The flare to end all flares - Page 2 - PeachParts Mercedes-Benz Forum

tangofox007 · #16 03-12-2012, 10:33 AM

Quote:

Originally Posted by JamesDean

Here's what the Mercedes transmission pdf I have says about shifting elements:

As you can see, there is no change in B2 during the 1-2 shift.

Junkman · #17 03-12-2012, 10:41 AM

Where are you measuring vacuum? My 85SD runs ~18#, not 13#.

tangofox007 · #18 03-12-2012, 10:43 AM

Quote:

Originally Posted by Junkman

Where are you measuring vacuum? My 85SD runs ~18#, not 13#.

Where are you measuring? 18" Hg is way too high at the VCV.

JamesDean · #19 03-12-2012, 12:26 PM

Quote:

Originally Posted by tangofox007

As you can see, there is no change in B2 during the 1-2 shift.

What are you saying here?

From that chart I got that the B2 brake band is actuated during the 1-2 shift. Thus the B2 piston engages. So if the OP is having 1-2 shift problem the B2 piston could be at fault?

mikethezipper · #20 03-12-2012, 11:10 PM

So here I was telling you all that I tried doing everything to my bowden cable and it had no effect. Well I was wrong. I had it "adjusted" so that there was no slack at the zero throttle position.... but looks were decieving. Well, pretty much, the rubber boot on it was what was giving it slack. I not only backed it out until the white bolt wasn't showing, but almost all the way out of the black retaining nut... thing, and .... well I had no idea this car could move like that... well, move like that AFTER it got into second. This means that shifts which used to occur at around 2.5k rpm now happen at more like the 3-3.5rpm area, giving my car a much sprightlier constitution (and more crap out the tailpipe). It was just so loose that what I thought was too much when I backed out the nut was just taking up slack that I didn't know was there due to the boot.

What this means is that it won't do a darn thing until after the car gets to like 3-3.5k rpm, then it dramatically shifts into second, and I can move.

It would appear to me at this point that what I have is a B2 piston failure?? The reason I wasn't sure was because it does go forward.... or maybe the proper term is it "gently rolls" forward, up until it gets to like 5-10mph, at which point it flares like a maniac wildly trying to get into 2nd. Does this fit the description of a B2 piston failure???

Adjusting the Bowden cable only changed the rpms to which it flares until it will go into second, not when it starts to flare (as in it starts flaring at a similar speed/rpm)

Thoughts?

JamesDean · #21 03-14-2012, 02:56 AM

Sounds like it to me:

Quote:

Originally Posted by MBZ.org

The symptoms of a B2 piston failure are unmistakable:

-Fails without any warning whatsoever
-Slips out of gear in 1st with any load
-Massive flaring going into second
-3rd and 4th work normally
-Reverse works normally

The (infamous) B2 Piston

Part Number:
1072700432, also needs 1262770850 gasket.

Some info on doing it on a w123:
B2 Piston Replacement SUCCESS W123

tangofox007 · #22 03-14-2012, 10:17 AM

Quote:

Originally Posted by JamesDean

What are you saying here?

From that chart I got that the B2 brake band is actuated during the 1-2 shift. Thus the B2 piston engages. So if the OP is having 1-2 shift problem the B2 piston could be at fault?

What I am saying is that there is no change in B2 status during the 1-2 upshift. (The change is B1 engagement.) A B2 failure would affect all forward speeds except 4th.

JamesDean · #23 03-15-2012, 02:50 PM

Quote:

Originally Posted by mikethezipper

So here I was telling you all that I tried doing everything to my bowden cable and it had no effect. Well I was wrong. I had it "adjusted" so that there was no slack at the zero throttle position.... but looks were decieving. Well, pretty much, the rubber boot on it was what was giving it slack. I not only backed it out until the white bolt wasn't showing, but almost all the way out of the black retaining nut... thing, and .... well I had no idea this car could move like that... well, move like that AFTER it got into second. This means that shifts which used to occur at around 2.5k rpm now happen at more like the 3-3.5rpm area, giving my car a much sprightlier constitution (and more crap out the tailpipe). It was just so loose that what I thought was too much when I backed out the nut was just taking up slack that I didn't know was there due to the boot.

What this means is that it won't do a darn thing until after the car gets to like 3-3.5k rpm, then it dramatically shifts into second, and I can move.

It would appear to me at this point that what I have is a B2 piston failure?? The reason I wasn't sure was because it does go forward.... or maybe the proper term is it "gently rolls" forward, up until it gets to like 5-10mph, at which point it flares like a maniac wildly trying to get into 2nd. Does this fit the description of a B2 piston failure???

Adjusting the Bowden cable only changed the rpms to which it flares until it will go into second, not when it starts to flare (as in it starts flaring at a similar speed/rpm)

Thoughts?

See the troubleshooting section of this PDF:
http://w126.pp.ru/akp722.pdf

It might be helpful. I'd change the B2 piston, what have you got to lose? If it doesnt work out, tow it to a reputable place and have them look-see at it

JamesDean · #24 03-18-2012, 09:07 PM

Any updates to this thread? I'm curious to the results.

There was another member over on Benz World with a 722.409 that had similar issues and he replaced his B2 piston and machined a slightly longer thrust rod for it, that seemed to solve his problem.

mikethezipper · #25 03-27-2012, 12:28 AM

People, I am the happiest person ever. I almost couldn't be happier, except if I wasn't covered in ATF.

So based on the responses I got, I went ahead and dropped the transmission, and had one (#&$@^ of a time doing the whole job. Sure enough, the B2 piston was in 6+ pieces. It was an older style piston with the aluminum sleeve/bushing. I went ahead and replaced the bushing along with the piston, put in a new filter and drained the torque converter etc.

This is amazing. I never new that the car is actually supposed to go FORWARD when you push on the throttle.... All this time it just made a lot of noise and flopped about helplessly... but now... I literally feel like I bought a new car. I also learned a couple fun things: My flex disc is ready to go, and I have no shifter linkage bushings to speak of, which explains why shifting from R-N-D is so awkward.

I'd like to say that the right way to do it, is to also loosen the .. bearing??? (held on by two 13mm bolts) about a foot behind the flex disc, otherwise you won't get the transmission down far enough to do the trick. Also, others have said that you should get a pry bar in there and do it move it over, but for me it just centered itself after I let go. To remedy this, I made a wedge from a piece of 2x4 and I jammed that in there when I had it moved over. All in all, I found it pretty straightforward, well except getting that stupid bushing/sleeve out. That took more work than the other things. After spending several hours with a slide hammer, a pilot bearing puller, and screwdrivers, it was my finger that somehow, completely inexplicably, was able to pull it out.

Thank you all so much for your wisdom on this matter. Now that the transmission is running right, I now deem this car worthy for a real proper make-over. I can't wait to have to crawl back under there to replace the flex disc..... :/

JamesDean · #26 03-27-2012, 02:03 AM

Congrats! I remember when I changed my B2 and drive it. It felt quite rewarding. Good job!

SD300 · #27 03-27-2012, 03:32 AM

have u played with the modulator key yet?
is on driver side, crawl under neath, look for the plastic cap, pop the spring u should see a key in it ( it looks like a brand new uncut key ) u tune clockwise the trans would shift much firmer.
If u cant find that, it would be on right side near the end of the trans, a 17mm nut, u open init and see a big screw inside. turn clockwise would tighten the shift.
cheers