Brake Proportioning Valve Question

[Charlie Chops 1940]

Would the device more accurately be termed a distribution block? I've also heard them called combination valves.

I had a '79 Riviera that the 3 boys all used at one time or another that accumulated 197,000 miles before the last kid refused to drive it any longer. The upholstery material would have went a half mill I'm sure as it never pulled a thread or had a tear. The distribution block on that car was the type that shuttled every time I went into the brake system and it would close one way or the other and it was always a * to get it to get it to recenter. I ended up removing the warning light sender and prying the piston back with an icepick.

I truly grew to hate doing a brake job on it...which was done 4 or 5 times...as retracting the first front caliper shuttled it, and the two replacement master cylinders shuttled it and the rear wheel cylinders. A great car, a crappy system.

Charlie

[Bruce Dorsi]

Strickly speaking, these are not proportioning valves. What they do is hold off brake application in the rear to get it in sync with the front brakes. Basically what it does is to make the rear brakes reach a higher pressure before applying.

=============

A Metering valve, aka Hold-Off valve, delays brake application of FRONT disc brakes in a disc/drum system.

The reason for this is to allow the rear brakes to overpower the return springs and move the shoes against the drums, before the front brakes are activated.  ....Caliper pistons require very little travel to apply pressure to the pads.

The metering valve also helps to reduce "nose-diving" by allowing the rear brakes to apply slightly BEFORE the front brakes.

Without a metering valve on a disk/drum system, the front brakes will do almost all of the braking in normal use, and the front pads will wear much quicker.

Drum/drum systems and disc/disc systems do not require a metering (hold-off) valve.  ....Drum/drum systems use different size wheel cylinders on the front and rear, or different size shoes on the front and rear to help equalize braking.   ....Disc/disc systems use different size caliper pistons, rotor diameters, or pad sizes to help equalize front and rear braking.  

A proportioning valve does not reduce the hydraulic pressure to the rear brakes, but instead, controls the RATE at which the hydraulic pressure rises to the rear brakes.  ....The wheel cylinder will ultimately receive the full hydraulic pressure of the rear brake circuit.

Combination valves get confusing because they are not all the same.  ....Some consist of metering (hold-off), proportioning, and rear residual pressure valves as well as a warning switch and the shuttle valve described in posts above. ....Some combo valves, mainly for disc/disc systems, do not have the residual pressure valve or the metering (hold-off) valve incorporated.

[flt-blk]

Whew, this has been quite an unexpected education.

I ended up with plan A which was to just block off one of the front outlets
and send the other one through the line lock then split it to the front.  I
bled the system and it never locked anything in the combination valve or
needed resetting.  None of my double flares leaked either.  

I can't wait to get the rest of the car done so I can give the brakes a try.  


Thank You everyone for your help and patience.
TZ

[enjenjo]

Strickly speaking, these are not proportioning valves. What they do is hold off brake application in the rear to get it in sync with the front brakes. Basically what it does is to make the rear brakes reach a higher pressure before applying.

=============

A Metering valve, aka Hold-Off valve, delays brake application of FRONT disc brakes in a disc/drum system.

The reason for this is to allow the rear brakes to overpower the return springs and move the shoes against the drums, before the front brakes are activated.  ....Caliper pistons require very little travel to apply pressure to the pads.

The metering valve also helps to reduce "nose-diving" by allowing the rear brakes to apply slightly BEFORE the front brakes.

Without a metering valve on a disk/drum system, the front brakes will do almost all of the braking in normal use, and the front pads will wear much quicker.

Drum/drum systems and disc/disc systems do not require a metering (hold-off) valve.  ....Drum/drum systems use different size wheel cylinders on the front and rear, or different size shoes on the front and rear to help equalize braking.   ....Disc/disc systems use different size caliper pistons, rotor diameters, or pad sizes to help equalize front and rear braking.  

A proportioning valve does not reduce the hydraulic pressure to the rear brakes, but instead, controls the RATE at which the hydraulic pressure rises to the rear brakes.  ....The wheel cylinder will ultimately receive the full hydraulic pressure of the rear brake circuit.

Combination valves get confusing because they are not all the same.  ....Some consist of metering (hold-off), proportioning, and rear residual pressure valves as well as a warning switch and the shuttle valve described in posts above. ....Some combo valves, mainly for disc/disc systems, do not have the residual pressure valve or the metering (hold-off) valve incorporated.

You are right of course Bruce. I wrote that off the top of my head, and my memory was faulty. I went and looked in the book, and it's just as you described it, we must have the same source. I still stand by the S10 combo valve, it has worked well on several cars for me.