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Yes, the way that works is the valve slides back and forth to activate the warning light. Normally, the sensor is open as the pin rides in the groove, only activating when the valve slides one way or the other. If the o-rings wear out or the valve hangs up, air and fluid leaks across the circuit causing your problem.
The other option is to put a tee in the front lines and go directly to the MC and a manual proportioning valve for adjusting rear bias (really just allows full pressure to the rear or attenuates the pressure based on how much you adjust it. This may be the better solution as you can fine tune your brake bias. Depends on how much originality you want to maintain.
Yes, the way that works is the valve slides back and forth to activate the warning light. Normally, the sensor is open as the pin rides in the groove, only activating when the valve slides one way or the other. If the o-rings wear out or the valve hangs up, air and fluid leaks across the circuit causing your problem.
you can get a plug that installs in place of the pressure switch which locks the pressure valve in place while bleeding .
I tap on the calipers with a nylon head hammer which helps move air pockets
Don't over-think this. The '67 brake system doesn't need to be redesigned or re-engineered - it's about as simple as a brake system can be. All it needs are correct parts and a Motive Pressure Bleeder. It takes less time to bleed the system with a Motive Pressure Bleeder than it does to remove the wheels.
i have and used the Motive bleeder device. over and over again with this car
i appreciate all the advice, but i have tried all of the usual, and not so usual stuff
i was hoping i could tell from a measurement of brake line pressure whether there was still air in the system, or something else. with caliper pressures of 500-700 psi, i am not sure if that has helped me out. i wish i knew what normal manual brake pressure is, in this system, from someone else who has been through similar processes
i was hoping i could tell from a measurement of brake line pressure whether there was still air in the system, or something else. with caliper pressures of 500-700 psi, i am not sure if that has helped me out. i wish i knew what normal manual brake pressure is, in this system, from someone else who has been through similar processes
justin
The line pressures you are seeing are more than adequate to operate the brakes. The test for air in the system is simply whether or not the pedal is spongy.
Are you sure the Wilwood calipers have the same piston size as stock C2 calipers? If the piston is smaller by any amount, front braking effort will be reduced.
Are you sure the master cylinder has the correct size piston? If the piston is larger than original by any amount, all braking effort will be reduced.
What brake pads are you using? If the coefficient of friction of the pad material is too low, all braking effort will be reduced. If the pads have to warm up before they will bite, initial braking effort will be low.
i took the system apart again - the distribution valve was open at both ends normally -
i re-bled everything and it feels exactly the same - spongy pedal with long travel. it feels like the master cylinder bore is too small - maybe a 7/8" bore when I need a 1". i have a exact repro unit - i wonder if this thing was machined with too small of a bore? probably not.
seem to be out of ideas. i know everyone has suggested there might be air in the system, but i used a motive power bleeder each time. i am pretty sure right now there is no air in the system. i am using wilwood calipers, but they say they come with piston sizes that are identical to stock, and the instructions call for stock master cylinder...
i'm going to take it out and try to bed in the new pads. maybe it just needs some use and I will report back. I will not drive it on public busy roads so dont worry, you are all safe!
i'll let you know since i am sure many are waiting for the final word on this (just kidding)
If everything was sized correctly, and everything appears to be operating properly, rotors not glazed, pads not hard ceramic, and I was sure there was no air in the system, I might take a look at the brake hoses.
it feels like the master cylinder bore is too small - maybe a 7/8" bore when I need a 1". i have a exact repro unit - i wonder if this thing was machined with too small of a bore? probably not.
It's easy to measure the M/C bore. Just unbolt the M/C, pull it forward, remove the rubber boot if there is one present, and measure the bore. The bore is the same diameter from end to end, so whatever you measure at the back of the cylinder will be your bore size.
If you use too much pressure in the Motive system I believe you can introduce air into the system because of tiny air bubbles that mix in the brake fluid. I would think less than 10 PSI would be plenty to move the fluid quickly.
If you let it sit overnight those tiny bubbles will be come big bubbles that you can bleed.
An old friend of mine inherited a 1966 Corvette, it had one bad caliper when he picked up the car. He replaced that caliper and like you fought to get air out of it.
He tried many times to bleed the system. A friend of his told him to gravity bleed the system after letting the car sit 24 hours for the air to gather into large bubbles.
He did the gravity bleed and it has been just fine ever since and he tells me the stock 66 brakes work great and he has no desire to add power brakes.
If you added performance friction to your car it will take more heat to get them to start working. More heat means more pedal pressure to get the brake pads to start working.
Performance brakes work very well at the race track but not so well around town or on gentle stops.
Your issue is soft pedal so it does sound like you have trapped air somewhere in that system.
its funny because the rear calipers are almost horizontal, so i did unbolt them to bleed them, although the piston bores are small in the rear, so I am not sure that is really needed
the wheels are back on, but i bet i can post some pics later on from my computer. the wilwood calipers look mostly just like the stock ones - they mount in same spots but use braided stainless hoses, so less of a concern for a hose to collapse.
i am looking forward to driving it and trying to bed the pads. i feel the pedal is just a little harder now than before my last go around with bleeding maybe. i have done all this on many cars, and i suspect everything is OK but maybe these wilwood street pads just need a little break in?
... i feel the pedal is just a little harder now than before my last go around with bleeding maybe. i have done all this on many cars, and i suspect everything is OK but maybe these wilwood street pads just need a little break in?
I think they need more bleeding based on what you report. Most here have suspected and continue to suspect air. Spongy pedal is air, or maybe bad rubber lines, but probably air. Hate to say it, I know you want to go riding. I would bleed and bleed, wait, bleed some more until that pedal feels right. It CANNOT be spongy.
12-02-2018, 10:55 AM
