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Old 10-26-2008, 05:08 PM
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bench bleeding master cylinder

I purchased a 67 Corvette master cylinder for my four wheel disc setup. My question is this. I bench bled the mastercylinder which comes with two plug nipple and a clear line for bleeding the master cylinder. The clear lines go into the bowls where the fluid is. When depressing the piston, the front line appears to flow very well, the rear, doesn't seem to do much. Are they both suppose to flow at the same rate? or is there something wrong with the rear portion of the master cylinder. It's a new one, not rebuilt.

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Old 10-26-2008, 07:34 PM
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I'm not positive on this but, did a '67 vette have rear discs? This may be the volume difference you are seeing. For instance the wheel cylinders need less volume to energize than a caliper.
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Old 10-26-2008, 07:42 PM
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I was told that the 67-69 Corvette MC would work on a disc/disc application? Maybe I was misinformed? I know it was for the 427 engine also.
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Old 10-26-2008, 08:18 PM
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You should get flow from both tubes, one will flow first, depending on which return spring is stronger.

When bench bleeding, push the pistons throughout their entire stroke, usually 1.12" . Push and retract the piston sloooooowly, or else you will pull air back in through the seals on the return stroke. This is a problem especially if using DOT 5 fluid, as it aerates easily.

If you still can't get one to flow, check to see that the port from the reservoir to bore is open .

Later, mikey
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Old 10-26-2008, 10:56 PM
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Hi Mike! I went with this Corvette master cylinder because I was told I needed a disc/disc type master cylinder and the 67-69 Corvette MC would work fine. The other problem I had was the pushrod on my booster is longer than the power brakes type rod. I've been using a manual MC which works on my application. I bled the MC as you stated going slowly. The front began flowing with a lot of volume and pressure first, I did get the rear to flow fluid in the line, but little to no volume and no where near the front. I mounted it on the car and connected the lines. I have a good pedal. I haven't driven it yet to see if it works or raise the rear end and see if I have stopping at the rear disc. My fear, is that this MC is another disc/drum MC, like I had, just a different design. Is there anyway to know if this MC is for disc/ disc? and if it isn't, is there anyway of changing something so that it will work? Or maybe I should pull this MC again and try and bench bleed it some more. I'm getting a little frustrated at this point, and could use some sound advice. I know why I hate brakes, they are a pain.
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Old 10-26-2008, 11:17 PM
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Much of this was discussed in the other thread you started ...If you have a good pedal, you should be set. I'd try a slow start test drive if you have a good pedal. Avoid stop and go traffic and roads with crosswalks.

Gradually work your way up to a full stop at speed. If it feels good, and the fronts lock up before the back, it's a good thing.


.A disc/disc MC is functionally no different in the bore, timing or fluid delivery than a disc/drum.

The difference is in the addition of residual pressure valves, (yours should have none, if you are running disc/disc and an above floor master cylinder..) and fluid reservoirs are larger on the disc/disc....which will not matter one bit..(if you had a MC with drum brake reservoirs and were using it with disc brakes, you have to check and add fluid more often, as the pads wore..that's all)

later, mikey
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Old 10-27-2008, 09:37 AM
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Thanks Mikey! I'll try it this afternoon.
Ed
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Old 10-28-2008, 10:03 PM
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Well it's been a whole day..I wonder if kleen56 survived the test drive?

Later, mikey
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Old 10-28-2008, 10:41 PM
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Quote:
Originally Posted by powerrodsmike
Well it's been a whole day..I wonder if kleen56 survived the test drive?

Later, mikey
Hey Mikey, I got the MC in. I still had the hydraulic brake switch in the line going to the rear brakes so I removed that and spliced in a piece of brake line. I drove the truck and I have brakes, about the same as before. I think the rears need to be bled more and may have some air in the line. I parked it and had other things to deal with. The neighbor said he'd help me bleed the brakes and at that point I'll see if I have braking at the rear calipers. I know the fronts work fine, but they did before. I'll let you know with an update.
Thanks for inquiring!
Ed
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Old 11-02-2008, 10:30 PM
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UPDATE: I bled the brakes about 4-5 times and there is no air in the lines. I am seeing some improvement in the rear with stopping since putting the new MC in. Still won't stop the vehicle if relying on rear disc only, but there is some improvement. I have the proportioning valve set to wide open and no change. I thinking about just leaving it like this or possibly pull the Cadillac calipers off, pull them apart and see if maybe something is defective in the caliper itself or self adjusters. I've heard several people have problems with the 85 Cadillac calipers working properly. May have to change to a different caliper???? Hell, I've changed everything else on the brakes.
Ed
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