Underfloor brakes help needed
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Tuned
Joined: Jul 2004
Posts: 263
Likes: 2
From: Moorhead, MN
Underfloor brakes help needed
I added disc brakes to my '56 F100, I used the CPP caliper brackets and the kit to keep the stock pedals and use a mustang booster and m/c. I also used the mustang prop valve and plumed everything as it was in the mustang. I then bleed the brakes and got a nice firm pedal. The other day I finally got the truck started, and now when running the pedal mashes to the floor with little to no resistance, when off, its back to firm pedal. What is the problem here? Do I need residual pressure valves instead of a prop valve? or both? or ??? Any help would be appreciated. TIA, Matt
Senior User
Joined: Jul 2004
Posts: 203
Likes: 0
From: Glendale, AZ
Could be a booster problem with the check valve that goes in the vaccum supply line. You said you have a firm pedal with it off. Are your brakes holding or working in conjuction with the firm pedal? just a stab in the dark.
Postmaster
Joined: Sep 2005
Posts: 2,958
Likes: 1
I just installed a underfloor power booster and dual reservoir master cylinder from cpp in mine. I did not go the disk brake route, but I did install the residual valves in both lines.
I am having no issues at all with this setup. I am loving it.
I do not have a proportioning valve, since I am running drum/drum.
I was told that with the front disks you need both 2# residual valve (disks) and a 10# residual valve (drums) plus a proportioning valve.
I bled mine, drove it a while, and then bled them again. There was a tiny bit of air trapped in the system somewhere. It is good to do it that way (at least that has been my experience).
I am having no issues at all with this setup. I am loving it.
I do not have a proportioning valve, since I am running drum/drum.
I was told that with the front disks you need both 2# residual valve (disks) and a 10# residual valve (drums) plus a proportioning valve.
I bled mine, drove it a while, and then bled them again. There was a tiny bit of air trapped in the system somewhere. It is good to do it that way (at least that has been my experience).
Lead Driver
Joined: Apr 2002
Posts: 8,813
Likes: 13
From: Littleton, New Hampshire
Originally Posted by 4tl8ford
If the master cyl is under floor you need both
Logistics Pro
Joined: Oct 2002
Posts: 4,489
Likes: 5
From: Valley Center, CA
You say the pedal is soft, but does it firm up on the second or third pump? If so, I think the 10# residual valves might be the answer. A friend of mine just put new brakes on his 59 and they ended up having to put the residual valves on even though he has the ms mounted on the fire wall! Jag
