Well I went to bleed my breaks today and in doing so found that the fluid coming out was foamy because of the amount of air in it. I pushed a whole bottle of Dot-3 brake fluid thru the rear lines and the foamy brake fluid just continued to pour out. I decided to try and drive it up the street to see how it was going to act and sure enough, I have next to know brakes. I'm pretty sure the problem is the master cylinder. I'm planning on going to carquest in the morning to pick up a new one but just wanted to know if they're any brands to steer away from or any that you've found to be particularly good. Thankyou in advance.
BTW the car is a S5 convertible

 

I cannot help you with the choice of Master cylinder or even if you should be chasing that down as your problem. I do however have some questions.

1: how are you bleeding the brakes? Vacuum pump or do you have an assistant pushing the pedal waiting for you to tighten the bleeder valve then release etc? if you are using a vacuum pump you will see some foam because the seal is not perfect to the bleeder valve.

2: are you letting any air back into the calipers? If so you are creating air bubbles in your lines.

3: have you ever let your fluid reservoir get completely empty so air got in the lines from there?

4: pump your brakes up a few times once you have bled your system and put the car back on it's own 4 tires. This is to pressurize the brake system. Not sure if this will do anything but I always do it whenever I change fluids.

Take care,
TR

Please do not bump, the admins do not like it. thank you.

 

is there any leaks anywhere else in the system?

By the sounds of it, its sucking in air somewhere

 

I changed the master cylinder today and it fixed the problem. My brakes are restored and the frothy brake fluid problem has ceased. I was just curious now if anyone knew why mazda didnt put bleeder valves on the front calipers?

 

umm they did. I have two on each caliper. i have tohe 4 piston disks up front though.

look on the back side of the calipers, they normaly have little rubber nipple covers on them.

jana,
TR

 

I looked on the backside of the calipers and found nothing in the front. The rears had them but the front didnt. I had to actually loosen the hydrolic line fitting to bleed the brakes. BTW, the fronts are the 4 piston calipers. If anyone has pics showing me where these bleeder valves are, it would be greatly appreciated.