We've all done it..........the plastic piece is not available.........you must purchase the entire line.

SteelBender... take a look at the vacuum pump-TO-brake booster line at this link on our sponsor's WebSite:http://img.eautopartscatalog.com/live/N402074174OES.JPG
This is for a 1985 300SD... Q - What is your car... YR & model and how many miles ?

If you are talking about a "T" like the smaller one that is mid-way on this line, then I I would think seriously about using copper/brass fittings available in the plumbing department of your local hardware store... but before I would try that I would try and get a measure of just how brittle this old plastic line is. IF the plastic line is strong and NOT brittle, you might make repairs but if it's the other orifice tap that is near the right end of this line, then I think there is also a check valve in this fitting!

Also IF you do attempt this, do not restrict the line too much for it is IMPORTANT to have a full flow of vacuum to the brake booster!
Regards

So...more junkyarding today. First, here is what I found from the MB parts guy.

For old style VCV's, PN:1230700046. (its printed on top of the VCV). He said that: They are supposed to bleed a little bit even when closed. The spec is an average 1 mmHg per second. Max bleed per second is 3 mmHg. Based on testing 10 of these things I have to believe this to be true. I now have one from an '85 TD that falls within this spec. I have 3 others that are bad now on my bench. Here is what I have learned from dissecting them:

- the internals are very simple. a simple spring that breaks a 'seal' is all there is.
- they are prone to moisture getting in and rusting the spring and metal prts out, seizing them or other wise.
- the primary failure is going to be the spring failing somehow. the symptom of this is the lack of ability to bleed vacuum off. On my original one the spring would no longer open the valve, no vac bleed ever. On another one I have the spring seizes at the top position, not pulling the valve back one max bleed has occurred.

Here's how to do a comprehensive test for those reading along:
* this is not an MB official thing, this is my inferred procedure.

Take VCV off IP.

1.) Test with MityVac. Disconnect all vac lines. Attach mityvac to top input. With throttle at min, it should bleed at a rate of 1mmHg/S from 10 to 0 or so. Much more than 2 mmHg/S I'd replace it. I think the rate will naturally be slower the lower the vacuum. From 5-0 should be slower than 10-5 etc. This makes intuitive sense to me.
2.) Feel throttle position input mechanism on VCV. Pushing up you should feel the resistance of a spring. If you fee no resistance it's busted. When you go to full throttle and let go of the throttle input lever the spring should push the lever back towards the min throttle position. If it stays at full it's busted.
3.) Mity Vac again. Pump up at min throttle. While vac is going down, move throttle lever slowly up. At some pint it will bleed out the vacuum. Good.
4.) Take off the two screws and remove the side panel of the VCV. Take a peek on the inside. Rust inside is bad. If it is a junkyard find look for one that still had the vac lines connected to it - this keeps moisture out. Look for general signs of mechanical unhappiness. Youll know it if you see it.

If it passes all of these then you have a good one, as far as I can tell.

Optional: When you have it open, clean it of big gunk that may have accumulated, and put some WD40 on the spring for rust prevention and lubrication. I also sprayed some WD40 on the outside moving parts. Careful not to get it near the valve. This all made my junkyard one a little smoother and good as new, far as i could tell.

If helpful I can post some pics. I plan to put all of this in a document at some point when I hopefully get my tranny working. Hopefully I am now on to the next phase of tranny fixing - I have replaced all of the vac components, so now its time to adjust the cable and modulator. Wouldn't it be nice if after all this the tranny actaully shifts correctly?

-dd

__________________
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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Brian, that one does not look like mine, my Car is a 1985 300d Turbo, it has 317,000 miles on it

Here's yours:

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1XL0VHEI01YN00RRFU&year=1985&make=MB&model=300-DT-001&category=All&part=Booster+Vacuum+Hose&appChassis=_any

DD - Excellent report above in POST #156 under the title:
"Everything you ever wanted to know about the VCV and were afraid to ask"...
I must admit the student has outdone the teacher IF I can be so brazen to think of myself as a teacher about VCV(s) for a brief moment. Also you made an excellent summary about testing used VCV(s).

In going forward, I hope you end up with an adjustable VCV. Keep up the good work and reporting back to this THREAD for your VCV subject is an excellent adjunct to my original premise regarding criticallity of getting the correct vacuum signal being sent to the tranny's modulator BEFORE you start adjusting the modulator.
Regards,

I broke this plastic tee today trying to get the hose off to take a vacuum reading. I started the engine but it won't shut off. I pushed the broken tee to seal and the engine shut off. Not knowing what other problems this will cause I got creative. I tapped the broken tee with a 1/4 -20 tap (after drilling out with tap drill). I machined a nylon adapter on a lathe with 1/4-20 die and threaded it in the newly tapped tee and connected the hose and all's back to normal.

I want to see if I can make the transmission shift better. It flares sometimes starting from a standstill and jerks forward. It also makes a pronounced clunk coming to a stop. Are these signs of vacuum problems to the transmission vac modulator?

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

(1) Extra Ordinary Fixes - IF you are inclined to perform such intricate work on these brittle plastic T(s) in the Pump-to-Brake booster chamber... I would recommend you fashion a metal "T" in this, the main vacuum supply line.
(2) Tweaking the Engine/Tranny Vacuum Control System - Yep, this is why this THREAD was started by me more than 250 posts ago. For those of us on this THREAD to help ya, we need for you to go through a series of vacuum tests and report to us the results. I trust you have a vacuum hand pump/gauge... the tests include:
(a) tell us what year and model diesel you have,
(b) go to the website : http://www.peterschmid.com
(c) and then their webpage: http://www.peterschmid.com/vacuum.htm
(d) follow thru the menu structure and find the appropriate vacuum diagram for your year/model/engine car.
(e) report back to us with all of the above.
Regards,

I wouldn't call that intricate work. It was done in less than 1/2 hour and done out of necessity because it was broken. That's a great idea to make it out of metal so it will not break again. Is that just a plain tee or an orifice that I broke?

I will go through the procedure you outlined and report back. I do have a Mighty Vac. Thanks for the guidance.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Funole,
A1 - I think most of the "T"(s) are also restricted orifices... that's why we need to try and find the proper vacuum diagram which will tell you [most of the time]. But even if it's not, you can put an in-line restricted orifice in the line just as MBZ did when they "tweaked" these cars as they came off the assembly line [IMHO]... or at least that's my explanation of their use of so many restricted orifices... orifices here and orifices there. I say that these were originally to do two things: (a) balance the vacuum to each specific vacuum using/powered component [as needed], and (b) to conserve vacuum for where it is absolutely needed... the vacuum assisted power brakes. I also think the later model cars went to a separate electric powered vacuum generated just for the door-lock, fuel door, and trunk-lock systems... they did this [IMHO] just to get away from possible lawsuits from the brakes being starved for vacuum when a door-lock diaphragm ruptured or a vacuum line pulled loose!
Regards,

The T's in my 1982 booster line were open (large holes).
The T's in my 1983 booster line were restricted.
When I ordered replacements, both lines sent had T's with the larger holes.

The only reason for having orifices of smaller size in the T's would be to increase vacuum to the brake booster, but as long as your system is tight enough to maintain ~25" to the booster, all is well.

__________________
1982 300CD Petrol/Black Leather

1983/300CD,
One way or the other, the restrictions are needed... unless your vacuum pump is wearing out!

I have gauged the I.D. of some of several of these "T"(s) on the main vacuum line and found most to be ~0.8mm. IMHO I would equate "open" to be ~ 2mm or larger which is the opening in the largest of the MBZ in-line orifices... thus also IMHO, IF new replacement main vacuum lines come with "T"(s) that 2mm or larger openings, I believe it would be necessary to use in-line orifices that are 0.9mm or smaller to reduced the "strength" of the vacuum such that you would be able to properly adjust the vacuum on cars with a vacuum control valves [VCV] mounted on top of the Injection Pump (IP). Otherwise you would NOT be able to properly adjust the VCV so that the tranny's modulator valve would see the proper varying vacuum signal simulating changing throttle.

I agree that restricted orifices [whether in the main line "T"(s) or in-line orifices]... these are there to help "conserve" vacuum for the brake system, but IMHO these restrictions are also there to provide a final degree of "tweak" or control of the vacuum being supplied to the various vacuum using components... for example EGR, VDC, modulating valve etc.

So IMHO you either have to restrict the vacuum at the main line or bother there and later with in-line restriction(s). One of the diagrams on the www.PeterSchmid.Com WebSite actually gives you the sizes of the 6 or so color coded in-line orifices!
Check out: http://www.peterschmid.com/vacuum/1977_1985/617_95/1981_1984.jpg
Regards,