I have seen several different photos of these plumbed up, down, sideways... and the like. But what seems to be consistent is that ‘stock’ cars rear brakes are plumbed from the MC and enter the block “closest to the nut.” Just as I have the block marked with sharpie... and opposite my setup. However, speedways diagram plumbs it differently.... Anybody have a definitive answer Sent from my iPhone using The H.A.M.B. mobile app
Those really aren't 'proportioning valves' per se... These came into existence primarily to allow the brake warning light operation, which for custom deals isn't generally used. Prior to '67 when the lights became mandatory (along with the dual-reservoir master) they weren't always used. Proportioning was done by selecting the right rear wheel cylinders to balance with the front brakes, and to a degree this was still true after the OEMs started using these, it just gave them a bit more latitude in which cylinders were needed. So unless your application mimics the OEM install (car weight, weight distribution front/rear, brake fluid volume/pressure front/rear), whatever 'proportioning' that's occurring probably isn't right for your car. I'd plumb the system without it, and if you have an issue with rear-wheel lock-up when done, then I'd install an aftermarket adjustable valve to the rear brakes.
I had a quick look at my 1970 Mustang and this one appears to be correct. I didnt follow each brake line exiting the brake valve only from the master to the brake valve.
The purpose of the block is to turn on the warning light as well as block off the fluid to the leaking portion of the brake system so the pedal doesn't go so far down.
I never looked at it that way but hell yes that makes sense. So!?, to all those that put a dual circuit master in place of that mason jar. Did it make things better/safer?
I would rather have "some" brakes in the event of a failure rather than no brakes. So yes, a dual master would be the way to go.
Providing drum brakes are still in good adjustment. Other wise there isn't going to be any lesser travel to be taken advantage of.
Jeremy, the picture RmK57 posted is correct, and matches your sharpie picture for the rears. A drum/drum combo valve is much smaller and only includes pressure differential along with distribution. That valve looks like a '70 Ford combo valve which includes pressure differential and proportioning. Metering, if included, would normally have a push button on the front end of the valve to allow low pressure bleeding. Crazy Steve, proportioning applies to both rear brakes, not just the right rear ??, unless the system is cross split, which would require two prop valves. Engine man, I don't remember ever encountering a differential pressure switch that blocked off any fluid during a system failure, although some valves may have done that. Kind of silly to prevent any available braking, imo.
Yeah many of them had a valve that blocked fluid that way you just don't empty the master cylinder brake fluid every where under the car and to keep brake pedal feel. The push button on the end was to center the valve back up in case it was tripped. That's how the light worked, by moving the valve and closing either end of the brake system made a ground in the block and turned the light on. Although most of the time I couldn't get the valve to 're center without pulling the connector and taking a pick and 're centering the valve. Used to see alittle of them tripped back in the day, people doing their own brakes and bleeding them and pushing the brake pedal down with the bleeder open and pushing the valve closed. They would bring the cars in and we would reset them.
The master cylinder fluid reservoir is divided, and will not totally empty when one system leaks. The push button (or pull pin) bypasses the metering valve, but does not recenter the differential switch.
I know it's divided, it was to keep from emptying that side that leaked, and to help keep from blowing fluid every where. Simple test, open a bleeder, jam the brakes a few times, once the light is set then check pedal feel and check fluid movement thru that open bleeder. You will find that the pedal feel isn't much different than before and almost no fluid movement thru that open bleeder when depressing the brake pedal.
I have run many failed system dynamic tests with pressure transducers on both master circuits, along with each brake cylinder/caliper, that would show any pressure resulting from the DPS closing off any fluid. Stopping distance tests require one fast initial apply, not multiple, so it's possible the valve can block fluid if the pedal is "jammed a few times, but the stopping distance would be well exceeded, something I had to prevent.
I should have typed 'correct' rather than 'right'. And the idea that the valve 'closes off' an open brake circuit in the event of a failure isn't correct. If it did, you would be unable to apply the end that did work (try plugging one of the master outlets and see how well the brakes work...). In terms of actual braking performance, these valves only perform two functions. One, they slightly delay actuation of the front brakes to aid stability. Two (and this usually only applies to disc/drum systems), it limits pressure to the rear brakes to prevent lock-up. This only comes into play during panic-stop situations. Again, this is usually calibrated to the individual car model; changes in weight distribution, overall vehicle weight, brake components, and even rear tire size will all effect this. And I believe the 'delay' is really only for panic-stop also. Older Jaguars (up to 1989) with 4 wheel discs (which aren't known for poor brakes) don't use these valves at all. Instead, they use a two-piece master cylinder piston separated by a spring. When applying the brakes, the rear piston moves first (there's your front delay) and once the spring is compressed, then the fronts. Because of this, Jaguar didn't fit a pressure-differential switch for a warning light because it would light up each time you applied the brakes. Instead, they used a 'low fluid' light as their brake warning light. I don't know how this got this past the Feds, but it did. And first-gen Mustangs with front discs didn't have these valves either. Using a single-circuit 'fruit jar' master, they simply split the lines to the wheels. I did a disc conversion on my '64 Comet I used to have, using the 'fruit jar' master. Asking about whether I needed a proportioning valve or not, virtually every vendor I talked to insisted I needed one. I installed one and ended up running it full-open for best results... so much for the experts...
Truth be told... I have a front disc rear drum, and the rear is overheating after 5 mile jaunts. And I can’t find a mechanical or hydro drag. It may be that this valve is letting fluid back way too slow. The MC, pedal, spring, hardware... all look to be in good shape. However this block seems to be plumbed wrong. I bought the car from a widow, who can’t tell me much... but the man was working on brakes when he passed. Sent from my iPhone using The H.A.M.B. mobile app
I’ve installed a few of those and always ask myself why later... every one has run full open Sent from my iPhone using The H.A.M.B. mobile app
Ok, first thing I’d do is figure out what master cylinder is currently in the car. Some have a built in proportioning valve. Sent from my iPhone using The H.A.M.B. mobile app
Haven’t quite figured out the pedigree yet... looks to be numbered 1511 300 ?!?!? MC rear circuit seems to open well... I’m getting the “pop” of fluid at the start of the throw
I can think of a couple things to check. First, are you sure the switch is centered? I assume there's no light connected, check to see if the switch is open or closed. If closed, that may be the problem. I have seen some valves that will close or partially close off one outlet when off-center, that could be a possible restriction. Second, are you sure the rear brake shoe return springs are good? They don't like to be overheated as they can lose tension and cause drag. And of course, make sure they're not adjusted too tight. Third, also check the 'shoe pads' on the backing plate (the six little square spots where the shoes ride). Sometime those will be worn enough to prevent the shoes from fully retracting (particularly with new shoes), these can be repaired by welding up the wear grooves then grinding them back flat.
Your booster and M/C appear to be Cardone brand aftermarket GM. Sent from my iPhone using The H.A.M.B. mobile app
This is what I run in my Ford. Less the lines and bracket. It worked out very well and I have it on the inner fender below the master. https://www.ebay.com/itm/CPP-HOT-RO...-PROPORTIONING-VALVE-WITH-LINES-/282451453153
Several GM cars used masters with the primary plumbed to the rears. ACDelco Master Cylinder Assembly for 1967-1980 GM Vehicles Part Number: 065-18M1878
Simply not true. Many Ford masters have the front LARGER RESERVOIR going to the fronts. There is no hard rule on which master circuit goes to the fronts or rears on vertical split systems.
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