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the search for the perfect brake pedal

28K views 97 replies 28 participants last post by  Alex W 
#1 · (Edited)
since my brake MC was dying anyway, i decided to try a little experiment with making the pedal feel better. having driven a couple formula cars, i really wanted a brake pedal that felt comparable to that- solid. so i did a little research. i figured that increasing the MC bore would move more fluid (less pedal travel- it always sank too low for me anyway) and generate less brake system pressure (requiring more pedal effort- increasing feel and modulation).

after a few hours of digging, i found that the stock master cylinder was 7/8" in diameter for the 91 turbo. the 93 turbo upgraded to a 15/16" bore. i wanted to know what else was available, so i went to rockauto and started researching, looking for a MC that was physically identical to ours but with a bigger bore. several options came up, with the largest being 1 1/16" bore. carroll smith stated at one point when talking about master cylinder sizing: "make the master cylinder as big as the driver can handle." so that's the strategy i decided to try first.

the MC is from a 1995 toyota 4Runner V6 with 4-wheel ABS (the 2-wheel ABS and non-ABS use the same 1" non-ABS style MC). i found one at a local yard for $25 +$2 core and snatched it up. took about 45 min to swap over and bleed (you really only have to bleed to to prop valve, since no air is introduced any further down the line than that).

the results were pretty much exactly as i expected them to be: the pedal is rock solid with excellent modulation and very little pedal travel. effort isn't increased as much as i thought it would be, but i suspect the booster is responsible for that. the brake pedal actually sits a little higher than i'd like it (relative to the gas pedal) but i can space the gas up a little to fix that. i'm very happy with the results, and i can't believe how much better it feels than it used to, even when the MC wasn't failing. i think if i were to try it again (and i just might), i'd start with the 1" bore. there are a few models that will work for that:
1995 land cruiser
1995 tacoma
1991 supra turbo

i'm going to try scavenging the yards for one of those next, since the swap isn't too hard or time consuming.

once i'm happy with it, i plan to flush and bleed the system again to seal it up.

i hope this helps someone else who wants a better feeling brake pedal.
 
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#3 ·
I have doubts about how well this would work in a performance environment. Just having a turbo MC on my NA brake system made the sweet spot for brake pressure difficult to find. (It was very easy to exceed tire traction threshold and lock 'em up) I can only imagine that going this large would make it even tougher.
 
#4 · (Edited)
the 91 turbo and all years of NA list the same size master cylinder bore- 7/8." did you put a 93 turbo MC on the car?

i also realize that brake feel is something of driver preference too. what i like, not everyone else is going to like. but that's why i stated what the goal was in the beginning- to make the pedal feel as close to a formula car as possible. i'm pretty happy with it, but i'm sure there are people out there who would rather have the pedal move more. for me it's easier to modulate pressure instead of movement- especially when downshifting. other people may be the complete opposite.

i'm also entertaining the possiblilty of going a little smaller, just to see how it feels.
 
#6 · (Edited)
well, if anything, i know mike told me you guys are planning to do wallcrawlr's suspension this weekend. i could swing by for a little while to help or something, you're more than welcome to take my car out for a drive to see how it feels. i'd love some outside input on it, and i think if anything it would make a good counterpoint to my original post.


edit: i just spent another ~45 min in the car (this time with normal shoes- last night i was wearing my simpsons) and the more i drive it, the more i like it. i'd really appreciate if you and mike could take it for a spin at some point to let me know what you think. i'm really looking forward to your opinions on this :D
 
#7 ·
I'm definitely interested. I would really like to test some of the other units to compare the volume of brake fluid held by the front and rear chambers. And when are you going to land on some better brake pads? We've been tracking on Carbotech XP-8's and haven't even managed to push them out of the pad's comfort zone yet.

I know it isn't an issue for you, but have you researched the bias valves at all? Right now Gariloch's car is still running the '91 NA proportioning valve, and I have to modulate against rear brake lock-up while I'm threshold braking at the track; we need to fix that. The original plan was to use an OE turbo proportioning valve that matched the calipers. With the XP-8's, I can lock all 4 Hankook RS-2's at will with about 80% brake. I can lock the just the rears at about 70% - it makes for some interesting trail braking moments .. I had some fun at turn 3 on BIR - almost every lap. :)

On a related note, alot of the guys we were at the track with last weekend were surprised at how hard BIR was on brakes - they were comparing it to Road America, but not quite as bad. If that is correct, then building a RA capable braking system for the MK2 should be doable with all OE or replacement Toyota bits. We could have easily run 1 hour sessions without overheating the current brake set-up.
 
#8 · (Edited)
pretty cool. i'd like to try it but my brakes already lock up the way it is.

eroshi not sure if brake pads help. my experiance with using porterfeld r4s is when i first got it i installed the rears only (oem fronts port rears). this setup yelded okay braking but at the lock up point the rears would lock up a little before the fronts it was so minor you could almost say both the fronts and rears lock up at the same time, this is of course on a stright line i'd probabally make your hands full with trail braking. when i installed the fronts now having all 4 corners with new rotors calipers and porterfeld pads the limit was much higher then the oem-port setup. this however cause the fronts to lock up at 80% braking. very annoying if you ask me, but it brakes nice and i like it.
 
#9 ·
erioshi said:
I'm definitely interested. I would really like to test some of the other units to compare the volume of brake fluid held by the front and rear chambers. And when are you going to land on some better brake pads? We've been tracking on Carbotech XP-8's and haven't even managed to push them out of the pad's comfort zone yet.
i'll land on carbotechs when i can afford $300 brake pads :D at the moment, i'm still pretty happy with the redstuffs, though i haven't had a chance to push them. iv'e had them smoking and they really don't change much in feel as they heat up. they seem to get a little stickier, but they're pretty consistent. for sure they're nowhere near on par with carbotechs, but i'd like to see how far i can push them.

I know it isn't an issue for you, but have you researched the bias valves at all? Right now Gariloch's car is still running the '91 NA proportioning valve, and I have to modulate against rear brake lock-up while I'm threshold braking at the track; we need to fix that. The original plan was to use an OE turbo proportioning valve that matched the calipers. With the XP-8's, I can lock all 4 Hankook RS-2's at will with about 80% brake. I can lock the just the rears at about 70% - it makes for some interesting trail braking moments .. I had some fun at turn 3 on BIR - almost every lap. :)
haven't looked into the prop valves at all. mine still has the stock balance, but i'd be interested to see what kind of bias you're getting with the NA prop valve on turbo calipers. i'm still locking the fronts well before the rears, but that could also have a lot to do with the differences in tire sizes. the stock rears were a bit narrower than 245 :p

On a related note, alot of the guys we were at the track with last weekend were surprised at how hard BIR was on brakes - they were comparing it to Road America, but not quite as bad. If that is correct, then building a RA capable braking system for the MK2 should be doable with all OE or replacement Toyota bits. We could have easily run 1 hour sessions without overheating the current brake set-up.
hmm. so i may as well scrap that 12" rotor upgrade for the stock calipers that i've got drawn up then, huh? hehe
 
#10 ·
Tire size and compound is such a huge issue when setting up suspension and brakes, lol. And any changes can start the whole process over.

With the NA bias valve we were both getting rear lock-up even in straight line braking. I always end up trail-braking into turn 3 because the corner is so long - otherwise I waste about 1/3 of the corner just coasting towards the apex. I think there may also be a couple of other tweaks that could help control things. If an OE prop valve will cause early front brake lock-up then I think I'll tweak the NA system instead. More stuff to play with, lol.

A rotor upgrade might be exactly what the doctor ordered - for a turbo or v6 set-up. Gairloch's car is an NA, and a turbo car would put more heat in the brakes. I'm expecting that with good pads and a well balanced system, my ('93 turbo) brakes should still be faster than my v6 swapped chassis.

Of course you can overheat almost any brake set-up if it's being driven poorly - part of being a good performance driver is maximizing your results within the limits of your equipment. What I expect though, is braking comparable to my Evo; even with putting on R-compounds and pounding the car hard for an hour, the brakes didn't fade. At least until the pads were badly worn at the end of the season - then they would fade just a little.
 
#11 ·
After driving scarecrowX's car both before and after, I can offer that his solution definitely decreased pedal travel in increased clamping force.

In my case, my brake pads are so aggressive (go Carbotech XP-8s) that I actually want a bit more brake travel to make modulation easier. What have found, though, is that the 93 turbo master cylinder still requires more brake travel than I prefer. My next step is going to be testing a 1" bore master cylinder for 1991 supra turbo. Everything should be ready to go by my next track event; Mid-America Motorplex on June 17-18th.
 
#12 ·
The '91 Supra master cylinder I received is manufactured with a top exit for the line nearest the front of the car (like an ABS MR2) so it is not a drop-in replacement for a non-ABS MR2. Unfortunately I needed my new MC by today so I had one sent to me by 2nd day air - ouch. So either they sent me the wrong part, or the Supra part isn't a drop in solution for non-ABS cars.

I have located a Tacoma MC locally that has the correct line exits - I will be picking that up later today. Hopefully this part will be what I'm looking for.
 
#13 ·
The '99 Tacoma master cylinder was a bolt-in replacement - as long as I was willing to use the Tacoma brake fluid reservoir. Since I was going for an OE stealth look, I ended up needing to modify both the MC reservoir mount and the MR2 OE reservoir very slightly to make everything bolt up clean and look 100% OE MR2.

My next challenge is that the "93 turbo rear rotors" that were shipped to me are actually 91 turbo rear rotors (boo partsamerica.com - bad part number). It looks like I will need to build up some hybrid calipers using the 91 caliper brackets and the 93 calipers. I'm out of time to order new parts.
 
#14 ·
wow, i'm sorry to give you bad information mike. based on my research, the supra non-abs looked like every other MC i looked at, but i guess i was specifically looking at the ABS units since my car has it. i shouldn't have been so presumptuous.
 
#15 ·
scarecrowX said:
wow, i'm sorry to give you bad information mike. based on my research, the supra non-abs looked like every other MC i looked at, but i guess i was specifically looking at the ABS units since my car has it. i shouldn't have been so presumptuous.
No problem at all - Parts America provided a full refund (including shipping) so all I was out was a bit of time and some last minute pre-race weekend stress. :)

Everything is finally installed and working. My current set-up is 93 front calipers & rotors, 91 rear rotors and brackets with 93 caliper bodies and a 99 Tacoma master cylinder. The SS lines didn't make it, so I will be hitting the track the weekend without them. The brake pads are Carbotech XP-8 all around.

I will provide more feedback after I do more testing, but my initial impression is very positive. The brakes have amazing bite, very short pedal travel, are easy to modulate, and so far seem to be well balanced front to rear. Since I just finished bedding in the brake pads, I haven't had a chance to do any threshold braking yet, but I did try some trail braking and the car felt neutral.

I need an alignment before I can really push the car, I also installed new H&R coilovers and TRD bushings at the same time as the brakes.
 
#17 · (Edited)
The link is dropping to a zip code request. The MC I used was from a '99 Tacoma without ABS. I ended up grabbing one form a yard; not my preferred solution, but I was flat out of time to get the brakes done.

FYI - The salvage yard MC was under $20 out the door with a waranty. At that price I figured I could afford to experiment.

The Parts America MC that did not fit shows as part number 112233 - Cardone Master Cylinder: Reman.; Import Brake Master Cylinder: Remanufactured; Without ABS
 
#19 ·
steeb said:
the only part number i can find for cardone master cylinder reman is 112617. it is for all tacos 2.4, 1.7 and 3.4.

am i doing something wrong? i cannot find any master cylinder with 112233 part number.
The 112233 PN was for the Supra MC.

For the Tacoma MC I called a local salvage yard and had them visually verify that the MC had two side exits for the brake lines as opposed to one top exit and one side exit. Non-ABS NA MKII MCs have two side exits on the MC - I believe that also applies to turbo cars.
 
#20 ·
i rechecked the info on rockauto that i was using to check the specs and it seems that the supra is the only one to use a physically identical MC for ABS or non-ABS. all the other ones i looked at use the double side exit for non-abs and the single side exit for ABS.

i double checked the info for the 95 land cruiser too. the ABS and non-ABS correspond with the styles we need for our cars, so the land cruiser is also an option. the 91 supra MC is still an option for ABS cars.
 
#21 ·
Back from MAM and the new (99 Tacoma) MC was perfect! Just the right amount of pedal travel with easy to modulate feel. I didn't notice any change in pedal travel the entire weekend.

The '93 trubo front brakes (with Carbotech XP-8 pads) are amazing - not even a hint of fade with great bite and modulation. The '93 turbo rear calipers mounted on 91 brackets with 91 rotors still provide a bit too much bite.

I was threshold braking the car amazingly well and could even trail brake it without issue. I was able to late brake with anything on the track in my run groups, even the r-compound tire cars. However, there is still a bit more stopping power available that I can't reach with the current configuration. I need to get a bit more front brake bias to take maximum advantage of the car's potential.

Anyone have ideas? I am hoping to be able to accomplish this without installing a manual bias adjuster or changing out the rear pads (for now). I know I can try more aggressive front pads, but would like to avoid that expense for a bit. I may try installing '91 rear calipers to see if the slightly smaller caliper pistons will help reduce rear bite.
 
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