Ive got a model A frame , bell front axle , 40 model ford drum brakes , speedway model A frame mounted master cylinder non boosted , ,3/16 steel brake lines , and camaro rear end drum brakes. Bench bled master cylinder, new front wheel cylinders , . I have to rapidly pump brake pedal twice to get good brake pedal. Bled brakes multiple times. No air seems to be in system. Any ideas ?????
When i first hit the pedal it literally hits the floor with no resistance. Second pump is full brake stop
Do you have 10 pound residual pressure valves for drum brakes installed front and rear near the master cylinder?
If your master cylinder is lower than your wheel cylinders the brake fluid will bleed back into your master cylinder. You need the residual pressure valves to maintain a slight pressure on the lines to keep fluid in the wheel cylinders so you will have ample fluid the first time you apply the brakes. This is why you are experiencing the problem of not having brakes until the second pump. Wilwood, CPP, Speedway all sell the 10 pound valves for drum brakes. They are directional and are normally marked with the direction. They should be mounted as close to the master cylinder as possible. Good luck.
I'd suspect that the brakes need to be adjusted up. The first pump takes up the slack in the adjustment and the second pump applies the brakes. Release the pedal and you lose the adjustment again. Unless you are older than dirt, drum brakes can take some getting used to. Disc brakes don't require adjusting for a good pedal...drum brakes do. Not a big deal on modern cars but very critical on old 4W drum brakes.
I had the same problem with mine. In my case, after bleeding the brakes numerous times, convinced there was still air in the system, I discovered that the problem was that the rod that goes into the (firewall-mounted)master cylinder was not adjusted right and did not push all the way in. A small adjustment, lengthening the rod, solved my problem. This might be worth checking out. Good luck.
Oddly enough we fought with brakes last night. Make sure your rear brakes are properly adjusted. Check all the fittings and make sure you don't have any leaks,,hold the brake pedal down after they are pumped up and see if there is any dampness. Did you bench bleed the master cylinder? HRP
The master lower than the brakes needing RV, only applies to disk brakes. ALL drums need them no matter what, whether inline or in the master.
My understanding of the residual valve is that they maintain pressure (not enough to overcome the springs) so air isn’t pulled past the cups in the wheel cyl. when brakes are released. Fluid cant drain back with out opening the line - bleeder - or a leak
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