Broadening proportional valve range - PeachParts Mercedes-Benz Forum

BoostnBenz · #1 03-28-2003, 09:57 AM

I'm having problems getting my proportional valve to cooperate, it started as 14 – 7, then I did the 10mm procedure the manual recommends which brought me to like 11- 5. What do I have to do to get 15-0? Is there anything other than a new valve?

On the modulator I keep hearing different things about which way to firm it up, is this because of different versions or what? CW is firmer correct (on a W123, white mod)?

Thanks in advance.

Diesel 924 · #2 03-28-2003, 12:15 PM

Quote:

Originally posted by mpnye
Try this:

(a) Tighten it until you break it off.

(b) Back it off 1-1/2 turns.

(c) Take it to a QUALIFIED TECHNICIAN so you can show him what you learned on the Internet and how much money you saved.

[Applause] And the award for lack of sensitivity towards a fellow MB enthusiast who desperately needs help goes to....[sound of envelope ripping]...MPNYE!! [mad applause] And now the award for being a flaming internet troll......[a hush descends]

#3 03-28-2003, 11:28 PM

I wish I could offer some good advice. Just
to clarify the proportioning valve is the white
plastic apparatus afixed to the injection pump,
and its purpose is to bleed off vacuum as
throttle position changes. I changed mine
to make sure this was not the problem.
I remember reading that 5.5 to 6.5 Hg was
preferable when the lever was 10mm from
the stop pin. At full throttle the lever should
nearly touch (.5 mm away) the stop pin. At
this point I think vacuum is supposed to be
completely bled off, but when I applied vacuum
it seemed to be slow to release. I can't help
but wonder if that charactaristic is normal.
I had more websites than I could handle when
doing a websearch on the subject. I take pride
in my 82' 300Sd and it will be the last automatic
Mercedes I buy (unless getting a steal) because
I do not have the brains to troubleshoot modulator/
vacuum parameters. Good luck, sorry in advance
if I have only stated the obvious.

BoostnBenz · #4 03-29-2003, 10:17 AM

I left it like the manual suggested for a short while, but I didn't care for the loud clunk and being jolted when downshifting gears. I re-adjusted it so it is approx. 13" - 6", now I only hear the clunk going into first, but the flaring got worse. Guess it is time for a new proportional valve. I'm now wondering, well if this part is scrap anyway, I'm going to take it to 6" - 0" or whatever it takes to get near zero then drill the opening in it to give it more vacuum. Vacuum pump may not appreciate this but it seems like that would work.

Mark, thanks for your reply, yea I knew most all of that. Given enough adjustments these trannies should be quite agile, but until then are quite a PITA. Right now mine has maybe one good trait, it can downshift on demand, but the harsh 1-2, flaring 2-3 & 3-4, and a clunking first gear kind of out weigh that. I'm thinking if I get the vacuum range opened up though it should help the cause greatly. My 84 can roast them in the 1-2, but otherwise is pretty decent.

#5 03-29-2003, 11:25 AM

Hopefully you get to read this before drilling. I do
remember reading that the vacuum bleed valve
is internally adjustable. I can't find the website
but I think the top will come off if the screw are
removed and a means of adjusting it might be
found. Just in case you want to do some more
reading first here are sites with in depth discussions:
www.mercedesdismantlers.com
www.continentalimports.com/ser_ic20242.html
or www.babcox.com/editorial/ic/ic20242.htm
If you need another valve in the event the operation
is not a success I have a few from the junkyard
I can send. (I'm out of town til 4-7) Hopefully
I said something you didn't already know.

BoostnBenz · #6 03-29-2003, 01:45 PM

Quote:

The proportioning valve adjustment allows the range of vacuum to be expanded. For example, a range of 10 in. to 0 in. could be expanded to 12 in. to 0 in. or 15 in. to 0 in. and, in some instances, raised above zero (such as 12 to 2). Generally speaking, a wider range is better, but older trannies with a lot of clutch wear often benefit from a reduced range. Worn clutches are more susceptible to shifts at low pressure. By adjusting to a smaller range and reducing the basic modulator pressure, a slow shift can be modified. Moving the vacuum range also has been of use to cover up valve body problems concerning shift spacing (for example an early shift into 2nd or 3rd).

The only adjustment I see is that little nut under the dome on the side of the valve. So the top of it can come off to, or were you thinking of the nut on the side? Hmm I didn't drill it, was going to open up the 'manifold' line from the pump to the booster and ended up snapping the fitting off, sigh. So I'm trying to get a temporary cobble for this right now, guess it is time for a new line there. Then hopefully later today I'll get back to adjusting this valve.

#7 03-29-2003, 05:37 PM

I found the site that explains how to adjust the valve.
http://transmission.articles.mbz.org/adjust/
I don't know anything other than this MIGHT
be useful info. This is what my previous statements
were based on, I have no firsthand knowledge.
My problem with the NEW transmission is slamming
into the next gear. I have turned the modulator
adjusting tee ccw until it barely fits back in the slot.
This helps a little, when I disconnect the cable (or
over slacken it) this shifts are smooth but it goes
through the gears immediately. There lies a balance
between the two undesireable behaviors, now
I let it upshift too quick since I figure it is better
for drivetrain wear. (Including the new trans)
I thought a new trans would solve my problems,
now it appears I need a vast knowledge of pnuematics,
unfortunately I do have the motivation/ability to
learn. I wish you good fortune with fixing the problem.