Well that was a giant PITA, but worth it.This is on a 126, otherwise you have to drop the tranny. I'll try to rememember everything I did wrong to save somebody else the hassle. First off, find a better place to break down than a windswept parking lot at the beach where everything you drop has to be cleaned off. Then, if you are pretty sure it's the piston, don't be cheap and just change the fluid and filter, it really sucks to get it all reassembled, have it not work and then have to open it all back up again. Clean everything around the cover (pass. side near rear of tranny), and find the notch to pry out the snap ring. It's at about 4 o'clock position. Then jam a screwdriver into the slots around the cover to work it out of there. I took it out about 5 times, and sometimes it would fall right out and others it would wedge in there and need to get jammed all the way back in to restart. Be careful putting it in or you can pinch the orange O-ring and break it. (it's not as hard to put in the new as the articles said) When you pull out the piston, there's a connecting piece ( the dogbone, it's a little rod with round ends) that will fall out and lay in the opening where you can't see it. I didn't even know it was there and reassembled the original piston (which I think is what broke it, wasn't cracked like the picture shows at first) and didnt figure it out 'til installing the new piston!

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater

Then after you get the piston out you have to remove the bushing from the tranny, which was the hardest part physically, not much room and easy to drop pieces in the tranny. there's no way to grab it so you have to mercilessly pry it out without wedging the lever inside that it actuates. There's an outer seal that prys out first. Once I got that out I thought it was all downhill until putting the piston back in with the new bushing, when the dogbone fell into the tranny! This led to pulling the pan again, looking and looking and finding it on top of the filter, had to pull that to get it, just glad in didn't disappear in there! Then it's put the cover in (not pinching the o-ring this time) and the snap ring. This is leaving out the tedious details like the repetitive jacking the car, then jacking the tranny to pull the rear support, then rebolting it and lowering the car every time I took a break so as not to get a ticket for car maintainance in a city lot

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater

You can tell the new style piston by the way the teflon ring covers the whole edge, didn't get a picture of the new one, too gooped up by then.

piston and bushing-$126.00
o-ring -$5.60
filter kit -$22.00
fluid -$35.00

Maybe one day I'll find out what the little c-shaped pieces of metal in the pan that looked like broken pieces of a small spring are for:p

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater

Soy,
Very nice work! I'm glad it worked out for you.
Adam

Thanks Adam.

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater

Not to beat a dead horse but could you make a short list of your symptoms before the replacement and then maybe a short list of what got fixed?
Congrats bye the way...

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

It all started the Monday after Easter in the heavy stop and go traffic, the tranny started not engaging the low gears, pulled off and let it cool,gave up on getting home as the highway was empty the other way, and it was fine in the higher gears, but back on the surface streets every time I slowed down it wouldn't go without furiously reving it slipping along until it was fast enough to engage third. Over the next few days it got worse, I could reverse out of my parking spot 10 or 20 feet, but no fwd. If I reved up and down while going between 2 and 3 on the shifter it would bump forward 5 feet or so, then get pushed the rest of the way. Didn't think it was the pump or torque converter the way you could feel something happening in there, so I worked up through the cheapest fixes first, fluid and filter, then the B2. After all the days of working on it and getting nowhere, when I got the B2 in and rolled out out the space the feeling of putting it in drive and having it engage was an incredible relief, after only having the car 2 weeks the thought of putting a $1200 tranny in this $1400 beater was killing me. It seems fine now except for a harsh kickdown. Also midway through it started shooting fluid out the tailpipe, making me think it had blown some seal during the reving, turned out to be condensation from the starting and shutting off the engine cold mixing with soot and looking oily. Another huge relief that it wasn't the head gasket...

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater

I just changed the fluid and filter in the 81 SD and then took it to California where it decided (only after a hard freeway run) to stop using 1st gear unless I am really kind to the throttle.

Reverse does not engage very well either as it takes about two seconds to engage and then if you hit it hard it slips. After picking up speed in reverse when you back off the throttle it just freewheels until you use the brakes to slow it down.

Now in first from a light when it is really hot after the run it will engage 1st enough to get to 2nd then you cna punch it but I almost got crushed th first time as I was pulling in front of someone... go fiure.

After the car sits for maybe 10 minutes then 1st works like normal so I don't think I'm toast yet just getting there. I think I'll try the transX treatment first but if that doesn't do it then your solution is the one I'll need to persue.

Thanks for the writeup.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

I'm no expert but one of the B2 symptoms is no forward but normal reverse, so maybe something pump related? At least the B2 replacement is relatively cheap compared to some of the other options. You have the right body style for doing it somewhat easily...

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater

SoyMattDriver,

Did you have to do this down by the beach in Ventura? Its pretty windy down there at times.

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

After going through the same exercise as SoyDriver Matt did, I would add that that dogbone is a real PITA to get in place. I has loaded my 81SD on a trailor and had it in my clean and well lighted garage, so the job was easier, but the dogbone presented a problem to install.
I was able to fish it out when it dropped in there with a magnet. I called the trans shop and they said to use a dab of grease to get it to hold in place long enough to install on the end to the piston. That worked, but it was still an adventure.
When I had the B2B failure the symptoms were just as reported by Matt, would bump along when put into drive, but it degenerated to the point where it would not engage in drive at all before long. Reverse continued to work seemeingly unaffected.
I did replace the B2B, but by then the rest of the trans was toast. I drove it for another month and it let loose. Another trip home on the trailor and a trans replacement.

For Eric, no, this was in Santa Barbara, at the harbor. For Old Deis, your post helped a lot. the grease tip,and the pic of the new style piston, but I was wondering did you pull out the whole bushing? I ask because the new one on mine did fit flush down...
BTW, you can just call me Matt...

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater

Are you talking about the wide teflon bushing in the transmission? This was a year old rebuild and the teflon bushing was not damaged. I just replaced the B2B.
In my discusions with the trans rebuilders they said that flange in around the hole the B2B fits through is why they fail. The earlier versions were very narrow and the B2B would either leak or get jammed in there and not slide in and out as it is designed to do.

Yes, the bushing in the tranny, not the piston itself, but mine was so old it still had the metal bushing that has to be removed to put in the teflon one.

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater

bump

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'84 300SD veg-oil bliss
'83 300SD veg-oil beater