W123 brake booster check valve - replacement unavailable?
 

Hello, I have a 1983 300d with a broken check valve on the main vac line running from the vac pump to the booster.

Unfortunately, the replacement part #1234307429 doesn't seem to be available anywhere anymore. I ordered it from Pelican Parts but the order was cancelled because their supplier no longer makes it.

My understanding is that the check valve can't be purchased on its own. I have already used epoxy to repair the broken nipple on the valve once, but it didn't last and the nature of the break makes a permanent repair very difficult.

Has anyone had any luck fabricating a replacement? It seems like it would be possible to pull the check valve out, replace with a generic check valve and then add a tee in the line to feed the rest of the vacuum system. Does anyone here have thoughts? Thank you.

When I made less money and had more time, I'd be inclined to farmer up a fix. At this point the whole hose at $42 isn't expensive compared to a few hours messing around with no good result or sleeping easy on a brake repair.

https://www.pelicanparts.com/More_Info/1234307429.htm?pn=123-430-74-29-INT&SVSVSI=3389&fs=0

Thanks for the link - unfortunately, that hose is not actually available from Pelican Parts, as I learned after I ordered it and then had the ordered cancelled because their supplier no longer makes it. I have been unable to find the hose in stock anywhere, hence my predicament.

Agree with "moon" 100%. Dont waste your time only to end up with a substandard repair/part. Although it "looks" like you should be able to pull the old one out and slide in a new one, these lines dont work like that. Not that flexible. Similar connections on the fuel systems and MB def doesnt want them coming apart. Dont risk your brakes/vacuum system for 42 bones. One less thing to worry about and you'll know it's "right".

I would happily pay for the hose 123boy, but I can't actually find it in stock. It sounds like, after talking to Pelican Parts on the phone, Cohline isn't making the part anymore.

If anyone finds a link where it's in stock or has one they'd like to sell please do let me know! Unfortunately I live way out in rural Maine far from any MB junkyards and I can't seem to find the part on eBay, so I'm looking at fabricating something unless I can order the hose somewhere...

https://www.*******.com/products/mercedes-power-brake-booster-line-300d-300td-genuine-mercedes-mer-1244301229\\]

sorry, this is for an 87.

Try the classic center, or find a junkyard at car-part.com and have them ship the part.

Appreciate your help - yeah, the 1987 looks quite similar but apparently it doesn't fit.

I have a few calls out to junkyards listed on car-parts.com so I guess I'll see what happens. So frustrating that the main feed to the entire vacuum system is so fragile!

Sorry, my mistake. Thought you looking for the hose only, without the check valve, to do your own repair.
Sorry I cant be of more help. Nothing worse than important parts for our cherished old cars becoming NLA.....

If you wanted to construct a new line with rubber vacuum hose you need to save the end fittings and nuts. Check valves can be had as in the attached picture or they have plastic ones. EBay and Amazon sell them.

You will have to find something that works for the little nipples to T into the main line. It could be done with Brass fittings.

I replaced the plastic tubing on my Power Brake Booster Vacuum Line with rubber vacuum hose. I increased the length so I could run the line over the top of the fender well were it was less likely to be damaged.

That's odd, I got one off pelican a few months ago. Are you sure it's unavailable? You've also tried ebay?

Make sure you save the old flare fittings.
For whatever reason, the fittings of the new hose -at least for my car- made some odd angles that left me unable to install it without a little surgery.
The hose can be manipulated with a heat gun but you have to be fast and precise.
I cut the old line up and practiced a few times.


-

Shern - It appears that Pelican Parts just ran out of stock and the supplier no longer makes it. If you go to PP it will allow you to add the item to your cart, but your order will be cancelled - I spoke to someone at the parts warehouse and they said it's no longer available. I've been checking ebay but nothing has popped up.

Not having a lot of luck with junk yards, many places refuse to do anything with brake or vacuum lines 🤷

Diesel 911- thanks for the tip. I may end up doing that. I wonder if anyone knows the pressure differential spec for the check valve - or is it pretty standard? Something like this seems like it might work - Aluminum One-Way Check Valve 12mm Barbed - it says it holds 90 PSI.

I just called the dealer and they told me NLA, but they did sell it not too long ago for $26.

That really sucks.

This sounds like great advice and a good solution. The phrase "necessity is the mother of invention" comes to mind. Really does suck when these parts just go "NLA" with no warning or recourse.
I, too, just bought one for my 83 240D from PP "not too long ago", as well.
I was recently looking for an ac line for my 97 E300D, guess what? NLA. It's the main low pressure line from the compressor to evaporator with the "low side" charge port in the middle. I found one on eBay from Germany, for $20!!!, but the guy wouldn't ship to the U.S. The new part from MB was over $300. Not having much luck.
My local dealer kindly did a "national search" of all the MB dealers, hoping to locate the line in someones parts dept.(no bueno). I wondered if you could get a dealer to perform that same search for your brake booster line? Surely, there's gotta be a new (or used) one of those, somewhere on this planet, yes?
I know there are also a lot of members here who also stock up on old parts. Have you tried placing a request in the "wanted" section?

Where are you? I have several spares (Sacramento, CA). If pressed, you could custom plumb. Post 9 shows some parts. I recall seeing generic vac booster check valves in bubble packs at Autozone. Most are for the type which push into a rubber grommet on the booster, but might be some inline hose type. Also search on ebay and Amazon.

This from post #5...."Unfortunately I live way out in rural Maine far from any MB junkyards".
Surely this isn't an insurmountable problem. I understand wanting new, NOS or a good used part. But, certainly, something could be cobbled together with satisfactory results.
I'd like to hear how Diesel911's solution is working out and holding up.
I tried to PM the OP to suggest a few specific members that I've purchased used parts from in the past. PM'd mainly for discretion and not broadcasting the info "all over the internet". The "PM" feature of the OP's account is not turned on or enabled? So, who knows.....

I have a friend that is currently working on fabricating a quality solution to this issue (Dutch, same fellow making the pivot mount balls, bless him). But, it seems like it will be a while.

The issue with whole new construction is the line end fittings. See attached picture.

However the check valve and a fitting for the 2 little nipples and rubber hose could be provided and the owner could remove the plastic hose/tubing themselves and replace it with the rubber hose.

Another way would be to cut the plastic hose/tubing as close as possible to the stock Check Valve Assembly and use rubber sleeves to attach the new check valve and nipples. That leaves most of the plastic line/hose intact.

I am in Maine, but would be happy to Paypal you and pay for shipping if you're interested in parting with a spare. If not no worries.

I'm not sure what's going on with PMs - possibly it's because my account is too new.

I'm thinking that's what I'll do if buying the part doesn't work out. In my case the hose and metal fittings are intact, only the check valve/nipple is broken.

I've been curious about the material of which these lines are made, since I got my 240D. I don't think it's plastic as that wouldn't hold up to the temperature extremes and harsh under hood environment, in general. Extreme heat or cold and everything in between and they don't lose their grip, shape, texture, etc. I'm guessing/speculating possibly nylon or maybe even teflon? Does anyone know for sure? Whatever it is, it's very strong and quite stable through all operating parameters and age.

Is the problem that the nipple on the check valve is broke? If that is the case, then carefully drill the broken nipple area to accomodate another piece of tubing (copper, plastic or whatever you can find) to act as a new nipple and epoxy that in. Have done that several times and it works. A good source of nipples are windshield washer line connectors.

I did a quick look and didn't find any of my spare check-valve sections on top. It would be too much digging to find them. Sounds like just the plastic nipple on the check valve snapped off. That is common and could easily happen on a used one you source. You could do like me and others. On one, I cut it flush, drilled a tight hole for a small copper tube to serve as a nipple. To be safe, I epoxied it in. Worked for years until I found a pristine one at the salvage yard when picking other stuff.

Just thought I'd update this thread to say that I ended up drilling out the broken check valve hole and gluing in some sturdy vacuum line, per the suggestions up-thread. Went slow, was careful to remove all the plastic that I drilled out. It's doing the trick for now, no delay in the fuel shut-off, etc. I decided that chasing down a more complex replacement or expensive part isn't worth the effort until I go over the rest of the vehicle and make sure it won't need major repairs after sitting for a long time. Thanks everyone for your suggestions.

Thanks for getting back to us on your solution.

JB Weld makes a plastic bonder that is stronger than the original plastic. I used it on a headlight bezel and the bezel broke somewhere else but the repair was solid.

Concerning the JB Weld Epoxy the slow curing one takes a higher temp then the fast curing JB Weld. I also think the slow curing one is stronger but have no proof.
Duro is another company that is still around used to make Epoxy in that has the same temp range as the slow curing JB Weld.
If you think you are going to have a temperature issue be sure to read the label.

With the fast curing JB Weld you could make an on the road repair on your vacuum line if nipple broke off as long as you are careful to reinforce it with enough epoxy.

I have used brand X type cheap epoxy and it sometimes won't even take the heat in the interior of a car on a hot day.

If you look closely at the check valve with the two fittings located on the valve they aren't just plain open tubes. There are numbers stamped into the plastic, 0.5 and 0.6. Those are restriction values. One fitting is even color coded with a white ring to signify they are different. A general drill-out repair will get the system closed again and often works fine but if you ever start to notice things like a change in shifting or engine shut down you could possibly adjust it out farther down in the system or you could add in Mercedes' little color coded plastic inline vacuum restrictors to make adjustments. This is just an observation for people who are still experiencing vacuum issues after a repair.

Hi guys - good news, we'll have Brake Booster Vacuum Hose 123 430 74 29 available in a few months! Shooting a photo of an early production piece this afternoon, and will share it asap.

URO:
Your website shows 20 of these in stock but no way to add to cart. I need one. Timing on production?

It appears there is someone making a replacement per Diesel911's comments. Thoughts on this one?
https://lermscustoms.com/products/w123-brake-booster-line-replacement-or-repair?variant=40430502805654

I'm also finding a supplier for just the check valve with the 2 nipples:
https://ppembzparts.com/i-30510935-mercedes-brake-booster-line-check-valve-double-vacuum.html
Thinking I might use Diesel911's suggestion to repair mine, "Another way would be to cut the plastic hose/tubing as close as possible to the stock Check Valve Assembly and use rubber sleeves to attach the new check valve and nipples. That leaves most of the plastic line/hose intact."

Hi Chris, good news - our warehouse (we only sell wholesale) just received the production run and these should be available from Pelican soon. We'll ask them to add it to their catalog.

Edit: Pelican says the hose should be available on their site by the end of the week.

Good to know! Mine is more epoxy than plastic now. Looks like I sneezed on it.

Awesome news Uro! Thanks!

Some pix:

https://apaindustries.com/apasite/pa...1234307429.jpg

https://apaindustries.com/apasite/pa...34307429_1.jpg

https://apaindustries.com/apasite/pa...34307429_2.jpg

https://apaindustries.com/apasite/pa...34307429_3.jpg

W123 Brake Booster Vacuum Hose Assy.
 

Good to see it's in production again ! .

********.com has it too .

Just yesterday I stumbled across the check valve alone and can't recall where .

Update: FYI still out of stock.

I have a question. For the turbo diesel 300D brake booster vacuum hose, the two nipple check valve type, the nipple with the white ring base (0.6 coded) will freely pass air when blowing through it or drawing on it.
The second nipple, black base, and farthest from the brake booster ( 0.5 coded) does not pass air freely (or at all by mouth) either way. I have two of these assemblies and they act the same.

How does the system work? How does the check valve interact with each individual nipple?? In other words,what is the mechanical function of each nipple having different restriction codes?



Thanks. I am trying to figure this out academically.

Kind of an odd way to look at it because I don't know if there is a such thing as a flow of vacuum. What I am going to call a flow of vacuum comes from the brake booster and goes towards the vacuum pump. So, the check valve with the built in plastic nipples has the check valve not doing anything to the vacuum at the nipples.

If I remember correctly the check valve is to allow you some few brake applications if you lose vacuum. The check valve sort of crates a small vacuum reservoir between it and the booster.

Differences between the flow of the individual nipples I don't know about except that they go to different areas of the vacuum system.

I have the one with 2 nipples and somewhere between the vacuum valve on the fuel injection pump that controls the vacuum to the transmission modulator and the main line there is a plastic restricted fitting inside of the line.

Some of the older models only have a single plastic nipple.

Thanks Diesel911, your insight makes sense.

Yet there seems to be a mechanical difference between the two nipples.

So directionality does exist since the two nipple check valve does have an arrow designated "to motor" for proper installation.

The difference between 0.5 and 0.6 does not seem extreme, that is why I am befuddled about the 0.5 black nipple not allowing pressure by mouth as the 0.6 white nipple does.

I can't figure out because at this point I am not educated on the actual vacuum behavior designed for that 0.5 black nipple.

Anybody?

TWO Vacuum Nipples
 

Correct ;

The check valve causes residual vacuum pressure to remain inside the big brake booster can for 'emergency' use .

The .05 nipple should be open but slightly harder to blow / such through ~ for this reason I use it for the V.C.V. on the injection pump as I don't often want much vacuum going to the tranny's modulator .

I am not sure if Mercedes says to use this nipple for the tranny vacuum control valve .

If your nipple has any glue around it's base it has been snapped off and repaired, the glue used plugged the nipple and you can ever so gently drill it open again is you wish .

In any case, if the white plastic part of the check valve looks chalky, cracked or simply isn't shiny anymore it's toast and is just waiting to snap and cause no vacuum at all, I'd buy a new vacuum pipe before you get stranded .

There is a picture of a vacuum diaphragm. In the upper left corner it shows the nipple closet to the brake booster check valve as being a restricted orifice and goes in particular to the door lock circuit. The other items that connect to the 3-way rubber connector are not shown.

The other nipple is listed as going to the transmission shift (modulator) system. However, on mine that part of the circuit has a restricted orifices inserted into the line and according to the manual that is supposed to reduce the vacuum to a certain amount that I cannot remember.
https://www.pinterest.com/pin/224476362663302238/

My own main line had been repaired. I broke the nipples off on the first oil change I did.

In the crowded picture you see the front nipple with the yellow dashed line goes to the vacuum valve on the fuel injection pump that controls the vacuum to the transmission modulator.

The read dash line comes off of the nipple nearest the check valve and it goes to the door locks and one other item. I think the other item is it supplies the vacuum to the vacuum shutoff valve on the steering column lock. But, I am not entirely sure on that.

The green line with the red stripe I believe goes to the climate control vacuum pods.

The yellow circle is where the restricted orifice is in the line. Mine is reddish brown and I have seen are green or yellow I am guessing depending on the size of the orifice.

Well Put
 

I like "The Jungle" .

Reminds me of the rats nest of wires behind the headlight on some Motocycles .

Thanks vwnate1 and diesel911, it is a puzzle coming together.

Interesting that the 1979 240D diagram seems to indicate a brake booster line with two nipples. My 1979 300D's brake booster line only has one separate check valve and one 'open' nipple separate from the check valve.

haha I also liked the "Jungle" note on that spaghetti.

Multiple Nipples
 

My feeling is the .05 aperture nipple was for the V.C.V. simply because you want less vacuum to the modulator .

As you mentioned, Mercedes came up with the idea of color coded restrictors to make quick and easy changes but I've not seen any of those in some years .

They also made a multiple arm vacuum spider that has more arms than the usual ones, I sadly lost the part number, it was used to adapt a single nipple vacuum pipe .

The main thing here is to understand what you're doing, then you can fix the problems and after that fine tune it to where you like it .

Thanks vwnate1,that makes alot of sense.

URO Parts Brake Hose/Line; Brake Booster/Servo Line with 2 Vacuum Connections at Check Valve | 1234307429

$58 on sale at an online source near you. In stock !

URO W123 Brake Booster Pipe & Valve
 

FWIW :

I put one of these on my 240D some years back and it's still going strong .

Well worth the $ IMO .

Cheap insurance while available !

Not much to them other than the check valve.

Brake Booster Service
 

Indeed there isn't .

The special rubber grommet when it fits into the booster should be replaced every time as well .

Once you take the time to sort out a weepy / leaky vacuum system it not only all works better but it's far easier to maintain and trouble shoot .

Lasting fix, grommet
 

The grommet on my 601 might be similar, sits over vac pump and fixates the main booster line until it meets the booster fitting. AFAIK i replaced a worn grommet with a new one from an assortment box, and cut one end open to ease installation over main booster line, with the cut turned towards center of hook (inwards), not to the open end, outside.

Old line ok, not rubbing anywhere. Only searched for spare. I went through 3 vac line purchases until I got a correct spare, correct length and placement of check valve. I contemplated going for a 2-4" longer line, if correct was not available and space in compartment without rubbing against other stuff, or adding padding/cut-up hose where needed.

Sure also understand the will and way of repairing/replaced the faulty part only (checkvalve). So long as there is the proper, low risk of line collapsing/detaching/cracking/leaking. A vacuum alarm switch, tested on regular basis, comes to mind.
I also like regularly testing switches for coolant level (AFAIK normally open, draining coolant, suction, and refilling) and oil level (AFAIK normally closed, OHM'ed before/during oil change).

EDIT: OK, not the same grommet.