My Brakes Suck!

[jeffball610]

I went a different route when building my car, so "the formula" doesn't completely apply to my setup. I've tried a few different things, but I'm still not happy with my brakes. Here's what I've got going on:
S12 V6 struts
11" Z31 front rotors
Z31 2-piston calipers
Porterfield pads
11.5" Z31 rear rotors
Maxima (maybe other) single piston rear calipers
Parts store pads
7/8" master cylinder
Willwood proportioning valve
Motul R600 fluid

I had a 15/16" MC at one point and went smaller to hopefully get more pedal travel. I also tried a B210 brake booster, but it didn't change the feel. The pedal is pretty stiff with little travel. I can manage to lock them up with extreme effort, but they feel like wood most of the time. I've considered swapping in Z32 4-piston front calipers, as they should be a bolt-on solution, but I've been wanting to figure out what I'm doing wrong first and make sure that this change won't just make things worse.
I've got good tires as I'm running the new Bridgestone RE71-RS 205/45/16. The brakes work and I've done multiple track days on them, but they are not confidence inspiring. I want to be at ease when I get on the brakes knowing they will do what I need them to and get some feedback through the pedal. Right now it's more about how stiff my leg is to gauge how the car will stop

[datzenmike]

You have brake booster? Pump pedal several times to exhaust any residual vacuum. Apply brake and hold. Start engine. What you should observe is the pedal will drop slightly towards the floor as manifold vacuum quickly builds. This is normal operation.

The brake booster increases the line pressure by up to 50%, you should be noticing a difference with it.

A stiff pedal is relative. Maybe a gym membership?

[jeffball610]

You have brake booster?

A stiff pedal is relative. Maybe a gym membership?

I no longer have the booster. It didn't help at all and it actually felt worse. I'm plenty strong enough to work manual brakes. I've only had a couple of other people drive my car, and they all state that the brakes are poor. I understand that manual brakes take more effort, but there is little to no modulation and it feels like wood most of the time. I can still lock them up under extreme cases, but it's nearly impossible.

[bertvorgon]

Unfortunately, this type of thread has been common over the years on the Realm.

As you departed, I think, from what was "kinda" convention for a lot of our brake systems, as have others, everyone has their take on how to do something.

Is it just that the Brakes..PADS...feel like they have no LINEAL grip? There is no real "soft" feel for most of us, the pedal is very firm. But, the LINEAL grip is what stops our cars, as any race car in someways, and, gives us the braking control until incipient lock-up..

Have you made sure your Porterfields up front are not full race by mistake?

I don't know if you ever saw what I did with mine, I put a 1" extension into my brake pedal, that increase in leverage made all the difference in the world. Also let me heel and toe easier too, at least for me and my small feet.

Maybe try to match compounds front to rear and get something as soft as possible. That is what I finally did for both Solo and Hillclimb, run the softest pads I could get. Our cars are light and getting brakes to temp is not easy unless your solo events are stupidly fast with heavy braking areas. I out-tricked myself over the years running race pads, at least for Solo events. Even with my soft pads now, I hardly ever get my brakes hot on the fastest canyon carving.

Have the pads had time to transfer to the rotors? I'm sure you know some pad and rotor combo's need a break-in time.

[datzenmike]

The stock master is only 3/4 or 12/16" so 7/8 (14/16") may still be too big for not having a booster. Larger masters definitely increase the pedal effort. Maybe the booster you had wasn't working properly. A 50% reduction is effort you would most definitely notice.

1/ put the booster back on if you have it and perform the test I posted earlier.

2/ if you have the original 510 master put it on and try it. I bet the feel will be very soft with lots of travel.

I have a 710 that has a 3/4 master, and a booster. I went to 15/16" with Maxima calipers and noticed no difference with the braking effort. I have had the one way valve accidentally blocked and it was like stepping on a concrete curb! I used both feet to stop in the driveway!!!


Your 510 is at least 500 pounds lighter than me and the brakes should be excellent.

[James]

I have been thinking about this (I recently put on a 7/8" master from a z). I was wondering if you were to raise the attachment point of the clevis to the brake pedal. This would effectively increase pedal travel for the same master stroke - which would soften pedal feel and effort.

I did a quick drawing of my concept. I realize this would add some eccentricity to the system, but would it work? It would an easy thing to make.

MASTER CYL..pdf

(16.39 KiB) Downloaded 28 times

[icehouse]

Your combination is close to our racecar, only difference is we have Z32 calipers instead of Z31 front and rear we run the same rotors z31 front and rear. We have the 15/16 master it was 3/4 for the first couple years way to squishy. Downside of the z32 calipers is that wheel clearance becomes an issue. maybe they will fit easier under 16" wheels.

Do you have a proportioning valve? The balance is very critical 1/2 a turn in our racecar goes from feeling like my 64 vw bus to feeling what I imagine driving Keith's car to be like! Also we tried the best "performance" pads off rockauto they didn't even last an hour before they were burned out. We run Porterfield RS-4 pads. Rears last 40ish hours the fronts 20 hours. They are good out of the gate. No warmup required which we like. My autox skills like to pass everyone on the first couple laps while everyone else is warming up still

[bertvorgon]

Not sure the diff would be worth the effort to notice.

That is why I just put a 1" piece in brake pedal. Easy peasy and leverage increase was substantial, with really good feel.

This increase in the "lever arm" means I have so very good modulation with lessor effort.

Brake pedal is still FIRM to say the least, which is what we want and expect, as in any race system with minimal deflection. The pedal feel comes from a pad selection that starts to grip very early in the rising temp cycle, without undue pedal pressure to accomplish that, only way to have a good brake pedal for modulation, the HUMAN ABS so to speak!

I still would look at pad choice as Mike ( CARTEL SAID)

[jeffball610]

The Porterfield pads I have are the RS-4 like Icehouse is using. I've wanted to try Z32 calipers, so I might as well give it shot. The increased caliper piston area might help the feel and I could run a less aggressive pad. If that doesn't work, I like Bertvorgon's advice on the adjusted pedal location. Barring any of that, a decrease in master cylinder size seems to be the next step like Datzenmike suggested.

Thank you all for the good advice. I have considered each of these, but it's good to know that others have used them with success. I didn't want to do something just to chase my tail or make things worse. I'll report back. I also desperately need to update my build thread. A few things have changed since my last post

[bertvorgon]

You can see where I did mine, near the steering column, good strength there.

[James]

Not sure the diff would be worth the effort to notice.

That is why I just put a 1" piece in brake pedal. Easy peasy and leverage increase was substantial, with really good feel.

In terms of ratio - moving the mounting point up on the brake pedal arm is effectively doing the same thing in terms of lever arm: The lever arm ratio is longer so greater pressure, and the stroke in the master is shorter - so the increase in the pedal travel for the same result is what is desired. I have big feet, so putting the pedal closer to the floor may not be as useful - but I guess I should take a look and see. I was going to try this concept out. Fashion a bracket and drilling a hole in the pedal, which can remain in place. Plus I can always go back to the original. I guess I'll have to figure out the math to see where moving the hole would provide the same leverage effect as 1" added to the length of the pedal. It's probably not much.

[bertvorgon]

Yah, I figured that.

here is how mine look, nowhere near the floor upon major braking, but not a lot of travel either, they are race brakes after all.

Sure made it easy for heel and toe, or, in the real case, left side of foot, right side of foot.

[Byron510]

I would agree that changing the pad material is the first step. Pads need heat and friction to start to work. A rotor that big has significant swept area, compared to what your car came with. I run a really high pedal ration Tilton box on my “street” car, due to that I need both legs, one arm and my left nut to stop the damn thing. It ain’t fun on the street. I let few people drive it because of the brakes, you really have to use a lot of effort. I run ZX hubs & rotors on S12 struts with Keith’s old Willwood Dynalite calipers.
I settled on Polymatrix A compound pads for my application. They are not the best pad, but a good compromise. On track days, I can stand on these brakes till my ass is coming off the seat lap after lap and they go all day long but the pedal effort when cold is high, and I accept that.
For full street, the softest, dustiest pads out there are likely your friend in this case. Have you tried just a good quality street pad? Maybe even get the Z31 factory pads from Nissan? You may be pleasantly surprised!
Byron

[Danthewire]

The Brake Bible by BillaVista Pirate 4X4.com
Try that write up.

link here

[jeffball610]

I took my brakes off this week to check things over and swap in some "street pads". The pads I ordered didn't fit, so I just reassembled. I noticed the grease in the caliper slides was pretty sticky, so I replaced it with good stuff. This seems to have helped the pedal feel slightly. I haven't done any hard braking or threshold braking yet, so I can't confirm it's any better. I think I'm still going to get some Z32 calipers as long as they fit with my current wheels. Parts Shop Max has repos that seem nice for a good price. I just need to find a template so I can mock things up to see if they fit.