Wow, I'm really struggling with this. I pulled the flare seat from the rear port of my '69 #309 Master Cylinder ... and there is no check valve. So I looked at my other #309 Master, and again no check valve.

So I called the placed that sleeved my master (Ron Karp's) ... and he's telling me that they really never had a check valve in the master cylinder. GM mis-wrote the Service Manuals, and the check valve is somehow incorporated with the Metering Valve.

Can some of you confirm, or deny this?

I'm thinking more like my master was "rebuild" by an AutoZone type place along the line ... and they did a hap-hazard job leaving the valve out. But both of my master's ... and the one I have apart doesn't even appear to be machined for the little valve/spring?

What's the scoop?
Neal

As far as I know residual check valves are only for drum brakes not discs. Correct me if I'm wrong.

residual check valves are for drum brakes UNLESS the master cylinder is mounted BELOW the front disc brake calipers. We just put disc brakes on a 51 ford, and the kit we bought came from master power brakes. the instructions say that there should be a 2 lb. valve to the front brakes, and a 10 lb. valve the the rear drum brakes. the master cylinder is a corvette style unit mounted under the drivers floor pan.
hope this helps
Chip
p.s. the ford had brakes when we were thru!

Yeah, I got the part that the residual valve is for drum brakes. That's why I thought it perfectly normal that the Overhaul Manual said it would be in the rear MC port.

Now neither of my original's have the valve, and my builder is saying they were never there.

I'm trying to find someone who has actually removed the rear flare seat on an original Master ... and either found or not found the check valve. I honestly don't get how the system works without it?

Thanks, Neal

I pulled out the flare seats on a 70 a couple of months ago looking for them. There were no residual valves under there. I remember seeing them in drum/drum masters on some Wagner replacement cylinders, but that was years ago.
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Jon N.

so what would hold pressure on a disc brake then if they are not there???.We have a 69 camaro that with a different master(not sure what it is from)the left front brake is holding and if you crack the line loose at the cliper it releases.Were lost

Purple ..... the condition you are describing usually comes from a bad hose. A hose can get a "flap" on the inside that will restrict the flow out of the caliper back to the master.
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Jon N.

they are the original hoses.Car only has 25,000 original miles and its mostly 1/4 at a time.I will let him know and have hime check it,he said when he pumps up the brakes the right one turns but drags like normal but the left one takes two hans and barely turns.If he lets it sit for awhile (couple days) then it spins free.
Dennis

dyno would this cause a caliper to lock up. my driverside is locked but the pass side isnt. i just changed the front to discs back is still drum. im confused on my situtation. do u think u could help

In the scenario purple66bu described the caliper released when the hose was loosened at the back of the caliper. If that works for you, suspect a bad hose. If the caliper is still locked up or dragging badly, the problem is in the caliper.
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Jon N.

jon what in the caliper might that be?
sorry for post steal purrple
jon

Rust, dirt, pits or a combination of them. A torn boot will let water and dirt get into the area between the piston and caliper. The thin chrome plating on the pistons gets scratched off from the dirt and the whole thing rusts. A rebuilt caliper should cost $20.00 or less with exchange for a single piston caliper. Check the caliper bolts too. Cost about $5.00 each. Replace them too if they're badly rusted and pitted.

Jon N.