B2 piston repair questions - Mercedes-Benz Forum
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post #1 of 21 (permalink) Old 01-27-2011, 09:38 AM Thread Starter
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B2 piston repair questions

Hi,

I would like to know what all parts I need to order to fix the B2 piston. Th tranny is having hard shifts between 1 and 2, and hard down shift. I replaced the K1 and K2 springs didn't make much of a difference, but I think 2 to 3 and 3 to 4 is better now.


Thanks
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post #2 of 21 (permalink) Old 01-27-2011, 10:11 AM
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Having been through this set of problems I might be able to help. First, I think you are mistaking one problem for another. The K1 and 2 spring thing will cure the 2-3 shift flare and supposedly the harsh 1-2 shift, although in my case it didn't fix the 1-2- shift. So, that was a good thing to do; you probably didn't waste your time.

You still have harsh shifts, though. This probably relates to engine tuning as the throttle position, not engine load determines oil pressure at the time of a shift. As has been discussed time and again. Diesels have no manifold vacuum and turbos have pressure. So MB had to create synthetic vacuum to control the 722.3xx transmission that was used on the gassers and diesels. Aside from base case-pressure that affects all shifts, throttle position alone determines how hard it shifts at part throttle. If it shifts hard on wide open throttle then the case pressure may be too high.

So, if all part-throttle shifts are hard, that indicates that the engine is putting out less power than it did when the vacuum control was last adjusted. Low power has a raft of possible reasons: clogged fuel filters (there are 3), dirty injectors, low compression, poor fuel quality, incorrect injection timing, heavy engine load from A/C, high altitude for which the ALDA has not compensated, low turbo boost and the list goes on.

I would chase down engine performance issues first. If you want, you might replace the B-2 piston as a preventative measure. Buy the piston which comes with a bushing and a seal as I remember. You need to replace them both according to the instructions that come in the box.
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post #3 of 21 (permalink) Old 01-27-2011, 11:25 AM Thread Starter
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I have replaced the fuel filters recently and have noticed some minor leak around the fuel injectors and haven't messed with them yet. How do I check for the injection timing? I feel like the engine sometimes have good power and sometimes a little slow when driving, but now with the transmissions issues 1 and 2 hard shift and hard down shifts, feels like the car is not getting enough power. I changed the K1 and K2 springs, installed new bowden cable, new modulator, new transmission fluid, gasket and filter. I have been having problems with the modulator pressure too. I can set it to the right pressure, but when I slide the black cover back, the pressure drops instantly, when I take the cover off the pressure come backs to normal to were I had set it....very strange.

Also, another thing I noticed is that there is some oil residue coming out from the exhaust, this happens each time I accelerate the engine. Could it be the injection pump timing? How do I adjust or fix that?


Thanks.
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post #4 of 21 (permalink) Old 01-27-2011, 11:31 AM Thread Starter
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So, basically it's just three parts needed for the B2 piston replacement?

B2 piston

Bushing

Seal


Thanks
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post #5 of 21 (permalink) Old 01-27-2011, 05:47 PM
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Yes. Three parts as I remember. Don't pry the big o-ring out of the piston cover bore. The new piston design is much more robust. You'll immediately see the difference when you get the old one out. The old setup was a steel piston running on a steel bore and it tended to bind when it wore a little. The new setup is a steel piston running in a nylon bushing, which the instructons say you MUST change with the piston. Even if the new one binds I don't think it'll break. It might shift oddly, though. I could not get the bushing/sleeve out of the bore with the trans in the car. Nor could I get the seal out. Actually it was the seal issue that blocked the bushing change. I could have gotten the seal out but I could see no practical way of tapping or pressing the new one in. So I just replaced the piston. That was 60,000 miles ago and I've had no problems so far. If I pull the trans someday I'll replace the seal and bushing.

As to the modulator, why did you have to change it and the Bowden cable? Sounds like you have a pressure gauge. I have found that if you have the Bowden cable too tight the shift points are too high and it shifts hard both up and down. I had compensated for a tired engine by raising the shift points with the Bowden cable and had to put up with harsh downshifts; but I could soften the upshifts with the vacuum adjustment.

I don't remember about the modualtor cover. I vaguely remember something about a breather hole or a tight seal or something like that. Perhaps you should replace the cover. Can't cost much. Oh it's coming back to me. If the cover leaks it will shift poorly so you should probably should put on a new one just to be safe. I think case pressure is a bit of an art. If the trans is basically in good shape full-throttle shifts should be crisp regardless of the B. cable adjustment. So set the case pressure to get crisp but not harsh full-throttle shifts, then work on the bowden cable to get the shift points where you want them. Then, work on eingine tuning, get it right and finally adjust the vacuum bleed to get the shift quality you want. A little snappier shift is consistent with long band and clutch life.

All the while you should consider what transmission fluid you are using. If you use type F,(God forbid) it'll take your head off when it shifts. Straight Mobil 1 Mercon III spec will result in a little too soft a shift, I've found. It's a balancing act because of the differing friction materials they used on the various bands and clutches. 83 and earlier transmissions were notorious for a harsh 1-2 shift. If you set the vacuum bleed to soften this then the 3-4 shift was really soft. Not good for longevity. In 84 there was a running change to a better friction material for second gear. Being an 83 you have the earlier setup as do I on one car. The flulid formula that has worked for me is 1/2 Valvoline Max Life Mercon III and 1/2 Mobil 1. That strikes an acceptable compromise
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post #6 of 21 (permalink) Old 01-27-2011, 06:47 PM Thread Starter
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Do you have the parts numbers for the B2 piston items? I changed the modulator because it was not holding pressure and the bowden cable, the adjustment part was snapped. I used the Valvoline Mercon III fluid for the tranny.

The cap on the modulator is new too, so not sure why the pressure drops on the gauge right after I slide the cap on. I adjueted the pressure to like 42 or 48PSi and then with the cap on it drops to like 25 -30 PSI.


Also, do you have a good link or instructions on how replace b2 piston?

Thanks
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post #7 of 21 (permalink) Old 01-27-2011, 07:47 PM
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post #8 of 21 (permalink) Old 01-27-2011, 08:22 PM
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Great posts Thomasa98! Thanks!
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post #9 of 21 (permalink) Old 01-27-2011, 08:53 PM Thread Starter
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What's the exact torque specs for the transmission pan bolts?
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post #10 of 21 (permalink) Old 01-28-2011, 07:48 AM Thread Starter
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Has anyone used the OEQ brand B2 piston (brake band) W0133-1603886?
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