Prop valve question

[DAVE68]

In the process of installing manual ls1 front brakes on my 68 chevelle, still drum on rear for now. Tobin at Kore3 recommended 76/77 impala mc, thanks for all your help Tobin. I know i have to change out the drum/drum prop valve. Can i run a original style A body disc/drum prop valve or a aftermarket adjustable prop valve? thanks for any info in advance!

[MonzaRacer]

Just use an adjustable valve to the rear, and remember if you still have rear drum they may need a pressure check to allow them to activate before the front disc do, but adjustable might do it.

[DAVE68]

Sorry, new to this, but why would it need a pressure check at the rear? Years ago i converted a chevelle from front drum to single piston original style disc calibers from a donor car using the spindle assembly, m/c and the prop valve? Is the pres. check needed because of the dual piston ls1 calibers? Sorry for all the questions!

[MonzaRacer]

Sometimes in a drum disc set up you need to delay the disc application so the rear drums can get out and start workingbefore the disc activate, if you get a dive in front that wont go away or lock up or a deep pedal.
Also remember most people dont have the proper technique for keeping there rear drums adjusted. big trick on drum bake equipt cars is when backing up is leave your foot on pedal after backing up, drop car into drive and allow the car to move forward againts the brakes,,, this keeps the rear brakes adjusted up.
Also if your car doesnt have a pressure check in the rear you may need to install one, this keeps the drums sort of held out to let them actuate quicker.
Kind of fun designing a brake system isnt it?

[DAVE68]

Yea its fun alright! Thanks for the reply.

[mm065]

The master cylinder that you put in has the residual valve (check valve) in the output port for the rears, no problem there. This keeps fluid there to overcome the springs upon brake application. Adding a wilwood adjustable valve to the system will really help you dial the whole thing in.

[NOGO]

Sometimes in a drum disc set up you need to delay the disc application so the rear drums can get out and start workingbefore the disc activate, if you get a dive in front that wont go away or lock up or a deep pedal.

Monza stated why you should run a combo valve which incorporates a metering and prop valve in one.

[DAVE68]

MMo65, my m/c is for a non-power 76/77 malibu, not impala as i stated, but Tobin from Kore3 also informed me that it should have a built in valve. Thanks for the replys, this saves me some $ and plumbing work. I just ordered my adj. prop valve from Tobin. Thanks to all that replied, i'm new to the pro-touring scene and this site is very informative!

[NOGO]

It may have a built in residual pressure valve, but I doubt it has a built in combo valve.

[DAVE68]

Was told that a drum/drum car does not have a prop valve but a distrubition block, and all that was required for my front ls1 disc swap was a 10lb residual valve and a adjustable prop valve. So if my m/c is equiped with a residual valve, all i have to do is plumb in the adj. prop valve?

[NOGO]

Ditch the adjustable prop valve and install a combo valve. You need the rear drums to actuate first to balance the braking load properly. If you do not run the prop valve your braking performance and brake wear will suffer.