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1983 300SD
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Discussion Starter #1
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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84 300SD (2 ea.), 98 E320 4matic Wagon, 51 Chev 1T pickup, assorted british motorcycles
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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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1983 300SD
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Discussion Starter #3
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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1983 300SD
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Discussion Starter #4
So, basically it's just three parts needed for the B2 piston replacement?

B2 piston

Bushing

Seal


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84 300SD (2 ea.), 98 E320 4matic Wagon, 51 Chev 1T pickup, assorted british motorcycles
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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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1983 300SD
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Discussion Starter #6
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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'84 500 SEC Euro 040 black Lorinser 2005 sl500
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84 300SD (2 ea.), 98 E320 4matic Wagon, 51 Chev 1T pickup, assorted british motorcycles
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OK, here's the B2 piston part number off my invoice. MBS1072700432 Price $141.75 as if 6/15/06. The part number may not be an MB no. It was sourced through Autosport Seattle ph. 206) 612-1940 if you want to call and ask who their supplier was.

Here's an instruction sheet from my computer files:

Note: the Baylor site referenced now returns a 404 error.

B2 Piston Failure in Mercedes-Benz 722.xxx Automatic Transmissions

Introduction

The technical material for this FAQ (Frequently Asked Question) was provided by Stu Ritter of Stu Ritter Mercedes-Benz Technician, Inc. of Denver, Colorado, was edited by Richard Easley of Baylor University, and is provided as a service to the subscribers of the Mercedes-Benz Discussion List.

To receive similar quality tips as described below on a daily basis, consider subscribing to the Mercedes-Benz Discussion List, which is located at the following site:

http://hsb.baylor.edu/html/easley/mercedes/welcome.html

The B2 Piston Problem

The B2 piston in specific transmission numbers within the 722.3/.4/.5 category of Mercedes-Benz automatic transmissions is a known problem part that is likely to catastrophically fail. There is an improved version of the part available as a replacement part from Mercedes-Benz parts departments . The B2's design was improved in the late 80s, so there are still a lot of MBs running around with the old-style B2. And, the addition of the "T" sealing ring purportedly did not occur until late 93/early 94. Check with your dealer for specifics for your particular Mercedes-Benz.

Specific modifications related to B2 pistons include:

1. The outer sealing ring was modified from a flat ring to a "T" ring ). [It is important to note that the important purpose for the improved "T" ring: there is more surface area to contact the outer bore, but even more importantly, the outer parts of the "T" seal effectively preclude piston-to-bore contact which could result in binding, not to mention wear of the outer bore's surface.]

2. The early style B2 piston's mold was changed to beef it up to reduce the potential for breakage.

3. The sleeve in which the B2 piston operates was changed from metal to plastic to reduce the possibility of binding (and it is imperative that this sleeve be changed.)

4. Finally, the release clearance specification for the B2 piston was changed by the factory to reduce delayed engagement complaints.

I would strongly recommend preventative maintenance on this item if you have one of the affected cars and that would be roughly any pre-94 MB for the "T" sealing ring and pre-87-89 for the sturdier B2 piston. Note that if you have a catastrophic failure with a B2 -- and you are away from your trusted shop -- it is very unlikely that a shop will replace the B2 piston alone, particularly if it is a non-MB transmission shop. Nonetheless, I would recommend that you at least print out this FAQ and keep it in your car. This way, if you haven't replaced the B2 and it fails, a shop might be more willing to do the replacement for you if it happens.

As an owner of a Mercedes-Benz with one of these transmissions, it is highly recommended that you replace this component as part of a preventative maintenance schedule. The part is reasonable in price (~$110.00 from MB) and the part can definitely leave you stranded if you are driving an automobile with an older-style B2 piston. Undoubtedly, many 722.3/.4/.5 transmissions have been rebuilt or replaced needlessly as a result of the catastrophic failure of this one critical component.

On the other hand, if you are a risk-taker, these pistons have been known to survive for years and years (mine had about 135K on it when it failed). So with this in mind, make your own personal risk-assessment and go from there. I like peace of mind and the general extreme reliability of Mercedes-Benz products, so I will automatically replace this known problem part on any subsequent Mercedes-Benz product in the future that is within the relevant range.


Assumptions

1. Using the categories of mechanical ability from the Mercedes-Benz Discussion List <http://hsb.baylor.edu/html/easley/mercedes/subscribe.html>, you need to be at the level of "Medium Do-It-Yourselfer" at minimum, to replace the B2 piston. If you are below that level, you may want to provide these instructions for someone who is at the medium level or beyond.
2. Please note, however, that is your transmission has suffered catastrophic failure (as indicated below), it would be beneficial to you to either 1) print this FAQ out and take it to a professional for analysis of B2 piston failure or 2) if you are comfortable with doing the removal of the piston (if you are at a medium DIY level or beyond), there is no additional "cost" is checking this component prior to a transmission rebuild or replacement. In other words, it would be advantageous to rule this problem out before spending major money on a (potentially) unneeded transmission rebuild or replacement.
3. A scrupulously clean transmission housing, including B2 piston cover, surrounding area including transmission tunnel, transmission pan, and work area should be evidenced before commencing B2 piston check and repairs. Automatic transmission repair work requires a level of cleanliness far beyond typical repair standards. For example, even a task as simple as checking the fluid level in an automatic transmission is best performed by wiping the dipstick clean with one's fingers and then wiping the fingers with a rag. This ensures that no lint enters the transmission.
4. The W126 chassis (S body) is the only affected chassis in the Mercedes-Benz line that will permit easy removal/replacement of the B2 piston with the transmission remaining in the vehicle. All other bodies: W107s (SL series), W124s (86-on 250Es, 300Es, 300Ds, 300TEs, 400Es, 500Es), W201s (190 series), and W123s require transmission removal for easy access to the B2 piston. Note that it may be possible to do the replacement with the transmission in the car (see the W107 replacement done by Barry Stark), but it will be difficult due to clearances.

Symptoms of B2 Piston Failure

1. Catastrophic failure of transmission in forward gears
2. Partial engagement of forward gears, with slippage progressively reduced as transmission is shifting from 1-2, 2-3, and 3-4.
3. Reverse gear engagement normal


Tools needed for checking B2 Piston

1. Professional-size floor jack (or lift)
2. 4 heavy-duty jack stands (or lift)
3. 10-15 shop rags
4. Small high power light
5. Assortment of flat-tipped screwdrivers
6. Prybar

Checking/Replacing B2 Piston

1. Jack up the car as high as safely possible for undercar-access.
2. Drain the transmission and torque converter, removing the transmission pan in the process.
3. Put gentle pressure on the rear transmission mount with a floor jack. Then, remove the four bolts that attach the rear transmission mount to the body. Slowly release the floor jack. The transmission should only drop about 1-2Lay a protective pan or sheet directly underneath the right side of the transmission toward the rear.
4. Locate the B2 piston cover [the second (rearmost) of two large circular covers on the right side of the transmission toward the rear].
5. Using a pry bar, push the rear of the transmission to the extreme left. This will enable you to shift the transmission to the left to gain greater access to the B2 piston cover.
6. While pushing the B2 piston cover in, remove the circular spring-type circlip that retains the B2 piston cover. [Note that the B2 piston cover has spring pressure behind it, but this tension can be held with your hand.]
7. After removal of the circlip, let the cover release gradually. You will need to have several shop rags handy, because you will lose some fluid in the process.
8. At this point, the B2 piston can be removed by disconnecting it by going up through the pan opening and removing it out the right side of the transmission. If it has already fallen out into your hands in several pieces, well, you know that you've found your problem.
9. A most important point: do not, repeat: do not, remove the very large "O"-ring that seals the B2 piston cover. It is near impossible to re-install on a transmission still located in the vehicle.
10. If your transmission has a metal sleeve for the B2 piston to slide in, replace it with the improved, plastic version that reduces the potential for binding.
11. Installation is reverse of the above, using extreme care and cleanliness in the work area and the transmission.
12. Replace transmission filter.
13. Clean transmission pan, ensuring that no lint remains in the pan before mounting to the transmission.
14. Using an inch-pounds torque wrench, torque transmission pan bolts to factory-specified settings.
15. Replace transmission fluid. [Checking the fluid level in an automatic transmission is best performed by wiping the dipstick clean with one's fingers and then wiping the fingers with a rag. This ensures that no lint enters the transmission.]
16. Note: Do not overfill transmission. Automatic transmission fluid expands when heated, so it is best to leave the level around a pint low until transmission is adequately warmed up.
17. Road test.

Finally

Please let me know if you complete this procedure successfully; it took a while to type this, and I'd appreciate knowing when each person has completed the repair! Please e-mail me at [email protected]

Note: To receive similar quality tips as described above on a daily basis, consider subscribing to the Mercedes-Benz Discussion List, which is located at the following site:

http://hsb.baylor.edu/html/easley/mercedes/welcome.html

Return to Mercedes-Benz Discussion List

Return to Richard Easley's Website
 

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84 300SD (2 ea.), 98 E320 4matic Wagon, 51 Chev 1T pickup, assorted british motorcycles
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A little more digging and I come up with the part no. for the nylon sleeve. it is: 126-277-08-50. Price - $7.26. The part no. I listed in the previous post is the MB part no. near as I can tell.
 

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1983 300SD
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Discussion Starter #13
Thanks Thomasa98 for this additional information. I'm going to work on the car today, see if the B2 piston is bad or not and will keep you all posted.


Thanks.
 

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1983 300SD
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Discussion Starter #14 (Edited)
Just an update! After the wrestling with the B2 piston for about 7hrs, I was able to get all the parts out. I know it takes about 1.5 hrs or so to do the whole thing but had so many issues getting the parts out.

First, The cover would not come off the b2 piston, was stuck and after applying brake cleaner multiple times it started to loosen up...once the piston was out I noticed there was good signs of wear, where it meest with the metal sleeve. It took about 1.5 hrs just to get the cover out and then piston came easily.

Second, the black seal was jammed in there and looked like as if someone welded that part to the transmission body. The outer side of the rubber seal was squished really bad and stuck to the transmission body. I tried several different tools and finally it came off (2 hrs spend on that)


Then, took a break!!!

Third, the metal sleeve would not want to come out, it would come all the way where the rubber seal use to be and then stuck, would not come out any further or go back to where it use to be, spend another 3 hrs and after couple hits with a small screw driver and hammer it came off.


Now, have to order the parts.


Thanks.
 

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1983 300SD
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Discussion Starter #15
Another update! Ordered the parts and was suppose to come in on Wednesday, but due to very bad weather and road conditions here it might be next week before I can get it.


We had record breaking snow in OK (14.5 inches) and the roads are really bad!
 

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1983 300SD
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Discussion Starter #16
Update! Finally the parts came in today...after waiting for an extra week due to bad weather....and more snow to come in tomorrow night into Wednesday. Anyways, I had a question about the rubber seal, which side goes in first or does it matter? The rubber seal sides look different and not sure if it matters which side goes in. Any pictures of the seal in the transmission will be greatly appreciated.


Thanks.
 

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'84 500 SEC Euro 040 black Lorinser 2005 sl500
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Update! Finally the parts came in today...after waiting for an extra week due to bad weather....and more snow to come in tomorrow night into Wednesday. Anyways, I had a question about the rubber seal, which side goes in first or does it matter? The rubber seal sides look different and not sure if it matters which side goes in. Any pictures of the seal in the transmission will be greatly appreciated.


Thanks.
The picture has already been listed here in post #7, 5th link. Open it up and you will see pictures of each stage of the replacement.
 

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1983 300SD
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Discussion Starter #19
Update! Installed the B2 piston, seals...etc today. I haven't test drove the vehicle yet. I also decided to do the diesel purge and completed that, replaced the fuel fiters started the car, heard a very strange noise under the air filter area. When I turned the car off I could hear the whining sound which slowed down and then stopped. The noise was not there when I did diesel purge!! Now, when I try to start the car all I can hear is a click, click, click...the car would not start. Any ideas, what could be the problem? Could it be that that starter made that strange sound at first and now it is dead?


Thanks
 

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84 300SD (2 ea.), 98 E320 4matic Wagon, 51 Chev 1T pickup, assorted british motorcycles
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It sounds like the starter drive failed to kick out of the flywheel when the engine RPM rose above starter RPM. If that happens and the overrunning clutch is seized for some reason the starter will turn fast enough to throw the windings off the armature. Frequently the armature will explode and have to be removed from the the field coils with a press. But because you heard it spinning after you shut the engine down I'd guess that the drive finally released from the flywheel and the armature still rotates. But it may have thrown the windings; in which case you'll have to get the armature rewound or get a reman starter. It's probably nothing you did with the purge, just coincidence.
 
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