Got a 1950 Ford Crestliner w/396 auto and am running power brakes with discs/drums. but I do not have a proportioning valve in the system. My issue is that when pressing the brakes, I press as hard as I can and it acts like the pedal is bottoming out. Oh, the car stops, but as hard as I try, I cannot do a 'panic stop'. Is this because there is no proportioning valve, or is it really maybe bottoming out?
Had the same issue with my Galaxie w/4 wheel disc conversion, had nothing to do with the proportioning valve. Turned out that the MC bore was too small...I switched out the 1" bore MC for a 1 1/8" MC, problem solved. Turned out that the 1" bore did not move enough fluid to support a "panic stop". Not the brakes will put you through the windshield. A proportioning valve limits the amount of fluid going to the rear drums. It takes much less fluid to activate drum brakes than it does discs, so the proportioning valve prevents the rear drums from locking up before the front discs activate. Chris
As stated the proportioning valve will not cause the peddle problem. But when you get that handled if you have a problem with the rears locking up first then install one of the adjustable valves in the rear line.
Excessive pedal travel plus excessive pedal pressure required to stop usually indicated that the master cylinder is the wrong size, too small for the unit. Backyard mechanics rule is the master cylinder to be used must be the same size master cylinder as the donor car brakes required, ex. if brakes used 1" bore master then you need to have a 1"' bore master cylinder.
1. Update the master, you are not pushing enough fluid through the system. Disca require more fluid than drums, some discs require for fluid than other. The rule of thumb mentioned earlier works well. 2. Once you have the pedal issue resolved you mey require a proportioning valve. If the master has the same bore for both the front and the back, you will lock up the rears during hard/panic stops. the proportioning valve with reduce the pressure to the raer brakes to limit their lockup during hard braking due to pressure/weight transfer. Take car of the master first than look at a poroportioning valve.
I'm not running a proportion valve on my converted disc front/drum rear set up and it works great. I did have to play with the stroke of the pedal. Had to move the hole where the rod connects to the pedal up and down until I got a full stroke of the piston. My friggin post sounds R rated
re....proportioning valves Fit smaller bores for less rear brakes and bigger bores for more rear brakes. This might be more likely if fitting larger rear drums, 9 inch diffs etc. A well-designed brake system should always lock the front first. If the rear wheels lock, the car will spin around. The purpose of rear proportioning valves is to ensure that line pressure cannot rise to the point of rear lock up. Up to that point, front and rear line pressures are usually the same. A proportioning valve is not a band-aid for a badly balanced system.
So does this same theory apply to drum/drum set ups with a dual reservoir master cylinder? Would you still have to have a proportioning valve to prevent rear drum lock up?
on the drum drum the answer is no. on the disc drum you need a disc drum master cyclinder or a proportioning valve a the least. 2lb to activate disc 10 lb for drum. most standard masters are set for drum brakes unless they are made for a car that came with disc drum from the factory.
If your production drum/drum vehicle has a habit of early rear slide, or if you are using a late duo-servo drum-braked rear axle with old Ford Lockheed non-servo front brakes on a custom build, a prop valve may be necessary.
Is this a case where you want to make sure that there's a residual valve in the circuit for the rear drums?
if you look at most older vehicles with just a drum set it is a simply set up. Single master to splitter to left and right. with right adjustment they work great besides occasionaly rear lock and if you blew a line all brakes went. With a newer set up you have seperate chamber in the master for front and rear as weel as disc and drums. a prop vavle help to keep the rear from locking up berfore the front. typically 70/30 60/40 to get the car to stop on a nice level stance instead of nose dive and then the back coming to a rest. the prop vavle stop this from happening. Put the right parts together and you will get a good result. Don't mismatch a system it will get expensive and can become a PITA. Plenty of aftermarkets setups that are great. Some may get away with different parts mixed together and get good results.
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