damigos

Hi guys.
Since I bought my FD I had this brake problem: I had to press the pedal 2 times in order for the brakes to work good (1st stroke worked so and so, 2nd stroke fine and with stiffer pedal). I did a stainless steel high pressure brake line job and bleeded the sysyem 2 times but with no luck so I came to the conclusion that it was my Master Cylinder. I ordered the overhaul kit from Mazda (110 Euro!) and did the job, bleeded the system once again but again no luck. The one way check valve works great.
Any suggestions???
Next thing I am going to check is the Vacuum chamber and the BPV valve.

clayne

It's a result of wheel bearing play and rotor runout causing the pistons to be pushed back into the calipers. Since the stock caliper (which is a good design BTW) doesn't use a sprung piston design, you just have to get used to double-tapping it - after that it's not that big a deal.

http://www.stoptech.com has a good article on the technical details of this phenomenon. Fairly standard mechanics.

skunks

where is the artical?

DaveW

Also possible that you have taper wear on the brake pads that results in long pedal travel.

mfigr1

I have the same problem but haven't figured it out. I bled the system a couple times and no luck. I noticed that the Mazda manual states not to let the brake fluid level drop below 3/4 when bleeding the brakes. This happened the 1st time i hope i didnt ruin the Master Cylinder.

clayne

http://www.stoptech.com/whitepapers/knockback.htm

skunks

ahhh cool, i saw that page before but never really bothered to read the entier artical

thanks for the link

Kento

That site has some great tech stuff on brakes. The "warped brake rotor myth" section was especially eye-opening for me.

paw140

I don't buy it. He should not have this problem with this brakes. I've never known anyone else to complain about it, and I don't experienece that problem.

I have heard that bleeding the system the conventional way can be impossible due to the ABS pump. Apparantly air can get trapped in the ABS pump valving, and it's not open to the rest of the system during the bleeding process. I've read that the dealer can hook something up to make the pump cycle and get all the air out.

This may or may not be your problem. I'm also speaking from second-hand knowledge, so keep that in mind.

Kento

If there was air in the system, you'd know it, and tapping the brake pedal twice wouldn't make any difference in the feel, which would be the same either way. I've experienced the same thing in my FD when running on the track or aggressive canyon driving.

damigos

Thanks a lot guys for your help but unfortunately it is nothing of the above given to the fact that when I press the pedal with the engine on the pedal hits the floor after a while. It seems not to be able to keep stable pressure in the system and it looses it from somewhere. Given the fact that I overhauled the master cylinder we can assume that it is not it, but it could be the master cylinder's body damaged... (Not likely because it was in very good condition without any oxidation). Could there be a valve or something else in the ABS unit that looses pressure? (Which of course is not repairable) I have no leeks (doublechecked), my pads are in good condition, new brake fluid, power brake assist unit seems to operate as described in the inspection sector in the manual... New maste cylinder then?

PaulyDee

I wanted to ask why you decided to buy the rebuild kit vs. just buying a whole master cylinder. I'm sure it's cheaper witht he rebuild kit but the new master would have given me peace of mind.

The problem sounds like fluid bypassing in the master cylinder (pedal going to the floor).

Tim McCreary

If your pedal is going to the floor, change the brake master cylinder over to the Mazda 929 Master Cylinder. It is larger and will give a better pedal feel.

My car is doing what that website says. First pump, the pedal goes down about 1/3 of the way, second pump about 1/2 of an inch only (every time).

There is a website that goes through the conversion. It is almost a direct bolt up. I think the line configuration is different though.

Tim


Tim

clayne

Double-tapping is totally basic and a standard thing on many cars with 4-piston calipers and unsprung pistons.

Now pedals dropping to the floor under constant pressure is the sign of a problem.

911GT2

Ever driven a car with air in the brake lines? Tapping the pedal certainly does make all the difference in the world. Think of the physics of it: Air is compressible. The first time you hit the brakes the air in the lines is compressed between the fluid between the master cylinder and the fluid in the calipers. Then if you quickly hit the brakes again the air is already compressed, so it actually pushed on the fluid on the caliper side causing it to pinch.

Try it sometime. Purposely put air in your brake lines and drive the car. Hit the brakes once and feel the pedal drop the the floor, and hit it again and the brakes will be rock solid as they should be.

damigos

It seems to me that I'll be going for a new master cylinder and a good bleeding. Does anybody know if the ABS unit has any valves that may be causing the pressure loss if damaged or if the BPV (bypass proportioning valve) may have to do something with this? As for the 929 master cylinder...It is a good idea but unforunately the car was never imported officially in Greece. Pitty...