Geeesammy Posted June 6, 2016 Report Share Posted June 6, 2016 (edited) Hoping to get the opinions of some more experienced and knowledgeable guys in terms of brakes than I. I'll try to be as descriptive as I can. So I am about to order some parts to finish up my braking system on my Supra, I was on Wilwood's website researching their adjustable proportioning valves and noticed them selling RPV's. I don't have much experience with them in anything but an OEM application so I was intrigued as to what it could fix in the aftermarket. I read up a bit and saw mainly people using them in situations where the master cylinder is below the horizontal plane of the brake calipers allowing fluid to essentially gravity bleed back into the master. After thinking, reading and talking to a few friends running big brakes on their cars and hearing the common theme of "low pedal engagement" come up I came to the conclusion I may try a RPV as an answer? I have seen a few forum posts here and there of guys using them to help with pedal height and responsiveness. I don't have the brakes installed yet so I can't really test it, but I'm running much larger front and rear brakes and would rather run an adjustable proportioning valve versus the stock one since it is discontinued from Toyota and I don't trust a 20+ something year old used brake related part. Any opinions? Do I just re-plumb the system as planned, see where the pedal feel is and then go from there? Skip putting in an RPV and find a new booster/master setup that can solve the pedal engagement issue? Am I taking the use of a RPV way out of context and principal? Edited June 6, 2016 by Geeesammy Quote Link to comment Share on other sites More sharing options...
craig71188 Posted June 7, 2016 Report Share Posted June 7, 2016 I have owned several formula cars where the master cylinders are below the calipers and have never had to run an RPV. Granted, we are running dual master cylinders with a bias bar to adjust them so it's a little different in that we can run two different size master cylinders if needed. I did look at them, but have never seen the need. Low pedal engagement on disc brake cars most often comes from excessive pad knockback (to much lateral rotor movement-warpage) or mis-sized components. OE's did combat some of this problem with "quick take up" master cylinders that moved a lot of fluid early in the stroke to take up the gap between the pad and the rotor. My guess is using the RPV's in the application you describe will lead to dragging pads and more brake heat. I would suggest replumb the system and try it. If you don't like the feel, look at a later model master cylinder, perhaps with a slightly larger bore (more fluid movement but will increase pedal pressure) if needed. Quote Link to comment Share on other sites More sharing options...
aussiek2000 Posted June 7, 2016 Report Share Posted June 7, 2016 RPV's are only used in drum brake applications to my knowledge. Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted June 7, 2016 Report Share Posted June 7, 2016 RPV's are only used in drum brake applications to my knowledge. This. Drum brakes usually require about 10lbs of pressure to counteract the internal springs. If you have a 4 wheel drum car with stock brakes this is sometimes built into the master but if you have a car that you convert to disc front drum rear and you use a modern master you usually have to add a 10lb RPV to keep the rear drums functioning. some guys add a proportioning valve that has residual pressure built in. The piston/bore size of the master is the relevant measurement to how much volume you move and at what pressure. Too big and you will move a lot of volume but have little pressure so the brakes will feel spongy, too small and you will have a lot of pressure but no pedal feel. If you have a spongy pedal you may want to go one size smaller in the piston. Call Wilwood's tech line and tell them the rotor size, the caliper bore piston size and number of pistons, and distance of the caliper from the master and they should sort you out. here is a good read about figuring out the right size master. Quote Link to comment Share on other sites More sharing options...
Geeesammy Posted June 7, 2016 Author Report Share Posted June 7, 2016 Thanks for the replies. Ive seen Jag's use some on disc brakes, not in the modern age by any means. I was trying to get around hacking up my firewall for a booster and master upgrade but I found an old school guy who was into some time attack stuff in the early 00's with his Supra and found a direct replacement master cylinder from another Toyota that has a 1/8" larger bore which will help a lot. Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted June 7, 2016 Report Share Posted June 7, 2016 oops...forgot the link: http://www.markwilliams.com/braketech.aspx Quote Link to comment Share on other sites More sharing options...
craig71188 Posted June 7, 2016 Report Share Posted June 7, 2016 RPV's are only used in drum brake applications to my knowledge. Yes, 10psi for drums, there are 2psi for discs, but again...never have run into a need for them (personally) Quote Link to comment Share on other sites More sharing options...
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