My left front caliper froze up on me today. So I need to do a complete front brake job.
my question to you is.... do you know of a big front brake kit conversion utilizing the stock bolt pattern?
I want to keep my old enkei 92 wheels.

 

I don't believe there's anything you can do to retain the 4x110 bolt pattern and get bigger brakes, however unfortunate. FC brake swap would get you bigger brakes, but change the pattern.

 

You can do it, but it takes some work. Machine the rotors off the front hubs and the second gen rotors slide over the hubs. Redrill the rotors to 4X110 and make some brackets to hold the calipers.

 

^ Someone needs to streamline this ^

 

Anymore info on the fc brakes?

 

There are several way people have put second gen brakes on a first gen. Once way is to use a spindle bushing and bracket. I use to make and sell the kits but my machinist decided to stop making them for me because the orders where to small. It's based on the RE-Speed kit.

Another way is to do what mhr650 did in the thread. I really like this method but it does require a machinist.

 

I am starting to like the big brake conversion that mhr650 built for his race car.

Because the FC brake rotor/iron hub is heavier than the OEM 12A rotor I would recommend using only 84-85 spindles. All 84-85 spindles are thicker and use a bigger inner bearing than the earlier spindles.

My question for the thread starter would be why do you think you need bigger front brakes? Is your car a street car?

 

I have built this brake system with both the 84-85 large bearing hubs and the earlier small bearing although not because I particularly wanted to… I originally built the big brake system for the old car, which although the chassis was an 84 had the small bearing spindles on it, it also had a small bearing rear end but that is another story of buying a set of axles that I didn’t need. After that car was wrecked and I built the new chassis I tried to transfer over as many of the parts from the old car as possible but it turned out that the spindle on one of the struts was bent so I had to make a new set of struts.



Those were the original 84 struts from the new car, when I went to put my modified hubs on I discovered that they wouldn’t fit so I had to make another set of hubs, now I have 3 modified small bearing hubs that I don’t have a use for.

The IT7R guys have found a vendor to make aluminum hubs that will bolt onto the first gen spindles and let you use the big brakes so in the future I don’t know if I will build any more of these setups, it will be so much easier to get replacement wheels if I have 5 lug hubs.

 

Yes it's a street car, however, now running street port four port 13b with conservitive 160 hp. Why would you not consider better brakes for a car original fitted with a 100 hp motor?.

 

You really don't need bigger brakes for the street. My 12A puts out about 155 hp at the
flywheel and the brakes have no issues, even on long mountain runs that last hours.
What you may need is better brake cooling or like I did switch to a high heat range
fluid so you don't get brake fade.

 

This is kind of off-topic but I'd like to get more info on those front struts mhr650.

 

I am happy for you, I would still enjoy larger front brakes, fortunately I have gsl rear disc brakes.
Mazda improved the brakes on the gsl-se, due to added hp. Most common mistake, build hp and forget about stopping!

 

Because when I raced my 100hp car I never had an issue with the GSL brakes. That's over 2000 miles of club racing where the car always went over a 100mph every lap. The brakes on my car were prepped for racing - racing pads, fluid and brake ducts but that is it. They got so hot the rotors would turn blue but they never stopped working. That level of abuse shouldn't happen to a street car.

I do think it is wise to think of a performance car as a total package. It should stop as well as it goes. In the case of an RX7 that is seeing street duty, Mazda helped you out with a very workable setup. All a person needs to do is take advantage of modern pad and fluid technology.

 

I did a write up on how I built the struts in this post.

https://www.rx7club.com/1st-generati.../#post11904648

 

Be careful about upgrading the front brakes and leaving the standard GSL rear brakes on the car. It will probably be OK for a street car but I have talked to racers who have done that conversion and their results was that it turned the car into an unbalanced nightmare on the track. I did both front and rear brakes when I did mine, and it works fabulous, we have a car that can pretty much out brake any car on the track and it is very stable on the brakes. That was the biggest problem we had with the standard brakes, the rears locked up too easy and the car was very unstable and difficult to drive resulting in multiple spins under braking.

 

I don't have any GSL rear calipers laying around but what is the difference in piston diameter between them and FC rear calipers?


At the start of a race I would occasionally have rear brake lock up issues. But once everything warmed up the problem never returned on my car.


I did see other RX7s do this during a race but I think their rear lock up issues are mostly attributable to the shocks they were running. Not enough rebound dampening on the rear shock and or too little compression dampening on the front struts.

 

I totally agree that it is a whole system and we could have probably improved other areas that would have helped. One big thing that upgrading to the bigger brakes did was to open up better brake pad choices, with the original brakes we ran the traditional Hawk Blue front Black rear which is one of the few combinations that are available for these cars. With the big brakes we run the DTC 60 front and 30 rear and they work fabulous, lots of power and very progressive unlike the very on off characteristic of the blue black combo. Of course people who really like that hard initial bite of the Blue pads hate a progressive pad, they are used to getting all the brake power right now and have adjusted their driving to match,

Funny you should mention about having problems until the brakes got warmed up, several of our problems came after driver change pit stops which in ChumpCar are 5 minutes minimum. I have a good friend who is a rep for Wilwood and he pointed out that the Blue pads have an almost linier heat to grip curve while the black have more plateau once they get up to heat. I believe that with the pit stop it allowed the brakes to cool just a little bit which caused the fronts to lose power while the rears kept their grip which caused the balance issue. Maybe a 5 minute pit stop is not nearly long enough for the front brakes to lose grip but it may have been the case, of course putting a fresh driver who hasn’t had any time to get acquainted with the way the car is behaving on that day on that track right out onto a hot track in the middle of a race probably doesn’t help either…

 

I always ran Hawk blues front and rear on my car. So they came up to temp fairly evenly I guess. I liked the blues but they sure were brutal on the rotors. I am trying Hawk HT10s on my car now.

To the thread starter - sorry we have high jacked your thread.


There is one more 4x110 big brake option that I forgot about. KC Raceware - www.kcraceware.com - sells an CNC aluminum hub that can be drilled for either 4x4.5 or 4x110 that is designed to accept a Coleman Racing brake rotor. The set up was designed as a direct replacement for the GSL/SE front brake because of safety issues encountered with the OE cast iron rotors in club racing. The standard kit would use the GSL/SE caliper and bracket. This would give you a 10" disk brake on the front with the option to go to a bigger diameter rotor if you are willing to fab up a different caliper mount. Ask for Charlie Clark.


This set up is used on allot of race winning E Production RX7s and at least one vintage IMSA GTU RX7.

 

That was the option I went with, except I used FD four pot calipers. Here is the write up:

https://www.rx7club.com/1st-generati...twist-1029145/

I went with 4 x 114.3, but like hammer said, he can drill it for either one.

I am very happy with these, I have been tracking the car with these for awhile and they take all the abuse I can throw at them with absolutely no problems.

 

I agree with mhr650. If you do big front brakes, do the rears too to keep things balanced. Our chumpcar was probably one he referred to that started with big front brakes only. It was a total disaster. Car was undriveable. Upsizing the rears solved the problem and resulted in much longer life of brake components. Also are using the mhr650 4x110 solution on the front.

I also agree with those that say a street driven car does not need bigger brakes. The only time you will have problem with the stock brakes is if you are braking from high speed (>90mph) to low speed (30-50mph) a couple times per minute. And even then, they will keep working if you have high temp pads and fluid. They will just wear them out. In any case, if you are driving like that on the street, you need to have your license taken away.

Having said all that, I have two sets of front spindle adapters, front caliper brackets and rear caliper brackets, that I am selling. I am happy to sell them for a street or race car.

Carl

 

this may come off confrontational, but i assure it's not meant to be. your wanting/enjoying bigger brakes and your needing bigger brakes are two separate things. that said, they are not mutually exclusive though. your wanting bigger brakes is not invalid, it's your car (and money, time, etc.), but using the SE as "proof" doesn't necessarily make the case for you. based on the fact the SE was "just a S3 Rx-7" everywhere else in the world, with a 13B, i tend to think it was less about it needing bigger brakes and more about it needing to be different enough from the GSL.

 

After looking back at some information that I collected for our Chump Car about a year ago, the GSL-SE rear brakes probably will work fairly well with a front big brake kit. Here are the rotor sizes for all the RX7 options. As you can see, the rear GSL-SE is only a little smaller than the 5-bolt solid rotor that is also paired with the 4-piston (all 5 bolt applications) front brakes in some applications.

Front 5-bolt 275.5mm
4-bolt 249.7
GSL-SE 250
GSL 227

Rear 5 bolt vented 272.9
5 bolt solid 261
4 bolt solid 261
GSL-SE 257
GSL 236

If I remember correctly the caliper pistons all had about the same surface area for all front brake applications and all rear brake applications. That means that the main difference with the big brakes in terms of actual braking force is due to the difference in rotor sizes. Someone should probably check me on the piston sizes though. Just remember that 4-pistons only count as two when calculating the effective area.

I have someone interested in buying just the rear part of the brake kit, so if you (or anyone else with GSL-SE rear end) want to buy the front pieces, I would be glad to split them up.

Carl

 

OK, I looked up the caliper piston sizes and came up with this info. As you can see. All the front and all the rear calipers have pretty close to the same area. I could not find the info for the GSL-SE, but I am pretty sure it is the same as the 4-bolt 2nd gen and GSL.

Carl

 

I thought that when calculating piston area on fixed mount caliper you count all of the pistons - like the 4 piston FC Turbo caliper.


When working with a single/dual piston sliding caliper you double the area of the piston(s).


I have the Fred Puhn Brake Handbook floating around my house somewhere but can't find it right now. He has a formula for calculating caliper pressure based on pedal pressure, master cylinder bore and pedal ratio. In that section of the book he discusses how to calc caliper piston area.

 

Scott. I believe the clamping force depends on the piston area on one side of the rotor. The frictional force on the rotor though is based on the clamping force, the coefficient of friction and the pads being on both sides of the rotor.

The following article does a nice job of describing how the brake components work together. I think you can pretty much use these calculations to make sure that you have the same balance with a new system as the car originally had with the stock system.

scR motorsports | Braking Systems?in Plain English

Carl