Hard brake pedal before starting the car

Post by **misha** » 28 Mar 2017, 07:01

For last 2 days i'm experiencing a hard brake pedal before i start the car,but ONLY when car sits overnight.
As soon as i start the engine everything works normal.Brakes works normally,pedal feels normal and no other symptoms when engine is running.
Brake booster check valve or damaged hose somewhere?

Post by **scot850** » 28 Mar 2017, 10:16

I'm trying to recall if this is the same issue I had a while back misha. I am not sure if I had the hard pedal before or after the engine was started. Which ever it was, it was cured by replacing the check valve in the brake booster. It was faulty so was not maintaining any pressure in the booster once the engine was switched off. On start up if I recall correctly, it took a little while for the pedal to return to normal feel and then it was fine.

Neil.

Post by **misha** » 28 Mar 2017, 10:26

scot850 wrote: 28 Mar 2017, 10:16...I'm trying to recall if this is the same issue I had a while back misha. I am not sure if I had the hard pedal before or after the engine was started...

It's a bit important,because it could point to a totally different direction.

Did you used OEM part or something aftermarket?

Strange...it appeared two days ago and 3 days ago i noticed some mouse cr*p under the hood.

Post by **scot850** » 28 Mar 2017, 10:38

Appreciate the importance of the exactness of the issue, but as it was maybe 2 years ago I am not sure if it was on start up. I am 100% sure it was like that shortly after start up when backing out the garage. The pedal was brick hard and really had to jump on the pedal to get the car to stop. A definite but cheek clenching moment for sure.

I used a spare OE part to replace it. I have a bunch of them I pulled at a junkyard in case it happened again, but so far so good.

Not sure what mouse crap would do to affect the brake system unless they chewed through the vacuum pipe from the intake manifold. There is a wire to the brake pressure switch so that is the only electrical issue here unless it is with the ABS system. However, if it was electrical, I would expect it to be a continuous issue even after starting the car. Some cars have a small one way valve/filter in the line to the booster that can get blocked over the years. My view is the OE part was good for 16 years and 265,000km so another OE one should see out the car. It is a little tricky to access in the P80's but not too difficult.

Neil.

Post by **tryingbe** » 28 Mar 2017, 11:13

Power brake system works by putting vacuum into the brake booster. Your car probably have a slight vacuum leak from the intake to the brake booster. Do a vacuum test.

Post by **misha** » 28 Mar 2017, 11:32

I'll check the hose and the valve.
Check valve,when removed,should let air only to one direction,right?

Post by **scot850** » 28 Mar 2017, 13:53

Correct. One way only.

Neil.

Post by **misha** » 29 Mar 2017, 04:30

I removed brake booster hose from intake manifold side and it wont let air towards the booster,only towards the manifold.
So,i assume that check valve is good.
In removal process of the hose from manifold side i noticed that 1cm of hose which was on the nipple..was like hard plastic.
I shortened it about 1cm and reatached the hose onto manifold.
I'll see tommorow if problem was solved...since it needs to sit overnight for problem to re-occur.

Post by **oragex** » 29 Mar 2017, 05:25

Can you hear the brake booster pump working (whirl) after leaving the car?

Post by **misha** » 29 Mar 2017, 05:28

Nothing from the brake booster,neither with engine running neither when it's turned off...there is no sound.