Master Cylinder upgrade?

[KULTULZ]

Dave mentioned the main problem with splitting the system - once you split the system it becomes 2 braking systems with separate reservoirs and master cylinders for each system. The back could be working great but not provide much stopping power if the front was out of adjustment.

The valve makes up for that and balances the system. You could probably get by without it but would have to keep a constant check and adjustment on your brakes. I can understand wanting to have one set working if another failed.

Eric

The valve needed (ideally) (as one is not needed specifically) on a drum/drum application would be a PRESSURE DIFFERENTIAL VALVE, not a PROPORTIONING VALVE. If not using this valve (PDV), the system if experiencing a failure on either circuit, will still have braking effort on the working circuit until a loss of brake fluid would disable the non-affected circuit.

The valve (PDV) senses loss of pressure in either circuit and then would close that circuit to prevent further fluid leakage and also trip a warning lamp to warn the driver of the hydraulic failure.

A PROPORTIONING VALVE is not needed in this system as brake bias is determined by wheel cylinder size, brake line size and foundation brake size. This valve only comes into play during a panic stop situation. It restricts pressure to the rear brakes to hopefully prevent rear lockup and resultant vehicle swing around. If one deems a proportioning valve necessary, one should find one from an original OEM drum/drum application for proper bias setting (OEM) or if using an adjustable, it should be calibrated on a skid pad.

[simplyconnected]

I believe I specifically said it correctly all along with full explanation:

...A combination proportioning valve uses a piston BETWEEN the front and the rear systems. It also does much more: It meters, so the rears come in first, then it proportions (in your case 1:1 with drum/drum or disk/disk - it's the same valve), and it shuts off the ruptured side if you get a leak, so your M/C doesn't run out of fluid. When the piston shuts off one side, the valve grounds an electrical contact so you can use a dash warning light.

I did NOT specify a proportioning valve without the word 'combination', and I never will. If you read my prior threads/posts, I have always advised members to use a Ford or GM (OEM) type valve which is a COMBINATION, not just a differential or flow control valve. I also encourage everyone to peruse professional brake companies' web sites. BTW, I did Excellent in Hydraulics 101. - Dave

[KULTULZ]

I believe I specifically said it correctly all along with full explanation:


I did NOT specify a proportioning valve without the word 'combination', and I never will. If you read my prior threads/posts, I have always advised members to use a Ford or GM (OEM) type valve which is a COMBINATION, not just a differential or flow control valve. I also encourage everyone to peruse professional brake companies' web sites. BTW, I did Excellent in Hydraulics 101. - Dave

Dave, glad you did so well in class...

The point I am trying to make is the differences in valving. For some reason, and it is difficult to understand, many do not know the purposes of valving.

A COMBINATION VALVE most likely will also include a front METERING VALVE which is definitely not needed on a drum/drum application.

[simplyconnected]

For some reason, and it is difficult to understand, many do not know the purposes of valving...

Gary, there are many functions on your car that folks don't understand, but they work and we use them. Modern science cannot explain why we sneeze, or why passing a wire through a magnetic field produces electrical current. All that maters is we take full advantage of these truths.

We both agree that an OEM valve is necessary. All the OEM valves installed on cars ever since split systems came out have been 'combination' (with metering, proportioning, differential (even if it's 1:1 like disk/disk systems), but not flow control).

Metering is a good thing on all brake systems. It ensures the rear brakes apply first, for better traction control. Do we need it? It has already been included from the factory and yes, I want it on my family car whether the wife understands it or not. Old drum/drum systems never had Metering because they used a 'mono' system and all wheels got the exact same pressure (thanks to Louis Pascal's Law).

In any event, if you are using a dual master cylinder, you need an OEM-type combination valve suitable for your system whether it is drum/drum, drum/disk, or disk/disk. Dave

[KULTULZ]

Gary, there are many functions on your car that folks don't understand, but they work and we use them. Modern science cannot explain why we sneeze, or why passing a wire through a magnetic field produces electrical current. All that maters is we take full advantage of these truths.

What I was trying to convey Dave is that brake valving is a not fully understood subject. There are even many modern techs that do not fully understand the older systems, and the techs of older years were even worse (IMO).

Often, conflicting descriptions of the actual part(s) adds additional confusion.

We both agree that an OEM valve is necessary. All the OEM valves installed on cars ever since split systems came out have been 'combination' (with metering, proportioning, differential (even if it's 1:1 like disk/disk systems), but not flow control).

Not all valving Dave. If you study just FORD valving as the split system was being introduced, the valves were separate. The actual combination valve was not introduced until the very late sixties.

Metering is a good thing on all brake systems. It ensures the rear brakes apply first, for better traction control. Do we need it? It has already been included from the factory and yes, I want it on my family car whether the wife understands it or not. Old drum/drum systems never had Metering because they used a 'mono' system and all wheels got the exact same pressure (thanks to Louis Pascal's Law).

In any event, if you are using a dual master cylinder, you need an OEM-type combination valve suitable for your system whether it is drum/drum, drum/disk, or disk/disk. Dave

A metering valve is not used on a drum/drum application. The first valving had the pressure differential valve (for safety) and a proportioning valve (for panic stop situations).

Excerpt From- http://freeasestudyguides.com/brake-metering-valve.html

The metering valve is a used by front disc rear drum type brake systems to delay the front calipers enough to overcome the rear brake springs and linkage.

A proportioning valve is a height sensing valve located in-line to the rear brake system. This valve is used to prevent rear wheel lock-up during sudden and hard braking situations.

NOTE-

The above description of the proportioning valve is not correct. The text is defining a vehicle height sensing valve as used on a truck and or passenger van. See the problems?

OK, I have stated my position and of course you have a rebuttal...

[simplyconnected]

What I was trying to convey Dave is that brake valving is a not fully understood subject. There are even many modern techs that do not fully understand the older systems, and the techs of older years were even worse (IMO).

It's even worse than that. GM used the Teves ABS system in Buick Reatta and a host of other models. There are many pages on the net regarding deaths from catastrophic failure of this fine German-engineeered system.

In other examples, Ford used the cross-wheel split system on early models which did a good job of spinning cars around when a brake line ruptured.

The point is, we learned a lot about how NOT to do brakes.

All modern cars are built with disk/drum or disk/disk brakes with combination proportioning valves. Investing in a stock drum system doesn't make much sense except to bring a car back to originality. Anyone who really likes drum brakes will be astounded by the vast improvement in brake performance if they retrofit disk brakes. - Dave