MK1 Brake Booster/Vacuum Issues?

[wolfsburged]

1984 Jetta GL Turbo Diesel.

Recently got the car back on the road after being parked for about 4 years... Brakes at first were horrible, very little braking ability and a rock hard pedal.

Since we have replaced the master cylinder, front rotors & pads, and new stainless steel flex lines all around. Hard lines look to be in good condition. Have not pulled the rear drums but bled fine all around and rear e-brake works great.

Now the brakes work better, but I feel like there is only partial power assist and it is spotty. First drive around with the new brake components started out with what felt like power assist and after an hour or so they were back to rock hard.

I pulled the vacuum tube at the booster with the car idling and it was sucking very strongly. I reconnected it and the brakes felt a ton better, at least at low speeds. At higher speeds or when I have to hold the brakes down for longer than a quick jab, I get good initial bite and then it feels unassisted.


Connection at booster


vacuum pump and check valve

If I turn the car off, I can get one good jab that feels assisted, and then hard, so I think my check valve is working.

I can hear a faint whoosh like the power assist should sound like.

I'm wondering if I have a minor leak around where the vacuum line connects to the booster, perhaps a leaking booster, or something else??

I feel like the vacuum pump is doing its job, at least at idle. I have not verified under load and higher RPM, but I imagine it would only pump more vacuum...

Also on a semi-related vacuum question, I have an AC equipped car (broken), and I don't see a vacuum reservoir/collection of balls looking thing, and it looks like there are two vac lines out of the air box, one of which is plugged.



Am I supposed to have something there, and could that also be contributing to my brake issues?

[burn_your_money]

Hook a vacuum gauge up to the pump and monitor it in various driving conditions to see what is going on.

Since it's the newer style I don't think that it wil have gone south

[wolfsburged]

I can try finding a vac gauge and watching it. I assume that I can tap into one of the smaller diameter vac lines before the check valve for that.

What does the engine oil pressure have to do with the issue? Not driving the vac pump properly?

I'm waiting on someone from vwvortex to send me a cabriolet triple gauge setup including the oil pressure gauge and dual sender. So at the moment I can't say for certain. I have some grounding issues with the cluster which is out so I can't even comment on the oil dummy light.

[wolfsburged]

Ok that makes a bit of sense.

What I will do next I think is go ahead and hook my mity-vac up to the smaller diameter vac line that is current going to the airbox and run it out one of the hood vents to monitor as I drive around.

That will also eliminate any potential vac leaks from the HVAC side. I'm going to also try to seal the grommet connection at the booster with some silicone to make sure that I'm not loosing anything there.

Right now I have no real means to measure oil pressure but being able to watch vacuum from the pump should indicate whether or not there is an issue at the pump which could jump back to the pressure problem.

I've got some Shell Rotella oil in there, honestly can't remember what grade it was. I usually run 20w-50 in my older cars, and I know the Rotella oil was something like a 10-30 or maybe 15-40. What viscosity would you recommend on an older diesel like this? It's got 174k on the clock.

[burn_your_money]

Rotella is wonderful oil for these engines.

[wolfsburged]

Looking back I put in Rotella-T 15w40 last change with a Bosch filter. Don't have the instrument cluster in right now or gauges so now way to verify, but seems to run fine.

Today I went and put a nice bead of RTV silicone sealant around the outer part of the booster grommet and also a ring around the vac line barb. Let it set nice and it seems thorough.

Took my Mity-Vac and connected to the line that was going to the HVAC. This line is tapped after the vacuum pump and before the check valve.

As soon as I start the car, the vac gauge rose to 28ish in. vacuum, which is good. No matter what conditions, while the car was running it stayed at a constant reading. After turning the car off, it still stayed at 28. Now somewhere I read that a working booster should drop vacuum when the pedal is depressed - but I'm not sure if that is correct, and I'm not sure if that is only true if measured after the check valve. Regardless, no change on mine. I get one solid assisted pump after the car is off.

Now if I hit the brakes hard while driving (like panic stop hard) I definitely get a full power assisted screech to a halt kind of stop. But if I'm giving it a constant medium braking effort like I would to stop normally I get some vacuum assist to wherever I hold the pedal constant, and then seem to run out. For example, if I were slowing down gradually and then had to panic stop, it is hard as a rock to depress it that second level.

Also when slowing gradually and coming to a halt when I give it a lot of pedal pressure I get this sort of vibratory/knocking feeling and noise. Not sure where it is coming from, but almost sounds like the motor shuddering. Does not seem to vary based on speed, only on braking pressure (and very hard, end of the pedal like). Don't know if maybe I've got some warping or binding at the drums, or something more sinister.

I took some video of it driving and stopping with the gauge visible. You can't really read it, but you can see that it doesn't move. The noise I'm describing is barely audible at around 0:15-0:18. Don't mind the squeaking, its just the clutch pedal.

http://www.youtube.com/watch?v=jcALI2KUFUI

At this point I feel like the vacuum pump and grommet are fine, and that it is probably a small split/leak in the booster diaphram. The only options I can seem to find on this model booster is a reman from Cardone via Auto Zone or a used booster. My normal FLAPS guys don't carry anything.

[BlastIt]

Hey check with Viking imports in Charlotte 1-800-742-0222. I just got a rebuild kit for my vac pump. It was only about $20 shipped.
They normally carry it in stock. I got my the next day.