[alanmay0]

I went to a car show today and was looking at some 1967 GTO's and noticed that most had a brake proportioning valve attached to one of the bolts holding the master cylinder to the power brake booster. My 1967 GTO has disc brakes on the front, I believe they are an aftermarket set up but not sure. Anyway I do not have this proportioning valve in my brake system. So was wondering if this is ok or not. The car has power brakes and they work good.

One other question what position is correct for the brake master cylinder lid to attach. Some had the one spring lid fastener that attaches on the front and rear of the master cylinder and other have the two spring lid fasteners that attach on the left and right side of the master cylinder.

thanks in advance
alan

['ol Pinion head]

Alan you might survey the following '66-67 A-body thread for pics, if you are looking for info on how the factory did it for '67 (& 68-70 ) A-bodys with factory disc brakes.

http://forums.maxperformanceinc.com/....php?p=5284778

GM did not use a true "Proportioning valve" on its disc brake A-body's until the '71 models. Before the '71 models, a brass distribution block (same as used w front drums) was mounted to the inside of the frame and on factory disc brake cars a round metering valve was mounted up off a small stamped steel bracket which mounted under the master. The true proportioning valve arrived for '71 models. It was a longer cast iron piece made by either Delco Morraine or Bendix, depending on the application, and mounted off the inside of the frame.

There have been many aftermarket suppliers out there for the last 20 years offering varying qualities of front disc brake "conversions" utilizing an aftermarket brass proportioning valve which mounts via a thin stamped steel bracket straight inline under the disc brake master cylinder. This streamlined positioning was basically copied from at least one used parts vendor who was using a late 70's stamped steel proportion valve bracket (originally sourced from a late '70's 4 wheel disc Seville) to mount a common cast iron '71+ proportioning valve so the proportioning valve would mount up away from clearance issues with aftermarket headers.

[alanmay0]

Thank you so much for your information. So If my car has front disc brakes and no proportioning valve under the brake booster does that mean that my car is a factory front disc brake car??

Once again thank you.

['ol Pinion head]

No problem, would need more details than what you've detailed. No PHS docs?...that would clear up the issue. Most likely a previous owner installed the disc brakes & skipped the metering valve, as for many years a nice functional used or rebuilt metering valve was an expensive piece. Have you examined the calipers? Is the GTO running factory 4 piston disc calipers? '67's and '68's with factory disc brakes both used factory 4 piston calipers which used their own specific caliper brackets.

The common '69-72 single piston caliper disc brake swap uses its own style of caliper brackets which have to be swapped onto a '67 or '68 factory disc car in order to run the less troublesome '69-72 A-body single piston caIpers. By far the single piston caliper setup is the most popular swap, through the 80's up into the 00's personally pulled and pieced together well over 250 factory single piston disc changeovers. The '69+ setup is also also what several entities have copied with offshore caliper brackets & junk disc spindles so there are tons of A-bodys & early F-bodys out there with a combination of used & aftermarket copied parts.

[alanmay0]

Hello and thanks again. My build from the PHS does not show disc brakes. So mine are probably aftermarket add ons. They are one caliber pistons. The main question I have for you is Do I need a proportioning valve??? Is it a safety issue??
thank you again for your help.
alan

ps do you know the answer to the second part of my original question that is which master cylinder top is correct the one or the double top hold down devices?

[STEELCITYFIREBIRD]

Yes you need one, it allows the rear brakes to actuate first, then proportionally adjust the brake bias to keep one end from locking up, the front. The proper valve is required for god brake balance. You can set it up with pressure gauges, dynamically for best fell, or get the correct valve based on the rear drum size and front calipers used.
Do you known what pads the front brakes take (possibly D52? if production calipers, single piston)and/or the rotor diameter.
I know the look of 70's stuff if that's what they came from.
I like an adjustable, but if your just wanting stock look/performance others here can probably advise on the proper valve for your application.
ID what calipers/pads/ rotor diameter you have and rear drum size/width of shoes.

Some pics of the front calipers/pads will really aid in ID'ing them.

Prop valve is likely on the frame below boster.
Looks like:
https://secure.amesperf.com/qilan/De...A&web_access=Y t

HTH

[Schurkey]

A PROPORTIONING valve is in-line with the REAR brakes ONLY. It has NO effect on the front brakes. The purpose of the proportioning valve is to limit pressure to the rear brakes above a certain point. At low-to moderate braking, the proportioning valve does NOTHING. Under heavy braking, the proportioning valve will progressively limit the pressure to the rear.

The METERING (also called a "HOLD-OFF") valve is in line with the FRONT brakes ONLY. It has NO effect on the rear brakes. The purpose of the metering valve is to prevent front brake engagement until after the rear brakes have enough pressure to overcome the shoe return springs. The metering valve allows the hydraulic system to "breath" with zero pressure--so that temperature changes causing fluid expansion/contraction do not apply the brakes or create a vacuum in the calipers. Under light pressure--20--100 psi or so--the valve closes so front brakes cannot apply. Above the set point--100 psi or something like that--the valve is blown off it's seat, and the front brakes apply normally. The only time the valve blocks fluid flow is from "about" 20--100 psi.

Many pressure bleeders use enough pressure to close the metering valve. The metering valve has a "pin" that can be pushed to allow the front brakes to be bled with a pressure bleeder. I keep my pressure bleeder set to 10--15 psi, not enough to close the metering valve. I have NEVER needed to dick with the "pin" on the metering valve to bleed front brakes. Gravity and vacuum bleeding uses no pressure, doesn't close the metering valve. Pumping the brake pedal creates enough pressure to open the metering valve, so with any of those bleeding methods, there's no need to dick with the "pin".

Add in a safety switch, and the proportioning valve, metering valve, and safety switch in a single brass housing becomes a "Combination Valve".