1940 Lincoln Trying to correct someone's attempt at building a hotrod. Aftermarket power brakes (cheapest catalog find, my guess) l. Pedal travel inside is 6 1/4". Using original pedal setup with extension to underfloor power brakes, only have 1/2" of travel with pedal bottomed out. Is my thinking correct in the throw is wrong abd I need to revamp the pivot to get more throw at the m/c? Brakes are spongy, won't lock up and merely slow as a suggestion. Funny it ties into my screen name from 20+ years ago.
For all the "experts that reinvent the wheel" with brakes. Simply restore the brakes to stock specs [maybe with a tandem m/c of identical bore] If boosted brakes are a "must" use an inline PBR VH44 booster which can be mounted anywhere [VH24 for drum/drum]
Typically, the ratio of pedal travel to master cylinder travel for old cars with non power brakes is about 6:1. You need to be about 4:1. See this page. https://help.summitracing.com/knowl...or power brake systems, the,A 4:1 pedal ratio
There is a shitload of math involved. And most brake threads here are to justify the clusterfuck they've already made . Sometimes you need to start from scratch and bin half the expensive mismatched componentry. Try and find a common denominator with your brakes [eg matching front and rear brakes] and copy the vehicle that it came from The manufacturers have done all the calculations for you. eg: It you have "G-Body" discs and calipers , then try and match the rear drums, shoes and wheel cylinders. [this gets the bias close enough] Then look at the G-Body combination valve and similar M/C diameter booster size and pedal ratio. [You can alter pedal ratios with bore size "fluid mechanics" to get the same results, but this requires maths] Under floor M/C's require the addition of residual valves to prevent syphoning back [pad retraction] If a person can get their Hotrod to stop as good as a mid 80's Honda they will be miles ahead of most of the hackjobs out there.
A suggestion if you don’t mind a partial start over. Remove the vacuum assist canister, replace the rod, and try the system as a non power. If you know the ID of your MC great, if not find out now. Even with a power assist MC your brakes should work but have a hard pedal because the MC that’s there is too large. If it were me and I found it that way I would install a 7/8” bore MC and see how you like it. (Wilwood has them) If needed, a Midland vacuum assist canister on an inner fender well to the front disc brake line on the MC. If your cars rear end has been upgraded to more modern drum system which came from a vehicle with power brakes you also need to replace the wheel cylinders with a smaller diameter. I speak with experience on converting to what works on a mid 50’s Ford conversion to disc brake front and later larger drum brake rear. The only difference is a firewall pedal. Good luck
Idk what your solution is but I installed one of those cheap units in my car and I never could get it to work properly. I cut up the pedal assembly and modified it for correct pedal ratio and it still wouldn’t work right. I finally gave up and installed a non powered hanging unit which works great. I would prefer a floor pedal and may revisit it in the future but I wouldn’t know which assembly to buy. They all look the same to me.
I've bled a pint through the system with no air. That was my first thought, then I double checked the rear drum adjustment and front calipers. I hoped it was a simple solution like a bleed.
@nobrakesneeded (cute!) please provide as much information as possible. As @Kerrynzl said, most of these threads end up like a battlefield, with big holes in the ground and no safe place to walk. Front spindle, rotor, caliper including size. Master cylinder, brake pedal and booster including size. Rear axle, drum, wheel cylinder, and shoe sizes. Any other components in the system.
And getting information requires "waterboarding" So far all we know is "he didn't build it" What collection of parts is this made from.
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