4-pot front brakes

Don't get me wrong, M3 front brakes are good brakes. Front calibers are made by ATE and are 1-piston floating type.

One day I was at the junk yard and noticed a 1995 Mazda RX-7 turbo with 4-piston calibers. Calibers are made by Sumitomo, aluminum construction and really light. Caliber weight compared to M3:.

OEM M3, caliber and support, no pads	4.2kg (9.2lbs)
Mazda RX-7, no pads	2.2kg (4.85lbs)

So, half the weight, here is the pad size:

 

All this is great, but calibers are not direct fit and adapters are impossible to make due to spacing. I also didn't want to modify the strut since I want to be able to go back to OEM calibers just in case if calibers wouldn't work. I also wanted to use OEM brake discs, OEM hoses and calibers must work with 15" OEM wheels.

Went to see Butch and after discussing it for a few minutes, we thought to give it a try. Butch is an old Newman-Haas mechanic and if he was able to stop the car from 247mph, he should make my car to stop. More about Butch, see www.dennisoninternational.com.

 

Here's the caliber when we started:

Below when finished:

Fitted to strut, from back. Note that the caliber is a direct fit, no adapters:

Next problem is the brake hose, Mazda uses M10 inverted flare compared to bubble flare used by BMW. Mazda port looks like this:

But, there is a trick how to fix the problem. Inverted flare is actually an adapter and under the adapter is a bubble flare port. Just take a screw and screw it into the hole Then pull the adapter out as shown below:

Below is the port after adapter removal:

But, will it work? Easy way to testi it is by painting the end of the bubble flare and fitting it into the caliber. Here is the result, it is perfect!

Here is the male end:

And here is the port in the caliber:

 

Now I can use the OEM stock brake hoses and I don't need to use M10 male inverted flare/M10 female bubble flare adapters like some do.

So, it should work great and stop. Obviously front will have more stopping power now and I most likely have to adjust the bias, but that's an other story. This is a good reason to go to floor mounted Tilton pedals with separate front/rear master cylinders. More about it later...

03/21/2011: Testing is now complete and with stock ABS, calibers and street tires I get about 0.9g deceleration. See picture below:

 

I will be installing the Mazda calibers this weekend, so stay tuned for further tests

04/19/2011: Did some testing with the Mazda brakes. Max braking is about 1g now, so significant improvement. This is with the unknown, used brake pads I got with the calibers.

As expected, front brakes lock now easily. Next project is to add a balance bar to adjust the brakes.

06/11/2011: Brake force sensor installed to measure the brake pedal forces. Log below shows how pedal force corresponds to LonG, wheel speeds etc...