Mazda RX7 brakes

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I've had this project on the back burner for quite a while. Finally got around to designing the hub. Uses 3rd gen RX7 rotor (294x22) and 2nd gen 4 piston aluminum caliper. The good think about the RX7 rotor is that it has a large diameter to give sufficient brake torque, yet isn't as thick and heavy as the P-car stuff. See here for pics:

http://www.vdubcustoms.com/Wedo/mazdabrakes.htm

The kit will be bolt on to stock drum, cb drum or stock super spindles.
I'll post the caliper bracket as I get it manufactured.

Easy,
Lanner

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I posted some more pictures of the kit. The pics show the caliper placement aswell as the caliper bracket.

http://www.vdubcustoms.com/Wedo/mazdabrakes.htm

Easy,
Lanner

[gcmarchi]

Lanner,
Can the hubs (and rotors) be supplied with a different bolt pattern (5 x 4.75")? This setup is just what I have been waiting for but what about rears? Are you going to do a similar Mazda based set?

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Yup,
I can machine the hubs for any bolt pattern. The downside is that the rotor needs modification and that is no problem if you purchase pre-modofied rotors from me. The problem arises when you have to replace the rotor....time to find a machine shop. I can make up a jig so that you can drill the rotors on a regular drill press if you wish.

As for the rear, the RX7 ebrake actuation cable faces the wrong way when adapting to a T1. It can be done but requires a weird lever 'see-saw' which seems a little exotic. Nothing is impossible, but sometimes I have to evaluate whether the effort matches the reward.

Easy,
Lanner

[martilo]

Hi Lanner,
so what do you propose to match the mazda's bolting pattern in the rear (with e brake)?
Don't you have another killer app for the rear in the work?
Also, can you supply your front mazda kit complete with the calipers?
Also, what master cyl can be fitted with these without reinventing the whole car?
Thanks for your lights bud!
Louis
ps: its a shame nobody wrote the "fitting big brakes for dummy" yet...

[rip]

well if you get a CB rear disc brake kit you can order them with out a pattern and then have them drilled. I don't know if Lanner has come up with a rear kit yet, shouldn't be hard though either way.

I have the Rx7 kit and that's what I planned on doing.

Rip

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Martilo,

I'm still trying to figure out the rx7 rears. It's a nice size vented rotor (292x20). The caliper has a built in ebrake. The only hurdle is the ebrake cable. Give me some time, it'll happen.

The front kits can be supplied with calipers. They will be rebuilt units.

Lanner

[martilo]

That's a great news Lanner. I will wait for it I guess. Keep us posted.
Also, I saw the aluminium (or at least looking like it) hub for the front RX7 and I was wondering if it can be made out of something stiffer (like preheat 4340, 32Rc)? I think it would definately take the age better.
Louis

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Martilo,

I can make the hubs from chromoly. I don't because they would be heavier and harder (read more time consuming) to machine. I think material costs are also higher than my current material. This would translate to having to increase the price of the kits. It's already too expensive.

As far as strength, it would be stronger than the aluminum hubs. But you'll run into the law of diminishing returns. The current design of billet amulinum hubs are already way over-engineered. I'm using huge section thicknesses at the mounting face and bearing diameters. These sections are designed considerably larger than even P-car hubs. Also the P-car stuff is cast while my hubs are machined from billet. If these hubs were on the landing gear of a 747, then maybe 4340 would be a better material. For the application, I assure you they are over-designed.

As a side note, I'm working on one kit right now that uses all early 944 rear brakes that are machined for 5-4.5". I machined and studded the 944 hubs, aswell as machined the rotors for the new bolt pattern. This is an option for anyone out there who likes the 944 rear brakes, but not the P-car bolt pattern. I can do any 5-bolt pattern.


Lanner

[martilo]

Hi Lanner,
well don't get me wrong, i'm not trying to be the smart *** here. My only concern was about the bearing fit as i know that the aluminium don't resist frequent mounting-dismounting.
The rear 944 in 5-4.5" would be a great news. Would it balance well with the front RX7?

[flat]

Martilo,

No worries, I appreciate the conversation. You're right that aluminum doesn't like the removal/installation of the races. My billet hubs (and 944's) require a preheat when you install/remove the races. If you just pound them in/out you will mess things up. I recommend cleaning out the old grease and repacking the bearings on a semi-yearly (about 5K kms) basis. Also, the bearing preload is very important. I set up the bearings at .001"-.003" axial endplay. There is no way you can do the job right just by feel, you need a dial indicator. Following these instructions, the bearings will last decades.

The 944 rear setup works well with the RX7 front. You can get away with a stock master cylinder, but you'll have a long pedal. I'm working on adapting the RX7 master into a T1 chassis.

Lanner

[martilo]

That mean you install your bearing adjusted on a dismounted spindle? .001-.003 is not a big thing to measure... Do you have pics of your setup with the dial?
As for the master cylinder, the RX7 is a power brake unit right? How is it supposed to work on the bug? (power brake is one of the thing I really don't understand... )

[flat]

Martilo,

I've attached some pics of my dial setup when I'm adjusting bearings. It's easier to do it on the car, because the weight of the indicator base will keep the rotor in one position.

As for the rx7 master cylinder. It is off a power unit (vacuum). I'm gonna take it off the booster and figure out a mount to bolt it up. The booster in this application (and others) uses engine vacuum on one side of a diaphram that is typically 5-10 times the diameter of the master cylinder. Therefore, with engine vacuum (8-10psi) helping, you have to press a lot less on the brake pedal. Some cars use a hydraulic assist and some newer VW's and Audi's are using an electric assist. Without a booser, most people find 50-65 lbs of force at the pedal acceptable. With a booster you may only have to give 10-20lbs of leg pressure.

Race cars never run boosters because the give a spongy feels and don't help with driver confidence. When you're running 340km/hr, you need all the confidence you can get. Depeding on your driving style you may want a larger diameter master cylinder that gives you a very short travel at the pedal, but will require more leg force. I personally prefer a short travel pedal. The increased pedal force doesn't bother me. If the lady of your house also drives the car, then she'd probably not like the pedal effort required to stop the car.

This rx7 unit I'm looking at adapting is available in 2 flavours 23.8mm and 25.4mm. It's a aluminum master and tandem just like the stock VW MC. I think the 23.8mm unit will work well with P-car brake conversions. The 25.4mm would require a strong right leg!

Lanner

[martilo]

Good, that should be fine. (BTW *that* driver seat is a no lady territory )
I'm getting more and more discouraged about finding all the required ingredients. I'm in Algeria these days for 1 more year and the very last thing you'll find arround is a P944 (needless to talk about the parts...). Even if I try to source it in France, its freakin' complicated to find all of what i need for the rear (caliper might be playable, but the rest... ).
Can you supply the complete kit out of a box (i mean front RX7, rear 944 in 5-4.5" complete, like in *very complete*) or should i wait to be back home and start wondering arround scrap yards?
I don't want to end up with a compromised kit that i will regret too soon but there is not that many options...

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Martilo,

I can arrange any parts you need. Email me and we can talk details. lanner@vdubcustoms.com