722.120 Transmission Shaft Seals Not Replaceable Without Rebuilding Transmission?
 

My 1980 W116 300SD with 722.120 transmission appears to be leaking at the gear selector and Bowden rod shafts, as well as the piston covers. I am recently starting to lose quite a bit of fluid (puddles on the ground), which is disappointing because I replaced this transmission with one that was used, but rebuilt in the 1990s a little over 100,000 miles ago.

I planned on replacing the leaking seals at my next fluid and filter change. I took apart the original transmission to see how accessible everything is. But, it appears that the selector shaft clamp bolt can not be accessed, even with the valve body out. It appears that the rear casing has to be unbolted to reach it.
http://www.peachparts.com/shopforum/...n-dsc00526.jpg
http://www.peachparts.com/shopforum/...n-dsc00527.jpg

Then, the Bowden rod shaft cannot be removed because the gear set is blocking it. It appears impossible to replace the seals unless the transmission is taken completely apart. How frustrating!
http://www.peachparts.com/shopforum/...n-dsc00523.jpg
http://www.peachparts.com/shopforum/...n-dsc00524.jpg

I also tried pushing in the piston covers and removing the clips. It is a bit difficult, and I don't know what it is like with the transmission installed in the car. To make matters worse, the B1 piston cover is leaking the worst and seems to take extreme force to push in. I don't know if I will be able to change it.

It seems moronic that the selector and Bowden shaft seals would be designed such that they cannot be replaced unless the transmission is taken completely apart. It seems I am going to be forced to keep adding transmission fluid until it won't hold any at all, or rebuild the transmission just for the sake of 2 small O-rings!

I wonder if I should get the surfaces surgically clean, slide an O-ring of the appropriate size on each shaft, and then JB-Weld a washer over the O-ring with some pressure. If the JB-Weld holds, then it should hold the O-ring in place and seal out the leak. It's a bit of a rigged repair, but I guess it's better than rebuilding the transmission or constantly adding fluid and leaking all over the place.

SD:

The shift and control pressure shaft seals are installed from the outside, and hence, are removed from the outside. With a bit of cleverness, sharp tools, and excessive force the seals can be collapsed, bent, broken, and pried from the bores. Make sure you have the replacements in hand first.

(Unnecessary and self-serving note):
There ain't no such thing as a "Bowden Rod". The term Bowden is a proper name, and refers to the person and the subsequent company of the same name which invented and produced an enclosed cable of that name.
The rod in question is a "control pressure rod".

Yes a sharp ice pick type tool nailed into the face of the seal (metal ring) works great. Just bend it sideways after it is in the metal, and the seal should pop out. Another way: I once made a puller to pull a seal out of the front of an injection pump (VE). I drilled 2 small holes in the metal ring and larger holes in a washer about the same size. I screwed sheet metal screws into the metal ring and through the holes in the washer. I then used a 2 jaw puller to pull on the washer. It pulled the seal out with ease.

Have you guys done that particular job with out removing the connection for that blessed throttle linkage rod?

Here's the thing... the O-rings are made to be removed from the outside, BUT not with the shafts in place. With the shafts in place, there is not even enough room for a needle to fit in there. It is impossible to remove or fit the O-rings with the shafts in place. The O-ring on the control pressure rod shaft is not even visible.

It appears there is some sort of metal ring holding in the selector shaft O-ring, but I don't think it is intended to be removed, and the metal ring (or retainer) is probably obsolete.

I see no possible way of replacing the O-rings without taking the transmission entirely apart. The only thing I can think to do is fit some new O-rings on the shafts up against the case, and then JB-Weld some metal washers over them to hold the O-rings in place.

Is the B1 piston cover O-ring realistically able to be replaced with the transmission in the car? I tried removing the one on my original transmission, and I could not compress it enough with my hands. I imagine it is even tougher working with it bolted to the car.

I called it the Bowden rod because it's been a while since I have used the term and couldn't remember what it is called, and remember other members calling it such. But, I remember in the past that I used to call it the control pressure rod.

...Unless I'm missing something and the seal for the selector shaft isn't an O-ring, and the metal ring comes with the new seal.

But the O-ring for the control pressure rod shaft is not visible or at all accessible with the shaft in place. It does have a plastic washer that fits on the shaft, but plastic isn't any good for sealing. I could place an O-ring in the sunken area around where the shaft protrudes and have the plastic washer keep it in place, but I doubt the surface between the O-ring and case will seal.

Well, it seems very possible that the seal for the selector shaft is a lip seal, not an O-ring, and that the metal ring is part of the lip seal. So, in this case, I imagine the whole thing can somehow be pried out.

But, I still worry about the control pressure rod shaft seal. I think this is where I am having the biggest leak. But, EPC does not show any kind of seal for this part. But surely just a plastic washer can't do a full job of sealing. Unless there is somehow no fluid pressure in this area, and the wetness I am seeing is all from the B1 piston cover seal that is next to it.

I purchased a new ATSG service manual for the 722.1/722.2 transmissions to see if it helps me figure this out. I also ordered a whole bunch of new seals. I'm losing a quart per week and have a big puddle under my car. At least I can ride my bicycle to work if absolutely necessary.

Well, the service manual came, but it is of no help. It does not even acknowledge the existence of the shaft seals. Sigh.

I could have told you that but you'd already bought it so I was already too late.

The ATSG manual is a strange one for the 722.1 - if you insist on buying a manual go and get the German language FSM

I'm pretty sure you'd have to pull the front bell housing off the transmission to reach this modulating pressure control rod / throttle linkage control rod seal.

I did ask the others who have contributed to this thread if they have managed to get the job done with the rod in place.

The problem with removing the front bell housing is that you stand a chance (may be only a small one) that the gear set moves out of place. Ideally when building a 722.1 you start with the front bell housing part in place and then put in the gear set and then measure the clearance(s) and then put on the tail cone =>

http://www.peachparts.com/shopforum/diesel-discussion/304903-722-118-automatic-transmission-rebuild-monster-diy.html

Its technically called the Control Pressure Rod.

My is leaking too, one thing that the "re-builder" Also didn't replace, you can look through my posted thread. I have posted about the mysterious "rod" numerous time as Stretch was the only help but he also only knew so much. It was a totally learning experience but I am glad to report my transmission is finally fully working! Minus this seal leak, which can only be replaced with the trans out.

Here's the part of Stretch's thread that help me figure it out.

http://www.peachparts.com/shopforum/diesel-discussion/304903-722-118-automatic-transmission-rebuild-monster-diy-5.html

The transmission on my 79 450SEL is also leaking pretty badly - leak is coming from behind the neutral safety switch, so I bought a selector shaft seal and will attempt to change it next month. The seal is an MB original part and is a thin ring (30 mm OD) made out of black rubber with no metallic reinforcement or ring, so it may be held in place by either a circlip or the the safety switch itself - P/N is 115 997 074 0... I wonder what gives, because the seal in the below video appears quite wider and press fit.

Can anyone confirm that the selector shaft can be removed without removing, or lowering the transmission?

Also, this video applies to the newer 722.3 trannies, I hope it's a similar process for the removal in the 722.4 transmission on my car (although the oil pan is smaller and does not appear to give the necessary access to unbolt the selector shaft):
https://www.youtube.com/watch?v=KUzBeXCPPBI

I found a fix for the control pressure rod shaft seal without having to rebuild the transmission!

The leaking control pressure rod shaft seal is the one leak my car has had and it's been driving me crazy. Here is what the shaft looks like from the outside, with the lever removed from it:
https://lh3.googleusercontent.com/Ys...c=w800-h448-no

The seal is not located at the outside of the case, but rather it's on the shaft close to the inside of the case. In order to replace the seal, the shaft has to slide out from the inside of the transmission, but one of the drums is blocking it. I really dislike this design and want to change it. I thought about having the case bored so a lip seal could be installed on the outside of the case. But, this wouldn't work because the shaft steps down at the area where it would need to seal.

Then I had another thought--the lever welded to the shaft on the inside of the transmission is keyed, so if the weld was ground off, the lever could be removed and then the shaft could be drilled, threaded, and the lever made to be removable with a screw, allowing the shaft to be removed from the outside. I had envisioned removing the valve body on my transmission, taping a plastic bag around the area where I would need to grind off the welds to prevent contaminating the transmission with metal particles, and then doing the modification so I could replace the seal without taking apart the transmission. But, there is just not enough room to reach a tool in there. Oh, well. I still might do it when it comes time to rebuild the transmission.
https://lh3.googleusercontent.com/32...E=w800-h448-no

In the past I had attempted to stop the leak by putting an O-ring on the shaft, sliding it up against the case, and then letting the force of the nylon washer and the spring washer push against it. It did not work. But, I tried it again using a thicker Viton O-ring, size 8mmIDX12mmOD.
https://lh3.googleusercontent.com/XK...k=w800-h453-no

I put the nylon washer and spring washer and clip in place against the O-ring, and though it felt like they were pressing hard against it, I noticed the nylon washer was deforming at the open end of the clip. So, I replaced it with a steel washer from a flex disc bolt of similar dimensions (11mmIDX18mmODX1.5mmT)--I think the nylon washer had a 10mm inner diameter, though.
https://lh3.googleusercontent.com/9Q...0=w800-h453-no

It was a bit difficult to get the spring washer and clip on after the O-ring and steel washer, but it was putting firm pressure against the O-ring.
https://lh3.googleusercontent.com/H0...s=w800-h453-no

It actually worked! Ever since I shoved an O-ring of the proper size in there, it hasn't leaked at all. Now I can have a spot-free driveway without having to rebuild the transmission.
https://lh3.googleusercontent.com/ps...Q=w800-h453-no

To see exactly where this seal is, look at this picture from Stretch's 722.118 automatic transmission rebuild thread: http://www.peachparts.com/shopforum/diesel-discussion/304903-722-118-automatic-transmission-rebuild-monster-diy-5.html#72
http://www.peachparts.com/shopforum/...2-seal-rod.jpg

Unfortunately, a leak had also developed at the selector shaft seal. But, this seal is located on the outside of the case. Unfortunately, the proper way to replace the seal is to remove the entire rear cone of the transmission so the shaft can be unclamped and then slid out of the case.

I had a new selector shaft seal which I purchased four years ago and didn't install because it wasn't needed at the time. I decided that I didn't want to remove the tail cone of the transmission in order to replace the selector shaft seal, and since the seal is on the outside of the case, I took a small flat blade screwdriver and tapped it into the seal so I could remove the seal.

After much work, the seal came out, but to my horror the selector shaft was very deeply gouged all over the seal surface from tapping in the screwdriver. I was in disbelief and wish I wouldn't have messed with it, as now not only would I have to take off the tail cone anyway, but I'd have to get a new selector shaft on top of more seals and gaskets.

I had planned on having to buy the parts (with money I don't have) and go through the whole process, but in order to keep contaminants out of the transmission, I put a little sealant on the outside of the seal and then tried to push it over the shaft, but there is a sharp lip that makes it very difficult to do, which is yet another reason why the shaft is supposed to be removed when the seal is installed. I tried to tap it in place, but it wasn't going in straight.

I pulled the seal back out (and scratched the steel outer diameter in the process), but went too far and it came off the shaft, when I noticed that the sharp edges of the shaft had cut the seal. I applied more sealant to the outer diameter, forced the seal back on and tried to tap it in again. It was going in crooked, but I didn't care. I just kept tapping it into place and denting it in the process. Then I installed the neutral safety switch and selector shaft rod.

The next day I went out to the car and looked under it, hoping it wasn't leaking too much. To my surprise it was completely dry. There was no leak anymore! Somehow the seal must have contacted a very small part of the shaft where it wasn't gouged, and there must be enough pressure against the seal that the cut isn't leaking. What a relief! I still eventually want to fix it correctly, but that can wait. It is so wonderful having a transmission that doesn't leak!
https://lh3.googleusercontent.com/1p...o=w800-h453-no

My car doesn't leak on the driveway anymore! Yay!
https://lh3.googleusercontent.com/o3...M=w800-h453-no

Lesson learned on the selector shaft seal; don't attempt to do it any other way than by taking off the rear section of the transmission and removing the selector shaft first!