Bit of a newb but here goes.53 chevy hardtop with 78 camaro front clip SBC mil. GM discs in front gm rear with drums.. I just replaced my master cylinder with a new manual 1inch bore MC from CPP. It came with the combination valve all plumbed and ready for installation. I bench bled the MC before install and have bled the system several times now and am pretty sure its free of air. No leaks as far as I can tell. My problem is the pedal goes pretty far down when first pumped but by the second or third time it gets peasantly firm. Pedal doesnt seem to drop if pressure is maintained on pedal only when released and allowed to rest for a moment. When driving it takes way too long on the first pump to stop the third pump stops well but I dont feel I could lock em up if I wanted too. The pedal ratio is 6.25/1. I used the pushrod out of the old master which looked to be a 1 inch bore mustang unit. And after a pump or two the pedal firms up about 3 inches from the floor and stops just above the floor. The whole car is plumbed with 3/16 line except for the plumbing for the rear MC port to rear port on the combination valve. That stuff looks to be .25". No residual valve is installed to the rear drums unless its built into the combination valve?? I have started looking at the brakes now. front brakes:The front pads look fine although the front driver has a shim of some sort between the piston and the pad that has slipped out of place. That wheel also seems to spin a little less freely than the other front but otherwise the fronts look fine. rear brakes:I have the rear pass drum off and peeked behind the cylinder seals and looks clean. That drum rear pad shows uneven wear with no wear on lower 1/3 of the pad. The other drum is stuck and after gettin the adjuster star wheel loosened and beating on it with sledge and hammers and using liquid wrench I will hit it with some heat tomorrow and see how that goes. So thats about it. Any ideas on how to proceed are welcome. Thanks Joel.
Make sure the rear brakes are adjusted up where the wheel is just free showing a bit of drag. But I thing from the sound of things you need a 10psi valve in the rear. with the brakes released your push rod should have a bit of clearance, 1/4-3/8 inch pedal movement is about right.
Since you didn't give the location of the master I will assume it's on the firewall in which case you don't need inline residual valves. If it is under the floor, then you will need them to maintain slight pressure in the system. If you can pump it and get a good pedal, it still has air somewhere. If the master is in fact on the firewall, try to garvity bleed them. Start with the back and open both bleeders and let the fluid run out till you have emptied about half of the fluid, then repeat with the front. Do not let the master get empty. Sometimes a light tap on the calipers and wheel cylinders with a hammer will urge the air out of the bleeder. The uneven wear on the drums indicates a drum that has been excessively turned and no longer matches the arc of the shoes. If you happen to be lucky enough to have an old shop in you town with a brake shoe grinder, they might be able to grind the shoes to match you drum diameter if it hasn't been over turned. Doing this is the best thing you can do to any drum brake application.
Don't take this the wrong way, only speaking from experience. Are you using a bunch of adapters coming out of the MC to the existing brakelines or anywhere else? If so are you sure they're correct and the flare type? Had similiar symptoms as you that I believe were from using a female-female barrell connector that was flared on one side only (never make that mistake again, still can't figure out what purpose that adaptor would correctly serve). Is the brake light switch plumbed into the lines or are you using the type that is activated by the pedal? I've had trouble plumbing those inline too. Have you been checking the MC and are you losing fluid?
The master is on the firewall. But I still dont know if I do or dont I need the 10lb residual valve to the rear drums? As far as the drums not having the same arc as the shoes. Would new drums and shoes fix this if I cant find someone to grind the shoes to match. Thanks so far for the suggestions.
No wear on the bottom 1/3 of the shoe sounds like oversize drums to me. Get them off and have them measured. Flatman
Nobody wants to arc shoes anymore...they come "cam" ground so after a few thousand miles they wear round to match the drum. The symptoms you describe are typical drum adjustment issues. The return springs push the fluid back to the m/c. Pull the other drum to get a good look, make sure everthing is ok. Adjust them so they have a slight drag. Sometimes you have to pump the pedal to center everything and then readjust..A couple of times !! With the m/c on the firewall and a proper disc drum m/c you should be able to get and maintain a good firm pedal..I don't see any need for rpv.. good luck Dave
Ok. so I have finally gotten the other rear drum off. Same thing happening on that side as on the other. Rear most brake shoe shows no wear on bottom 1/3 of it. So does this still sound like adjustment issue??
Yes! With a frozen star wheel adjuster, there is no way that you could have had the proper adjustment. Get the adjusters working right, adjust them up until the wheel locks up and can't be turned by hand. Then back off on the adjustment until there is a drag but the wheel can be turned. When I bought my truck it had terrible brakes. When I took it apart, everything was brand new but it had never been adjusted. Mine had a frozen star wheel too so I knew it was never adjusted. You will want to readjust after a few thousand miles once the shoes seat into the drums.
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