I'm having some issues with my brakes but cannot seem to pinpoint the problem so if anyone has any suggestions they are most welcome.

Basically when running the brake pedal goes almost to the floor before giving any real braking effort

I have followed the tests in the JTIS for the brake booster and it appears to be working. (pump pedal till it is hard, start engine and pedal drops almost to the floor) Master cylinder shows no signs of leakage or damage.

Bled the brakes using a pressure bleeding system with no improvement.

My thoughts are that either the booster or master cylinder has some kind of issue but as these parts are expensive would rather get a second opinion before changing them out.

Thanks

 

Yo have already answered this yourself as you have said that the booster is working and the system is bled ,it has to be the master cylinder. You can change the seals but better play safe and change the whole unit.

 

Have you checked the integrity of the Brake Booster vacuum pipe?

Graham

 

Vacuum pipe seems ok - gives good constant vacuum. I'm going to try rebleeding the brakes in case I made a mess of it and if that doesn't work then the master cylinder will get changed when I can get one.

Thanks for the advice

 

Are you loosing brake fluid but see no evidence of an exterior leak? Your master cylinder may be bypassing internally. Brake fluid will not always be visible at the joint between the cylinder and the booster, but brake fluid will be leaking into the booster.
Regards,

 

fluid level isn't dropping at all. Thats what is pushing me away from master cylinder

 

Problem sorted now.

I had put the car into a garage to get new rear calipers fitted (brakes were poor before this) and it came back worse. The garage had suggested that it was either the brake booster or the master cylinder that was faulty so didn't think to bleed the brakes myself until this afternoon.

I did the fronts with nothing really noticeable (took the chance and ran enough new fluid in to completely replace what was there) and then went to do the rears. (Are the bleed nipples meant to be on the base of the calipers at the rear ?) As soon as I had the first wheel off I thought that they may have bled them as is so took off the calipers from the mounts and turned them so the nipple was at the top. Opened the nipple on the fist one and got a little fluid followed by a large air bubble and got the same on the other side. Ran enough fluid through each to replace all in the lines and reassembled.

Brakes now work as they are meant to.

Lesson learnt ? if you hear hoofbeats think horses, not zebras.

Thanks for everyones help.

 

Yes, the bleeder nipples ALWAYS goes to the top. Pros even make this error sometimes. Glad you got the problem corrected w/o additional cost.

 

A failed booster will always give you a system that has no assist. The pedal will be high and hard to push. A master cyl. or air in the system will give you a low pedal. Amazing that a shop could put calipers on upside down!! Brakes should be bled first by the furthest caliper from the master, usually the right rear then the left rear then the right front ,then the left front. Glad you got it figured out! IMO stay away from that shop.

 

You may want to start looking for another garage in your area that is a bit more reliable.