did work normally afterward, but at that time it was a few months later and now lives in a 76 450SL (the unit came from a 79 450SEL originally). I'll try to answer any other 722.0 questions to the best of my ability since there is such scant documentation on them these days.

rs899 · #3 04-20-2011, 12:56 PM

Did you try adjusting the reverse ( frontmost) band?

The adjusters on these frequently like to back out- I picked up a 240D auto cheaply a few years back that just needed a tweak.

Do a search on reverse band adjustment and look out for the 722.1s involved. You will find some ideas and pictures of how to do this.

Rick