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  #1  
Old 03-11-2012, 01:30 AM
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The flare to end all flares

Ok, so I have been trying to figure this out myself, but I'm tired of almost dying every day so I'm just gonna ask for help.

So my 84 300d (non-cali) tries to shift into second, regardless of throttle position, or vacuum, at around 1500 rpm. I don't know if that is where it is suppossed to do it, but it tries. What happens at this point, is that it just flares, and I am left in the middle of an intersection trying to get it into second. So it won't successfully shift until it drops back down to 2000rpm, and then it'll act all pissed that I am asking it to move, and stutter for a second, then it is in 2nd.

So Here is what I have done: I have tried everything with the bowden cable from all the way loose to tight, and everything in between. The vacuum line to the trans reads 13ish to 0 when at full throttle. I have tried everything from giving it no vacuum at all while driving, to full vacuum, and it has little percieveable difference to this part (the 1-2 shift) of the shifting curve. It happens regardless of the temperature of the trans, and doesn't get better or worse when hot/cold. I changed out the filter and used the recommended fluid as per this forum's suggestions, with no effect.

What should I do next about this? Is 1500rpm the normal shift point? Seems a little low to me, especially if I am flooring it.

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  #2  
Old 03-11-2012, 09:28 AM
Gene
 
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Do you have a bowden cable adjustment on yours?
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  #3  
Old 03-11-2012, 09:33 AM
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Have you replaced the transmission filter and changed the trans fluid?
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  #4  
Old 03-11-2012, 11:27 AM
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yes

I do have a bowden cable, and as I mentioned earlier, I tried adjustin it to both extremes, and everywhere in between, to no effect.

I also put int a new filter and new fluid about 4 months ago, (this started about a year ago), to no effect.
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  #5  
Old 03-11-2012, 12:09 PM
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If the Bowden cable adjustment has no effect and a vacuum adjustment (elimination) has no effect, and a transmission fluid and filter has no effect, you're done.

There is nothing further that you can do externally.
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  #6  
Old 03-11-2012, 01:25 PM
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Perhaps the bowden cable has broke or is not connected properly down below?

If you unplug the vacuum line to the transmission the shifts should be noticeably harder/firmer. Doing this will not effect the shifting point of the transmission.

If you still have flaring present, the next step is to replace the K1/K2 springs with springs from the Superior Shift Kit for 722 Diesels This helped my 2-3/3-4 shift flaring immensely.

I'd recommend putting the stiffest springs they have in the kit for your K1/K2. Its fairly easy to do and only requires you to drain and remove the pan.

The only other really serviceable thing that doesn't require major invasive surgery is the B2 piston. But I'm not sure if the B2 symptoms line up with what issue your having. I dont remember them off hand. I dont think I had to drop the pan to change the B2.. I could be wrong.
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  #7  
Old 03-11-2012, 01:42 PM
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Quote:
Originally Posted by JamesDean View Post

I'd recommend putting the stiffest springs they have in the kit for your K1/K2.
The information provided suggests no problem whatsoever with the K1/K2 accumulators.


Quote:
Originally Posted by JamesDean View Post

Its fairly easy to do and only requires you to drain and remove the pan.
Strike the word "only."
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  #8  
Old 03-11-2012, 05:21 PM
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Quote:
Originally Posted by tangofox007 View Post
The information provided suggests no problem whatsoever with the K1/K2 accumulators.

Strike the word "only."
I think OP has two problems, the flaring as well as the shift point problem. If the flaring goes away with disconnection of vacuum THEN suspect K1/K2 accumulator spring replacement. This was the case on my 300SD.

The fact that it doesn't shift until a specific RPM indicates something is wrong with his bowden cable. Either its broken or disconnected or the adjustment nut is broken and not adjusting properly.

The 560SEL had a similar problem this was fixed by adjusting the slide linkage for the cable.

OP said he removed vaccum but didn't indicate exactly how, disconnect the vac line to the modulator and test drive. There should be no flaring.

I said ONLY because its pretty straight forward, drop the pan and remove 4 screws on each compartment cover. You don't need to drop the valve body or transmission to replace the K1/K2 springs.

EDIT: Realized OP has a 300D not SD. B2 Might be more difficult in this case. Not sure.

There is only a few things that are moderately easy to service on the bottom of the transmission. K1. K2. B2 piston, filter,etc. When the B2 went on my 300SD, it wouldn't shift into second, it would just rev all over the place. Perhaps OP has the same problem?
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  #9  
Old 03-11-2012, 07:27 PM
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Quote:
Originally Posted by JamesDean View Post
I think OP has two problems, the flaring as well as the shift point problem. If the flaring goes away with disconnection of vacuum THEN suspect K1/K2 accumulator spring replacement.
I suspect that the K1 and K2 accumulators have nothing whatsoever to do with a flare in the 1-2 upshift.
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Last edited by tangofox007; 03-11-2012 at 08:36 PM.
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  #10  
Old 03-11-2012, 08:26 PM
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Woe is me

I assumed the vacuum thingamabob on the IP is what bleeds the vacuum from 13 down to 0 depencing on throttle position. I completely bypassed this, going straight to the black vacuum line which goes down to the tranny, giving it either full vacuum or none at all. This did have an effect on the rest of my shifts, but not the one I actually care about. Once again, I don't give a crap what my other shifts are at (I will eventually, but when you are stuck in the middle of an intersection, there is only ONE shift point you care about), flaring or rough, I just want to deal with the 1-2 shift.

I guess what I am trying to figure out is what is the first shift point suppossed to be at? I thought it wasn't based on RPM's per se, but on your current speed and the rpm's both. Mine will try to shift at exactly 1500, regardless, which invariably leaves me stranded until I can get into second, a "thrilling" experience to say the least. I have read about the B2 piston (or was it B1?) which when it fails, leaves you unable to go into first gear. I can go into first and second, it is just the transition (or lack thereof) that really bothers me.

So for those of you with working transmissions, when does your's shift into second? I just don't get why it would try to shift so darn early, at least a full 1000 rpms sooner than would seem to make sense to me (when flooring it).

Thank you all so much for your advice I really appreciate it. If I sound like an angry mean jerk, I assure you all of these emotions were meant to be directed at me almost dying several times a day, not ya'll.
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  #11  
Old 03-11-2012, 11:10 PM
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Adjusting the bowden cable only makes a difference if you have your foot on the gas pedal significantly. The section of cable between the white nut and the linkage (covered by a red 'ribbed' rubber sheathing) should not give much slack. If it's loose, it won't make a difference.

The pedal pulls the linkage, which pulls on the bowden cable, which adjusts the pressure tolerance in the transmission before it will shift. If adjusting the bowden cable to both extremes does nothing in terms of shifting later than 1500rpm (the white nut should be pulled out as far as possible to raise the RPM), then there's a chance it's broken on the other end, requiring the removal of the transmission pan to inspect. You can rule out the bowden cable by turning the white nut out all the way and seeing if your other gears shift really late or as quickly/near to 1500rpm. Your shifting should be more around 2500-3000RPM+ if the white nut is fully extended. If it's unique just to 1-2 then it's some other issue.

The K1/K2 have to do with 2-3 and 3-4 shifting. The B2 piston is 1-2 related. Unfortunately, the W123's have very little clearance underneath between the transmission and the chassis, so if there's any chance of changing the piston without removing the transmission, it will have to be lowered to do so (probably by unbolting the rear crossmember that holds the transmission mount). The W126's are much more accommodating in general.

The (infamous) B2 Piston
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  #12  
Old 03-11-2012, 11:49 PM
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Quote:
Originally Posted by tomas_maly View Post
The B2 piston is 1-2 related.
The B2 brake band might be related to the 1-2 shift, but it doesn't do anything (except remain engaged) during that shift. When upshifting, B2 disengagement does not occur until the 3-4 shift.
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  #13  
Old 03-12-2012, 12:00 AM
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does your model transmission even start out in 1st? are you maybe talking about the 2-3 shift?
either way, can you just put your shifter into L when you're at the intersection and upshift when you're on the other side? or, if you can, floor it so that the kickdown switch engages (make sure it's working, from your description it might not be) thereby forcing it into 1st and holding it there
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  #14  
Old 03-12-2012, 06:09 AM
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Quote:
Originally Posted by tangofox007 View Post
The B2 brake band might be related to the 1-2 shift, but it doesn't do anything (except remain engaged) during that shift.
When upshifting, B2 disengagement does not occur until the 3-4 shift.
Here's what the Mercedes transmission pdf I have says about shifting elements:


I was mistaken when I said K1 spring kit helped my 1-2 shift. It did but not nearly as much as a new B2 piston. Prior to the new B2 piston, the 1-2 shift had always been like a punch in the neck. Now its not even noticeable. So perhaps the B2 is a possible problem for the OP.

Some other info that might be helpful to OP:


To answer your question on when it should shift:

The pdf this came from is for the G-wagon, but it looks like all the transmissions should shift from 1-2 by 10kph.

From what I recall, the same is true for my 300SDs... From what I can recall, at partial throttle the shifting is RPM independent. This is from the 300GD (722.399)

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  #15  
Old 03-12-2012, 08:42 AM
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See these and see if the symptoms match up:
Yet another B2 piston question...

300SD Transmission Dead...

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82 300SD 145k
82 300SD 265k
87 420SEL 230k
89 420SEL 210k
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90 300SE 262k RIP 5/25/2010
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