Brake bias question

[ZR8ED]

Ok I've been doing some reading the last night or two, trying learn a bit about brake bias. Thanks John C. for some excellent posts in the FAQ section.

 

Now after some of this reading, I understand some of the things I have done to the car, and something that I am about to do this wed to the brake system. I am also now wondering how i'm going to dig myself out of this..

 

Some info.

2900lb 280z. very close to 50/50 weight bias..mainly due to engine setback position of my vg30ET motor.

 

Upgraded sway bars

tokico shocks,

chevette springs in rear

cut springs in front, some new poly bushings

(coilovers to be installed possibly this season)

300zx vented rotors.

S12W Toyota calipers

Metal master pads

SS braided flex lines front and rear.

Stock rear drums

upgraded rear pads.

235/45/17 Yokohama AVS sport tires.

315/35/17 rear tires..same kind.

 

Stock brake proportioning device. and brake M/C

 

Adjustable brake proportioning valve to be installed this week.

 

Why? the new valve. I'm locking up the front wheels under hard breaking, and the rears do not "appear" to ever lock up.

 

Why? I have increased my front bias by upgrading the front brakes and not the back brakes. I also have a lot more rubber on the ground out back.

 

This is not likely to change this year. no more budget for brakes this season.

 

I see some track time will be required for experimentation, but I think I need a bit more braking sent to the rear brakes.. maybe only a couple of %

 

Any thoughts? warnings? ideas? Am I on the right track?..even if it is a bit half a$$ed?

 

Thanks,

Scott.

[JMortensen]

I've got a few comments/suggestions:

Is your distribution really 50/50, or are you just guessing? My Z with the L28 and a R200 and a roll bar but otherwise basically stock was 49.5/50.5. If you just said I have a 280Z with a VG30T I'd guess that it was going to be 47/53 or something like that.

 

If you have really big fronts compared to the rears the adjustable proportioning valve might not be enough to fix it. I had Toy fronts and 280ZX rear disk and I couldn't get enough rear bias. Even took the prop valve out completely. Still not enough. Other ways of fixing the bias: different pads front and rear, dual master cylinder setups, different wheel cylinder sizes, suitable rear disk brake upgrade. If you want to keep the drums I'd see about changing the wheel cylinders out for something bigger then use the prop valve to dial the back end in.

 

You have gigantic tires in the back as well, so you can probably push a little more bias to the back just as a general rule.

 

If you drive this car on the street the safest thing to do is do the lockup test in the wet and set it there. Don't want it set for perfect dry conditions then find out that it wants to loop around as soon as there is water on the road.

[ZROSSA]

You can run more rear brake bias in the wet becuase you dont have as much forward weight transfer when wet. This means you will then be locking up the rears in the dry. Always a compromise. You choose.

 

Cheers, Douglas

[Clifton]

My only suggestion would be to put it arms reach in the car. Mine is just behind the passenger seat on the trans tunnel so no one can accidently turn it.

[ZR8ED]

Well you got me there Jon. I am mostly guessing at the weight distribution... Car weighed in at 2900lbs when weighed in its current setup...it actually weighed less a long time ago.. I had the weight down to approx 2680, when it was much more stripped down.. Adding the weight up has suggested to me that the distribution is still close to 50/50.

 

Rear disks are in the plans, but have just not found a setup that I like..at least a set that fits my budget...Its hard to find the $ to fix stuff that I haven't broken, when I still have things to fix that I do break.

 

I'll settle for minor improvements, as long as I can work towards a better balanced solution/setup.

 

Thanks!