Brakes working too good…

I would say you should upgrade the rear to get more braking power there to even things up. Going with a 6 piston in front was probably a bit overkill. I haven't read all of it, but this thread may help you. http://www.nissanroadracing.com/showthread.php?t=2781

Overkill? What's that?? lol

I'm a firm believer in it's always better to have too much than not enough!


But thank you, great info in that thread…good read.

Sounds like my first step should be to change the rear pads to something a little more aggressive…it might just be that simple.

Thanks again much appreciated.

You have too much pressure and probably a long pedal. What was the piston area change from the previous setup?

Most likely going to the larger M/C will improve the issue. It will move more fluid in the stroke but have less line pressure at the caliper. So, your pedal will feel taller/firmer but require more leg effort to lock up the brakes.

Actually the pedal feels fine…just like stock.

The piston area now, according to Wilwood, is 4.04…I'm not sure what the Z32 Caliper area is honestly.

Interesting…makes sense…however I read in another thread that the Z32 BMC would increase front bias.

Not really a bias problem, but a pad compound issue. Step up to a more aggressive rear pad.

I have 17/16" BMC, cheapest of the cheap Centric front pads for my front Z32 30mm setup, and more aggressive "ceramic-performance" on stock rears. The rears lock up first on very hard panic stops and moderate trail braking. My more spirited drives I swap out the fronts to more aggressive front pads and the fronts will lock up pretty quickly on moderate-to-heavy braking.

The calipers are what shift the bias in this situation. You've altered the difference between the front piston area and the rear piston area, but kept the hydraulic side, therefore you've altered the brake bias. The master cylinder changes the pedal stroke and the caliper pressure, but since its a single bore master the front and rear circuits are changed equally. The only way to change the brake bias via the master cylinders is to run a dual master setup on a pedal box.

4.04 square inches of piston area? That would be rather small…

http://brakepower.com/help_abc_27_PAC_t.htm

My BBK calipers come out to 7.8 square inch… (change N to 1)

Perhaps I'm reading it wrong?

Billet Narrow Superlite 6 Lug Mount

Piston: 6 Piston Area: 4.04 Pad Volume: 3.8 Mount Description: 3.50" Lug Mount Rotor Width: 1.1 Billet Narrow Superlite 6 Lug Mount

PISTONS: Type: Stainless Finish Red Powder Coat Piston 1 Dia. 1.62 Piston 2 Dia. 1.12 Piston 3 Dia. 1.12 Piston 4 Dia. - MATERIAL: Aluminum FIT: Maximum Rotor Dia. 14

I plugged the numbers into the calculator and got the same - 4.04


http://www.wilwood.com/Calipers/Cali…dth=&pistarea=

looks like Wilwood only calculates the 3 piston areas, I think you need to multiply that 4.04 by 2 for full-floating calipers, resulting in 8.08.

Wilwood does use some pretty small pistons, and unequal size pistons for the 6-piston setups.

I've got the Wilwood 4 pistons, and doing the math myself I get 8.24, and Wilwood lists it as 4.12, so it does seem like they are only calculating half. That said, if yours really is only an area of 8.04, your issue isn't really with the BMC. I'm running a stock BMC on mine as well and under normal driving I don't have issues. If I really get on the brakes hard the front locks first, but that is expected since it has larger brakes and also a lot less traction than the rear (235 profile tires vs 275).

Also, I did some research prior to buying my calipers and my piston size is only a touch larger than a Z32. So at least as far as hydraulics go, it shouldn't operate much different than Z32 calipers.

The Wilwood 4 pistons have more area than the 6 pistons…go figure! Your experience sounds pretty similar to mine in regards to braking reaction. I also have a similar tire disparity with 245's in the front and 275's in the rear.

I gave Dave at Arizona Z a call today to get his perspective and he echoed much of what you and some of the others here are saying.

Passing along his take:

- from the sound of it that the brakes are actually working just as they should and that, simply put, the front brakes are disproportionately powerful compared to the back and that, like Bremsen mentioned, that in and of itself has increased the front bias.
- upgrading the BMC would increase front bias
- He suggested upgrading the rear calipers/discs, disabling the proportioning valve built into the BMC (mentioned in the thread jaq posted link to), and implementing an external proportioning valve
- He asked which size BMC I had currently have. I wasn’t sure off the top of my head but I told him it was the stock Z31 and I guessed 15/16. He said that’s the size he recommends for his full front/rear BBK.

I started perusing proportioning valves. Google brought me to StopTech’s site where they have a technical write up on proportioning valves and list items that will increase front or rear bias:

Factors that will increase front bias
• Increased front rotor diameter
• Increased front brake pad coefficient of friction
• Increased front caliper piston diameter(s)
• Decreased rear rotor diameter
• Decreased rear brake pad coefficient of friction
• Decreased rear caliper piston diameter(s)
• Lower center of gravity (i.e. lowered vehicle)
• More weight on rear axle (i.e. loaded)
• Less weight on front axle
• Less sticky tires (lower deceleration limit)

Factors that will increase rear bias
• Increased rear rotor diameter
• Increased rear brake pad coefficient of friction
• Increased rear caliper piston diameter(s)
• Decreased front rotor diameter
• Decreased front brake pad coefficient of friction
• Decreased front caliper piston diameter(s)
• Higher center of gravity (i.e. raised vehicle)
• Less weight on rear axle (i.e. unloaded)
• More weight on front axle
• More sticky tires (higher deceleration limit)


Taking all of your valuable input into account, my thought process is
- Upgrading the rear pads to a more aggressive compound
- Upgrading my tires to a softer compound…currently my NT05’s have 200 treadwear. I’m looking at NT01’s (treadwear 100 and feel much stickier than that) or Toyo Proxess 888’s (treadwear 100 with a more uni-directional pattern).

This should be a good start in improving the bias balance by themselves until I can tackle the rear brake upgrade and proportioning valve.

The easiest/free upgrade you can try is shimming the rear bias spring in the master cylinder until it binds, it can be a pain to do…

It will eliminate the regular split point that stops the rears getting additional clamping above a certain pressure

It's very likely that's _all_ you need to do

My plan is to upgrade both my rear calipers and rear pad compound. I just haven't actually gotten around to doing that. Need to swap my rear control arms first, along with getting the M30 ebrake drums installed.