No a clue here but I would bet you are correct. It's likely from the hydraulics or from what controls the hydraulics. I'd be real nervous driving with such a problem. I hope you find the answer soon!

 

Next time it happens try giving it a decent amount of gas right after you start it and get your RPMs up and see if it fixes it.

There's a vacuum pump that runs when you start the car that is supposed to supplement vacuum to your master cylinder on cold starts and heavy/often braking because the vacuum from your intake manifold sometimes just isn't enough especially on cold starts. Just a stab in the dark. Usually your pedal wouldn't be jammed like that unless somebody pumped your brakes firm while it was off unless something's wrong.

 

I strongly doubt it's the hydraulics. The power booster system is more likely. Only happens after sitting for days + the "whoosh" when it comes back. Lets do a little testing:

Checking the vacuum pump
Check the function of the vacuum pump
Ignition off

Check the hoses and connections. Check for leakage

Before the next corrective action - wait approximately 3 minutes after switching the ignition off (system relay disconnected).

Pump the brake pedal a few times to that all negative pressure in the power brake booster disappears.

Check the function of the vacuum pump by pressing the brake pedal with the ignition on. The Vacuum pump should start and run for a few seconds to build up a new vacuum and then stop.

Select an option:
The vacuum pump is functioning normally

The vacuum pump is operating constantly

The vacuum pump is not operating.

Let us know what happens.

Is your chassis number before ~ 440000? "A service kit has been developed to reduce the current through the vacuum switch for the brake vacuum pump." "If fault tracing leads to the conclusion that the vacuum pump requires replacement, also install the cable harness kit."

 

Select an option:
The vacuum pump is functioning normally

The vacuum pump is operating constantly

The vacuum pump is not operating.

Let us know what happens.

So what does it mean if the vacuum pump is running constantly? Mine runs a whole lot. Not always but a lot...
No problem with brakes however.

 

i agree with checking the vaccuum pump and all the lines that run to and from it ...

 

The pump is there to supplement engine vacuum making sure the power brakes have a sufficient vacuum supply at all times. For example, if the engine were to stall or under boost conditions. There in an integral pressure sensor/switch that tells the unit when to turn on & off. The sensor/valve at the brake booster also has influence over the system. I'll post the whole pressure testing procedure below.

Reasons for the vacuum pump not working can include:
Open-circuit, short-circuit in the wiring to the vacuum pump

Damaged switch for vacuum pump.

Damaged vacuum pump.

Causes for vacuum pump running constantly can be:
Short-circuit to supply voltage in the cable to the vacuum pump

Damaged switch for vacuum pump.

Damaged vacuum hoses for vacuum pump.

 

 

This is great! I'll have to do this once I got a vacuum gauge...
THX!

 

Not sure if you're question has been answered by this, but if I push my brake pedal to the floor with the car off (automatic though), you will feel the brakes become very firm, not willing to budge an inch. Once I start the car, I either have to use the brakes a few times before this goes away (I normally test it in Neutral in the driveway before moving) but sometimes just having the car on for a while fixes the problem. It sounds very similar. I was just figuring that it was the car's way of saving it's own brakes when it's off (the pedal shouldn't technically be being used then).

 

guys, you're great! I'll have to check the vacuum pump and get back to you.

@mynameideasweretaken: I know the situation where you pump the brakes and the car is shut down. but that's not it. I don't do anything, the car just sits there and then the pedal is jammed. no idea how to reproduce the problem either.... some time it works, some time it doesn't.

 

As mentioned, pumping the brakes is the opposite of building vacuum. Frankly it sounds a little as if the one-way valve from the manifold is stuck, although the auxiliary vacuum pump could be dead/weak too.

To build vacuum and see if that's the cause, after starting try holding the revs at 4000-5000rpm briefly, then snap off the throttle. Before touching the throttle again, see if the brake responds. Snapping off the throttle raises vacuum briefly, it might be enough to "prime the chamber".

 

Is there a PN or otherwise a number for this new harness for the vac pump?
Going to pick up the pump tomorrow, would like to have the updated harness too.

 

31270987 Harness
PM me with your email if you want the install directions. You will do a how-to for the forum, correct?

 

The 2.0D does not have any vacume from the intake manifold. The brake servo is all powered by a little vacume pump. Diesels don't generate enough vacume to power it.

@ Crossie

When you put your key in your ignition, does it sound like there is a pump running constantly from the front? Like a little "zzzzzzzzzzrrrrrr"?
When you start your car, does the pedal stay firm for a couple of seconds and then go soft?
Does it stay soft after letting the engine run and take a long time to go hard (example: stop car, stop engine, pump a few times, goes hard or stays soft?)?

I would think it is one of two things:
1. hose between servo and vacume pump has a leak
2. brake servo has a leak

Answer the three questions and it can be determined a little easier

PS: the new harness for that pump is ONLY for the 2.4i/T5 engines! The 2.0d is not affected by it!

 

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