I posted a thread about replacing an abs delete brake line and found out that the guy who I got the kit from is out of business. So i have to make my own and if im gonna go through all that I may as well try and improve things.

Ive always been very keen on weight reduction especially up front and when I was removing that huge master cylinder I was surprised at how much it weighed. I did a google search and found nothing then a few weeks later Istumbled onto this rx7 that is for sale that has exactly what im looking for.

does anyone know if this is a kit or something custom? Id really like to delete that huge heavy booster and reduce weight and clean up my engine bay at the same time​​​​​​​





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That appears to be one of the Chase Bays master cylinders. Manual brake system conversions are not for the weak-willed. There is quite a bit of formulae and experimentation involved to get the system working properly. I strongly suggest you put a lot of thought into exactly how you are going to design your system because, in addition to being a means of controlling the chassis, it is also a safety system that was designed by trained engineers who did their due diligence when conceptualizing how everything was going to work.

One of the issues you will run into is that the stock pedal ratio is largely incompatible with a manual braking system. The stock pedal ratio is approx 4:1. For a manual setup a good starting point would probably be closer to 6:1. You could retain the stock pedal assembly, but it would necessitate some cutting of the firewall to clear the master cylinder pushrod. M/C bore area is also very important as it will directly correlate with how much brake fluid is moved for a given pressure applied by the pushrod and into the lines and then caliper pistons. You will need to determine your caliper piston bores, desired line pressure, pad area, piston area, M/C bore area, the torque applied at the rotor wrt brake rotor diameter (larger rotor dia. requires less piston/pad area and line pressure to generate the same amount of torque than one of a smaller dia. which is why you see piston dia. decrease proportionately with the number of pistons in calipers that accommodate big rotors), and a few other things.

There is no reason it can't be done, but understand that to re-engineer this system, you must have a solid assessment of what needs to happen for it to work properly, how and why they work, and all potential modes of failure. (both design and mechanical)

If you wish to do it that way, I suggest reading up on brake system design. There are many circle track racing informational resources out there that will have the pertinent information and even show you how to generate and make sense of the information required to properly design your system. FSAE white papers and other technical documents may also be of use.

Wrt the chase bays master cylinder, I have no clue what the bore/bore area is so you would need to find that out from them. I don't think there is any real way to do this the "right way" without increasing the pedal ratio at a minimum. At best you will not be able to achieve the correct line pressure to generate the requisite torque on the rotor and have to press harder for the same deceleration, and at worst someone/something gets hurt/injured/maimed/killed, hence my suggestions regarding the design of the system when attempting to re-engineer these systems.

I understand wanting to reduce weight, but I really don't think you're going to have any quantifiable difference in performance unless you do what I did and deep-six your interior and everything else on the chassis that doesn't actively relate to the performance of the vehicle. The booster is behind the front axle centerline. It's not like it's hanging off the front of the car. You may actually be better served to find methods of distributing weight closer to the rear axle since I presume your car is powered by an LS3 and is probably rather powerful. The only thing stopping you from going faster is being traction limited by weight dist.

Hope that helps.

 

Wow thank you very much and after hearing your in-depth explanation, Im not qualified nor do I have time to re engineer my brake system. Ill get more creative in other areas and just leave the oem booster alone.

 

I think if you are just wanting to change the booster from a power brake system to a manual system, it could be done in a relatively straightforward manner. If you've got the rest of the stock system in place (calipers, rotors etc) all you would need to do is calculate how much line pressure you would need to generate for a given deceleration. The pedal ratio acts as a lever that multiplies the force you place on the pedal into the master cylinder bore. With our stock 4:1 pedal ratio and an approx 2:1 vacuum assist, 100 lbs of force on the pedal gets multiplied by a sum of 6:1 (this is the addition of the stock pedal ratio and vacuum assist) and you have 600 lbs exerted on your master cylinder. The stock master cylinder is a 15/16th in. bore IIRC it will also multiply braking force from the pedal. If you are using aftermarket front calipers with larger piston diameters you will need to use one with a large bore to move more fluid. M/C bore area and caliper piston area (both can be calculated without much trouble).

I'll link a resource that I found very helpful. It will show you how to generate the numbers you need to do what you were trying to accomplish.
https://www.joesracing.com/master-cy...lf%20an%20inch.

I forgot to note in my previous post that chase bays also offers a master cylinder that is advertised as providing the same force multiplication as a 6:1 pedal ratio. Minor trimming of the firewall where the pushrod is will likely be required, but I think this may be the best commercially available solution that doesn't require you to do all that math. No firsthand experience but it may be of use for what you wish to do. I was strongly considering this setup before I decided to work on implementing a dual master cylinder w/ balance bar and a remote pedal assembly.
https://www.chasebays.com/products/c...-1-pedal-ratio

 

Brake booster doesn't actually weigh that much, it's a couple lbs. Some of the latter model ones are a little more compact, albiet most are RHD.

 

Thanks, i think ill be going the chase bays route and even if its 3-5lbs it really adds up over time.