41 replies to this topic

[Parity]

During my last open track day I started getting pad kickback pretty badly.  This was the first time this happened after two years at this track with this car. It took three good pumps to get a pedal back. My pads had about 50% life left and the rotors maybe a little less. I decided to swap out rotors (NAPA brand), reused the existing pads,  and bled the brakes. Driving around the paddock I tried to bed the pads in but couldn't seam to get the pedal back. Pedal to the floor, backs would lock up and turn me sideways, fronts were gone. I got home and noticed one of my front pads was actually bent so I changed both front calipers (Wagner rebuilt) and switched to another used pad with about 50% life remaining. After bleeding the brake several times I still have little to no front bite. Should I be looking at the master cylinder next or something else? 

[svvs]

To me it sounds like the backs are grabbing and the fronts are not.

 

Do you have spare front calipers lying around?  I would start there.  Isn't there a proportional valve built into the system somewhere? 

 

warning...Paul you know me.....i can barely wrench on my car.  Email Tony.

[Parity]

Yeah I already replaced the calipers but fronts still barely grabbing. The proportioning valve doesn't have any adjustment that I can see.

[fotostars]

Yeah I already replaced the calipers but fronts still barely grabbing. The proportioning valve doesn't have any adjustment that I can see.

 

Correct, it's a fixed proportion.

 

Master Cylinder next... It is effectively 2 pistons "in series" inside it, so one seal could have gone wrong inside... It's a cheap and relatively easy fix.

Just make sure you bleed/prime it properly before installing it back...

[Parity]

...

Just make sure you bleed/prime it properly before installing it back...

Is there a procedure somewhere for this?

[Tom Hampton]

The replacement Mc should come with instructions and needed parts. But, in short... You clamp the Mc in a vice or something to hold it still. Then attach some hoses to the outputs of the Mc, and feed the hoses back into the reservoir. Fill the reservoir with fluid, and pump the Mc until bubbles stop coming out of the tubing. Then pump several more times to be sure all the air is out of the Mc.

Finally install the Mc with the tubing still attached, the quickly swap the tubing for the brake lines and banjo bolts. Then bleed the heck out of the system.

[Parity]

Thanks

[Alberto]

FYI Bent pads could be caused by install error.  Most likely cause IMO.  The pads can get hung up on the ears (especially on the inside where you can't see them) then they bend when you apply the brake.

[AW33COM]

Is there a procedure somewhere for this?

 

 

There are many different procedures to do it.  Having it done many different ways on cars and more importantly motorcycles (tricky to do it perfect) I found out the best way to bleed a master brake cylinder (both level and not level) is not to remove it from the car. 

 

Jack up the car in such a way (rear up high) to level your master brake cylinder.  Remove all wheels.   Use something like Phoenix System Brake Bleeder to pump the fluid from the back forward (just like you do a motorcycle).  If you do it properly, not a single air bubble will be in your entire system. This procedure does not require a second person to bleed your brakes, and you don't have to remove anything. 

 

Btw, if you inspect the brake system (master, pipes, and how they enter the cylinder) on any car, and you analyze how air and fluid travels, you will know how to properly bleed that car.  In my opinion Mazda Miata brake lines are tricky to do it perfect, and it's better not to remove the cylinder. 
 

[Jim Venable]

Paul,

 

You may have already bleed the brakes in the following order. If not, you may want to give it a try before replacing the master cylinder.

Note: Some will say it doesn't matter which may be true. For our team I prefer to stick with what the design engineers built into the system. 

 

ABS - Bleed order for actual furthest to closest:
LR, RR, LF, RF 

Non-ABS - Bleed order for actual furthest to closest:
LR, RR, RF, LF

 

Be sure to let us know what the issue was once you figure it out.

[Bench Racer]

 I got home and noticed one of my front pads was actually bent so I changed both front calipers (Wagner rebuilt) and switched to another used pad with about 50% life remaining. After bleeding the brake several times I still have little to no front bite. Should I be looking at the master cylinder next or something else? 

 

 

One of you NEW front pads was bent. That tells you that that caliper was working to some degree.

 

What does "I still have no front bite" mean?

 

Where is your brake pedal today with new front calipers/old pads? At the floor? Half way to the floor?

 

If you have an OEM brake system, the left front brake line does not flow through the proportional valve. Try bleeding the left front brake caliper simo with one of the rear brake calipers. Remember all you need to do when bleeding brakes is just crack the bleeder screw open so fluid flows and you don't get air coming through the threads. Do you now have a left front brake compared to your "no front bite"? 

[Parity]

One of you NEW front pads was bent. That tells you that that caliper was working to some degree.

 

What does "I still have no front bite" mean?

 

Where is your brake pedal today with new front calipers/old pads? At the floor? Half way to the floor?

 

If you have an OEM brake system, the left front brake line does not flow through the proportional valve. Try bleeding the left front brake caliper simo with one of the rear brake calipers. Remember all you need to do when bleeding brakes is just crack the bleeder screw open so fluid flows and you don't get air coming through the threads. Do you now have a left front brake compared to your "no front bite"? 

 

The front brakes are barely slowing the car while the rears lockup. The pedal is about 75% to the floor. Both fronts seem to be behaving the same. 

 

I am using a Motive booster to bleed at about 15 PSI. and do get plenty of fluid at each corner. I've tried these sequences:

 

RR, LF, RF, LF

LF, RF, LR, RR

[Parity]

Replaced the master cylinder, used the priming procedure described here, then repeatedly bled the system. Pedal now moves about 1" and is firm. Unfortunately I can't road test right now since we're getting about 12 inches of rain...every hour!

 

Hope I'm not jumping the gun but I think we may have got it. Road test will tell for sure. Thanks to everyone for all the help. That priming procedure worked well.

[AW33COM]

Paul Redante, I know this is off topic, but very soon you'll have an amazing race track (Liberty Bell) in your backyard. 

Btw, use Jim's sequences above.

[Parity]

Paul Redante, I know this is off topic, but very soon you'll have an amazing race track (Liberty Bell) in your backyard. 

Btw, use Jim's sequences above.

Yes I'm familiar with it. There's also one Alpine Racetrack supposedly in the works but not progressing nearly as fast.

[Glenn]

FYI Bent pads could be caused by install error.  Most likely cause IMO.  The pads can get hung up on the ears (especially on the inside where you can't see them) then they bend when you apply the brake.

I ALWAYS seat the pads in the caliper before lowering the car by pumping up the pedal.  After you bend one you will understand why, LOL. 

[Brandon]

Yes I'm familiar with it. There's also one Alpine Racetrack supposedly in the works but not progressing nearly as fast.

 

Alpine has been canceled.  The property has been returned to the PA DNR last I heard.

[Parity]

I ALWAYS seat the pads in the caliper before lowering the car by pumping up the pedal.  After you bend one you will understand why, LOL. 

I'm not using any retainers and I noticed how sloppy the pads are in the caliper. Once pads and rotors wear a little and you get increased knock back I can see the pads moving out of the slots and getting bent.

[AW33COM]

...

[Alberto]

I'm not using any retainers and I noticed how sloppy the pads are in the caliper. Once pads and rotors wear a little and you get increased knock back I can see the pads moving out of the slots and getting bent.

What is your running position in a typical SM race?  I've only seen front running National racers get enough knockback at rough tracks to complain about it.

Generally speaking, the Miata doesn't suffer too badly from pad knockback. 

Furthermore, there isn't enough room for the pads to move out of the slots once everything is bolted together. It can happen when the caliper piston is fully compressed - like when installing new pads.  However, once everything is installed correctly and the brake is applied to seat the caliper piston to the pad backing and the pads to the rotors while the car is still in the air, the pads won't fall out of place.