Brake Balance - 4 spot front calipers

[260DET]

Something just occurred to me if you have 4 piston front calipers with single piston rear calipers so as to keep the handbrake, the front/rear brake balance is going to be way out.

 

Assuming for the sake of the argument that all the pistons front/rear are the same diameter, you will have 4 times the pressure on the front brake pads as on the rears. So having adjustable bias on the rears seems pointless.

 

Would it be better to fit the bias adjuster into the front brake circuit in that case?

[74_5.0L_Z]

I have the Outlaw 2800 4 spot calipers on all four wheels. The front have 1.75" pistons, and the rear use 1.38" pistons. The front rotors are 11.5 x 0.81, and the rear are 10.75 x 0.81. I installed a Wilwood Proportioning valve in the rear line, and had to decrease the rear line pressure almost to the limit of the proportioning valve in order to prevent rear wheel lock up.

 

With your set-up, I would install the proportioning valve in the line going to the rear. You just won't need to decrease the rear line pressure as much. When you install the adjustable proportioning valve, be sure to remove the factory propotioning valve. All I did was splice the line where the factory valve was with couplers

[blueovalz]

A floating caliper (with one piston) must be considered as "two" pistons when comparing calipers. For instance, The OEM Z caliper (2 spot non-floating) would have identical clamping power as a single piston floater (if the single piston has the same diameter as one side of the non-floating OEM design). So basically you just look at one side only for both designs in comparing piston areas.

[Guest scca]

Dan and Terry touched on the piston size....

 

its not the qty of pistons but the piston area.

 

the size of the pistons affects the reaction time

pedal pressure and pedal feel is controlled by the size of the master cylinder in relation to the calipers.

 

i have yet to see a car where the fronts lock up so easy as to be uncontrollable. generally the rears will lock too soon as to be effective. most braking force is up front 65%? so the rears are not as important.

 

oh and there is a way to have a handbrake

with 2 piston rear calipers..

i should have a relatively inexpensive setup up soon.

[Ray]

Nice explaination without getting into the mathmatics of it Terry ... BTW how are the supra front brakes working out ??? I have been looking for a set cheap...

[blueovalz]

Love them. The brake modulation is much better (which surprised me as I didn't expect much difference). Unless you like doing this kind of stuff yourself, and don't have a lot of money, then this is a neat swap. BUT, there are a lot of aftermarket (one of our members here) rotors and calipers that can set you up for more money, but less hassle. The point, BIGGER is BETTER (my wife says that's not true, but we guys know better)

[260DET]

Thanks all for the advice

 

Seeing that I'm committed to big fronts, the rear rotors and caliper piston will be big in diameter, too, to help balance. The present setup uses a Willwood adjustable proportioning valve in the rear circuit so that will be left as is. If there is still a problem I can try using grippier/softer pads on the rears.

 

Scca, your 2 piston with handbrake rears should be a winner. I considered using two separate calipers on the rears, one two piston, one sliding for the handbrake only, but concluded that would be too messy and difficult to fit in.

[blueovalz]

The brake hydraulics is just like breaker-bar technology only reversed. The bigger the caliper/master piston ratio (in area), the slower the caliper piston will move in relation to the master, BUT, it will have more "torque" . The breaker-bar analogy is like using a longer breaker bar (bigger caliper). You will have to move the end of the bar a longer distance (more pedal movement), but you can torque the hell out of the nut better (higher clamping force at the caliper). This is why using larger calipers without using a larger master cylinder makes the brakes feel soft. It takes more pedal movement, but will lock up easier without as much muscle (again, the breaker bar). What we need is a good ratio that gives not too much pedal movement (feels like firmness) without requiring a Charles Atlas leg building course to bring the car to a halt. And the OEM ratio is preatty good.

[Tim240z]

Charles Atlas!!!!!!!!!!!!!!

Dang Terry, you're showing your age

Tim

[260DET]

Nothing as neat as your setup, Pete, I didn't know that there was such an item as that Wilwood handbrake only caliper.

 

No, my present rear setup uses a PBR combination caliper, but that is now too small compared with the fronts. So I considered using the PBR for handbrake only duties and adding a two spot.

[pparaska]

You mean like this? :

 

More pics at :

http://members.home.net/pparaska/brakemods.htm

 

I agree a single caliper with handbrake provisions would be preferred.

[BLKMGK]

Pete, can you please provide details, especially pics, of how you did your parking brake cable? I'm about to do the same thing and Mike's giving me the option of putting the brake down low or high - cable hookup may make a difference. I've got room to put it either place I think but cable hookup is giving me pause...

 

Thanks!

[Guest scca]

or and the wilwood spot calipers are acutally

AIRHEART.....

i was picking at the sticker and underneath one of the ones i have it says "A" and a couple have no sticker and no markings.

and one under the sticker said Airheart...

 

are they still around - wonder if wilwood bought the rights to this caliper or just has them "relabelled" for them???

[BLKMGK]

Cute, another thread I can't read for some reason. Posting to bump and try and make it readable fo rme. Sheesh, this is IE for kripes sakes. Will update if I have anything of value to add

 

There, now I can read it. I've not heard anything from Airheart lately but they mostly did airplane brakes I thought. Maybe check out some aircraft sites to see what's up? Perhaps Wilwood is one of THEIR divisions? Dunno'. Pete, pics of how ya' hookd that up would be awesome Me an Mike are haggling onwhere to mount mine - high or low and cable ease of install makes a big difference to me. I've alreayd had the car start to roll away once or twice

[Tim240z]

Since I am running an autobox, can I get away with not running a handbrake? Is the Park of the Auto strong/reliable enough?

Thanks,

Tim

[pparaska]

Jim, the little bracket on the right in this photo:

 

 

 

(Larger version here)

 

is the bracket that holds the stock handbrake cable. I cut part of the stock bracket off and added a little angle bracket to it by welding. It mounts to the top hydraulic brake caliper to AZ Z car bracket bolt on my setup. From that same bolt is another small bracket with a spring that you can see in this photo:

 

 

(Larger version here)

 

It makes the cable housing point down and out towards the lever on the spot caliper. But you have to watch the housing inboard of the caliper, etc, as it wants to smack the unibody frame rail in a bump. I need to work something out for that yet.

 

If you need anymore info, let me know.

[BLKMGK]

What did you do for the cable attachment? The cable? Stock Z stuff or did you have to source this elsewhere?

[pparaska]

Since I used the stock cable and the stock (but modified) bracket t hold the cable housing, that part was easy - just had to find the angle and position to mount the cable bracket at to point the cable end near teh lever on teh spot caliper and to not have the housing stick up too far so it wouldn't hit the unibody.

 

At the lever end, you can see the stock cable end attached to the lever on the spot caliper:

 

 

(Larger version here)

 

I did have to use a smaller pin through the lever arm, and some bushings I made up to make it not fit slopily in the cable end.

[TimZ]

quote:

---

Originally posted by scca:

its not the qty of pistons but the piston area.

 

the size of the pistons affects the reaction time

pedal pressure and pedal feel is controlled by the size of the master cylinder in relation to the calipers.

---

 

Mike is right about this, but I believe that the assumptions about the resulting brake bias are backwards, and I hadn't seen anybody mention this.

 

The reason that larger pistons make the brakes fell mushy is that the amount of fluid volume that it takes to create a given amount of braking force increases with increasing piston size. Since the master cylinder volume has not changed, the amount of pedal travel required to achieve a given amount of braking force increases.

 

Now - if you increase the volume consumption in the front with bigger calipers, but leave smaller stock calipers in the rear, the braking balance shifts to the rear (rears lock first), since the brake force/pedal travel relationship didn't change in the rear. Make sense?

[pparaska]

Makes perfect sense to me.

 

The issue is that the pads will always move back away from the disc. A larger caliper total piston area requires more volume of fluid to move the piston(s) and pad(s) that distance and start to apply force. If the front brake piston area goes up but the rear doesn't, the rear brakes will take up the space (whether between shoes and drum, or pad and disc) sooner than the front take up the clearance. So you will start to develop friction in the rear first. Added pedal travel to get the fronts to start to produce friction (take up the clearance) will mean more force on the rear before the fronts start to have friction.