I have an auto-x event tomorrow, and Im just trying to get my car tuned up so it's ready for tomorrow. The only problem is that I cant get good braking power out of my car. I've bled and re-bled the brakes many times, all in proper order, and there are no fluid leaks in the system, BUT I just can't get very much pedal resistance. Ie. the pedal goes all the way to the floor and the car brakes, but not hard.

My brake booster is working well. I have plenty of brake pads left, and the rotors are fairly new.

What's my problem? I have tried messing with the pedal freeplay, both all the way in, and all the way out, and it doesnt make much difference as far as I can tell.

I dont know too too much about brakes so maybe theres something I am missing that a more car-savvy guy can tell me?

 

It sounds like your master cylinder is bad. Peelback the boot where the rod from the brake pedal goes in and see if there is fluid there. If there is the fluid is leak past the piston in your master cylinder.

 

It does sound like the master cylinder but I have no idea what examining the input shaft of the booster will show you.
The MC can be bad with no external signs at all.

 

old brake lines?

 

Mastercylinder.

 

I had a similiar problem last year. I replaced the master cyl and now my brakes and pedal are solid.

 

The general consensus is the master cylinder then. ****.

I cant get a new one for tomorrow morning. Looks like I'll be making some damn shitty corner entries.

Babbs - did u get a used/repaired/reconditioned/new cylinder?

 

When dealing with something as relatively cheap as a master cylinder, best to go new in my opinion. They can be rebuilt, but I wouldn't bother.

 

i installed a new brake master cylinder and bled the brakes 50 ******* times and i still have **** brake performance.

I didnt "bench bleed" the master before installing it so that might have been a problem but I have passed through a liter or more of brake fluid so i dont see how there could be air still in the system.

once again I have a race on sunday that I doubt I can go to because of shitty ******* brake performance D:

 

You are bleeding the brakes at the calipers right?

 

Hmm. I'm wondering if it has something to do with your pistons in your caliper. If you have time you can make sure they're working properly. But usually you can tell by the amount of wear on your brake pads after a while.

 

Pull the lines off and "bench bleed" your MC installed in the car. Bench bleeding shouldn't be considered optional, especially if you're having brake issues. Presumably you don't have ABS.

 

yes I am bleeding at the calipers

there is contact on both surfaces (inside & out) of all 4 rotors, so I think the calipers are fine.

I have "bled" the MC in the car

No ABS


Maybe I dont know how to bleed brakes? this is my procedure:

1. Have driver push brake pedal and hold down
2. open bleeder and leave open until no more fluid shoots out
3. close bleeder
4. have driver lift off pedal
5. Repeat steps 1-4 for all 4 calipers in the order: pass. rear, driver rear, pass front, driver front.

Does someone have a procedure that works better for them?



EDIT: does the elevation of the calipers come into play in bleeding? When I bleed the rears, I have the *** end of the car in the air, and when I bleed the fronts, I have the front end in the air. You would think that the air would tend to move toward the more elevated end of the car, but maybe its continually being trapped in the end of the car on the ground, somehow?

 

^ possibly. I have bled brakes where I get 3-4 times of solid fluid only pumps only to drop the car and have **** brake feeling.

My buddy didn't watch his MC to close and ran out of fluid once....that was a giant bitch to bleed.

 

Have you tried any type of vaccuum bleeder?

If you're still having trouble, try back bleeding, or pushing fluid backwards through the lines. I haven't done this on my Mazda, so I don't know how it to work it out, but I've done it on a few vehicles I had trouble sucking fluid through. I use a large syringe with a small ID hose and push it through the bleeder. Remember to suck some from the M/C every once and a while so you don't spill over.

 

Your bleeding procedure is fine (except for the changing the car pitch angle). However we should be clear about bleeding the master cylinder.

To keep Murphy at bay and ensure you only do this once, you should just bite the bullet and remove the MC for bench bleeding. This is the best way to ensure the plunger is pushed all the way in with the rod. You must remove the lines, screw the tube adapter fittings into the ports (with an airtight thread seal BTW - easier said than done), and recirculate the fluid into the MC reservoir with tubing to ensure all air is evacuated. The MC should be fairly level for this procedure.

Pitching the car fore and aft isn't really needed. The idea is to ensure the bleed screws are at the high point since that is where the bubbles will collect. Skipping bench bleeding is an oversight you must correct ASAP to ensure success. Good luck. Diligence will be rewarded

 

Take it to the shop and have it pressure bled. I bought a pressure bleeder, **** works awesome.

 

I bench blEd the master and put thru about a litre of brake fluid and I can finally lock the wheels. It appears persistqnce is the key when trying to attain good braking performance

 

Sweet! Now go smoke some brake pads.
Hope you make it to the next Auto-X.
FYI, in my experience, Mazda master cylinders seal rubber doesn't hold-up real well. I think they're all rebuilt these days.