Tranny problems, later model 4 speed manual - PeachParts Mercedes-Benz Forum

junqueyardjim · #1 09-19-2011, 06:29 PM

Since I finished this swap this summer, in the course of normal driving I have noticed at times things are just not right in that gear box. I didn't get the shift fingers really aligned tell last week when I made that 6mm pin to get and hold them in the correct position for attaching the shift rods. So until I had that right, I felt the occasional slipping out of 1st gear was an adjustment problem. But now, all of a sudden the problem has grown, to where now if anything more then minimal throttle is given in first gear it looses it's "gearing" we might say, makes a grinding type of racket, and as soon as I get off the throttle it hooks back up and will throttle up if I don't over do it. This is in first gear only, although perhaps one time I had it in 2nd. The transmission does seem a bit noisy, but unless it has been rebuilt, has about 300,000 on it. Has anybody been really deep into the "one piece aluminum case 716.21 MANUAL. This transmission undoubtedly took an awful blow when the PO blew the 240D in front of it and it locked up at interstate speed - If I remember Nate said he was pushing it hard in 3rd, maybe 2nd on an on ramp and this thing locked up totally. Well we know that before one can get to the clutch this gear box really bought the load. Since this is a constant mesh transmission, would it be possible that this massive load on a well worn transmission took enough teeth off the shaft that it can't hold the load. Here is an exploded view of the box. This is from the Russian EPC. http://mb.ilcats.ru/part/class/1/ccode/F/cat/03G/type/716/subtype/210/group/26/subgr//vers//imgno/3 Anyone know of a mid western shop that will go through this. Also, could the cast iron 2 piece transmission be used in place of this one with a correct set of shift rods.

Stretch · #2 09-20-2011, 03:46 AM

Jim - I can't really help other than to say it might be worth while trying to get hold of a W123 Haynes diesel manual. There is a section in there for a manual transmission rebuild. It looks straightforward to me...

t walgamuth · #3 09-20-2011, 05:53 AM

I thought constant mesh trannies were mainly found in motorcycles. (I realize that is a minor point and not helpful).

I think popping out of gear often means the synchros are very worn. I have had this in the high gear. First does not seem a logical choice for synchro problems. I think second usually wears out first since it is used the most.

lutzTD · #4 09-20-2011, 09:57 AM

are you sure your rods are cut to a length to allow it to positively lock in gear? Also you had a thread on vibrations which in my case was attributed to a very worn transmission.

winmutt · #5 09-20-2011, 10:01 AM

AFAIK Syncros are only used during shifting.

Pull the first gear rod, manually shift it into first from below and see if that fixes the problem. Otherwise its time for a rebuild.

junqueyardjim · #6 09-20-2011, 10:50 AM

Thanks for the help guys! That is what keeps this Forum so wonderful. I do have my rods adjusted to perfection, I made the 6mm tool for aligning the fingers and have them set as perfect as I can. I will check that suggestion however, about placing it in first gear without the shifter and see what it does.

47dodge · #7 09-20-2011, 06:39 PM

yes syncros are only when shifting. If removing the shift rod does not help, then it is likely the nubs and ring that slide to engage first gear. Gear teeth themselves stay engaged all the time. Each gear has a section of what looks like gear teeth that are straight, and the brass part of the syncro fits into this. A ring with internal teeth slides over the the entire assembly, while still be engaged to the input shaft, which also has matching nubs/teeth. Its the nubs that get worn generally. Sorry no pictures, but hope this is well enough explained to make some sense.

Just be glad it is not in a tractor, then you have to split the tractor keeping both halves in alinement. Done it a few times.....