Brake problem

My roadster has a few hundred miles on it now and the brakes have worked fine till today. It has disc brakes on all 4 corners, CNC brand master cylinder is under the floor with a remote brake fluid reservoir mounted to the back of the driver side cylinder head, Wilwood 2-P.S.I. residual valve in the main line off the MC before it splits front-to-back. While I was driving it today I thought it was losing power but it turned out the brakes weren't releasing. To get them to release I had to push REALLY hard on the brake pedal and then pulled back on the brake pedal with my hand to get them to release. Just pulling back the pedal after applying a little pressure didn't work. I really had to build some serious pressure and then do the "release". I don't have a external pedal return spring, but hadn't had any problem till today. Didn't have time to check anything this evening. I know residual valves have gotten a lot of criticism, especially Wilwood's, but is what I described the problem others have encountered? My other thought is that the push rod is too long and not uncovering the port in the cylinder bore. Brake pedal has always been "right there". Just looking for input and possible solutions till I have a chance to check into it.

For what it's worth, I'd say the top of my remote reservoir is at most a couple inches above the highest point of any caliper and I debated whether or not to even use a residual valve.

Thanks in advance for any input.

 

Although my brake system is a drum/drum system I had the same problem.
After trying different 'fixes' the final fix was to re-bleed using the pedal pumping method (not vacuum). Right/rear,left/rear,right/front,left/front. Hope this solves your problem.

 

Thanks for the feedback. You think it may have a bubble keeping the residual valve from releasing or air in a caliper building pressure from dragging ever so slightly? I did use the pedal pumping method to bleed the brakes. Recently I had a rear caliper off to take care of an axle seal but didn't break loose any fittings so didn't re-bleed the brakes and had driven probably 50+ miles since with quite a few stops and no problems. I'm going to see if I can find a cutaway or schematic of the residual valve. I guess it's a glorified check valve.

 

I built my 34 with 67 mustang master it has the res. valve in it for the rears but put the wildwood 2 ibs on the front for the implala disc brakes. they worked good but did have a lot of drag on them the first time I drove it pushed the brake hard and car would not move. jacked it up and fronts where locked up. I loosened the line at master and nothing came out but when I loosened the line between the wildwood res. and the front calipers the fluid came out and the brakes released. I took the valve and gutted it. The brake don't drag anymore and I still didn't put a valve back in and they work great. I am using silicone fluid and that could have made the valve stop working.Darrell

 

You might be on the right track regarding the proportioning port not uncovering fully when the pedal is released. Like you, I'm wondering why you might need a residual pressure valve with a four wheel disc system. Might be worth checking each caliper to make sure the pistons move freely and aren't affected by heat. You may have seen flexible brake lines act like a check valve if they had internal defects. If you can get to the brake lines when the thing is acting up - opening a line and seeing if there is excessive pressure might be a clue to the nature of your problem. Best of luck. I know these things can drive a guy crazy (short trip at this end). LS

 

Check for the amount af freeplay at the pedal rod to mc cylinder. Most likely not coming back far enough to release all the pressure from the system.

The 2 lb reiduals are needed when your mc is below the level of the disc cylinders. Keeps fluid in the calipers instead of all draining back to the mc.

Remote possiblity is the residual not really releasing all the pressure.


jerry

 

drive it a little ways and carefully feel which rotors are hot, so you know if it's just a problem at one end of the system or both....that might help diagnose it.

 

Thanks for all the replies so far. I'm almost certain it isn't the lines. They were all new braided lines. My brake light pressure switch is between the residual valve and the MC and I forgot to check if the brake lights were still on. I'll check and maybe shorten the push rod. I'd rather have a little more travel than this! Crazy though that the problem just happened after a few hundred miles if the push rod is too long, even though that's what I hope the problem is.

 

have you pulled the boot back from the face of the master cyl, and physicalled looked to see if the piston is returned when the pedal is released, also check any rubber lines, or braided hoses with rubber core, for internal collaspe, creating a one way check valve effect, has pedel bent or moved from hard application causing it to rub floor opening?, blow some brk clean through your residual vales, the offive in whildwoods is very small, any small particle, such as thread or metal filling will easily plug these valves, also check valve in master can stick, and dual stage piston in master can brake in two, and only one half returns with piston, rare, but have seen, , if all four wheels or a pair are sticking this will help determine just where to start, hope this helps,

 

Ive heard nothing but problems with the Wilwood Residual valves. I too have them on my 35 and they worked fine when I first plumbed the system and bleed the brakes. Give it 6 months later and the pedal went all squishy and soft unless pumped up. Got it running, and first few drives around the block, still had to pump them up but not as bad. Now they are working just fine. Guess the valves just needed excersise. Im still overly cautious with the brakes and start braking far away, just cause I dont have confidence in them.

I have bought the Stainless Steel Brakes Company's residual valves (supposed to be a much better and mroe reliable product) but by time I was ready to re-do my brakes, I didnt need them. Ill probably still make the switch.

You might have had a small particle of crud in the lines and it worked itself into the residual valve.

No matter, Id open them all and re-bleed the brakes. Brake fluid is cheap.

 

I wonder if it's because your remote resevoir is mounted to the cylinder head and thats getting too hot? I'm in the middle of a disc brake upgrade and I thought I read somewhere to keep all that stuff 3 inches away from a heat source.