POwer brake question (should be easy for y'all).

[jorgensensc]

Hey all,
I have a '68 with a front crossmember and disc brakes off of a '73- 87 truck. I pulled a power brake booster off of a '67. It is missing the lines to the proportioning valve (although after reading some info, I think it is actually just distribution block since 67-70 only had drum/drum setups, but it looks very similar to a prop valve.) I currently have manual brakes (obviously) but I have a wilwood adjustable prop valve on the rear brakes. Can I hook my lines up the same way to the power brake master cylinder, using the wilwood adjustable on the rear instead of buying a prop valve like is commonly on there? Also can I use the master cylinder off the drum/drum setup off the 68, or do I need to get a disc/drum master cylinder from a 71/72? For the 24.00 I may go down to autozone and buy a new master cylinder instead of jacking with this old crusty one. I'm also a little confused about the residual valve that has a certain pressure to the rear brake lines. Do I need that too, or is that also the function of the prop valve. Let me know what y'all think. Enlighten me please!
Shawn

[Ole Blue 68]

I'm not 100% sure but I don't think you're gonna be able to use that block.

I converted my 68 from power drums a few months back. I kept the old Booster but went with a disc/drum master (NAPA Part #47-36306) which has a little bigger reservoir than the drum/drum. I haven't had any problems since doing the switch.

[jorgensensc]

Can I skip using the original style prop valve if I have the Wilwood prop valve?
Shawn

[Ole Blue 68]

You should be able to. I actually kept my old prop valve and it's worked fine.

[jorgensensc]

Originally Posted by Ole Blue 68

You should be able to. I actually kept my old prop valve and it's worked fine.

THe problem is that I don't have an old prop valve. The manual brakes never had one, and the brake booster setup that I got is from a 67 and has a distribution block that looks like a prop valve but isn't. The adjustable prop valve I have is a wilwood one that was installed when the p.o. installed disk brakes and left the original manual brakes in place. I think that the Wilwood prop valve may work, but I'm confused as to the purpose of residual valves vs prop valves. Thanks for the help so far. Does anyone else have any ideas?
Shawn

[SCOTI]

Originally Posted by jorgensensc

THe problem is that I don't have an old prop valve. The manual brakes never had one, and the brake booster setup that I got is from a 67 and has a distribution block that looks like a prop valve but isn't. The adjustable prop valve I have is a wilwood one that was installed when the p.o. installed disk brakes and left the original manual brakes in place. I think that the Wilwood prop valve may work, but I'm confused as to the purpose of residual valves vs prop valves. Thanks for the help so far. Does anyone else have any ideas?
Shawn

Use a prop valve & front hard-lines from a 73 ~ 80. They work w/minimal tweaking & are easy to find in the 'yards'. They will bolt right up to your 71 ~ 72 master cyl/pwr booster set-up & only require .250" spacers where the prop valve bolts to the front splash apron (I used oversized nuts as my spacers).

You'll have to drill the holes to secure the prop valve to the apron (@ least one of them anyway) & you can use 73 ~ 80 rubber lines/retaining clips.

Not as fancy as the Wilwood/hybrid combo but a very functional & pretty straight-forward install.

[68C15]

I would go with a factory prop. valve instead of the willwood unit. in case of a hydraulic failure (front hose or wheel cylinder etc.) it shuts offf fluid and sends it to the sealed side so you can stop. the willwood thing merely restricts flow.

a residual valve is designed for when the master cylinder is mounted lower than the wheel cylinder. it keeps a small amount of fluid pressure at the wheel so your pedal doesnt travel as far before braking action begins.

when converting to discs you may want to step up to power assist. disc brakes dont have the advantage of self-energization like drums have therefore you will not stop as well. I did this on my 68 using modified parts from a donor 80 C10. unless you are a good welder my method may not be right for you. I did it for 2 reasons. 1. I am too much of a true old fashioned hot-rodder (I am too cheap) and have access to alternate parts . 2. I seriously HATE the way the 67-72 boosters hang out from the firewall.

[jim zag]

A residual valve is needed for drum brakes to keep the piston rubber seals from relaxing and leaking. A drum brake residual valve is about 10 PSI. A disc brake is only about 2 PSI. The disc brake master SHOULD have a residual under the brass seat where the line connects. YOU SHOULD be able to tell it is there by GENTLY testing with a small punch. BE GENTLE!!!! A drum brake master will make disc brakes drag because 10 PSI will not release the pads enough. The WILWOOD valve allows you to reduce the pressure to the rear brakes. You want the front brakes to lock up FIRST in a panic stop. YOU need to adjust this by road testing. You do not need a residual on disc brakes unless the master is lower than the calipers. In fact you should be able to bleed the front brakes by gravity alone. DOES THIS HELP?

[STP67-72]

Just like Scotti said, use the 73-80's lines and p.valve. All of it works. 73 up rubber hoses and all the lines will work. Hook it up under the pass. floor pan area. You can use old line there back. It hooks up to a 71-72 booster and master cylinder.
Hope this helps.