Can't Get a Solid Brake Peddle
 

So I have a bit of a mash-up of parts. However, It all worked fine once before. I have a 71 chevy truck that has been retro fitted with hydro boost from an 08 Chevy express van. Since the van master cylinder didn't fit under the hood, I used a refurbished 95 Chevy truck master cylinder. I put it together about ten years ago.

I added a Hurst roll control cylinoid to the front bake circuit. Now I'm tryin to bleed the front brake circuit and the brakes won't firm up. The brakes pressures up until I start the engine. I get some pressure at the peddle but with a little effort I can push the brake peddle to the floor. When I turn off the engine and the brakes will hold pressure. I don't have any leaks that I can find, however, the bottom of the master seems to always be wet with brake fluid. But, this could be from the mess I keep making when trying to bleed the system.

One thing I have noticed is that when I forget to put the master cylinder cap back on and press the brake peddle, brake fluid shoots out of the reservoir. I was wondering if that was normal?

https://photos.app.goo.gl/BSNwS4FQv67SCeic8
https://photos.app.goo.gl/sSmmeZ7K8RPLv9YZA
https://photos.app.goo.gl/FQvRe7DMiUJsPDbE7

Re: Can't Get a Solid Brake Peddle
 

I took a video of what I think is the problem. I have a Wilwood proportioning valve. Idon't know if the prop valve is the problem or not.https://drive.google.com/file/d/1pG8...usp=drive_link

Re: Can't Get a Solid Brake Peddle
 

spurting up in the master is not unusual, especially when there is still air in the system and the pistons are travelling further/faster.

wash everything off with water and let it dry -confirm no leaks

if you don't have a firm, high pedal with no boost pressure it will just feel worse with engine on /accumulator filled.

My guess is air in the roll control or proportioning valve as they look to be higher than the master. Have you tried cracking those lines and bleeding there?

old school fall back for these sorts of problem is to pinch off the rubber hoses, needle nose vice grips work well if you don't have those hose shut off pliers. if you don't have a pedal with all the hoses pinched, the air is not at the wheels. when you have a pedal release the lines one at a time and check if that wheel needs bleeding/adjusting.

Re: Can't Get a Solid Brake Peddle
 

So, as it runs out. I was just being paranoid. I got someone to look at. Since I'm running hydro-boost, the extra power allowed me to push the peddle to the floor with enough force. After one more round of bleeding, the truck stops on a dime and the line-lock works great.

Re: Can't Get a Solid Brake Peddle
 

While it might be good now, I'll 2nd the mention that the master cyl needs to be the highest part of the system. OE prop valves or proportioning valves should be below the fluid reservoir.

Re: Can't Get a Solid Brake Peddle
 

I don't view keeping things below the master as essential , but it does make it much easier to bleed. An upwards loop right near the master may require a pressure bleeder or repeated re-bleeding near the top of the loop until the system fills up.