I am trying to figure out if my hard brakes are a fluid issue or brake booster issue. (before going out and buying parts).

When i press on the brakes they have a lot of resistance, but do stop the car. They do not go to the floor or anything like that, but they almost have a numb and are not too responsive. I tested my vacuum pump and it is getting like around 22 psi with the engine running. Door locks are not functioning correctly and the engine shutoff is very slow, and sometimes when the car is really hot it will not even shut off all the way( have to stall it out or kill push on engine).

Any suggestions?

What does your vacuum reading do when you step on the brakes? How fast does it recover? Sounds like it could be a booster. It could also be a master cylinder that is leaking into the brake booster and has filled it with fluid...

Is the 22inHG you have a steady reading or does it flutter?

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Sounds like a leaking booster. You can usually hear it hissing thru the firewall opening. Rust inside the brake hydraulics would cause sticking calipers and MC and leaks.

One way to test the booster is to turn off the engine, wait 20 sec, and see if you still get assist. The booster should store vacuum (via check valve) to allow one braking cycle after the engine dies, as a safety feature. Of course, the check valve must also work.

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its 22psi steady. It is not fluttering.

I will test out the brakes after shutting off the engine. I assume if i disconnect the vacuum line from the brake booster and attach a hand pump, it should be able to hold pressure. If it does hold pressure, does that mean the booster is ok (or more diagnostics to do for that?)

There is difference with the brake hardness with the car turned on and off but it is not too different.

Sometimes there is a gasket/gromet in the booster that goes bad. W Hunter can give you the parts # very cheap fix and worth trying prob less than $3

First ensure there are no other leaks. Any pre-existing leaks can exhibit symptoms elsewhere.

Plumb the handheld vacuum pump directly to the booster 17mm opening (engine off) and test to see if the booster holds vacuum. If not, you need a new booster.

Immediately after shutoff I heard a hissing noise by the booster area. See if yours does the same.

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It deff sounds like you have vacuum issues, locks, shut off are all vacuum related.
You can plug your vacuum lines into the cabin up by the brake booster, usually there is a yellow check valve near that controls the doorlocks. Test by plugging with a golf tee, that usually means your vacuum pods that control the doorlocks, gas lock and trunk need some
attention. Isolating can help you with the rest of testing.

anybody have a picture of this yellow plug in question?

Going to test the booster now.

ok i have an update and picture attached below.

So i tested the brake booster.. it holds vacuum no problem.

I then started testing lines in the engine bay. I have an 82' 240d manual transmission.

In vm1: the green round thing holds no vacuum, and the thing the green round thing is going into holds no vacuum.

in vm3: this black wire that goes back into the firewall holds no vacuum either.

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vm3: in this picture. the brown wire on the right holds vacuum well.

the green wire on the left does not hold vacuum at first, but if i pump it up to around 15 psi, it holds vacuum very well. (so if i just pump it up to 5 it will go down to 1 or 0... but if i pump it up to 15... it stays at 15.


the yellow/white nipple thing in the middle holds vacuum at 5psi... but i can't get it to hold vacuum at any higher level. it always falls back down to 5 instantly.

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You'll see it when you open the hood, up close to booster.
I had same issues you are having and ended up replacing the booster, but it was probably just the gromet/booster seal, the part I previosly mentioned.
With that yellow check valve line plugged, it'll probably shut
off faster, but your locks wont work anymore with vacuum
bypassed

Black is a vent line, open to cabin
Brown is shut off
Yellow check valve is door locks
That is how my 85 is set up, yours may be different
Plug off the vacuum line to yellow check valve and test if you get any difference. Shut off may be better. By removing some of the vacuum issues you may get some response from brakes maybe not

but i tested the booster and it holds vacuum well. pumped up to 15psi and held perfectly (i unscrewed the metal line going into the booster and plugged the hole with a hand pump and it worked fine.

why would i need a green vacuum if i have a manual transmission (what is that doing? Is it for cruise control maybe?)

what does vent mean.. the black one (vents to cabin? not sure what that means /does... it holds no vacuum though).

yea the brown one (both on the right and on the left that goes into the shutoff valve holds vacuum very well).


But like you said... that yellow nipple thing in the middle... holds very little vacuum. At 5psi it will hold but never go beyond that.


Thanks for any input!

You may need to do what the other guys suggested. Plugging some of the lines will help some of the issues but not the hard pedal