Hi folks, I get an air noise every time I depress the brake pedal on my Octavia. The pedal is not spongy and the brakes work fine.

 

I recently installed a disc brake rear end from a VW bora replacing the stock drum brakes. I also installed brand new pads front and back. I had no issues bleeding the brakes as well.

 

Fearing that the booster may be "leaking" I replaced both the booster and master cylinder however I ended up with the exact same problem. I did notice when replacing the booster that there was a sponge like material around the booster rod where the pedal connects. This had disentigrated when removing the booster. Unfortunately the replacement booster does not have the sponge material. Is this what dampens that air noise I keep hearing?

I almost forgot, I replaced the vaccum line from the booster to the manifold together with the valve but the problem still persists.

I am still experiencing this braking issue even after I swapped just about all the parts on the brake system. The only component I did not replace as of yet, is the ABS pump.

 

I recently noticed that my catalytic convertor was clogged, which caused some issues with the idling and performance of the car.I assumed that maybe this may have been the cause of my booster problem as the engine was basically stifling. However even after replacing the cat, the brakes remain in the same state. It is very much drivable however the brake peadal feel and response is poor.

 

Does anyone have any suggestions or have experienced this before?

 I bet one of the calipers is partialy seized.Spray some WD40 on the cilinders and screw them in few times.

 I bet one of the calipers is partialy seized.Spray some WD40 on the cilinders and screw them in few times.

 

I would assume it would be one of the rear calipers as the front was fine when the car was rear drum brakes. I may end up purchasing caliper rebuild kits one time.

 

As these rear disc brakes where taken from a MK4 Bora/ Jetta I thought that maybe the master cylinder would be different on the Bora, however both the octavia and bora master cylinder are the same with the ID number 23 on both.

I would try to screw in and out the rear cilinders first...I bet they sat alot in the scrap yard or the previous owner.

Both rear calipers seemed to be stuck so I took both rear calipers out, removed the pistons and cleaned the calipers. The seals were also in very good condition and the piston was now moving a lot more freely than before.

 

I also noticed that the guide/ slide pins on the front calipers were dry. I lubricated the pins then reinstalled.

 

I then bled the brakes starting from the master cylinder, on to the right rear caliper, left rear, right front and then finally the left front. The brake pedal feels great until I start the car, and then the pedal goes lower to the floor and I get the same air noise from the booster.

 

I noticed when bleeding the brake system that the pressure from the bleed nipple is about the same for the front and the back. If I recall correctly the pressure at the bleeder nipple on the front caliper is usually greater than the back causing it to actually squirt out of the nipple. This did not happen this time around as it just flowed out the front.

 

Could the ABS pump have any effect on this?