I let this sit for a day while I stewed on it. There are only a couple of reasons for a long soft pedal. Air in the system or a MC without enough volume. After bleeding the system repeatedly using 4 different methods of bleeding, I decided to swap out the Wilwood 7/8" MC and install the 1" Corvette cylinder that I had in it before. In order to do that I had to drop the left side all welded exhaust. This is a 30 % increase in MC volume. With the 1" MC, the pedal effort is definitely increased. But I still have a long pedal on the first hit. I have "lock 'em all up brakes on the first hit, but there is "pump up" in the system. Second quick hit is higher and harder still though. This tells me there is still air in the system. DAMN! The MC swap produced the changes that we all knew it would. Less throw and more effort. Both MCs produced the same symptoms though. Long throw and pump up. Gotta be air in the system somewhere. Normal bleeding methods are not getting it out. I don't understand. There is only about 6 feet of 3/16" brake lines in each system. The front is only interrupted by a residual pressure valve. The rear is interrupted by a RPV and a proportioning valve. If the RPV is not holding this could cause the piston to retract causing the need for the second hit. Or there could be some natural pad retraction for some reason. I have thought about changing the 2# RPV's for 4# RPV's. 4# RPV's are sometimes recommended for race cars and off-road vehicles that see a lot of vibration. This car is neither, but it might be worth a try. Of course, RPV's have gone up to almost $25 each. This ain't rocket science, and it's starting to piss me off.
Are the bleeders at the top of the calipers? I have see the calipers swapped left to right by mistake and the bleeders end up on the bottom. This makes it impossible to get the air out.
Have you checked each fitting for leaking? I wipe all fitting dry and then go touch each with my finger to check for dampness. Doesn't take much for air to get in system.
Have you tried power bleeding the system with a power bleed tool? The tool is hooked to the top of the master, has a container you fill with fluid and is pressurized.
yes, I can easily use a coupler to eliminate the proportioning valve. The RPV's would be a little tougher., due to not enough line. Maybe 2 couplers and a very short line with fittings flared on. There are only 4 components. MC. calipers. rpvs, and PV. From testing I believe the MC and calipers are working properly. If that is the case, then the problem has to lie in either the PV or the RPV.
On my first of many circle track cars, underfloor MC, I had no rpvs in the system (1984). The first few races I had to hit the brakes twice going into the corner. I installed rpvs front and rear. The problem went away. I have used rpvs in everything I have built since. The proportioning valve is necessary because I have the same calipers front and rear. Without the PV I would have too much rear brake. My opinion is that both are necessary. Please explain your position.
No leaks. Checked and re-checked. No loss of fluid. No puddles on floor. All fittings are dry. Really!
I like to tap on a new caliper when bleeding to knock any air bubbles loose that may cling to the inside.
I took my suggestion out after I read this was an under floorboard system. It has been great reading but very understandable in the frustration. I wonder if the rear brakes were drum that it would not exist. My sons car is an all drum system under the floorboard and nothing like this happened. I’ll continue to read and look for a finish for jaw22w..
In the multiplicity of bleeding sessions, for which you have my sympathies, has the car ever been elevated, front / rear as appropriate, such that the end of the master points downward? Chris
I did read most of the posts, but forget, are you using all Wilwood parts? I know the calipers are fixed mount. What is the gap between pad and rotor on each caliper, are they close to the same on the inner and outer pad ? Not saying the same on all 4 wheels but each caliper. This may be a mute point but at this time seems like you have addressed all common points.
I bought a new power bleeder. Used it on the 7/8" Wilwood MC. I had to fabricate an adapter cover for it to hook up to the bleeder. I don't have an adapter for the Corvette MC. It will be a little more difficult. The 2 reservoirs are totally separated. so it will have to have 2 inlets. I'm working on that today. Maybe I will have better luck with it. I'm not holding my breath though.
Probably not, but since this has gotten to the point of "grasping at straws", is there any possibility that you have the front and rear reservoirs connected in reverse? From a picture, they appear to contain different volumes of fluid, so I thought I'd toss that question out there.
Interested to know if pressure bleeding does the trick. The symptom is the same with older and newer components so it seems likely it's not any of them. That would leave the original residual and proportioning valves...and the lines. If the res. valves are orientated correctly and working as they should, that would leave the prop. valve as suspect.
The system was all Wilwood until I swapped in the Corvette MC. The calipers are actually floating. Self adjusting within a range.
Wilwood says to hook the farthest from the flange reservoir to the front brakes. That's how it is hooked up.
Having battled ridiculously smart brake fluid here, my bleeding setup is checkvalves at the bleeders, my phone on a stand linked to my tablet on the passenger seat so I can see what it’s doing, and me pumping the pedal. What this allows me to see is that a good bleed is not just pumping the pedal, there has to be enough fluid flow velocity to carry the trapped bubble out. If you (or your wife) pumps slow, you’ll never get the air out. The pressure bleeder may help with this. Pressurize the system with enough potential flow, then open the bleeder.
Interesting, I had a similar problem with floating GM calipers with built in ebrake (Cadillac calipers) and could not get good petal until adjusted ebrake and ground pads to get equal spacing on all 4 rear pads
Interesting point. Yeah, you need to deliberately push the pedal down, but also don't go too fast on the return stroke. Take a second or two for full pedal stroke?
HaHa! I have the car on the lift and can't really tilt it, I have to get it on the floor to do that. I have been trying to avoid that 'cause then I got to crawl around on the floor. Kinda hard on this old man. Gettin' down is easy. I'm going to have to do that though.
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