Before people throw in their two cents and say to keep my abs or power brakes, I'm trying to do this the "right " way.

That being said, I want to convert to manual brakes.

I will be going with the Wilwood tandem master cylinder with a 1" bore, incorporating a proportioning valve JUST for the rear brakes to get some kind of bias.

After some research, I see that the "optimal" pedal ratio for that size of a piston would be 7:1. The stock FD brake pedal ratio is around 4.5:1 and I would have a killer leg workout on the track.

Wilwood has a single cylinder pedal setup that could potentially work. But it would require some modifications that are beyond my capabilities.

NOW.

The simplest way to get 7:1 out of the stock brake pedal would to move the clevis hole up about an inch. It looks like the pushrod will not be manipulated too much to create any binding and the throw of the pedal will be changed minimally. There is plenty of room to do so and is completely reversible if it doesn't work out for me.

That being said, here are the part numbers I am referring to.

Rywire Master cylinder mounting plate: Rywire.com
Wilwood Tandem remote Master Cylinder: 260-8794
Wilwood Forward swing brake pedal: 340-1290
Wilwood Proportioning Valve: 260-8419

I'll be building my own DOT approved brake lines and will spend the majority of my engine break-in period figuring out this setup. (Since I can't rag on the car, I won't be using the brakes too aggressively.)

Now for those of you who have tried to tackle this before, by all means, share your experiences.

More to come as this progresses.

 

i am running manual brakes and will get back to your thread when i have some time.

howard

 

Thanks Howard.

I saw your thread from a few years ago and it looke like you were going to stick with boosted brakes. I assume you have since changed that?

 

I'm interested in this as well. I'm researching the rx7 platform for a daily driven electric conversion and don't want to install a 12v vacuum pump.

 

Small update.

I was waiting on parts and was too busy to get anything done.

Pics coming tomorrow with my theory put together.

 

in for results and pics

 

Depending on what you plan to do with the car, you'll probably be fine. I'm going to share some of my experience to hopefully help.

I fought with manual brakes for a long time. There is some information sprinkled throughout my build thread, but here are a few specific posts: post 78:
https://www.rx7club.com/race-car-tec...-875889/page4/

there is more here a couple of pages later:
https://www.rx7club.com/race-car-tec...-875889/page6/

I don't think the 1in mc will give you enough modulation. That is what came in my car and they were bad... really bad. I spend a lot of time researching, reading brake books, and on the phone with tilton and wilwood to get where I am now. I'd go back to a stock set up in a moments notice if I could have, but my cage went through the firewall where the brakes use to sit. I know Blackey's car had the same issue. He was trying to install abs back in the system. I know the owner after him and he had the same thoughts. Not sure on the current owner though.

You can fine tune and fine tune and fine tune. Adjustability for days. I don't think that is necessarily a good thing. For example, on my set up: If I'm running DTC 60(or equiv. like a PFC 01) and an HT-10 in the rear, my bias is pretty good with my tire set up. If I change to DTC 60's all around (as recommended by a pretty large brake distributor), it throws my balance waaaaaay off where my rears are locking, and locking significantly faster than the previous set up (where the fronts lock before rears). That also creates a much more dangerous scenario. If you have ABS(which I highly recommend), it will keep the brakes from locking. I AutoX'd and did track days/time trials for a few years in a different FD before I got my yellow FD that had the full manual set up. As Fritz and Pete will also agree, there is nothing wrong with the stock FD system. I'd guess it's probably 2 seconds faster than what was on my yellow car.

Hope this helps and good luck.

 

Granted a different platform, I had to change from boosted brakes to a Wilwood master cylinder when I did a LS1 swap on a 944 turbo.

The brakes were very firm and required a lot effort. While bearable during stop and go traffic it still stopped fine, but required so much effort.

I had a concern with the effort if I had to track the car. The amount of pedal effort might affect your driving style.(I am pretty sure you will not be able to heel/toe)

Other concern is the firewall flex I see when bleeding the brakes of my FD. If you would pursue this, you will need to reinforce it to help keep it from fatiguing.

Not trying to talk you out of it, but a lot of 944 guys who did the swap really try to keep powered brakes.

good luck!

 

You can reduce the stiffness by reducing the size of the master cylinders. In theory, the softer it is the more modulation it allows for (ie more precise through a larger range of motion). That being said, a stiff pedal offers confidence for a lot of people. You also have to take into account brake system compliance. You want a system that has the largest range of pedal travel with it hitting lock up at the end of it's range; while taking into account a safety margin for fluid boil, system compliance, etc... so you can ensure 100% braking at all times. Oh BTW, without ABS, that point of lock up constantly changes due to all kinds of variants to include brake pad material, tire material and size, environmental conditions, etc, etc, etc... Correctly sized master cylinders will allow you to make large changes, your balance bar will allow your fine tuning. Most of the time, the balance bar will allow you to get where you need to be. Again, I would really try to keep ABS.

 

I came up short when doing this conversion and will be re-addressing this when I move on to my next chassis.

 

any updates on this?