Just dreaming - 300D automatic gearbox replacements? - PeachParts Mercedes-Benz Forum

Stretch · #1 09-20-2010, 02:08 PM

Dear All,

The engine and gearbox (er sorry I mean automatic transmission) are currently out of my 1981 W123 300D.

I have read here that the automatic transmissions for 1981 in my car were particularly bad. I think it is a 722.1 (possibly 722.0 but probably not).

Reading through the FSM I see that 722.3, 722.4 and 722.5 transmissions are all covered by the same supplementary chapter 2702/1

Question 1:-

Am I correct in assuming that all of the 722.X transmissions will physically fit into the same place - and are therefore easily interchangeable without having to shorten prop shafts or put on new "bell housing" connector bits?

Question 2:-

Which of the 722.X transmissions is considered to be the best - and why?

Question 3:-

With my transmission currently out and on the bench what should I check before re-installing? I'm going to give it a new filter.

Question 4:-

I've been told that if the torque converter falls out too far from the end of the transmission (when moving it around) the shaft seal can easily get knackered. Which in turn can cause incorrect seating of the torque converter which will result in a collision with the pump behind. Anyone else ever heard of this?

As usual any help will be greatly appreciated!

panZZer · #2 09-20-2010, 04:07 PM

Me wondering too ,my 81 has a bowden cable.

aaa · #3 09-20-2010, 04:47 PM

722.x are not interchangeable. You can put a 722.3 from a 617 in though (there are also 722.3s from other engines that won't fit). Wonder if the neutral safety switch is the same...

my123ca · #4 09-20-2010, 06:35 PM

I dont know if the 722.5 tranny has a mounting for the starter of the 617. Mechanic said he 722.4 is longer than 722.3 but dont really know for sure.

ImBroke · #5 09-20-2010, 06:48 PM

722.4 is not longer than 722.3. The differences I saw were in the shifting linkages, NSS, and of course the filter/pan. This is why I had to use the .4 trans during my motor swap, when I really wanted to use the .3. Original car had the .4, so that's what I had to put back in. .4's are not particulary easy to find. Forgot to add the Bowden cable is different as well. $57 vice $18 for a .3.

panZZer · #6 09-20-2010, 08:18 PM

85 california is a 722.4

Stretch · #7 09-21-2010, 03:55 AM

Hmm thanks for the responses - so the short and sweet answer is to stick with what you've got then... isn't it always the way!

Stretch · #8 09-23-2010, 09:49 AM

I've just been cleaning everything up before I put it all back together again and I've taken a few pictures that may help others.

My transmission is actually a 722.1 - the identification numbers are stamped on the casing close to the oil pan.

I've also included a picture of the seal that I've been told to be careful of - just behind the torque converter.

rs899 · #9 09-23-2010, 11:34 AM

You might want to be sure that the reverse band adjustment bolt is secure ( it's in the extreme upper right hand corner of the second photo). If that backs out you will lose reverse.

If you really want to be safe, replace the torque converter seal and the huge o-ring around the front pump while you have it out.

Stretch · #10 01-04-2011, 04:03 AM

Ah ha - may be there is light at the end of the tunnel - a new thread has arrived with information that might be of use!

http://www.peachparts.com/shopforum/diesel-discussion/291397-there-differenc-transmissions-between-regular-300d-wagon-post2624617.html?posted=1#post2624617

Stretch · #11 06-11-2011, 12:53 PM

Like the title on the thread says

Just dreaming

What about a DSG gearbox as a replacement?

I fancy the idea.

There's a 7 speed light weight DSG that was introduced by VW in 2008 called the dq200. It is only suitable for low torque engines up to 250Nm - which suits even the OM617a

Here are some pictures I got from this pdf

http://www.volkswagenag.com/vwag/vwcorp/info_center/en/talks_and_presentations/2008/09/Sal__Oppenheim.-bin.acq/qual-BinaryStorageItem.Single.File/2008-09-03%20Sal%20Oppenheim%20engl.pdf

It looks nice doesn't it?

There are, however, two immediate problems with this dream:-

1) It is designed for transverse power trains
2) It needs an ECU to control it

But hey - it can't be that hard to solve those little problems can it?

Stretch · #12 06-11-2011, 01:54 PM

Here's a nice looking book on transmissions

http://www.amazon.co.uk/Automotive-Transmissions-Fundamentals-Selection-Application/dp/3642162134/ref=sr_1_3?ie=UTF8&qid=1307814542&sr=8-3

But for 153 GBP... well I'll see if I can get it through the local library...

And another one

http://www.amazon.co.uk/Control-Automotive-Applications-Advances-Industrial/dp/1849960674/ref=sr_1_15?ie=UTF8&qid=1307814542&sr=8-15

junqueyardjim · #13 06-11-2011, 03:06 PM

Army. have you considered putting in either a 4 or 5 speed stick in that car? You should have little trouble picking up the correct parts where you are.

Skippy · #14 06-11-2011, 03:40 PM

Quote:

Originally Posted by junqueyardjim

Army. have you considered putting in either a 4 or 5 speed stick in that car? You should have little trouble picking up the correct parts where you are.

You beat me to it. Or just buy a factory four or five speed car. I'm told they are reasonably common where the OP is.

Of course, I have a hatred of automatic transmissions that borders on the irrational.

Stretch · #15 06-11-2011, 03:51 PM

junqueyardjim and skippy - why oh why would you want to have to move a pedal and a stick every time you want to change gear? I don't get why you guys like manuals. Skippy we need to swap countries!