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  #1  
Old 06-24-2001, 02:48 PM
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Transmission shifting response vacuum span (Stevebfl are you out there)

I’ll try to keep this short…

If you check my other posting from today, you can see that I have been “dialing in” my transmission and have it working SO much better than when I bought the car, however there is some fine tuning that I would like to address.

The primary concern is that at any rate of acceleration, the shift from 2nd into 3rd gear seems a little softer than it should be for a MBZ transmission. (3rd to 4th is right on the money; firm but not jolting.) The other (minor) concern is that the shift from 1st into 2nd is still jusssst a tad to harsh at light throttle, but good & firm at both moderate & hard acceleration.

In a previous posting I found a reference to an internal adjustment on the vacuum valve (the calibrated leak point) on the injection pump. This adjustment apparently changes the span or range of the vacuum drop-off, independent of adjusting the length of the linkage rod to the valve. Could someone please explain how to adjust this function?

Please tell me if I am wrong on my approach here: I hypothesize that by increasing the range, the vacuum will be higher at the modulator during light throttle, which should soften the 1-2 shift at very light throttle acceleration. At more moderate rates of acceleration, if I tighten up the control pressure via the Bowden cable by maybe ½ to 1 turn beyond spec, this will help firm up the 2-3 shift, yet the 3-4 shift should not be that much harder because of the natural tendency to lift off the pedal as one reaches their intended speed and the resultant change in the vacuum signal received by the modulator via the increased span will keep the 3-4 shift from becoming too harsh.

Good lord, does that make any sense?

Thanks for all your help!


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  #2  
Old 06-24-2001, 03:29 PM
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Wow, yes it makes perfect sense. I think you actually understand at least one of the inter-related effects that can be mixed to fool the beast.

The adjustment of the proportioning valve is done at the end of the shaft that has the pivot arm. It is done on the other end. This end has a plastic cap over it on the outward side of the device (away from engine). The cover is about the diameter of a nickel. It will pull straight out with a firm grip.

NOTE: there are at least three different valves, only one is adjustable that I know of. On one the cap doesn't pull off (don't force it, it should be easy). On one, the nut on the end of the rod is crimped on and doesn't readily turn (I have not tried too hard as these are the way new valves come). The one that is adjustable will have two flats on the nut which will be 8mm apart (use an 8mm open end wrench).

The width of the vacuum range is different in each valve. Broad range can fix certain problems. On others a short range moved relative to the throttle is the best answer.

Unfortunately, it sounds like you have a 83 or earlier 300SD. The basic problem with that tranny was that they had too strong of a band application in second gear. The fix was a new band and a new servo piston which is also involved with the band going away in fourth gear. The servo piston can be changed externally and probably would help.

To a certain extent the shift overlap can be controlled by changing some springs in the valve body on the accumulator pistons. There is a company that makes a spring set with instructions for "calibrating" these shift irregularities. I have used it a few times. The real answer though is often to rebuild the tranny as there are so many improvements that can be made.
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  #3  
Old 06-24-2001, 07:06 PM
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Steve, Thank you for your reply. I feel like an idiot for not mentioning that it is actually a 1984 300D, produced in April (hopefully not on April fools day). I am proud to have actually figured this out to the point of earning (a little bit) of your respect. That means a lot to me considering the depth of your knowledge & experience. Seriously. (But enough brown nosing… )

I just looked, and lo and behold, mine has the removable cap and the slotted nut you described. Now I just need to know what to do with it. (Duh-uhh)

Is the adjustment accomplished via lateral movement of the cross shaft (‘tightness’ of the nut?), or is it done with the rotational relationship to the lever arm? If it is rotational, would this not be the same as adjusting the length of the linkage arm, or does the geometry of the linkage come into play? (Oh no, please stop me! I’m going theoretical again!) Anyways, if I back off the slotted nut, there is nothing to reference to or hold except for the lever arm on the engine side of the pump.

As you can tell, my earlier mechanical insight may have been of the idiot-savant type, and now I’m back to a room temp I.Q.

Thanks again!


P.S. Info on the car - It has 198,000 miles on it, was literally a one owner ‘grandma-mobile’, and was obviously meticulously maintained, although I don’t have the actual service records. The trans has a small leak most likely from the front pump seal, which indicates that the trans has not been rebuilt or resealed recently, if ever. However, it did have the green colored modulator on it (since replaced due to leakage). I am thinking that the relatively soft 2-3 shift may be due to seals not being up to par, and for about 10 milliseconds, I was tempted to use some ‘rebuild in a can’ just to clean things up & soften up the seals; however, I don’t want to tempt the fates; the trans is really O.K., I’m just being compulsive.
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  #4  
Old 06-24-2001, 08:58 PM
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The split nut one may not be adjustable. The adjustment is to tighten the nut on its shaft. This requires holding the lever on the reverse side.

Third gear is a clutch pack and the normal problem with 200k virgin trannies is the original loose clutch packs have grown more so. The seals are worn and hard, so they don't inflate as instantly and the clutch pack play which was set up too loosely on those models causes the drum to require more oil to apply. All this takes time. This time lag brings flaring or soft shifts
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  #5  
Old 06-24-2001, 09:57 PM
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Steve, Thank you again! This one is not a ‘split nut’. It is, as you described, a round nut with two flats on it, which are 8mm apart. I am assuming that you meant that tightening it would increase (widen) the vacuum span. Please tell me if I misinterpreted your reply.

The other thing that I would love your opinion of is the possible (temporary & Mickey Mouse) cure for the seals in the clutch pack. If I were to use a product such as ‘Trans X’ to soften the seals for a more effective hydraulic seal, is this one of those cases where the cure is worse than the disease? My thoughts are that IF the clutch pack is taking too much abuse in the form of slippage (although there is no sign of flaring, at least yet) what would be the lesser of two evils?

1. Allow the clutch pack to continue as it currently is (no “rebuild in a can”), and play with the vacuum span, control pressure, etc., etc. I have set the vacuum modulator to spec with gauges, so I am prone to leaving it alone, or at best, a very minor adjustment.

2. Use some “rebuild in a can” to soften the seals, and possibly even reduce leakage at the front pump seal as a bonus. The concern is that I have read in the past about these products making the seals leak even *worse* at a later date due to the softening agents.

Another alternative is to use the “crud” & drive around for maybe a couple hundred miles, then draining & replacing the fluid so that the seals are not *constantly* exposed to the softening agent, but perhaps long enough to do what’s needed.

I do recognize that I will need to rebuild the trans in the (near?) future; I am just trying to put it off until absolutely necessary.

Any thoughts on this? Once again, I really appreciate your help!

Thanks Again!
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  #6  
Old 06-24-2001, 10:35 PM
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I do not think that the additives will matter much one way or the other. I really don't think they will hurt.

I would do it. I also think that your condition can go on for ever. If you ever get to resealing the front pump, you should do the rest of the seals wear parts and the modifications.

Yes, the tightening of the screw should increase the range. It will only go so far and then it will move the range off zero vacuum. In other words if you have a range of 10inches to zero, as you change it somewhere after 15in to zero the range will lift to 18in to three. Actually a fifteen inch drop will probably be more than you can achieve.
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  #7  
Old 06-27-2001, 02:22 AM
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Steve, I hope that you see this posting, because I REALLY want to thank you for all your help!

Between the combination of your direct help, as well as researching your previous postings to others, I have this transmission shifting so well, it’s amazing.

For the record, I adjusted the vacuum span, increasing its range to the maximum that still allows the vacuum to go to zero at full throttle. On this car, it is 14.5’’ where previously it was set at just under 12’’. And it still is within specs at the 10mm distance from the stop. While making the vacuum span adjustment, it takes *very* little movement of the nut to make a significant change. I ended up moving the modulator only one castellation notch clockwise to firm things up a little. It was set to spec with a gauge last week, so I am particularly happy that it didn’t take much alteration to it’s setting. These two adjustments allowed me to set the Bowden cable exactly as it should be set, and the results are a real transformation - The trans behaves absolutely beautifully, without resorting to any “miracles in a can”.

Since it is working so well now that everything is very close to factory specs, I am hoping that this is indicative of the internals of the trans being in relatively good shape. I mean, if it took significant jury-rigging, I would still be more worried about the condition of the bands & clutch packs.

THANK YOU AGAIN!


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Old 06-27-2001, 03:21 AM
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Ahem, Uhh, NO. Leaning out the mixture will cause the combustion process to be hotter, which *encourages* the formation of NOx. IF, and I say IF your HC reading is *very* low, try RICHENING the mix a little. Your HC will go up, but the NOx will come down. Changing the oil will help a little, usually more with HC, but it’s worth a shot.

I don’t know about the Federal versions of the 1985 cars, so I can’t comment on whether it should have EGR or not, but it seems likely that it should. If it is a gray market car, it may have been mickey-moused. My Euro Rust Bucket V-8 had the frequency valve (part of the 02 sensor feedback loop) jury rigged into the control pressure line coming from the warm up regulator. An aftermarket mixture controller controlled it. This set up will work to some degree, at least in theory, but by controlling the center plunger pressure (via the control pressure line) it will not have as fast of a response as a system with the proper fuel distributor and pressure bleed point. Talk about Mickey-Moused, this was on a 1978 car which didn’t even need a 3 way catalyst!

You might try some of those “emission passer” snake oil gas additives – I’d be curious as to whether you get any results from those products. I would venture a guess that they are something to make the fuel more volatile and therefore more easily fully combustible. Who Knows. Not Me. I don’t know anything this late at night .
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  #9  
Old 06-27-2001, 03:25 AM
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Sleep Deprivation Rears Its Ugly Head

UH OH! Please disregard that last post. Sorry about the cross posting. I guess that’s what happens when you juggle to many open windows late at night.
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  #10  
Old 03-08-2010, 04:31 PM
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Bringing this one back from the dead.....

I tried to adjust the proportioning valve to get the 0hg at full throttle. When the valve is off and I am testing, I can get the 0hg at full open. When attached the best I can do is 4hg at full throttle. Would this mean that some adjustment would have to be done to the throttle linage just below to bring the proportioning valve to 0hg?

I hope that this makes sense and thanks for your help.


Quote:
Originally Posted by RunningTooHot View Post
Steve, I hope that you see this posting, because I REALLY want to thank you for all your help!

Between the combination of your direct help, as well as researching your previous postings to others, I have this transmission shifting so well, it’s amazing.

For the record, I adjusted the vacuum span, increasing its range to the maximum that still allows the vacuum to go to zero at full throttle. On this car, it is 14.5’’ where previously it was set at just under 12’’. And it still is within specs at the 10mm distance from the stop. While making the vacuum span adjustment, it takes *very* little movement of the nut to make a significant change. I ended up moving the modulator only one castellation notch clockwise to firm things up a little. It was set to spec with a gauge last week, so I am particularly happy that it didn’t take much alteration to it’s setting. These two adjustments allowed me to set the Bowden cable exactly as it should be set, and the results are a real transformation - The trans behaves absolutely beautifully, without resorting to any “miracles in a can”.

Since it is working so well now that everything is very close to factory specs, I am hoping that this is indicative of the internals of the trans being in relatively good shape. I mean, if it took significant jury-rigging, I would still be more worried about the condition of the bands & clutch packs.

THANK YOU AGAIN!
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  #11  
Old 03-29-2013, 10:53 AM
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Recycled

Quote:
Originally Posted by Koobos View Post
Bringing this one back from the dead.....

I tried to adjust the proportioning valve to get the 0hg at full throttle. When the valve is off and I am testing, I can get the 0hg at full open. When attached the best I can do is 4hg at full throttle. Would this mean that some adjustment would have to be done to the throttle linage just below to bring the proportioning valve to 0hg?

I hope that this makes sense and thanks for your help.
for me

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