proportioning valve questions
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wazoo64
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I'm pretty sure you can leave a drum/ drum distribution block for disc/disc conversion. . An adjustable prop valve in the rear line allows you to dial in to your liking.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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yes, see posts 2 and 4
And heres why:
Disc brakes require a lot more hydraulic pressure to do their job. Without the P-valve ,the rear hydraulics receive this same high pressure and they lock up.Edit; Come on too hard,and skid the tires.
The rear pressure has to be reduced, EDIT; to delay the rear system until the front is fully engaged.
If you still have 9 inch rear drums, you should probably get the aftermarket adjustable type. It will allow you to reduce the rear pressure by just the right amount.
EDIT; The rear system has to be delayed, and restricted,So that it comes on after the front is already working hard, and must not come on with enough power to skid the tires. If the rear skids uncontrollably, the car becomes very difficult if not impossible to steer, and likes to swap ends.
Remember when you were a kid, riding your 1-speed bicycle, with the brake in the rear hub.We would pedal as hard as we could and jam on that rear brake, and slide the rear around, doing awesome fishtails, all the while trying not to wipe out.
Well in a car thats kinda what happens except the front brakles are doing some 70% to 80% of the stopping, so the rear likes to get out sideways on the slightest of turns. And can put you backwards in a hurry.Unless al 4 tires are sliding. Then different physics take over.
And heres why:
Disc brakes require a lot more hydraulic pressure to do their job. Without the P-valve ,the rear hydraulics receive this same high pressure and they lock up.Edit; Come on too hard,and skid the tires.
The rear pressure has to be reduced, EDIT; to delay the rear system until the front is fully engaged.
If you still have 9 inch rear drums, you should probably get the aftermarket adjustable type. It will allow you to reduce the rear pressure by just the right amount.
EDIT; The rear system has to be delayed, and restricted,So that it comes on after the front is already working hard, and must not come on with enough power to skid the tires. If the rear skids uncontrollably, the car becomes very difficult if not impossible to steer, and likes to swap ends.
Remember when you were a kid, riding your 1-speed bicycle, with the brake in the rear hub.We would pedal as hard as we could and jam on that rear brake, and slide the rear around, doing awesome fishtails, all the while trying not to wipe out.
Well in a car thats kinda what happens except the front brakles are doing some 70% to 80% of the stopping, so the rear likes to get out sideways on the slightest of turns. And can put you backwards in a hurry.Unless al 4 tires are sliding. Then different physics take over.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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What he said^
The booster just makes it easier on your leg. Its a power assist device
The booster just makes it easier on your leg. Its a power assist device
Wrong....it is an absolute must change item, or go aftermarket....
wazoo64
Well-Known Member
That makes me believe the block I installed int BBody is wrong then. I thought I installed a drum/drum for my 4 wheel disc setup. Maybe that's why the brakes are so soft.
BillGrissom
Well-Known Member
Post #4, but your drum one is termed "distribution block". Nothing inside, just a "tee". You can use it, but add an adjustable proportioning valve in-line w/ the rear tube. That is what the factory did in the early disk cars (until ~1969). Or replace the block with a "combination valve" (post #10).
"Locking up" implies the rears don't release with the pedal. That could be from a loose flap of rubber in a hose, acting like a check valve, or rust gunk sitting on a port. Post #6 appears to answer a different issue (rears too forceful).
Drum MC's often had a "residual valve" in each port, which is a check valve. The intent was to hold slight positive pressure (~10 psi) in the wheel cylinders, but not enough to overwhelm the springs. That kept the rubber cups tight so air didn't get past them. I understand they weren't needed after they went to the "springs w/ cups" or "springs with tightly wound ends" maybe 30 years ago. All "wheel kits" today have those. Leaving residual valves in has the opposite effect. They cause front disk calipers to lock up.
"Locking up" implies the rears don't release with the pedal. That could be from a loose flap of rubber in a hose, acting like a check valve, or rust gunk sitting on a port. Post #6 appears to answer a different issue (rears too forceful).
Drum MC's often had a "residual valve" in each port, which is a check valve. The intent was to hold slight positive pressure (~10 psi) in the wheel cylinders, but not enough to overwhelm the springs. That kept the rubber cups tight so air didn't get past them. I understand they weren't needed after they went to the "springs w/ cups" or "springs with tightly wound ends" maybe 30 years ago. All "wheel kits" today have those. Leaving residual valves in has the opposite effect. They cause front disk calipers to lock up.
ir3333
Well-Known Member
residual valve in the front will not lock the discs up it will just cause them to drag and wear premature.
if you just go with the distribution block ( i.e. no proportion valve in the rear )it can work in heavy vehicles with large rear tires.
if you just go with the distribution block ( i.e. no proportion valve in the rear )it can work in heavy vehicles with large rear tires.
AJ/FormS
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^^ and make heat, and glaze the pads.I dont think they would drag enough to boil the fluid though, which would make the brakes soft, and the fluid might not recover.(WAZOO start a new thread, detailing your issue. soft brakes is dangerous)
Post#6 edited.
ir3333
Right u r. My Formula S has 295/50-15s out back, and 235/70-14s in front. It has the entire KH/10" brake system transplanted from a 70 Duster. With 3 adjustments; A gutted P-valve, and 7/8 rear cylinders, and a 15/16 M/C.. Proportioning is almost spot-on. I could engineer even more brake into the rear. But it stops so nice the way it is that Ive left it this way for many years now.Its a street car, it doesnt have to be perfect, just purrfect.
Post#6 edited.
ir3333
Right u r. My Formula S has 295/50-15s out back, and 235/70-14s in front. It has the entire KH/10" brake system transplanted from a 70 Duster. With 3 adjustments; A gutted P-valve, and 7/8 rear cylinders, and a 15/16 M/C.. Proportioning is almost spot-on. I could engineer even more brake into the rear. But it stops so nice the way it is that Ive left it this way for many years now.Its a street car, it doesnt have to be perfect, just purrfect.
Ok, I'm going through the same thing with my 68 Dart right now and my conversion kit showed up with a proportioning valve suspended right underneath the new master cylinder. I no longer need that splitter/prop valve thingy pictured in post #4 right? Essentially the new prop valve will replace that stock one bolted inside the fender right? I'm having major problems getting the old lines out of that splitter so I'm thinking of just cutting the rear line, flaring it, and then plumbing it and the two front lines directly into the prop valve suspended from the new master cylinder. Does anyone have any comments on this idea?
plumkrazee70
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If your car was drum/drum before, leave the block in post #4 it was essentially a distribution block. I would just plumb the new prop valve below the master in the rear line.
I did a disc conversion on my car (Scarebird) and left the factory block. I haven't installed an aftermarket pvalve yet.
roccodart440
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I went from drum/drum to disc/disc. I also changed the master. But I changed nothing else. It works fine and doesn't lock up the rears.
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Not sure what kit you bought but you can most likely remove everything from the factory set-up. Does the new one in the kit (under the master) have a warning light switch? If so that is all you will need. But you should check with the manufacturer.
Post #4 shows the distribution block used by the factory which has the warning light switch in it. The prop valve can be seen about 12-14 back from it in the rear line on the frame rail. That is pre-70 factory disc/drum set up. Drum/Drum just used the distribution block and switch.
The newer as shown in post #10 has that separate valve and distribution block/safety switch all built into one unit (combo Valve).
Either of these are not the best design IMO. The adjustable aftermarket units are superior.
Also when a BB is installed, heat from the exhaust can be an issue. The later factory style combo unit will not fit under the factory style shield. So you have to fab one or use the pre-70 pieces.
Post #4 shows the distribution block used by the factory which has the warning light switch in it. The prop valve can be seen about 12-14 back from it in the rear line on the frame rail. That is pre-70 factory disc/drum set up. Drum/Drum just used the distribution block and switch.
The newer as shown in post #10 has that separate valve and distribution block/safety switch all built into one unit (combo Valve).
Either of these are not the best design IMO. The adjustable aftermarket units are superior.
Also when a BB is installed, heat from the exhaust can be an issue. The later factory style combo unit will not fit under the factory style shield. So you have to fab one or use the pre-70 pieces.
Here's what the new prop valve looks like. It seems like it's backwards from the OE setup...so I think if I cut my rear line behind the distribution block and then use a union I can plumb it into the port coming out the front(1) of the new prop valve. The two ports (one on side(2) and one at 45 degree angle) I can run to each wheel cylinder in the front. I think the white plastic "port" is where the switch connects. Does this seem like a good plan to you guys? Am I thinking about this the right way?
AJ/FormS
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OK firstly, NO UNIONS!
If item #1 is an access port plug with a spring behind it, then do not use that port for anything. That end-of-the-device,should be used for the rear brake system.
That plumbing looks strange.
In the OEM system,the front brake lines usually have different fittings, than the rear lines. Thats supposed to make the hook-up foolproof.
Notice in the picture, Both lines have one of each fitting on them.I have never seen that.
It does however look right, in that the rearmost M/C port is entering the correct end of the valve, the end furthest from the proportioning spring(port#1)
Looking at your picture; the rearmost M/C line(which should be going to the front brakes) should immediately split out to the left and right,front lines.The remaining two side-ports then go to the M/C, and rear brakes in whatever position is convenient.
The rearmost port at the M/C, which feeds the front brakes should NOT have a residual valve in it.
(On the OEM combination valve the line for the front brakes comes from the port closest to the booster and enters the valve from the end,on the end furthest from the spring, and then splits immediately out to the calipers. The ports just a bit further down then go to the rear brakes and to the M/C remaining port.Since those rear ports on the valve are directly open to eachother, which goes where doesnt matter.)
If item #1 is an access port plug with a spring behind it, then do not use that port for anything. That end-of-the-device,should be used for the rear brake system.
That plumbing looks strange.
In the OEM system,the front brake lines usually have different fittings, than the rear lines. Thats supposed to make the hook-up foolproof.
Notice in the picture, Both lines have one of each fitting on them.I have never seen that.
It does however look right, in that the rearmost M/C port is entering the correct end of the valve, the end furthest from the proportioning spring(port#1)
Looking at your picture; the rearmost M/C line(which should be going to the front brakes) should immediately split out to the left and right,front lines.The remaining two side-ports then go to the M/C, and rear brakes in whatever position is convenient.
The rearmost port at the M/C, which feeds the front brakes should NOT have a residual valve in it.
(On the OEM combination valve the line for the front brakes comes from the port closest to the booster and enters the valve from the end,on the end furthest from the spring, and then splits immediately out to the calipers. The ports just a bit further down then go to the rear brakes and to the M/C remaining port.Since those rear ports on the valve are directly open to eachother, which goes where doesnt matter.)
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That is what I thought you have. Look at the intructions as there should be 2 ports for the front and 1 for the rear. There should have been a lead wire in the kit for the warning switch you can splice back to your original switch wire. Like already said confirm it with the manufacturer.
And ditch all the original blocks.
Thanks Gerald--yeah I did call Classic Performance Parts....they were less than helpful and basically said I would just need to look up GM instructions because that's all the components they use. None of their documentation online was helpful. I definitely learned a lesson about picking vendors this time around...but now I'm stuck trying to figure out how to use GM proportioning valve with my stock hard line setup. It seems like the best thing to do is to just replace all the hard lines...which is the direction I'm heading. There are two lines for the front cylinders and one 9/16 outlet for the back.
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