Check valve at brake booster line 1985 300D - PeachParts Mercedes-Benz Forum

mrskemp · #1 02-13-2011, 10:11 AM

hi everyone,

this is my first post. and it is going to be a long one. i have searched high and low for this answer, hopefully someone here can help me.

background:
i just purchased a 1985 300D, and as part of getting to know this beautiful car, i am going through normal maintenance procedures that i know the previous owner never did.

so, like everyone else, i found a few vacuum issues. first, i discovered leaks in my climate control. chased it to a leaky switchover valve, and a leaky defroster flap pod thingie. no problem, i isolated them and then my car shut off nice and quick and my door locks even work a few days after shutting off car. sweet.

next up was trying to work through wonky shifting problems. searching revealed that to start with, make sure vacuum is good. so, first i cleaned the alda banjo on the manifold, then i put on a vacuum gauge to the line to the transmission just to see that it was being supplied with proper vaccum, but then all hell broke loose, proper vacuum was not showing up anywhere. not even where i had just worked it out. car won't shut off, door locks don't work. uggh.

anyway, after two maddening days that had me checking everything six times over with crazy discrepancies in vacuum everywhere, i think i have figured it out. the second nipple in line on the brake booster line check valve is really slow to build vacuum. but to truly diagnose this problem, i need to know something about this check valve.

to start with, i have attached a vacuum diagram that is my system exactly.

what i have noticed is that my car, which is a W123, and is supposed to have part 140 on the diagram, instead has the W126 check valve, part 140a, which has three nipples instead of two. the third nipple is capped. but do the two nipples in use match exactly between the W123 and the W126? also, if either valve will work, isn't the capped nipple supposed to be at a 180 degrees from the other two? mine is at about 30 degrees. (i have attached a picture of my valve, 140a, the W126 valve)

also, is there a difference between the two nipples? knowing what stock should be from each nipple might be a nice place to start. is the second one 'downstream' (farther away from the vacuum pump) supposed to have a different vacuum reading?

and one more thing, anyone know the color coding of the orifices? i have clear, orange, yellow, and black.

ok. phew. that took a lot.

great forum here, and i look forward to the wisdom that will pour forth.

-carter

vstech · #2 02-13-2011, 10:15 AM

alda does not get vacuum....
alda ONLY gets pressure from the intake manifold.
if you attached your alda to pump vacuum, that could be your problem.

mrskemp · #3 02-13-2011, 10:19 AM

oh, oh.
i forgot to include a funny story:

in diagnosing my vacuum issues, i broke the little yellow check valve to the vacuum tank and door locks. it had been superglued once before, so it's time was passed anyway. local dealer didn't have any, so i thought i would try the junkyard. turns out they have about 10 mercedes of varying vintage. i ended up grabbing a bunch of rubber connectors and a sweet becker with shortwave for $20. yeah, you read that right, shortwave.
anyway, in my search for the yellow check-valve i found what looked like something super similar on an early nineties car. i figured, why not, worth trying, and went to pop it off, and it goes 'whooosh'!!! it still had vacuum in it! the car was half demolished, missing doors, and sitting in a snow drift, and it still had vacuum! here i am struggling to get some nice usable vacuum in my car, and this car that is sitting mangled in the junkyard has got tons of it! anyway. thought i would share. oh, and yep, check valve works perfectly.

toomany MBZ · #4 02-13-2011, 10:20 AM

vstech ^ Correct.

Check the amount of vacuum you get from each of those orifices, the lowest one (15 inHg) goes to the VCV, the highest one (~22 inHg) goes to "other consumers" and just plug off the last one, as you have now.

mrskemp · #5 02-13-2011, 10:22 AM

hey, thanks.

i worded that a bit wrong. i meant to say that i attached a vacuum gauge to the line to the transmission. will update.

mrskemp · #6 02-13-2011, 10:28 AM

thanks toomany,

but what is the VCV?
i have it setup exactly as shown in the diagram, the first in line has the most vacuum ~22, and the second in line is about ~15, but is slow to build, and goes to the 'other consumers' labeled 'c' on the diagram.

also, does the orientation of the thrid nipple matter? i saw somewhere that someone was having trouble with it, which was fixed by turning 180 degrees. do i need to take the whole line off to rotate it?

thanks,

carter

toomany MBZ · #7 02-13-2011, 10:38 AM

Item #65 in the diagram is the Vacuum Control Valve. The line making 15 should be plugged in there, slow building shouldn't be an issue, this is for the transmission. Every other vacuum consumer should get 22. AFAIK orientation has no affect. But the 85's are a different animal.
I imagine it's old and brittle, so the less you move it around, the better.

It's possible someone installed a line that fit, even from a different chassis.

mrskemp · #8 02-13-2011, 10:53 AM

ok. thanks for the clarification on the VCV.

i am still confused though about how much vacuum the two nipples should be supplying. according to the diagram, the transmission is fed by part 123, which is the Vacuum Transducer (which is the main part of 'different animal' in the 1985's). this transducer is fed by the same line as 'other consumers', which is contrary to what toomany wrote. his implication is that 'other consumers' and the transmission are on different nipples from the check valve.

i think the confusion comes from how the older W123's are setup vs. the 1985.

basically on my car, there are two groupings. the transmission is grouped with 'other consumers', and the VCV is with the switchover valve that works with the boost. my question, that i have left is; which grouping should get the nipple with the ~22inHg?

(and let's ignore for now the EGR, which seems to be intertwined with everything.)

thanks again,

carter

mrskemp · #9 02-14-2011, 10:01 AM

still hoping for a clarification of which nipple on the brake line booster check valve should have more vacuum. the one closest to the vacuum pump? anybody? anybody? beuler?

Cummmins · #10 06-12-2013, 10:45 PM

I need this valve at the brake booster line (140 in the diagram). Both nipples at the check valve recently broke off causing problems as you can imagine. I cannot find this valve anywhere. Anyone have any idea where I can find this valve. I need one soon. Thanks.

Diesel911 · #11 06-12-2013, 11:04 PM

Quote:

Originally Posted by Cummmins

I need this valve at the brake booster line (140 in the diagram). Both nipples at the check valve recently broke off causing problems as you can imagine. I cannot find this valve anywhere. Anyone have any idea where I can find this valve. I need one soon. Thanks.

The Valve is not sold by itself. The wole main Vacuum Line is an assembly that comes with the Valve in the Middle.

You gave no info on what Car the Vacuum Line if for.

Cummmins · #12 06-12-2013, 11:15 PM

Quote:

Originally Posted by Diesel911

The Valve is not sold by itself. The wole main Vacuum Line is an assembly that comes with the Valve in the Middle.

You gave no info on what Car the Vacuum Line if for.

Any idea where I can get the whole line assembly? Its for an 85 300d.

whunter · #13 06-13-2013, 01:23 AM

Quote:

Originally Posted by Cummmins

Any idea where I can get the whole line assembly? Its for an 85 300d.

Brake Booster Line with 2 Vacuum Fittings
MB# 1234307429
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

.

Cummmins · #14 06-13-2013, 12:02 PM

Quote:

Originally Posted by whunter

Brake Booster Line with 2 Vacuum Fittings
MB# 1234307429
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

.

Thank you!

tskraemer · #15 03-30-2017, 11:49 AM

I have run into the same issue with accidentally breaking the two nipples off of my check valve as well. Found the brake boost line and was about to order. My question is, is it possible/safe to operate the vehicle if I just plug the holes in brake booster line? I understand I will have to manually kill the engine. What is the impact of lack of vacuum pressure on the VCV? There were mentions above of transmission. Just trying to decide if I need to overnight this part.