master cylinder
 

69 Camaroand working on brakes. I replaced M/C and when bleeding front brakes both reservoirs in M/C went down. I refilled and found same on rear-both reservoirs go down. Is this a faulty M/C? I can't seem to get firm pedal. Thanks, Tom

What all have you done to the brakes and why? Power brakes or manual, disc or drum? You have air in the system.
Check at each wheel and under the car for leaks. If both the front and rear reservoirs are going down, you have air in both front and rear.
How are you bleeding the brakes at each corner - manually, gravity, or pressure tank?
Section 5 of the Chevrolet Chassis Service Manual gives you direction.
https://drive.google.com/file/d/0B0l...FAZ_3Yvv1v-q8w
https://camaros.org/forum/index.php?topic=9433.0

had front caliper seize and replaced both calipers and hoses. Power discs all around. Bench bled new M/C and used power Motive bleeder on all 4 wheels. Been on going problem with not locking up. Can't figure what's going on. Thinking maybe new M/C bad since drawing from both reservoirs while only bleeding front. I'm at a loss. Thnaks

is the shuttle valve closed in MC?

Its under the port the electrical connector plugs into for brake light

what is weird is if it is either forward or back, it would only allow the opposite bowl to drain....or is it missing?

The only devices that would allow both reservoirs to loose fluid when bleeding only the front brakes would be a defective proportioning valve, master cylinder, and distribution valve (with light contact). These devices will allow fluid to be drawn from both reservoirs if the seals are leaking by. Another option is the rear reservoir is leaking into your brake booster.
I had a friend that had problems with the front discs not getting full fluid flow and slow release of the calipers. He found restrictive sleeves on the front hoses. Are you getting good air free flow from all of the calipers?
Did you replace the master cylinder? It could very well be plugged or the incorrect master cylinder for 4 wheel discs.
This site might help
https://www.raybestos.com/resources/...cal-bulletins/

Sounds like to me you didn't bench bleed the master cylinder

I've got a distribution valve after M/C that is more a switch for brake failure rather than a proportioning valve. Yes, I did bench bleed M/C before installing. This is the second new M/C as the first was doing same thing. I think I'm going to get a new ACDelco cylinder and a new distribution valve and go from there. Both M/C were remans from NAPA and maybe both defective. I'm kinda at a loss. Thanks for replies

So, you still have a soft pedal, and the fluid still goes low?
Basically, means you are not done bleeding it yet
Have an assistant pump the brake pedal slowly as you inspect the fluid in the master cylinder for bubbles coming up
Gravity bleed the brakes over and over, watching each time foe a bubble to come out
"Tricks of the trade" are many
Just helped a friend work through his brake trouble with a BMW a few days ago over the phone
You can always power bleed it using your old master cylinder cap
On yours, you drill 2) 1/16 inch holes in the cap right above both reservoirs (through the rubber too)
Then take shop air and a blower nozzle, hold some real slow slight air pressure just above the holes with a good blower nozzle
That will force fluid out the ports where you can then double check the MC bleed and also bleed the brakes at the wheels using that method

You DON'T want 120 psi hitting that master cylinder
You hold your blower nozzle about an inch above the holes you drilled and just barely squeeze the nozzle trigger
I am assuming you have no leak
You need to fix any fluid leaks before finishing up the bleed process (or it'll never get all the air bled out)

I've been using the Motive power bleeder and have gravity bled before that. M/C was bench bled before installing. Looking at possibly bad distribution valve between cylinder and brakes. Luckily not a daily driver so not in hurry but want to get fixed before putting up for winter. I'm still leaning to replace M/C with new ACDelco unit and dist valve. About all I can think that could be faulty. Thanks for tips.