Good Morning, I am building a 31 Model A Roadster P/U. It is a Brookville frame and body with a 283 stock V8, T5 trans and a 9" Ford rear. Discs on the front and 11" drums on the rear. I was able to plumb the system fairly well (no leaks) but I am not able to get really good pressure on the first pump of the brake. Second pump is pretty good and the third is solid and does not drift. I am using Wilwood's two chamber basic MC, no booster, with a proportioning valve to the rear with 10lbs residual on the rear and 2lbs to the front. I bench bleed the M/C. Maybe not getting all the air out when I bleed the brakes but have tried multiple times. I am bleeding them the old way with my brother on the pedal and me cracking the valves. I am also not absolutely sure how tight the rears shoes should be to the drums but I do hear some drag but they are hard to turn by hand. I will say that all four wheels do bite when hand spinning them on the first pump, but I feel like that first pump should be more significant. Any suggestions would be greatly appreciated. Thanks, Dave
A way to tell if there is air in the system is to pump the brakes to get a good hard pedal and hold it down real hard. When you release the pedal, watch the master cylinder reservoir. If there is no air in the system you will see the fluid returning to the master as a slight swell in the fluid level. If there is air in the system the fluid will shoot back into the reservoir somtimes higher than the fill cap. If you do not get fluid shooting up out of the reservoir, you need to look at brake adjustment/shoe to drum fit. It could also be that the master cylinder bore is too small for your setup. It doesn't deliver enough fluid on one pump. I'm running a similar setup on my Model A with a 1" diameter master cylinder.
Had hell bleeding mine, basically the same setup except in a 55 chevy. IF, the MC is higher than the WC's, do a gravity feed bleed--just open the valve and let it go for 15-20 min. per wheel while, of couse, keeping an eye on the MC to be sure it doesn't get low. IF its lower (had a coupe with floor mount) use resid's on front (2-3psi) and rear (6psi, 10 sounds high), get a water bottle with hose to fit the valve, put some fluid in the bottle to cover the hose bottom, and (here's the trick) watch the bottle fill while you pump the pedal. Go with the rt. rear, left rear, rt. frt. etc. ---might have to do it a couple of times. Not for those who are hyperactive. Have fun.
If your rear drums are typical Ford/Bendix style, adjust the shoes for a very tight drum, then back off 10 adjuster teeth. This should give you .025"- 030" shoe-to-drum. Pull the drums to be sure the park struts are loose and shoes centered. If the prop valve is adjustable, run the knob full open or (usually) clockwise to allow max pressure to the rears while bleeding. You didn't state, but make sure the front calipers are NOT GM metrics with fast return seals.
Do you have some free play between the pedal and the master when the pedal is released? Is there a return spring on the pedal. If no free play you will never get a good pedal, about 1/16" to 1/8" is good.
https://www.wilwood.com/MasterCylinders/MasterCylinderLanding You provided a lot of useful info, but what @jaracer said kind of tickles the thought process. What MC and bore? It's got to displace enough to actuate with that first stroke. Rear adjustment can cause this, but if they still drag a bit after bleeding (and operating many times to center them), it's probably within tolerance.
75 % of the time when pumping the pedal to bleed brakes it is "how" you are doing the process of bleeding the brakes that is the issue rather than the vehicle. Before #1 you always start bleeding the furthest wheel from the master cylinder brake line wise first and work your way down to the closest. 1. have the master cylinder full, that is a given. 2. have your helper pump the pedal SLOWLY! it just flat does not work if they pump the pedal fast, they have to pump the pedal slowly to give the fluid time to flow into the cylinder for the next pump. 3. they have to hold the pedal down until you have the bleeder screw tight and tell them to pump it again. That is the other battle that I have had with too many helpers. They get tired of holding the pedal and let off before you tell them to. One could not get it in his freaking head that just because the pedal hit the floor did not mean that he could let off until I told him to. My daughter now 45 has helped me bleed brakes since she was four and is still the best helper for bleeding brakes around. 4. Never let the reservoir run out of fluid. Drum brakes have to be adjusted correctly or you have issues. Tighten the adjuster until you can't turn the wheel by hand and back off 11 clicks. you will still have resistance but you have to have that resistance for the brake to work right and the shoes are always slightly touching the drums if they are adjusted right.
Usually if there is still air in the system it won't pump up, if it does as you describe 2 or 3 pumps and you have a solid pedal the shoe adjustment is not tight enough.
I have a similar setup. Try leaving the MC lid off and very slowly push the pedal. You will notice very small (Champagne) size bubbles in the resivoir. Continue doing this until all the small bubbles are gone. Make sure you completely release the pedal to uncover the compensation port. May take a while.
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