I am wondering if anyone has PBR calipers and actually measured the pressure at the caliper?

If you have changed anything away from stock like master cylinder, combo valve, or braided lines that would be helpful too.

Thx!

 

why are you asking? feeling like back brakes not engaging?

 

I've made a lot of changes lately to the braking system - bigbrake upgrade, manual brakes some time ago (I have a thread on that), master cyl, combo valve. I've just rebuilt the rear calipers. I'm regretting changing (tossed it) the combo valve since it was a rare one and probably doing it's job and I misunderstood what putting a wilwood valve in would do.

I want to get a baseline to see if I'm in the ballpark pressure wise. I've been on the road course and fronts are working well and the pedal is very hard of course being manual. But I don't know what if any the rears are doing.

I'm not sure what I want is really what I want - that is to control the effectiveness of the rear brakes. There are a lot of considerations with rear brakes and me messing with them maybe is not the right thing.

In my case Brembo said change the rotors, pads and use braided lines but don't change the calipers, bias, or master cylinder.

I have the brake pressure gauge on hand so I will test this weekend presuming the Sienna power steering leak does not turn into a full on rack replacement :-(

Tim

 

kind of hard to tell what your setup is, but if you have adjustable proportion, maybe you could take it to safe place, so real slow and adjust so only the backs are working/primarily working and get a feel for what they are doing. or lift the car up and have someone apply the brakes while you spin back tire and see if they are even engaging.

 

Proportioning valve controls the rear line pressure ratio relative to front. I have the Wilwood proportioning curve if you're interested. Had to twist their nips to get it out of them.

Give this a read and then get back with us. I can do some calcs for you if you want.

https://www.thirdgen.org/forums/brak...ng-torque.html

 

Which valve would that be?

 

Combo valve for J65 PBR calipers.

 

Thanks for the offer to help. Today I measured just over 1500 lb of pressure at each rear caliper simulating a panic stop (jammed on brakes as hard as I could.) This seems like a lot from what I've read.

Next is to take it for a test drive to see what that feels like. Will report back. Storm here in S FL so it may be a couple days.

 

http://www.flynbye.com/catalog/i160.html

I bought this from Flynbye performance years ago . I'm not looking to sell but Ed (of Flynbye) may still have stock.

 

Thanks for that. In retrospect I would still have it but now that I seem to be in an overpressure situation maybe that **** on the Wilwood valve will be useful to turn it down some.

Some test driving necessary, once this tropical storm passes.

 

By my estimations, the Wilwood prop valve can achieve greater line pressure than any of the OE combo valves. Dial the Wilwood somewhere between 1/2 to 3/4 to end up in the ballpark of OE.

 

Interesting. So to me that means I have it open further than 1/2-3/4 and that's why I am getting higher than OE pressure. So I should get better rear braking. Will test drive on Wed and report back thanks!

 

Went for a drive today, only the left front locks up during a low speed emergency stop. Tried repeatedly on a uniform smooth asphalt surface and got the same results. I will bleed the right front and see if I can get consistent lock ups at the front. Will test the pressure there too.

I guess I need to start looking at more bitey rear pads and rotors if I want rear lock ups. If I get that then I can tune down the rear pressure with the Wilwood valve.

On another note I replaced the cones in the 9 bolt and have smooth action in tight turns and the tires both spin during burnout.

 

Be careful with rear brake. Bad things happen when the rear lock up. And they'll lock up easier when you come down hard from high speed. So you think things are dialed in on the street and then you go to the track and lock 'em up by accident.

 

Where did you source the cones from?

Thanks

 

Took 3 weeks to come in from 9 bolt.com in Australia. I bought the HF bandfile belt sander and their 60 grit warrior sandpaper cut into strips to remove the lip from the carrier sides. Worked great.

 

Any suggestions on how to dial them in?

 

You want to put the car in a condition with a lot of weight transfer to the front. The more weight transfer to the front the less rear brake is needed and the easier the rears will lock up. Ideally a hot day when the tires are real grippy. Or maybe find a downhill slope. You've got it right when you have the shortest stopping distance. That's when the front-rear brake bias is best.

 

And if you have drag radials then you'll need to dial the rear brakes down big time in the rain. The rear tires will lose so much traction with water that it completely messes up the braking bias of the car and the rears will skid around all day.

 

Well with my 4th gen manual master cyl and the Wilwood prop valve I have equal pressure at all four calipers during emergency braking - 1500 lb. The prop valve is turned all the way in so no reduction in pressure to the rear.

 

If we believe the pressure gauge then I guess that means there is no proportioning. The Wilwood can't do that when it's working right. If I remember right, I think it has a 43% proportioning rate after the hysteresis.

 

I think my plan now is to increase grip in the back with better pads and rotors since I've got max pressure. Then I can use the valve to reduce rear pressure to where the brakes are reliable and predictable.

 

I kind of doubt that because it's not lowering pressure now. According to the published pressure curve, the max hysteresis of Wilwood valve is 900 psi, so anything above that will be reduced no matter what the setting. Should be seeing no more than 1200 psi out back with the fronts at 1500 psi and valve at max adjustment.

 

I don't think I said before but the valve has been turned all the way in for testing resulting in full pressure 1500psi to the back. If I start unscrewing the valve the rear pressure is supposed to drop.

Wilwood says start with the valve all the way out (least pressure to the rear) then turn it in gradually (increasing rear pressure) until the rears lock from 30mph. Then adjust back for max stopping power with no skidding.

Right now at low speed with max pressure to the rears (**** all the way in) I do not get lockup. I haven't done emergency stopping from 30 so I'm gonna try that next.