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  #11  
Old 04-09-2018, 12:15 AM
JoeVac JoeVac is offline
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Using prestone DOT 3,, rear brakes and drums all new,,and all new hardware. adjusted fairly tight, slight drag. Hardly any miles on them, you're right, they may get better with use.

I rebuilt the proportioning valve a while back, but didn't trust it so I bought a Summit adjustable proportioning valve,,may reinstall original and see what happens.

How are the brakes on your bird? Minimal travel?
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  #12  
Old 04-09-2018, 04:52 AM
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I forgot to ask... what size piston is your M/C? I hope it's a one inch bore.

I have a '59 Galaxie Fordor w/two-stage 8" booster and dual-piston 1" M/C. My front calipers have 2.5" diameter pistons and my rear drums are stock 11". My emergency brake is stock as well.

This car is a huge grocery-getter but the brakes are right up there with most modern cars. The pedal is high and it will put everyone through the windshield if I jump on it (and I have, on I-75).

When the car had drums up front, it would pull one way when cold, then the other way when warmed up. Disk brakes with a prop valve straightened all that out. (I prefer the GM-style comb. prop. valve.) I can let go of the wheel, step on the brakes and the car stops straight as an arrow. My cousin has a '57 Chevy. I drove him to the airport when a little Asian car squirted in front of us. I had to slam on the brakes. Johnny was pinned to the dash when he said, "G'D@mn! I didn't think your car could do that!"

If you're using DOT-3 and a tiny bit of air is in the system, it will absorb out. Once your pads and shoes bed-in, they will work much better as well. So give your system a chance before passing judgement.

I see no problem with an adjustable prop valve EXCEPT, most of them are really 'flow control' valves. They don't adjust the proportioning feature at all. That means, they simply close down the size of the hole on the rear circuit. That's great but it won't work the same with different pedal pressures. - Dave
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  #13  
Old 04-09-2018, 02:06 PM
JoeVac JoeVac is offline
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I'm "assuming" it's a 1 inch bore MC, ordered it for the 65 bird. I may put the original proportioning valve back in as there was little change with the aftermarket one. Seems to me it does more than limit pressure to the rear brakes with all the parts and orifices in it. Does it also hold a small amount of pressure to the rears? Learning more about brakes than I ever thought. I always thought that the early cars had pretty sensitive brakes.
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Old 04-09-2018, 03:40 PM
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Quote:
Originally Posted by JoeVac View Post
... Seems to me it does more than limit pressure to the rear brakes with all the parts and orifices in it. Does it also hold a small amount of pressure to the rears?..
There's a big difference between controlling flow and controlling pressure. Disk brakes hardly use any flow. Rear brakes are the same when the shoes contact the drums. Getting the shoes to the drums is where flow control comes in.

Modern aftermarket M/Cs normally don't include a rear residual valve (to hold the shoes close to the drums). Old M/Cs did include the residual valve. I don't like them because that 'system' gives you a false sense of brake adjustment. In other words in the old days, when the pedal went to the floor it was time for a brake adjustment. Springs did a good job of retracting the shoes.

With the residual valve, wheel cylinders simply extended farther and farther. Sometimes the piston would come out of the wheel cylinder. A better choice is a self-adjuster that actually ratchets the star wheel out. By expanding the bottom of the shoes, the pistons don't need much stroke (or flow) to contact the drum.

I only use residual valves in brake systems where the M/C is below the wheel cylinders. - Dave
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