Multiple pistons allow a few things to happen. First, you get to distribute the force applied to the pad across a much larger area. Imagine the pad bending where the piston mashes the hell out of it; the extremities of the pad are not contributing as much as the portion actually under the piston. If you press on the pad in more places this problem is reduced.

Second, by going muli-piston and by varying piston sizes within the caliper you can fight taper wear of the pads.

Lastly, the reason you see opposing pistons (pistons on both sides rather than on one side) is that with pistons on one side the caliper must be able to slide along some sort of mount to stay centered around the rotor as the pads wear. With opposing pistons you can mount the caliper solidly as the pistons merely extend further out of the caliper as the pads wear.

 

Just for reference, the AP 4-piston kit (CP5200 calipers) has only 10% more piston area than the stock brakes, which is not a huge difference and will hopefully avoid any major hydraulic issues.

The AP kit has two each 1.50" and 1.62" pistons, versus four 1.42" for the stock caliper. Total area is 9.81 sq in, versus 8.92 for stock.

I might switch to the 929 master cylinder to reduce pedal travel and increase pedal effort.

-Max

 

Thanks for all the info guys!

What are the parts numbers for the 99 spec Type RS brakes?

 

Lunar 7 has all the parts numbers. I'm too lazy to look them up on my Mazdaspeed Motorsports Development Receipts.

 

Ok since this seems to be the right place...
I've taken out my abs
I'm running stock brakes for now
Pads Hawk hps for the street, blues for the track
My booster currently has the inlet capped off

Would I see a benifit, in terms of pedal feel, ability to modulate by going to a 929 master cylinder?

What proportioning valve should I use to dial in more rear brake? Any recomended / problem brands? What is the maximum reduction in line pressure I'm going to need to acheive a rear bias?

What was the total area for the AP 6 piston kit? Would they work well with the stock front's moved to the rear? Has anyone ever used the stock fronts on the rear?

Any more questions I should be asking?

Thanks,
Matt

 

I have compiled a parts list for this upgrade and I'll post it later tonight.

Since, I recently got a flat tire, it reminded me that there is probably a different spare tire & wheel required for the RS brakes.

I'll get those part numbers out of the '99 parts book and add them to my list before posting it.

 

Dang...that's right! I need a different spare tire! Jeez! When will this end??

 

Just curious... what's the pedal effort and braking performance like with the vacuum fitting on the brake booster capped off?

Someone else mentioned this modification, and I'd assume that it'd be slightly worse than converting to a true single manual master cylinder, since the brake booster assembly might act as a buffer. Anyone know?

I'm going to have to run a vacuum pump to augment my braking system more than likely, because my engine will probably be pulling very little vacuum. Possibly only 10-11 in. Hg. Just curious about any negative affects of capping off the brake booster vacuum inlet, since that's a cheaper alternative.

As for the 929 master cylinder, it'll move more fluid, so it can't hurt.

 

I don't know yet, I havn't driven the car since doing it.

It was me in another thread in reply to your vacume pump.

I'd love to go to a true ballance bar setup, but no one makes them, and I still havn't found anyone I like near me to fabricate one. Plus I'm not going to spend the money on Marks system, since it really isn't worth as much as they are selling for.

I'm kind of supprised you (Jim) are getting rid of your ballance bar setup, it seems it would be alot easier to swap out the master cylinder for one more sutibly sized for your application. So why arn't you using it?

Since I can't find a good ballance bar setup, it looks like my only option is the 929 with a proportioning valve, so far the cheapest(only) 929 I've seen was $218 from robuck now trussville mazda. Any other places sell these?

Matt

 

Here is the parts list for the '99 brake conversion.
Now including the 17" spare.

 

Lunar 7,

That's great information! I will place my order for the new spare wheel/tire!

Thanks, again!

Regards,

ML

 

I can't open that document.

Can you post it as a reply?
Thanks,
Ed

 

Ok I've been thinking some more, Since I don't know exactly how the brake assist servo is constructed this is just my guess...

Assumptions:
1)When a vacuum is applied to the nipple on the brake assist it makes it easier to depress the brake pedal.
2)When pressure is applied to the brake assist, in the case that the check valve fails, pedal effort is increased to the point that it is impossible to press down on the pedal.

If these two things are true, wouldn't it be better to leave the brake booster nipple open to the atmosphere?
The reasoning is that if you cap off the nipple there will be an air pocket that you have to pressurize while you depress the brake, by leaving it open the pressure will normalize with regards to atmosphere.

Am I making a logical argument? Does anyone know how the internals of the brake booster are designed?

Thanks,
Matt

 

Also does anyone know what the 929 Master cylinder bore is?

Thanks,
Matt

 

You removed the stock proportioning valve, so you should already have more rearward bias than stock. Installing a proportioning valve in the front line seems like a bad idea, but I know it has been done. You'd have to install it there to move the bias rearward.

The 929 master cylinder will give a harder pedal with less travel, but you'll have to push harder to get the same line pressure. The should make it easier to modulate, but if you have gone manual I am not sure you want to have to push harder.

Do you use Blues on all four corners at the track, or just the fronts? HPS pads have a low coefficient of friction and fade easily, so they probably aren't much help on the track if that is what you are running in back. I've been running like that for a while and I think it is time to change pads back there.

-Max

 

Yea, I didn't realize untill looking at the workshop manual tonnight that the stock proportioning valve was the thing attached to the ABS, I thought it might be inline ( at the rear of the car) or built into the Master cylinder. I'm guessing I'll have to add the adjustable valve to the rear line, not the front.

Quote:

The 929 master cylinder will give a harder pedal with less travel, but you'll have to push harder to get the same line pressure. The should make it easier to modulate, but if you have gone manual I am not sure you want to have to push harder.

Thats one of the reasons I wanted to know what the 929 bore size is, if it's smaller I'd need less pedal effort, if it's bigger (would be my guess) it will take more effort, the real question will be how much difference is there between the two. I don't want a pedal I can't depress, nor do I want loads of pedal travel.

Quote:

Do you use Blues on all four corners at the track, or just the fronts? HPS pads have a low coefficient of friction and fade easily, so they probably aren't much help on the track if that is what you are running in back. I've been running like that for a while and I think it is time to change pads back there.

-Max

Yea I use blues all arround, I had real problems last time at the track trying to get my brakes to feel right, I kept hitting abs, but the rear of the car didn't want to contribute to the braking in any way. Also more rear bias would help tremendously with trail braking. The only other cars I've driven in a track environment were both prepped race cars (lotus 7, and ford escort rally car) and the rx-7 should be able to run rings arround them, if I can just get it set up correctly.

Matt

 

Lunar7 & SleepR1

Where are you picking up the new spare tire, from Mazda Comp?

Thanks for posting the parts list and info on the brake up grade.

Later

 

I may try Tire Rack to see if they can hook me up with the right size temp spare wheel/tire. I presume that 40, is a 40-mm offset?

 

Here is a summary, in plain text:
Quantity Part# Desc. Year

2 F124-33-25XA Rotor, Front 314mm dia x 32mm thick 99
1 F1Z4-33-23Z Kit, Brake Pads Front 99
4 F124-33-696 Pin, Pad Retainer 99
1 F1Z4-33-98Z Kit, Caliper Front Right Diff Bore 33.9mm/38.1mm 99
1 F1Z4-33-99Z Kit, Caliper Front Left Diff Bore 33.9mm/38.1mm 99
1 F124-43-710 Line, Brake Caliper Front Right 99
1 F124-43-720 Line, Brake Caliper Front Left 99
1 F138-33-261A Plate, Rotor Backing Front Right 99
1 F138-33-271A Plate, Rotor Backing Front Left 99

2 F124-26-25XA Rotor, Rear 314mm dia x 20mm thick 99
1 FDY1-26-43ZA Kit, Brake Pads Rear 93
1 F1Z4-26-98Z Kit, Caliper Rear Right 34.9mm Bore 99
1 F1Z4-26-99Z Kit, Caliper Rear Left 34.9mm Bore 99
2 F124-26-261 Plate, Rotor Backing Rear 99

1 99650-14070 Wheel, Spare 4Tx17 114.3/O=40 99
1 90620-17627 Tire, Spare T125/70D17 99


Sorry if the formatting comes up screwed up, HTML is not too friendly to column aligned text, but then that's what tables are for.

 

Found out this morning that the 929 is a 1" bore. If my rough calculations are correct that translates into a 13% increase in pedal forceover stock needed to acheive the same line pressure.

As a thought for Jim what happens if your power fails to your vac pump?

Matt

 

the 929 is 1 inch. This season i am looking into a bigger master cylinder than that. I have researched and found out a 86 mustang svo is 1 1/8, and a 94 ish mustang is 1 1/16. This , with the right pedal ratio should be big enough for any brake upgrade. After all, the porsche 911 turbos have 4 big pistons front and rear and use a 1 inch m/c.

 

I added some pics at the bottom of the page with the brakes installed on my car:
http://www.maxcooper.com/rx7/parts_i...kes/index.html

SE37K wheels have huge amounts of room for brakes. My wheels are 17" and I probably could have fit 14" rotors in there (just guessing).

-Max

 

How much did those run ya?

 

Nice, my friend just recieved the same setup so I've seen the in person. He previously had the M2/Wilwood 6 pistons so I'm curious as to how much better these will be.

 

DROOL..............

max any pic for the rest of your cars? u have my favorite wheels on... se37K
=P~
wow.......

but i want them for a FC... wonder how they would look... oh well.. maybe C28Ns... we'll see...