How do you compress the combination valve pin that is needed to bleed brakes on a 1977 Trans Am?

There is a valve that allows fluid to go to the brakes, and I need to compress a pin in order to bleed the brakes. How do I depress this pin? Here is the website where I got the instructions, but his instructions aren't working. Thank you.How do you compress the combination valve pin that is needed to bleed brakes on a 1977 Trans Am?I have had luck centering the differential valve (i assume that is what you are trying to move.) by cracking the opposite bleeder screw like one on the front if you are trying to bleed the back tighten the back ones back up for now and depress the brake pedal slowly this should cause the valve to center its self again.

then opening all four and pressing the brake pedal slowly. this is easier with two people but i have gotten by using a jack handle to hold the pedal down while tightening the bleeder screws up

good luckHow do you compress the combination valve pin that is needed to bleed brakes on a 1977 Trans Am?visit www.mygmlink.comHow do you compress the combination valve pin that is needed to bleed brakes on a 1977 Trans Am?The proportioning or combination valve has a piston inside that floats between the front and rear brake line circuits under normal operation and brake pressure between the two branches so if one branch loses pressure, it cuts off fluid loss and trips an internal switch for the brake warning light. This piston is suppose to be centered in the bore it rides in and can be held in place for bleeding by holding or depressing the piston from the backside on the valve...it lies under a rubber boot. There is a special tool made for this purpose which looks like an L-shaped bracket about an inch wide and 4-5 inches long with a slotted whole that bolts to a mounting bolt for the valve and can be adjusted along this slot to depress the piston the proper depth or keep it from moving. It may not be a matter of depressing the valve piston so much as not letting it move when you crack the bleeder valves. A good service/repair manual like Chilton or Haynes will show the procedure.