So let me start with im a 53 year old auto mechanic by trade but this is my first experience with underfloor masters and early juice brakes. I'm putting a 29 roadster back together that has 39ish brakes, master, and pedals. I started with all new shoes, lines, wheel cylinders, and a 68 camaro drum brake master (1" dia). My pedals are modified so they have a 5.5:1 ratio. I couldn't get a pedal when bleeding and had very little fluid movement. I then put a manual disc/drum 69 camaro master on (1 1/8 dia). Still no pedal and little fluid movement BUT more importantly, on my last corner bleeding (left rear) I would get a 2 " slug of air in the clear hose on every bleed attempt. No fluid leaks either and only that corner. I remade that line, replaced the tee, rehoned/polished the cylinder, and then even replaced the cylinder. No luck. Last attempt before going back to a stock master, I ordered and installed residual valves. Bled tonight and fixed! No air getting ****ed in and good brakes (rolling the ch***is down my driveway lol). I searched and read a ton of peoples recommendations, I just wanted to share what ultimately solved my issues.
2lb for disc brakes and 10lb for drum brakes for under floor master cylinder, is what I have learned from reading too much on the HAMB………. Pleased that you got there in the end !
36roadster, I've read that some masters do have them built in... I'm guessing mine didn't, I used the commonly available 10lb inline valves front and rear.
Some MC do have them built in, if you slide a paper clip in the port and it stops they have them. I put one on my 40 Ford, I think it was out of a late 60's mustang.
I thought those were check valves that were set to a certain pressure. They were there to hold pressure in the line and not allow fluid to drain back to the MC. I was told they were needed when the MC is on the frame rail. Glad you took care of your problem.
yes - sorry, thanks gentlemen for the correction. Didn’t check my post before posting, (or after). I will edit my post in case someone only reads to that post.
Without residual valves the brakes releasing can allow air entrance past the cup seals in the wheel cylinders, this is the main purpose of residual valves.
Agreed, initially I thought residual valves only kept you from having to do the "double pump" to stop but in fact the lack of was keeping me from being able to bleed. I can't explain, however, why on a dual setup prior to the valves, I was able to get the fronts bled but ultimately after weeks of pulling my hair out, I don't care lol.
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