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Old 12-16-2011, 02:37 PM
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93 300D B2 piston woes

Last week my 1st and 2nd gear began slipping, but 3rd, 4th and reverse work fine. This after having the tranny rebuilt nearly 2 years ago with 50 k on it since then. My hunch is the tranny shop, which specialized in MB and other foreign car trannys, who said they completely rebuilt it, didn't change the B2 out. Since then they've sold out and the warranty has expired, so I have no hope of getting them to honor the warranty. So after researching the infamous B2 piston change out and finding the links at mbz.org, diesel giant, and one other site, I managed to get the info needed to try this myself. Only I've hit a snag.

After removing the circlip and attempting to coax the aluminum cast cover off, it got stuck and pushed back against the piston and slightly past the orange o-ring. The notch for circlip removal is at the 7 oclock position, and as I pry against the edge of the cover to lift it out, the top side cants and moves into the bore. So I tried tapping the bottom end gently back in to make the edges equal and try it again, only it goes slightly further into the bore against the piston. The problem is I can't get anything into the top edge to hold against the cover to prevent it from canting back while I pry on the bottom edge of the cover, and I don't want to exert too much force and break something else in the process. I've tried dental picks, but they are too thin and don't give enough leverage to pry the cover out. I tried a small suction cup on the face of the cover in an attempt to put equal force on all edges and pull it out, but it won't hold a vacuum against the plate (made in china). I then tried a staple puller from the hardware store that has a 45 degree angle and a notched blade to gently pry the edge up,while simultaneously holding a thin flat bladed screw driver in the top edge to prevent it from canting but it didn't work. It feels like there is very little spring tension against the plate to make it want to come out.

I looked up through the valve body and can see what I think is the pin that pushes against the B2 band, but I cant see any part of the piston itself, nor is there room to push it out from behind to get it out.

I'd post pictures but don't have a camera. Has anybody else here gone through this process on a W124 series and had the same problem ? I've searched the forum and can only find references to w126 and w123 solutions. Granted they're not that different, but I found nothing like the problem I've encountered.

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Old 12-16-2011, 02:41 PM
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where are you located?
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Old 12-16-2011, 02:50 PM
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where are you located?
Dallas
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Old 12-16-2011, 03:00 PM
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Maybe gluing something on it to pull will help.
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Old 12-16-2011, 03:11 PM
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Are you doing this with the transmission in the car? Iirc that is tough with the tunnel width in the w124.
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Old 12-16-2011, 03:25 PM
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Originally Posted by tbomachines View Post
Are you doing this with the transmission in the car? Iirc that is tough with the tunnel width in the w124.
Actually it can be done. See here:

B2 Piston W124

I did exactly as outlined here and had no trouble, other than having to remove the front exhaust pipe and disconnect the center driveshaft support bearing to allow the tranny to move a little lower, then supported it with a jack.

After my initla posting I went back out and did succeed in getting the cover off, by gently prying with a flat blade screw driver and the brad puller. After coaxing back forth, I managed to get the 45 degree puller just under the edge of the top part of the cover, then pried against the bottom edge until both side worked out enough to be pulled out.

Now the bad news:

The B2 piston is fine and has the updated seal and nylon bushing, so now I'm back to square one in figuring out why my first and second gear are slipping and not engaging. There is a leak where the torque converter mates to the engine, and has been since just after the warranty offered by the tranny shop expired. They said it could be a bad front pump seal, but refused to make good on their warranty since it was 200 miles past the 12k warranty, and wanted another $800 to re-pull it and put another in. I said no thanks and left. Since then I just added fluid as needed, and when I went to check it before starting this tear-down, the dipstick showed the fluid down to the "add" mark. Could a pint of fluid loss be the culprit? It has never slipped on me before when it got that low, I just added and it ran fine.

Any thoughts appreciated.
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Old 12-16-2011, 03:34 PM
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That is good news! I'd recommend checking the b2 band itself for the friction material, see how worn it is. Also, fluid will typically cause slipping from a dead stop, but can certainly cause other problems as well. Did you check it warm and it was low or was it cold? Did your problems seem to go away as the transmission warmed up? That is usually a sign of fluid level issues.
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Old 12-16-2011, 03:54 PM
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I checked the fluid warm with the engine running, in park. Problem occurred as I was driving with a warm engine and tranny. How do I check the B2 band material? Do I need to pull the tranny and do a tear down, or would there be tell tale signs like debris in the pan? If it requires a tear down, I'm out of luck since I don;t have the skill or tools, so I'll have to find a competent shop locally. Thanks for the help.

ETA:

Just checked your blog and your post on June 19th describes whats happening to mine, at the last paragraph. The piston body is scratched around the circumference close to the head of the piston, where it slides through the bushing and seal, so I guess this is a potential cause?
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Old 12-16-2011, 04:08 PM
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It could be a cause, but the cover depressing and not offering any counterpressure is not a good sign. If you have taken the B2 out, check the outer nylon/teflon seal for any severe wear, as that would be indicative of running back and forth over deep scratches. Usually when it binds, its a function of the old steel bushing rubbing against the inner rod of the piston (where the dogbone connects). Since it is metal-on-metal, it eventually wears bad grooves into the piston. However, since you said you found the updated nylon bushing, I doubt that is the problem.

Yeah definitely check the pan for any friction material or metal shavings. If there is no "spring back" on the piston/dogbone connecter then that is not a good sign. The band should press back against it...not necessarily hard and with a lot of travel, but you should be able to tell that it has resistance. You can look up around the valvebody and see the band material...iits kind of tough but you should be able to see it. Keep in mind my transmission is 10 years older than yours, they had several updates in that time IIRC, so things like that may have changed, though the general design of the 722.x transmsisions is overall the same.
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Old 12-16-2011, 05:27 PM
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I found a few metal shavings/flakes in the b2 piston bore, and upon inspection of the drain pain I can see and feel small metallic shaving and flakes as well. Looks like the transmission is gone.

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