I am having trouble with my '81 300D 722.118 tranny that is peculiar. It works fine when cold, and for as long as I leave it in D while hot/running. But when hot, if I shift out of D or shut the car off I have major slipping in 1,2,3 (reverse works perfectly). I've found that when this occurs if I nurse it up to speed, as soon as it shifts into 4, all is well again. I can speed up and slow down with no slippage in any gear. Alternatively, if I let the car cool for an hour or so, all is well.

From the ATSG manual I know the B2 piston is 'engaged' for 1,2,3 and released for 4. I also know that the B2 piston has some sort of valve built in (but don't know what it's purpose is, or how to test it).

I removed the valve body and used compressed air to measure the B2 band free play. It was out of spec, so I purchased and installed a larger pressure pin (26mm ~$13). Now the free play is in spec. In order to install the pin, I had to partially remove the B2 piston. The B2 piston did not appear to be broken --- no metal pieces or broken plastic on valve.

I did notice something odd when I applied air pressure to engage B2 --- occasionally it would only partially engage, and air would come sputtering out through the hole used to dis-engage B2! This never happened when I used air pressure to dis-engage B2.

It didn't say in the manual what PSI should be used to engage and dis-engage, so I used several pressures between 60-80psi. It didn't seem to make any difference. Unsure of what was normal behavior for B2 piston/valve
I reinstalled the valve body, etc. and test drove the car. The problem still exists.

Now I'm suspicious that there is something wrong with the B2 piston and/or it's valve. Before I remove, inspect, repair/replace it I'd really like to know if I'm on the right track. I'm sure a new B2 piston is pricey, and I'd hate to replace it and still have the same problem.

David Howard

you're on the right track checking the B2, David. Seeing as how you pressurized the piston and you knew enough to check and adjust the B2 brake clearance, I expect you can handle the B2 piston just fine. Sometimes these crack, sometimes they get metal bits impregnated in the outer teflon ring and sometimes the smaller, aluminum body gets a groove worn into it. Plus, originally an 81 had an aluminum bushing pressed into the case that the aluminum diameter of the B2 piston rode on. Well, you can guess what happened to a lot of these. I had a trans that had a sticking B2 piston. It would hang up applying, but would always return. When I pulled the piston, there was a nasty groove worn in the aluminum body and the original aluminum bushing. They make a nylon replacement bushing that fixes that problem. You could probably smooth out the groove in the B2 piston if there was one.

BTW, where exactly do you apply air to activate the B2 band? Do you know the points to apply for the other band and clutches? I'm currently rebuilding and that info would really be handy.

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

OK, so I opened up the tranny, removed the valve body, removed the B2 servo cover, applied a bit of compressed air to the dis-engage port, and viola B2 piston is out.

I've attached some pictures to this post to show the state of the piston and cylinder (as well as good views of bands, pressure pins, etc).

The cylinder has a grove worn in it which is clearly visible.

The piston look OK, but it has a single split ring metal seal. I imagine it leaks like mad when it's aligned with the grove in the cylinder.

How the heck can this be repaired?!

What supposed genius designed this? The ring is obviously going to wear a grove in the aluminum, as it's a harder metal, and since it's split, as the grove gets deeper the more the piston will leak.

David Howard

Attached Thumbnails

         

I see you have a different trans than I thought you had, so sorry about my incorrect statements about it. I think you need to ask someone with expertise with this type. Is that split ring really metal, or a teflon seal that has metal dust impregnated in it? Reason I ask is I have seals that look that color, but they are actually teflon. There has to be something else there I would think. Just doesn't seem right that it would be made with just that split ring and ever seal.

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

The split ring is solid metal. It feels/appears to be of the hardened variety.
I agree, it seems like a ridiculous way to seal the piston. If it's not fully compressed it will always leak a bit, and as the cylinder wall wears it will leak more and more.

I'm wondering if they might make an oversized piston/ring and maybe I have to bore the cylinder out so it's smooth again. It's also possible that the cylinder wall is a pressed in sleeve, but I haven't looked at it closely enough to tell.

Either way, it would require removing the transmission from the vehicle to fix.

If neither of the above are options, I'd say this tranny has had it. No rebuild will fix this. I may have to start looking for a junk yard tranny which is is better shape .

P.S.
Interestingly the exploded parts view image of the 722.118 tranny I got from the MB part dept. looks very different from what I pulled out of my B2 (which matches the ATSG 722.1-722.2 manual). Maybe MB changed the servo assembly. I'll check with them tomorrow morning.

David

I'd be pretty surprised if MB DIDN"T change that servo at least once. They changed the B2 servo on the 722.3 at least twice. If that's really a hardened metal ring on an aluminum bore, you can bet teh farm that lots of other people have experienced this, and there are fixes available. However, I've been pretty frustrated myself trying to accumulate GOOD information about my trans. I hope you have better luck. You might try Doktor Bert, another member on this forum, as I do believe he has done work on a 722.118 trans.

I wonder too, if a thinwall, hardened steel sleeve could be pressed into that bore, and matched with a piston like the one on the 722.3 that has a wide, outer teflon ring. - But that's just speculation, and you need hard facts. Hope you find the right source. It's out there. You might also try one of the moderators of the tech forum, Steve Brotherton. He has a Euro transmission shop. Good luck!

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

No such luck. MB doesn't have an oversize ring. It's not a pressed in sleeve. MB has not altered the servo assembly.

I'm going to try a hone to remove the ridge, and hope that the leaky B2 piston ring gap isn't going to leak so much as to prevent it's operation. It's a long shot, but at this point what else can I do?

I'd really like to replace the ring with one that was oversize, and teflon, but I don't have a clue where to start looking for one.

Anyone know of a shop that makes one off rings to customer specifications (and doesn't cost an arm and a leg)?

David

I would hold off on trying to use a hone. I understand where you are coming from, but I still think it's worth it to be patient and try to find a better solution. It will be difficult to hone with the trans in the car and much more difficult to avoid contaminating the system with fine pieces of aluminum. I'd be willing to bet good money that this is not unique -keep seartching, and good luck!

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

hi I know that this is an 13 old tread, but I will try anyway
I am working on the transmission on my wifes new old 1982 W123 300D 968000Km on the clock

and now I have a question on the hole in the bottom of the B2 servo cylinder,
is there a small air outlet hole? and in the case what size, see enclosed picture
the picture is from this tread.
in the case of my wifes transmission there is just a 5mm hole, that I think has been drilled out on previous repair job.

Attached Thumbnails

 

The hole that you are referring to is called a "throttle bore" in the Factory Service Manual (FSM). Its function is to control the rate of apply of band B2 by limiting how fast oil can escape from behind piston B2. This would be noticeable on the 4-3 downshift. There is no size stated in the FSM. 5mm seems quite large however.

In my point of view it gives not really meaning. B2 servo is a double acting servo. And its quite soft spring is trying to engage the band, and in my point of view it need pressure on the inside to disengage see enclosed picture of release port.
If you see the picture from my first post then it clearly looks like there is bottom in the hole and not a full size hole like in my wife’s case.
It is my plan to weld up the hole and then re drill correct sized small hole. Just need to know the size if any hole at all.

The cylinder bore also have damage. It is my plan to machine to 90mm and then install a thin wall liner with 88mm bore

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__________________
Kind regards Anders J from Denmark
1982 W123 300D wifes summer car
1977 Yamaha FS1-DX
1978 Yamaha FS1-DX
1974 Garelli Katia 1974
1973 Tomos Cross 5 gear
1978 Honda CB 750 F2 supersport
1992 Kawasaki ZXR 750J
1984 Ford Escort Cabriolet 1.6I
1985 Ford Escort MK3 RS turbo
2019 Tesla Model 3 long range
Audi A2 3L 2002 with DPF
Audi A2 3L 2003 with DPF winter car

Have now worked a litle more on the transmission
I have machined the bore and installer a new cylinder sleve in the B2 servo
I machined the bore to 89,8mm and then made a sleve with a tight fit.
Now the bore is back to perfect shape again and the piston now moves freely again

Attached Thumbnails

         

__________________
Kind regards Anders J from Denmark
1982 W123 300D wifes summer car
1977 Yamaha FS1-DX
1978 Yamaha FS1-DX
1974 Garelli Katia 1974
1973 Tomos Cross 5 gear
1978 Honda CB 750 F2 supersport
1992 Kawasaki ZXR 750J
1984 Ford Escort Cabriolet 1.6I
1985 Ford Escort MK3 RS turbo
2019 Tesla Model 3 long range
Audi A2 3L 2002 with DPF
Audi A2 3L 2003 with DPF winter car

Have also closed the hole in the bottom of the B2 servo
The hole was drilled to 6mm
I made M8 tread in the hole and then machined a plug to fit the hole. This Way I Can also change it again if it should show to be wrong
Transmission assembled again and ready to install in car

Attached Thumbnails

       

__________________
Kind regards Anders J from Denmark
1982 W123 300D wifes summer car
1977 Yamaha FS1-DX
1978 Yamaha FS1-DX
1974 Garelli Katia 1974
1973 Tomos Cross 5 gear
1978 Honda CB 750 F2 supersport
1992 Kawasaki ZXR 750J
1984 Ford Escort Cabriolet 1.6I
1985 Ford Escort MK3 RS turbo
2019 Tesla Model 3 long range
Audi A2 3L 2002 with DPF
Audi A2 3L 2003 with DPF winter car