manual brakes for 85.5 n/a car

You need a really aggressive pad to make this work. A Hawk HP70, Wilwood Polymatrix A, or similar. It made a world of difference for me.

It does sound like your pads may be the problem, especially if you can generate that kind of pressure you are listing. I'd look to an entry level racing pad and skip anything rated as street or a "street and track" crossover pad. I like Carbotech's XP8 for an entry level pad on a really fast car. Expensive, but a high level of friction across a really broad temperature range. It makes them very predictable and easy to drive, hot or cold. There are other pads from other vendors that will also work, but stick to real racing compounds. Some heat paint should help you fine tune compounds once you have pads that will grip.

id expect a whole lot better braking with 1300psi. i know its not going to be as good as a newer braking system that im more used to (my daily is a cobalt ss/sc, its got hawk hps pads and bfg sport comp 2 tires, it stops pretty decent). the biggest thing is the initial bite is ok, however from that initial bite you can push as hard as you want and it doesnt slow down any faster. its the worst feeling ever. the pads and rotors on the car are what were on it when i bought it. pads are unknown, rotors are drilled and slotted, looks like they dont have much mileage on them. they have however sat for almost 15 months, rotors got rather rusty, typical project car. the car did stop decently, i sort of remember how it felt for my 3 hours i got to drive the car before it caught fire.

so i thought about turning the rotors and flat filing the pads, but i just dont think its worth it. i have lexus ls430 calipers and wilwood 2 piece rotors, along with rx7 calipers, why bother wasting any more time with the stock stuff. ive got everything short of front brake hoses and front caliper brackets. i spent the evening tearing apart the front end, got the spindles and hubs cleaned up and blasted. tomorrow im planning to powder coat all that, blast and coat the calipers and figure out the caliper brackets, and hopefully get them cut.

Exactly.... get it done now and be safe! I had the same pedal feel with the 1" wilwood tandem. The car stops very nice now with the mustang hydroboost; it's like night and day. The front brake hoses will thread into the LS430 calipers, I just used a copper crush washer with them.

What setup do you think you're going to go with?

good to know about the brake hoses, my fronts are brand new. got all the adapters to run -3 hoses, however when i ordered all the stuff i didnt know how long the hoses needed to be.

im still planning to run manual with this. hydroboost is really my only feasable boosted option. i may need to use an mr2 electric pump to do it.

well here is the update on this. stuck the brake swap on with the 3/4 bore master and that was terrible. took about 1 and 1/2 pumps to get pedal pressure, no air in the system. after some more calculating and research i came up with the 3/4 bore master not moving enough volume for the lexus calipers. swapped the wilwood 1" bore master back on and it felt alright. drove the car around today and it just didnt feel that great. the car stopped decent, seemed like too much pedal travel though. for kicks i crawled under the dash and moved the pushrod back to the factory hole on the pedal, after that the pedal felt great. driving it around the parking lot i found it was easy to modulate, decent feedback and plenty of power (50km/h was able to lock all 4). so im going with it and ill re-evaluate it once the pads bed in.

pics just because lol

Thats one thing I never tried with that master cylinder (moving the pushrod back to stock location). Glad it worked for you.

so ive been driving the car on and off, i have roughly 350km on it now since the swap. the brakes have been alright, im not real impressed with them as of yet, but the car does stop and is safe to drive.

so ive made a couple changes since putting this all together. first off, i couldnt get the fc rx7 calipers to stop leaking, i ended up swapping them out for a pair of fd calipers. i also ended up changing the lines off the master cylinder to flexible braided hoses, i kept having issues with leaks on the steel lines off the master.

so the pads have bedded in reasonably well (the ebc break in coating is gone), and they do bite ok, but i feel like the front caliper pistons are retracting too far. it feels like the first press of the pedal the car has more rear bias (car squats down) and if i lift my foot and press it again the nose slightly dives as you would expect, and braking feels far better. tonight i added a 2 psi residual pressure valve to the front (despite the fact i shouldnt need one) and it helped a little bit, but i didnt get the results i was hoping for. when i was bleeding the fronts tonight it seems like the pads are retracting a long ways, after pumping the pedal up and walking to the front of the car i can freely spin the rotor without so much as a slight noise from a pad touching it. it doesnt seem right. when i put around 10 psi on my power bleeder the pedal feels a lot more solid on the first pump, and the pads are scraping the rotors at that point.

so im a little stumped. i shouldnt be needing a residual pressure valve at all (in theory) because the master is higher than the calipers. im thinking about a 10 psi residual pressure valve thats designed for drum brakes, however that just seems wrong to have to do. im want to get this sorted, i was starting to push the car a bit through some downhill twisties and it started got a little hairy. really thats the first time i noticed the problem.

It sounds like you have a volume mismatch to me. You haven’t mentioned an adjustable brake bias valve. With a 1” master cylinder front and rear you’ll need one. I’d also make sure the offset of your 2 piece rotors are centered on the calipers and the rotor thickness matches the minimum thickness for the Lexus calipers (32mm?).

I know the Lexus calipers have a large piston area and require a lot of volume when everything is correct. I couple of guys on here like the Mustang MC (hydroboost) with the Lexus/Mazda calipers, not sure what the bore of that master is or whether or not it’s a straight bore MC.

i do have an adjustable prop valve on the rear. i have been playing around with it however first pedal press is always the same. rotors are centered, i made sure of that when i built the brackets and shimmed as needed.

the nominal thickness of the lexus rotors is 30mm, or 1.18". the caliper can accept a 32mm or 1.25" rotor, and thats what im running.

the mustang master cylinder is a straight 1" bore, at least according to what i find on rock auto.

somebody else i talked to thought i might be having piston knock back caused by the spindle or caliper mount flexing, and that causes the pistons to move back in. i dont think im having knock back being i can have it happen in my driveway on jack stands.

I’m pretty much stumped as well. A 10psi residual valve should work as long as the rotors don’t drag too much. Have you tried leaving the MC cap loose (vented) to see if the calipers still retract?

yea ive tried it with the cap off, and also confirmed that the cap is breathing. i tried it again tonight with the pressure bleeder, 12psi is when the pads start to drag, i get no drag at 10 psi. i might try out a 10 psi residual valve and see what happens.

I don't know if you guys are still running with the ABS system or not, but here's a video taken of a  tech session at a track day.  There is a lot of interesting information in the video, but you will need to sift through the info to figure out what applies to your specific brake set-ups.  It has some good information that covers many different aspects of brakes and braking systems.  While the video pays lots of attention to ABS issues, there is still some very good info for non-abs set-ups.

I first saw the video a few days ago on a thread in the 928 forum about brake issues in a race car.  Ir was posted on renlist by Jim Devine.  I'm not sure who filmed the tech session originally.

Link: https://vimeo.com/88285081

I'll have to give that a watch when I have some time.

Btw: no abs on my car, it's a late 85. I'm not sure when the 944 got abs, but I don't think any of them that early did.

Not sure if you are still looking at brake options but I have two servos where the glove box used to be.
I will also be fitting new pads but for now that has solved the braking along with a faulty ABS pump.
Q

no i have my brakes on the car now, (ls430/rx7 combo) it stops fairly well for manual brakes, im just trying to sort out an annoying issue.

ive decided that this winter im going to change up my braking system a bit. ive been driving the car fairly hard of late and im just not happy with the manual brakes, at least the way they are. i wouldnt even entertain the thought of a track day with them, and thats what i want to do next year.

so ive come down to the conclusion that my master cylinder sizing is way off what i calculate it should be. ive been reading a lot about the dual master cylinder setup and the bore sizes used with the calipers im running, its all starting to make more sense. seems the most common sizes are 13/16" front and 1" rear for the ls430/rx7 setup. what has me confused is thats fairly close to the bore sizes of the stock tandem master cylinder, but everyone says that with manual brakes is terrible. im sort of confused as to why duals work and the tandem doesnt.

so im weighing my options. this winter im contemplating making some changes to the engine for more power and more room. (remember, i have a chevy ecotec swap) been looking at things and if i was to relocate my alternator to the passenger side i would have room to do an intake manifold that swept down and close to the block, opening up room around the master cylinder area, and that may allow me to mount a hydroboost unit. however, with the ecotecs power steering pump running off the back of the intake cam thats not an option, and id be putting the alternator in the only other location a power steering pump could go, meaning my only option is the electric mr2 pump to run the hydroboost. things are getting rather complex to get power brakes. i know the hydroboost on with these calipers gives you braking power to throw the passenger through the windshield, its kinda what im wanting after what ive been driving it with.

my other option is the dual master cylinder setup. im leaning towards this, its less complex and more tuneable. im just unsure how good the pedal feel and braking power will be.

I'm sure you could come up with a bracket to mount a power steering pump on the front of the engine. You don't really need to use the ecotec one.





Would those get in the way of the intake your planning? Maybe you could keep the pump in the location its in these pics and move the alternator over to the other side.

unfortunatly the power steering pump would hit the steering rack in that location. the solstice had one year with hydraulic power steering, it had a pump mounted on the passenger side of the engine, and used a balancer with a second pulley. its hard to find those parts, and i doubt enything would fit as it bolts in part to the oil pan, and my pan is very short so i figure itll hit the crossmember. my plan with the intake manifold would put the throttle body right where the alternator is.

Race cars with manual brakes have been diving into turns from over 200 MPH at Indianapolis, Daytona and Le Mans for decades. It doesn’t make sense to me that a 944 can’t be stopped without hydro-boost.

Power assist is a very effective band aid for less than optimum braking systems. Technically, power assist will correct/overcome flow issues. We shouldn’t be treating brakes as a “mod” but designing it from scratch as a system.  This includes large enough lines/hoses without adapters/restrictions that create differential pressures resulting in hard pedals and firewall flex. This is important in a manual system.

sharkey wrote:
so ive come down to the conclusion that my master cylinder sizing is way off what i calculate it should be. ive been reading a lot about the dual master cylinder setup and the bore sizes used with the calipers im running, its all starting to make more sense. seems the most common sizes are 13/16" front and 1" rear for the ls430/rx7 setup.  

You’re running 32mm front rotors, not 28mm Boxter rotors the 13/16 were sized for. Shouldn’t matter but ¾ might be better.

sharkey wrote:what has me confused is thats fairly close to the bore sizes of the stock tandem master cylinder, but everyone says that with manual brakes is terrible. im sort of confused as to why duals work and the tandem doesnt.

It’s possible that the tandem cylinders don’t have a full 1.1” stroke independently because there is only one piston. The balance bars of dual cylinders not only provide a mechanical bias but provide a more balanced, adjustable independent stroke as well.

i think my biggest thing on all of it is its my first manual brake car, and it so far hasnt been going that well. with the sort of power im going to be making next year im not wanting weak feeling brakes. hydroboost seems to be the tried and true method, manual brakes seems to still be a little hit and miss. that being said, ive decided to give the dual master cylinder setup a shot.

as for the front master cylinder size, i did try a 3/4" tandem master at one point, however i was able to push the pedal right to the floor. in the thread discussing the dual master setup the 3/4" and 1" combo was tried with the ls430/rx7 setup and too much pedal travel was observed. now i could be wrong but i dont think rotor thickness would make a difference in travel. the caliper pistons should relax the same amount no matter where in the travel they are. thats why i was leaning towards the 13/16 on the front, although the 3/4" seems to give more equal bias, at least according to the calculator.

speaking of calculator (im using the jake latham's calculator thats been recommended on here several times) ive been playing around with it a lot. at work we are building a street legal race car, its a 72 mazda r100 with a turbo 3 rotor, full tube chassis, quick change rear end, and some killer suspension design. wilwood designed and supplied the brake system. it was nice to punch in the numbers and see what a system they designed looks like. now i know what is acceptable as far as pedal travel, peal pressure, the difference in travel between master cylinders, etc.

im now a lot more confident with spending the time and money on a dual master cylinder setup.

sharkey wrote:i think my biggest thing on all of it is its my first manual brake car, and it so far hasnt been going that well. with the sort of power im going to be making next year im not wanting weak feeling brakes. hydroboost seems to be the tried and true method, manual brakes seems to still be a little hit and miss. that being said, ive decided to give the dual master cylinder setup a shot.
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This isn’t specifically addressed to sharkey.

Are the brakes weak feeling or week? Big difference. Hydroboost or manual, can you push the brake pedal with a reasonable amount of force and lock up all four wheels at exactly the same time? Take out a little rear bias and you’ve got low lap times. If you can’t it’s not right. I suspect few hydroboost systems can do this because of the tandem master cylinders. The tandems have to be machined correctly while the duals can simply be paired correctly. That’s why dedicated track cars usually run dual.

Hydroboost, manual, tandem, dual, all achieve this the same way. I’ll describe DMC because it’s easier to visualize. With the pedal depressed, both MCs should be in the same position in the bore with adequate stroke.(two different things) The balance bar will be perpendicular with the cylinders. If the pistons are not equal with each other we need to change one of the master cylinders. The balance bar will be used to adjust rear bias not equalize piston position. Tandem MCs are the same but have to be adjusted by remaking the pistons different lengths or diameters to equalize them in the front/rear bores. Bias is adjusted with a fluid restriction in the rear circuit.

Hydroboost is basically giving you some assistance in pushing the pedal and speeding up the flow to the calipers with less resistance. It is very good at overcoming flaws and restrictions in the line circuit.

Manual does not overcome anything and flaws in the line circuit will ALWAYS result in a harder pedal. YOU HAVE TO HAVE UNRESTRICTED FLOW IN THE LINE CIRCUIT! There's really nothing hit or miss about a manual system, it simply has to be correct.

Let’s look at a power steering system for a moment. If you remove the belt you have a non functioning PS system, not a manual system. It’s loose from no oil in the valving and sluggish from the wrong ratio. It simply isn’t very responsive. Power brakes are exactly the same, you can’t remove the booster and increase the calipers and call it good.

sharkey wrote:

as for the front master cylinder size, i did try a 3/4" tandem master at one point, however i was able to push the pedal right to the floor. in the thread discussing the dual master setup the 3/4" and 1" combo was tried with the ls430/rx7 setup and too much pedal travel was observed. now i could be wrong but i dont think rotor thickness would make a difference in travel. the caliper pistons should relax the same amount no matter where in the travel they are. thats why i was leaning towards the 13/16 on the front, although the 3/4" seems to give more equal bias, at least according to the calculator.

I agree with all of this, however we both used the word “should”. I pointed out a potential for less volume in the front because experience has taught me that any time there is a potential for something to bite you, it probably will. Rich L. called matching master cylinders with calipers a "crap shoot". Considering that in the past, I have come closer by flipping a coin than Wilwood or Tilton has with their fancy programs that calculate drag coefficients of brake fluid in given lengths and diameters of tubing , I agree with rich.

yea i kind of agree. experience goes a lot farther than a calculator. in reality i may end up trying both and see what feels better. those master cylinders arent all that expensive. i think i may have a couple of the older style kicking around the shop anyways.

I tried several combinations with my DMC and ended up with .625F/.70R. A long way off from what was recommended. My car is street driven with stock turbo brakes.