transmission problem B2 piston bore seal? - PeachParts Mercedes-Benz Forum

sebastw · #1 07-26-2011, 09:18 PM

My 300 SD Turbodiesel (w116, 1980) is currently grounded because of transmission problems. The car has 260 k miles on the clock.

Here is what happened:
- the transmission was flaring the past 5 months, the gears switched too early (only in L it switched correctly from 1st to 2nd).
- the rear gear engaged only after a couple of seconds
- past week the transmission only shifted into gears if I hit the accelerator very hard
- now the car is sitting in my driveway not shifting anymore at all

Here is what I did so far:
- changed the transmission filter and fluid
- changed the bushing in the rod from the selector to the transmission
- changed the modulator and adjusted it correctly
-> all this has no effect: transmission is not engaging

Now what I was thinking of doing next:
- replace the B2 piston bore seal (however the dieselgiant.com page only offers this for the w123/w126 but not for my w116, also peachparts.com doesn't have this part), so I have no idea where to get it and if this is even the solution
- the next thing would be to check if the transmission fluid is pumped through the cooler: any advice how to check this?

Any other suggestions?

Sebastian

Diesel911 · #2 07-26-2011, 10:10 PM

You might as well find and post the model number of your Transmission. It is supposed to be stamped on it somewhere.

On my later model the number is on the Passenger side above the Pan.

Stretch · #3 07-27-2011, 03:54 AM

My guess would be a 722.1 - possibly a .118 but I'll be interested to hear which model number you have so please go and check!

You say not shifting at all? No reverse? Check reverse that's important!

Get back to us and I'll look up some stuff for you.

rs899 · #4 07-27-2011, 06:49 AM

You have a 722.120 transmission. The 722.1xx series does not suffer from the B2 piston failure of the early 722.3xx. I would look into low working pressure. Remove one of the hoses from below the radiator, start the car and hope you make a mess....

sebastw · #5 07-28-2011, 11:24 PM

ok there is no pressure in the hose from / to the transmission radiator. That means the pump inside the transmission doesn't work. I only tried this in idle - now I think I should have pushed the throttle... to check if the pressure builds up... anyway I started already removing the transmission. So far only the hoses are removed.

If the pump inside the transmission doesn't work then this is most likely the reason why the gears won't engage.
The fluid itself looks brown although I changed it 2-3k miles ago (incl filter).

Any tricks I need to know for removing the transmission?

Seb

rs899 · #6 07-29-2011, 06:41 AM

Nothing special, really. The two top bolts are very hard to get to- probably best with some long sloppy extensions from way back on the transmission. You can remove the bellhousing when you have the tranny on the ground to keep from jacking the car up very high. You can drop it on a nest of cardboard boxes, then cut them away, one by one.

Stretch · #7 07-29-2011, 01:18 PM

To slacken the two big nuts on the prop shaft you need 41mm and a 46mm spanners. You can pick the bones of this out of this DIY

http://www.peachparts.com/Wikka/W123DriveShaftSupportBearing

Doing this makes it easier to get the front flex disc out.

Make sure you don't knacker the torque converter or the gearbox input shafts when you slide the gearbox away from the engine block.

When you remove the transmission the engine will be sitting on two mounts - don't let the engine move (too much) otherwise you'll be replacing then engine mounts too. Do not support the engine by jacking up against crankshaft pulley (at the front). Support the engine towards the transmission adapter joint.

Don't forget to separate the torque converter from the driven plate on the flywheel before you start to pull the gearbox!

I hope I'm not teaching you to suck eggs - good luck.

sebastw · #8 07-31-2011, 09:34 PM

ok - now all screws are removed from the transmission except the two upper screws that mount the transmission to the engine is there a trick how to do this?

One more question - how do I remove the pump for the transmission fluid. It seems that once the transmission is removed this pump is still mounted to the engine.

thnx
Sebastian

Stretch · #9 08-01-2011, 05:39 AM

Access to the top screw is tight. I've never done it that way but I've read that some people have managed with universal joints and extensions. May be tilt the engine and gear box to a more favourable angle but mind those engine mounts...

Pump - Are you talking about the torque converter or the front pump? It sounds like the torque converter - this is bolted to a metal plate that is attached to the flywheel. This plate is called the flex plate.

sebastw · #10 08-01-2011, 08:23 AM

ok - the symptons were as follows:
I disconnected the hoses to the transmission radiator to check if the transmission fluid is circulating through the radiator.

The result was: the fluid is not circulating.

My reasoning is that it must be something wrong with the pump - not sure where I have a front pump on my 300SD Turbodiesel.
So I guess the torque converter is somehow broken which is mounted directly to the engine but covered by the transmission.

Any thoughts how to fix this?

thnx

rs899 · #11 08-01-2011, 08:49 AM

The front pump is located inside the transmission, just behind the torque converter.

Stretch · #12 08-01-2011, 01:36 PM

Here's a pdf showing a break down of the transmission.

http://www.ganzeboom.net/images1/ganzeboom/parts/Mercedes/722.0,%20722.1,%20722.2.pdf

It isn't 100% fool proof but it shows the big bits and lots of the small ones too!

If you want to get to the front pump then you need to remove the torque converter. You will be able to see the front pump from here but you won't be able to get to it...

You then need to unbolt about 12 bolts to remove the front bell housing section of the transmission. Do not loose the shims that you'll find next to the front bearing. There are then 4 bolts to get to the front pump.

When you come to refit the front pump - look carefully at the way in which the holes and oil ways line up. It is possible to fit it incorrectly. Then it won't pump.

sebastw · #13 08-04-2011, 10:30 PM

ok - I have the transmission out - I actually disconnected the torque converter from "behind" meaning on the engine side - before taking out the transmission.

Attached are some pics.

If the torque converter is disconnected where is the front pump?

thnx

rs899 · #14 08-05-2011, 06:51 AM

Pull the TC out straight (you may have to turn it as you pull). You will see #11, the pump , in this diagram:

http://www.jie.com/Mercedes/4_bolt_pan.htm

Remove all the bolts that hold the bell housing to the back of the box and remove. On the back of the bell housing piece are the bolts that hold the pump to the bellhousing. Remove those then insert 2 longer ones of the same thread and push the pump out.

It's been 7 years since I did this , so I may be off a bit . Army or someone else who has done this recently needs to confirm this. Actually, looking 2 posts up, I think he did....

sebastw · #15 08-05-2011, 12:01 PM

Is there a way to test the front pump?

My plan is to use a "spare" transmission which I have from an other car.

Unfortunately I don't have much information on the spare transmission.
The transmission fluid looks ok in the spare transmission.

Sebastian