Odd Brake Issue

So a while back I converted to front disc brakes using Chevy caliper, brake lines and Jeep rotors. I also converted to power booster out of a 1991 Cherokee. I have had an ongoing issue where sometimes off road I will lose brakes completely but after a few pumps they come right back. This has never happened on the road. Someone here suggested a 2# Residual Pressure Valve which I have inline. I have always had great brakes on road with plenty of pedal.
Fast forward to a few weeks back. I lost a brake line a Hollister Hills and replaced it on the trail. Brakes worked fine all the way home. Parked it and decided to replace the brake line and both Calipers to see if I could fix the other issue. I bled everything and now the pedal goes straight to the floor. I can pump the brakes a bit and get some pedal and front brakes grab. I then replaced the M/C after bench bleeding it. Same story.
Any ideas what I am missing? No proportioning valve but they worked fine before. Pedal is super firm with engine off but with booster goes straight to the floor.
Thanks!

 

Still air in the Brake lines ....................or vacuum leak in line to booster or booster is leaking.

 

Thanks Tarry
I'll go try bleeding again. Not sure about the leak, wouldn't that make the pedal harder?

 

Oh and if there is a vacuum leak would I hear it?

 

OK I took Tarry's advice and bled them again. I can drive it and pump it 2 -3 times and get good pedal. First time I apply pedal goes to the floor. Engine revs slightly when brakes are applied. Any easy way to check for vacuum leaks? Does the brake cleaner trick work?

 

I am no expert, but thats not right and I think this is related to your problem.

 

Thinking about replacing the Booster. This is turning into a minor money pit!

 

Some type of non-flammable liquid works if you can apply it to or near the area's where the main line is running from...............normally that hose to feed the booster is 5/8 or 3/4".........get another new piece and change it out............the motor rpm increase is a normal tell-tale that manifold vacuum is escaping to the atmosphere...........Your booster may be the issue. Let me look I think I have it written down somewhere how you check them.

 

Is it possible for you to try and use the brakes without the booster? check the booster seals.

http://www.rockauto.com/dbphp/mak,J...29,Brake%2FWheel+Hub,1884,Power+Brake+Booster

heres my 5% rock auto discount
3038971020026087

 

Try this:

http://www.roadkillcustoms.com/hot-rods-rat-rods/hot-rod-power-brake-booster-test.asp#axzz3XQ2KrUlW
or
https://youtu.be/ogXIHfrhXsQ

 

I changed the line a few weeks back when I replaced the head gaskets. I suppose someone needs to apply the brakes for the test? I understand on the increased RPM makes perfect sense.

 

I love the Ballpark and for that matter , been a Giant fan most of my life.............but I had to turn the game off last night..........to brutal to watch! I guess the good news is that sooner or later they have to win a game!............Good Luck tonight.

 

Yeah it was pretty hard to watch last night.

My son works at SJ Muni. Brian Stowe is throwing out the first pitch tonight.

 

It sounds like the shoes and pads are retracting to far so you have to pump the pedal to get the brakes to contact the drums and rotors,maybe the shoes needto be adjusted out to the drums,or your residual valve on the front brakes isn't working.Good luck at the ball park

 

Jeff,
I just did some work on a '65 doing a conversion that sounds similar to yours, with similar issues.
Front disc conversion using Chevy 1/2 calipers and rotors, MC conversion to a dual circuit MC spec'd for front disc, rear 11" drums, with an 8" vacuum booter. MC mounted up on the firewall, using '78 Jeep overhead pivoting pedal set. Proportioning valve setup right below the MC, and a 10# residual right behind the rear output of the proportioning valve.

The issue was that no matter how much we bled this system, it still felt like air in the lines. The pedal would go clear to the floor on the first application, and would barely pump up. The MC seemed to be pretty stiff, like maybe the bore wasn't smooth enough and the cups had more friction than there should be. I don't think the quality of new replacement parts is what it used to be.

I finally got the air out using a pressure pot bleeder. I think part of what was happening was the MC, proportioning valve and residual valve all being mounted as high as they were was keeping the air bubbles trapped. Trying to bleed the brake lines using just pedal pressure wasn't getting enough volume of brake fluid through to flush the air down the lines and out the wheel bleeder fittings.

Don

 

Thanks Don,
I have tried a speed bleeder (pneumatic) with not much luck yet.

Hopefully today I will get some time to work on it and try the tests Tarry sent. I will give the speed bleeder another shot too.