B2 Piston thrust pin

[Douglas]

I have replaced the B2 piston and new teflon and black seals on 1981 500SEL Euro Trans 722.302. The fix didn't work still no forward gears but reverse works fine. When I removed the old one it came out in pieces. Anyway my question is if I use a longer thrust pin (49.8 mm) to engage the B2 band will this fix the problem or is there something else it might be

[J. M. van Swaay]

There is a service bulletin from ATSG about delayed engagement of forward gears after replacing the B2 seals. If you installed the new style seal on an old style piston, this could be part of your problem.

If your gearbox is from 1981, chances are you have (or had) the old style B2 piston. Did you replace it with the new style? Did you install the new style B2 piston guide?

Do you have any engagement at all of forward gears?

I'm not sure if it's possible to install the B2 piston without a properly seated thrust pin...... If so, that might explain no engagement. I can't remember for sure, but I think it is possible to see the pin from below if you remove the filter from the valve body.

I'm not an expert, but I would think a longer thrust pin would only help solve a slipping problem

Do a search, there is a link to the ATSG document somewhere on this forum. When you find it check out page 109.


"I'm a hobbiest DIY mechanic, not a professional tech. Evaluate my comments accordingly..."


J. M. van Swaay

[Douglas]

I installed the new stlye piston, sleeve (guide) and black seal, I was able to verfiy that the pin was seated properly and still no forward gears. there is a thump like it goes into gear but no forward motion. I have read that document but will look at it again , if you can throw anymore light on the situation it would help
thanks
doug J

[J. M. van Swaay]

Don't know if I have any more light to shed, sounds like you've already considered everything I might think to suggest.

Only other thing would be if the B2 reaction valve pin somehow wasn't properly engaged. (or somehow fell out while the brake band lug wasn't being pushed against it during installation of the new piston)

Did you install the new piston and seals with the tranny still in the car? I would think getting the old lip seal and piston guide out would result in some movement of the B2 band. Maybe that allowed the reaction valve pin to disengage.

The possible reaction valve pin problem is a long shot but its the only other thing I can think of right now.

What were the symptoms that lead to the replacement of the B2 piston?


J. M. van Swaay

[richland007]

Mr Swaay you are exactly right i have the same symptoms on my w124 1991 300 D 2.5 Turbo Diesel project car the transmission was working flawlessly till one day in a cold run i stopped at the red light and no more forward movement since. I opened the tranny fluid pan (fluid was in very nice shape no weird colors or residue or metallic parts nor smell) and in it i found the dogbone reaction valve pin floating and the plastic seal that covers it broken. By reading through countless post here about the B2 piston and the brake band i am 100 % sure that this is the part that is causing my problem i went to MB dealership and ordered the plastic part, a rubber gasket/seal and the reaction valve from whole sale parts for $40 something dollars now how do you replace it is there a way to reaplace the reaction valve of the b2 piston without completely removing the transmission??? I know you can remove the actual B2 piston but how about getting to this reaction valve can you get to it though the B2 hole/?? from reading through the posts i understand that the brake band is in the middle and around the center of the transmission right?? and than this reaction valve on the driver side and the B2 on the passenger side. Can you get to the reaction valve from the driver side some how??? how about removing the 10 screws visible from underneath the transmission valve cover that sits in oil ?? if you remove those can this valve be accessed or not really?? please help if i can get this myself without dropping the whole transmission i might tackle it but if i have to remove the whole tranny than i will take it somewhere
thanks again for the help
denis

Originally Posted by J. M. van Swaay

Don't know if I have any more light to shed, sounds like you've already considered everything I might think to suggest.

Only other thing would be if the B2 reaction valve pin somehow wasn't properly engaged. (or somehow fell out while the brake band lug wasn't being pushed against it during installation of the new piston)

Did you install the new piston and seals with the tranny still in the car? I would think getting the old lip seal and piston guide out would result in some movement of the B2 band. Maybe that allowed the reaction valve pin to disengage.

The possible reaction valve pin problem is a long shot but its the only other thing I can think of right now.

What were the symptoms that lead to the replacement of the B2 piston?


J. M. van Swaay

[loepke72]

The B2 reaction piston installs from inside the case, so the transmission will have to be completely disassembled to replace it.

[richland007]

I opened my transmission and ther guy that is helping me says that i need a K2 drum the B1 band and a overhaulin kit for all the gaskets etc. does any one know of any affordable place to buy them on line?? 722.418 trans type
thank you
Denis

[loepke72]

Overhaul kits should be readily available from any transmission parts supplier. Why does the K2 drum need replacing? If it's due to an internal leak at the rear of the drum, that can be repaired with parts supplied with the rebuild kit. The symptom with that problem will be either no fourth gear or it will drop out of fourth. What you'll end up doing is drilling out three rivets then tapping the holes to receive machine screws. This will allow you to replace the leaking O-ring that normally would require replacing the K2 drum assembly. Bands (if they're actually needed) you should be able to get from the same place that you get the overhaul kit. Make sure to get the overhaul kit that has at least the new clutch friction discs included. Last one I did had a "Precision" brand kit with the repair kits for the K1 and K2 O-rings.

[richland007]

Thank you for your valuable input very much i appreciate it. He is telling me that the bearing is broken on the K2 drum and needs replacing but at the place he had looked they sell it with the drum for like $80 at the MB dealership is close to $400 i found the bearing only for $25. What does the drilling and tapping do in this process i didn't get that part?? I ll ma ke sure i ll get the clutch disk as well
thank you again
Denis

[loepke72]

The needle bearing (013 981 94 10) looks to be a separately replaceable part of the K2 drum. Probably a press fit that will require a bearing/bushing driver to install.

The drilling/tapping is to allow replacement of O-rings that tend to get hard and cause fluid leaks and consequent clutch apply problems. These O-rings are not normally serviceable because they are held in by a piece that is riveted to the clutch drum (either K1 or K2). Look at the inside of the clutch drum with the piston removed; there will be a round aluminum part with "MERCEDES-BENZ" and a part number cast into it; this part has the O-ring under it and is held in place by three rivets. If you have the parts included in your rebuild kit you just drill or grind out the rivets which allows the aluminum piece to be removed along with the O-ring. Then simply tap the holes in the clutch drum to accept the screws supplied with the rebuild kit. Use a large drill bit to provide a countersink in the aluminum piece so the screw heads sit flush. Then use Loctite or similar on the screw threads, assemble the aluminum piece and new O-ring, then tighten the screws. Cut or grind off the extra screw thread coming out of the other side of the clutch drum flush with the drum. It's actually easier than it sounds reading this.

[richland007]

Lopeke72 thank you very much for your valuable input the guy that was helping me fell through and no longer wants to look at the tranny for me do you know of anyone that can help me with it?? i am stuck with a broken transmission in my hands and it hurts me to see my car in pieces. i am good with little mechanics and interior and electronics but not with transmission and major engine work
thanks again
Denis

[loepke72]

Since you're local, you could bring the transmission by me. Sounds like it's disassembled right now, but I have done two of these recently and could put one back together if the parts were thrown in a box.