Bleeding proportioning valve?

[88sclb350]

So did a rwal delete on my 88 k1500 5.7. Getting ready to bleed my brakes and master cylinder (because it ran dry due to my rear lines bursting through during last bleed) and I’m wondering if I need to bleed the proptioning valve as well or will that be bled as the rear lines are bled?

I’ve also heard of people saying there’s a button the on the front of the valve to reset or reposition it and I just want to know more info on that. It does look like my valve has one it’s a little black rubber piece on the front of the valve.

 

[Schurkey]

That's not a proportioning valve. It's a Combination Valve which includes the proportioning valve, the safety switch, and the metering (holdoff) valve. You'll have more trouble properly bleeding the master cylinder than you will with the combination valve.

The proportioning valve affects ONLY the rear brakes.
The metering (holdoff) valve affects ONLY the front brakes
The safety switch is in between, reacting to a pressure difference in the front and rear hydraulic systems.

The button on the front, under the rubber cover, is for the FRONT BRAKES ONLY, and if you can successfully bleed the front brakes, leave it alone. The ONLY time you need to dick with it is if you're bleeding the front brakes and can't get fluid flow. The holdoff valve is normally vented to allow slight fluid movement with changes in temperature contracting/expanding the fluid. It shuts under low-moderate pressure, and is blown off it's seat fully-open under moderate-high pressure. So the only time it would block fluid is at relatively low pressure--like when bleeding brakes with a pressure bleeder. Bleeding brakes by pumping the pedal creates enough pressure to blow the valve off it's seat. Bleeding by gravity doesn't add enough pressure, the valve is still venting.