New brake booster line = vacuum problems
 

Good news: I adjusted my steering box today and the slop is gone!

Bad news: In doing the adjustment, I snapped off the plastic nipple on the brake booster line where the transmission/shutoff vac line and the door locks/CCU vac line connect.

On my car, both of these vac lines were T-ed together and they connected to the booster line at the nipple closer to the brake booster. (The nipple closer to the vacuum pump had apparently been broken off by the PO, as it's gone and the hole is sealed up.)

I ordered a replacement booster line from Phil and installed it. I used both nipples this time. The door locks didn't work, the transmission shifted harshly, and the engine wouldn't shut off with the key. I double checked that everything was connected and even did the "suck test" on the shutoff valve just to make sure it was still good.

Thinking maybe the PO was on to something that I didn't know about, I replicated the one-nipple connection from the old booster line by T-ing the vac lines and plugging the unused nipple. No change. Then, I "fixed" the old booster line using some vac hose and epoxy/duct tape. The repair held long enough for me to reinstall the old booster line and confirm that the locks worked and the car shut off just like old times.

I feel I've narrowed down the problem to the new booster line, but what could be wrong with it? Any thoughts?

Thanks for reading this long post!

Charlie

It is obvious you're not achieving vacuum through the new line,
Did you check for vacuum at the connections for vacuum verification?
This where I start the troubleshooting , It could be a bad new vacuum line!

There is a check valve in the booster line. There is an arrow on the valve. When the line was installed, which way was the arrow pointing?

I was able to feel vacuum at both connections on the new booster line when I covered them with a finger, but (shame on me, I know) I don't have a vac gauge and so couldn't compare it to the vac level on the old booster line (assuming I could even get a reading with another temporary "repair").

The arrow points toward the vacuum pump (same with the old line). I blew through the new line just to make sure it wasn't blocked. Air goes through in the direction of the arrow but not the other way.

I just spoke with my indy and he suggested taking a drill bit and carefully reaming out each of the vac fittings on the booster cable. He said it's common for them to be "clogged" with plastic that wasn't properly removed in the manufacturing process.

I'll give it a try this evening.

Your Indy beat me to it. I had the exact problem, stuck a straightened out paper clip in each of the nipples and everything was sunshine and lolipops.

success!
 

A 7/64" drill bit fit perfectly inside each fitting. I started "drilling" by hand with vise-grips as my indy recommended to avoid going straight through the line, but eventually I switched to the power drill and went very slowly and carefully. Lots of plastic junk came out of both holes.

Now the engine shuts off instantly with the key, the door locks snap up and down... and my transmission is flaring like crazy! Time to dial back the vac to the trans--is this best accomplished by adjusting the modulator? I looked at my VCV before and I don't think it's one that's adjustable.

I just read your last post and I was mystified to why you would drill the (T's) in the main vacuum booster line.
the engineers purposely designed a certain size orifices to restrict the vacuum, and not to take away from the brake booster.
You should have not drill out the orifices in the main vacuum line that runs between the vacuum pump and the brake booster reservoir !
I would suggest adding inline vacuum orifices to create a restriction to the other vacuum devices.
Here is some orifices you could try to match your systems.
Color: I.D. P/N:
Yellow……2.0 mm..……..1162760929
Red……….1.1 mm….…….1162761029
Blue………1.0 mm…………1162761129
Brown……0.9mm….……..1162761429
White……0.8 mm…………1162761229
Green……0.7 mm…………1162761329

vacuum pump?; brake not working; still on when key removed; transmission shiftshard
 

Hi,
on my 1984 diesel 300 series, my brakes are not working at low speeds like parallel parking, driving around the grocery lot and stopping where they should at red lights. The engine keeps running when the key is removed, and the transmission shifts hard at low speeds. A friend told me to check the vacuum lines. I know nothing about cars. I took the car to a mechanic, he performed a smoke test, no leaks. He checked the pressure produced by the vacuum pump, and reported it was lower than the minimum required. Hence the car needs a new pump. The mechanic reported this fix to cost about $800.
I am a college student, and never had anyone teach me about car repair. My friend informs me that if I had the piece re-built and did the repair myself it would cost me about $300. That is a big difference, and I would not have to sell the car and be car-less. But if I do not learn how to do repairs I will not keep the car, it would be too expensive to take it to a mechanic every time.

My questions to you'll, is 1) based on the information I gave, would you concur with the mechanic that the car needs a new vacuum pump? 2) being of average intelligence, no mechanical background, no knowledge of tools, basically a blank state; what are the chances that individual could self-teach and correctly make a major repair?

Any other advice would be greatly appreciated: is this the right forum for me? if I sell the car, how should I calculate my asking price, (I've owned the car since May, 150,000 miles b/c the engine was replaced by a previous owner, A/C and heat work, really the car runs well, i'm kinda starting to like it, but as a college student I lack the time and money if its going to need work constantly, since owning it from May I put about $600 from mechanic visits, compared to about $100 would have been if I knew how to do the repairs myself.)....and anything else. really all the concise info you can give me.

Thank you

In answering to the 1st question, if I assume that the mechanic is correct in his diagnosis, $800 is not a bad price if he will replace it with a new Vac Pump.

If you plan to be a W123 owner (thats the body style of your 300D), unless you have a lot of money to spare, it would be a good idea to know how to work on the car. Most of the time and $$ involved is during initial ownership as there will always be something that needs to be done on the car until you get it to a point where everything is fixed. Depending on how the car was cared for, most of the issues with these cars are not terribly bad to fix for the DIYer. This forum will be very helpful.

However, you will need the TIME to get your feet wet in learning the hows. This may be a bit tough if you are a student.

The vac pump is not difficult to work on. Its fairly easy to remove and inspect. Its a pretty sturdy component but due to use, some components inside it may have broken especially when miles are high. Repair kits are available online.

Its also possible that this is not the problem of you car. IIRC, the pump should be pulling 21-23 in Hg of pressure.

If you can find a W123 forum member in the Reading or nearby area, that would be a plus. Otherwise, I would consider getting a vehicle that can "hit the ground running" that you don't have to mess with (Honda, Toyota,.....?)

You will need a little bit of mechanical background if you want to own a 25 year old mercedes diesel car or else you will be a cash cow for mechanics. Your problem could be a simple fix like an unplugged vacuum line or it could be the vacuum pump or brake booster(expensive).

Thank you-1984 300D vacuum issues
 

Thanks guys,
your input was very helpful. 2 new questions.
next question: How do I calculate my ask price, (of course I will be upfront about this vacuum issue, maybe the next owner knows an easy fix.)
Or
2) Is there a subscriber in the Reading, PA area that would like to mentor a college student and his 84'. haha...

I'm assuming you mean selling price? I believe you said its an 82 300D with 150K?

Price will be relative to the body and mechanical condition of the car. If the body is in good shape, it would be worth more. The mechanicals are somewhat secondary as they are fixable but its tougher to do body work.

If I were to take a stab at it, it can range from $1500 to $3000 depending on its condition. Maybe even more if the bidy is pristine.

I can't help you much with the other question. But even if theres a member in the Reading area, you have to be really mechanically inclined.

Post some pics...

Mazoot, my intent was to use the drill bit to remove the extra plastic (defect) from inside the fittings on the brake booster line, but not to make the orifices any larger than spec. There was so little vacuum getting through, it was clear something was clogged. My indy said he'd seen a number of booster lines with this problem, but that it was an easy fix to clean out the excess molded plastic.

I adjusted my transmission modulator and now the shifts are back to normal, too.