Brakes keep building pressure


#1

2002 VW Eurovan. It will (after some braking) not release the brake pressure and actually lead to undriveability. In other words: I can go for a drive, apply the brakes at the stop signs and then I can feel how the van gets slower and slower even though I am on the gas. All 4 wheels keep getting brake pressure, the pedal gets harder and I have to stop. Then I have to turn the engine off, after 20 secs I can hear a loud groan that goes through the vehicle and the brakes are released. If I restart the engine too soon, the same thing happens again right away. If I wait at least a minute before restarting, then I can drive away until it happens again (and it does not always do it). The van got a new brake booster 15kmiles ago. I am at a loss. Brake fluid flushed regularly, newer pads and rotors, 195kmiles on the van. Thanks


#2

When the vacuum brake booster was replaced, did it include a new vacuum brake booster check valve?

Tester


#3

I’m also wondering if the brake rod was misadjusted.

The booster uses the engine vacuum pulling on a diaphragm contained in the booster canister to pull on the brake rod and help you apply the brakes. When the pressure on the pedal is removed, a spring in the assembly should pull the rod back, and valves in the assembly should allow the vacuum pressure between the front of the diaphragm and the back of the diaphragm to equalize, eliminating the diaphragm’s pull on the rod.

If the rod doesn’t come back to its proper position, the valves will not allow the pressure to equalize and as you drive the engine vacuum will continually pull on the diaphragm, essentially continually applying the brakes. As the fluid heats, it’ll expand and the brakes will become applied harder and harder.

To test this, try disconnecting and clamping off (or plugging) the line from the booster to the engine (to prevent the engine from experiencing a vacuum leak). If the problem disappears, you have your culprit. BE CAREFUL… the brakes will be hard and not as strong with the booster inactivated. Don’t perform the test on a busy neighborhood street past a schoolyard!

Post the results.


#4

All good ideas above. If that’s not the problem, another possibility is a problematic rubber brake hose. If so, usually it would be one of the rubber hoses that connects from the frame to a wheel caliper. It would be sort of unusual for this to happen to a 2002, more likely older cars, but the lining on the inside of the hose can deteriorate and the hose will start to act like a one way valve, resulting in this symptom.


#5

Because this effects all four wheels, I would doubt that it is a rubber line internally collapsing.

I would concentrate on the Power Brake Booster, or the ABS actuator.

Yosemite


#6

I’ll throw my 2c at the lack of free play at the booster push rod.


#7

This is another vote for a misadjusted brake rod. I’ve also seen this problem when the master cylinder was too full. Heat will expand the brake fluid and cause the brakes to be applied on all four corners. Usually the problem occurs when disc brake pads are installed and the reservoir cap is not remove to allow for fluid expansion.


#8

My vote for a brake rod issue also. It’s possible that the replacement booster may not be identical to the old one and has tightened the brake rod up.


#9

@duncaneurovan;

If you have a set of metric combination wrenches you can quickly determine if the problem is caused by lack of free play on the push rod. Just loosen the bolts holding the master cylinder to the booster enough to get a dime between them and drive around the block and attempting to cause the problem. If the problem is eliminated by the loosening you can remove those two nuts and slip the master cylinder away from the booster an inch and access the adjustable push rod.


#10

Will work on the suggestions in the next few days. Thanks for the input.


#11

I had a very similar problem on my old Ranger pick-up.

Anti-lock brakes. The valves were corroded and wouldn’t release. Only way to move the truck was to open a brake line and let pressure bleed.

Check pressure before and after the anti-lock valving. And change the fluid more often, because that’s what caused the problem in the first place.


#12

Well, thanks guys for pointing me to the booster. I wanted to check if the brake pedal returns completely after releasing the brakes, so applied the brakes a few times by hand and then pulled up on the pedal. I felt and heard a slight crunch and the pedal came up a little more. I looked around under the dash to see if I could figure out what made that noise but no luck. Anyway ever since then the brakes have been perfectly fine. I have no idea what the problem was (what kept the pedal down a bit) but it seems to be fixed.
Thanks again


#13

Faulty Brake Light Switch?
I hope the problem is solved, but it may return
CSA


#14

That is a thought! I put in a new brake light switch just before this whole mess started. Could that already be faulty? I will check.


#15

I’m Not Called “Common Sense” Just For The Heck Of It, Eh? :wink:
CSA


#16

Some brake light switches are self adjusting when installing, they ratchet into position when the brake pedal is in normal up-stop position. Sound like the installation of your new brake light switch is now complete.


#17

The very first comment was right on the money. Sounds like your brake booster check valve is hung up and thus…applying brake force after you take your foot off the brake. This was the very first thought I had after reading your response.

Some WD40 sprayed onto the valve near the brake pedal…just might free the valve up…if it does…you solved the issue in knowing the valve needs replaced…or at least some attention paid to it as the lubricant might free it up once and for all…but thats wishful thinking.

Blackbird.


#18

I wonder if the new brakelight switch came with instructions.


#19

I wonder if the brake light switch is misadjusted such that it’s preventing the pedal (and thus the brake rod) from extending all the way back when the brake pedal is released.


#20

Who reads instructions?? Thanks again everyone. As Nevada 545 said: installation complete and lesson learned