Testing a Proportioning Valve?

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autopar3000

autopar3000

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Hey guys,

I have the Kelsey Hayes brake setup on my 70 Swinger with power brakes. Under hard braking the rear wheels lock up and the front wheels don’t, so I’m thinking that perhaps my 50 year old proportioning valve isn’t working well.

I have a couple of spares that are identical to the one on my car now, but I don’t know if they’re good. Is there any way to test one of these things?
20200721_235300.jpg
 
That is not a proportioning valve that is the distribution block or sometimes called the safety valve (switch). The proportioning valve is in line going to the rear brakes. These pictures might help.

PropValveEarly.jpg


View attachment PV-change.jpg
 
A 70 built after Jan 1 should have come with a combinaton valve.
upload_2020-7-22_7-59-18.png

If your car was built before then, then it has a proportioning valve after the distribution block with safety switch.
upload_2020-7-22_7-58-50.png

Pictures and chart in this booklet.
1970 Chrysler Imperial Hydraulic Brake Service Guide from the Master Technicians Service Conference Session 274
Test procedure is on page 10, and its also in the FSM.
But it requires having the pressure gages and adaptors.

I would
a) First bleed the brakes front and rear.
b) Then examine the rear shoes for signs of grabbing etc.

After that, then yes consider a rebuild kit for the prop valve or combo, whichever you have.
Also consider reducing the size of the rear wheel cylinders. Depending on the tires. pavement, weight distribution, front/rear heights, etc - sometimes slightly reducing the force on the shoes (by changing to slightly smaller wheel cylinders) is helpful.
 
Antilock brake system is the only true way to prevent rear wheel locking under hard/emergency/panic braking. The fronts are supposed to roll / be steerable after you're dragging the rears. Lock all 4 at once and you're sliding with no control. If rears lock under normal/light braking, arc or radius match of shoe to drum is possible cause. Shoes installed wrong is another cause. The shorter brake lining goes to the front.
 
did you turn the rear drums? /if they are to shinny or glazed or turned too rough not smooth they will grab hard or if they are full of loose brake dust
 
The factory bias on these cars was pretty heavily to the rear, they always lock the rear up first and by a pretty substantial amount. Redfish described some of the reasoning but on most of the factory cars I’ve driven the rear bias is too much even with those considerations. It’s like the factory about of understeer- sure, the factory assumes the general public can’t drive so they set cars to under rather than oversteer, but in the 60’s and 70’s they really got carried away.

The proportioning valves can be “reset”, that’s why the FSM describes the brake bleeding process as being passenger rear, drivers rear, passenger front, drivers front. Follow that order and the prop valve should end up “set” properly.

But as Mattax pointed out any changes from factory specs may change the needed bias. The most common thing is people run staggered wheel set ups on these cars, which changes things a lot in the braking department. Changing the wheel cylinder bores can help, or just install an adjustable proportioning valve.
 
Get it on a gravel road with a spotter and see which wheels are locking first, adjust
as needed, may need and adjustable. Pull the wheels before test and see if everything looks OK.
 
Or consider that your rear brakes are soaked in brake fluid or 90w rear ended fluid. That will make the rear brakes lock up.
 
Mine are doing the same thing, and the rear locks up way too early. I suspect that whoever upgraded my 64 dart to duel master with disks in the front, did something wrong. I am considering adding a proportioning valve for the rears. Right now I don't have to step on the brakes very hard before one of the rears locks up. If I ride the brakes for a while it doesn't do it as bad. I have inspected the rear brakes and they are fine, no leakage or glazing. So I am following this
 
trapster said:
Mine are doing the same thing, and the rear locks up way too early. I suspect that whoever upgraded my 64 dart to duel master with disks in the front, did something wrong. I am considering adding a proportioning valve for the rears. Right now I don't have to step on the brakes very hard before one of the rears locks up. If I ride the brakes for a while it doesn't do it as bad. I have inspected the rear brakes and they are fine, no leakage or glazing. So I am following this
Click to expand...

They probably just used the drum/drum distribution block instead of adding a proportioning valve. If you look at the pictures of the prop valves above and then look at where your lines split off down on the frame rail below the MC it’ll tell you. A distribution block is pretty small, just a splitter for the lines basically. If they left that and went disk/drum you’d get that problem.
 
Hey guys,

Sorry for the delay on this, I had a minor surgical procedure done on my eye so I was down for a while. Side note: getting needles in your eye sucks.

The amount of information you guys can provide is amazing. First, it's helpful to know that I'm not even talking about the proportioning valve! So the safety switch is not my issue and I'll be leaving it alone. My rear brakes lock up under hard braking, but under no circumstances do I ever feel like I'm getting enough braking pressure to the front brakes. The pedal feel is very weird, too. The amount of pedal travel is fine, then it gets super hard and pretty much all the braking is done within a quarter inch of travel. The level of braking is more about the pressure I put on the pedal, rather than how far I push the pedal down (because it gets super hard and won't go any farther down).

Like trapster, if I drag the brake for a little while and then try to stop the car, it feels like the front brakes do more work and it stops better. Maybe because the rear brakes heat up a little and don't work as efficiently, thereby leaving the fronts to do more work? Or maybe by dragging the brake the proportioning valve is cutting down a bit of pressure to the rear?

I think I'm going to try the bleeding procedure the way 72bluNblu described then see how it feels. If it's still the same I'll replace the proportioning valve (the actual proportioning valve), maybe with an adjustable one, then see how that feels.

I'm in the middle of an engine swap right now so it might be a while before I get back to this, but once I'm back on the road I'll let you guys know how it works out.

Thanks so much for the help!!
 
autopar3000 said:
Hey guys,

Sorry for the delay on this, I had a minor surgical procedure done on my eye so I was down for a while. Side note: getting needles in your eye sucks.

The amount of information you guys can provide is amazing. First, it's helpful to know that I'm not even talking about the proportioning valve! So the safety switch is not my issue and I'll be leaving it alone. My rear brakes lock up under hard braking, but under no circumstances do I ever feel like I'm getting enough braking pressure to the front brakes. The pedal feel is very weird, too. The amount of pedal travel is fine, then it gets super hard and pretty much all the braking is done within a quarter inch of travel. The level of braking is more about the pressure I put on the pedal, rather than how far I push the pedal down (because it gets super hard and won't go any farther down).

Like trapster, if I drag the brake for a little while and then try to stop the car, it feels like the front brakes do more work and it stops better. Maybe because the rear brakes heat up a little and don't work as efficiently, thereby leaving the fronts to do more work? Or maybe by dragging the brake the proportioning valve is cutting down a bit of pressure to the rear?

I think I'm going to try the bleeding procedure the way 72bluNblu described then see how it feels. If it's still the same I'll replace the proportioning valve (the actual proportioning valve), maybe with an adjustable one, then see how that feels.

I'm in the middle of an engine swap right now so it might be a while before I get back to this, but once I'm back on the road I'll let you guys know how it works out.

Thanks so much for the help!!
Click to expand...

Sounds more like an issue with the master cylinder. What’s the bore?

Riding the brakes helping is a little weird. Maybe the master cylinder isn’t pushing enough fluid to the disks under normal conditions? Which is they the fronts come on late but do better if you hold some pressure in the lines by riding ‘em. Or maybe it’s just cooking the rears so it feels like the fronts are better. But even that would indicate not enough fluid is going to the disks, because they should react faster than the drums (hence the residual valves for the drums on the disk/drum cars).
 
autopar3000 said:
Like trapster, if I drag the brake for a little while and then try to stop the car, it feels like the front brakes do more work and it stops better. Maybe because the rear brakes heat up a little and don't work as efficiently, thereby leaving the fronts to do more work? Or maybe by dragging the brake the proportioning valve is cutting down a bit of pressure to the rear?
Click to expand...
it could just be the disks and the pad material. I had (have) some Cyclpro - Chrysler pads that didn't have a lot grab or pedal feel - especially with a disk that's worn smooth. Or the calipers aren't working. If it feels like the front, I'd focus on the front.

Rear brakes help the most on the initial and light braking inputs. While under hard braking weight shifts forward reducing the traction of the rears. That's when the proportioning valve is needed.

As far as heat goes, with street use, you will have to try really hard to heat the linings to a temperature where the friction declines. A really long steep downhill in the mountains might get there if riding the brakes. That's true both for the fronts and the rears. In fact their performance may increase slightly after a couple applications in a row.
 
trapster said:
I am afraid that riding the brakes is just causing the rear drums to fade enough that they do not lock up anymore. this cannot be good for them I think we just need to add or adjust the rear proportioning valve.
something like this Classic Performance Brake Proportioning Valves PV-2 or Right Stuff Detailing RMB6801
Click to expand...

The first one is what you need, not the second one. Or just this

Summit Racing® Adjustable Brake Proportioning Valves SUM-G3905

The problem with the stock style prop valve is all the fittings are different sizes, so you can’t mix up the lines. On a drum/drum car that has a distribution block all the fittings are the same. So you either need adaptors, new lines, or reflare the lines with new fittings. But the lines aren’t all the right length either going from a distribution block to a combo valve.

So it’s a ton easier to add that in-line adjuster into the rear line than replace the distribution block with a combination valve


Mattax said:
it could just be the disks and the pad material. I had (have) some Cyclpro - Chrysler pads that didn't have a lot grab or pedal feel - especially with a disk that's worn smooth. Or the calipers aren't working. If it feels like the front, I'd focus on the front.

Rear brakes help the most on the initial and light braking inputs. While under hard braking weight shifts forward reducing the traction of the rears. That's when the proportioning valve is needed.

As far as heat goes, with street use, you will have to try really hard to heat the linings to a temperature where the friction declines. A really long steep downhill in the mountains might get there if riding the brakes. That's true both for the fronts and the rears. In fact their performance may increase slightly after a couple applications in a row.
Click to expand...

Also a good point. Could also be the front pads are just contaminated. A little grease will ruin those things for a long time. Or improper break in and they’re glazed over.

If either of those are possible you can sometimes “resurface” the face of the pads with some sandpaper (do not breathe that crap!!!). Then try again on the break in.
 
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72bluNblu said:
Sounds more like an issue with the master cylinder. What’s the bore?

Riding the brakes helping is a little weird. Maybe the master cylinder isn’t pushing enough fluid to the disks under normal conditions? Which is they the fronts come on late but do better if you hold some pressure in the lines by riding ‘em. Or maybe it’s just cooking the rears so it feels like the fronts are better. But even that would indicate not enough fluid is going to the disks, because they should react faster than the drums (hence the residual valves for the drums on the disk/drum cars).
Click to expand...

I replaced the booster a few years back with this:
1970 DODGE DART Right Stuff Detailing Master Cylinder and Booster Assemblies G80011001
So it's a 1.063" bore. I also replaced the calipers and pads around the same time. Is 1.063 the right bore size?

I was also thinking that maybe the front brakes aren't getting enough fluid (pressure), so I bought a new set of hard lines I'm planning to put on while the engine is out (that's why I was also looking at the safety switch). The thinking is maybe there's a blockage somewhere, but honestly I doubt that. However, I never did the full bleeding process described earlier, so that's something I'll do after I replace all the hard lines up front.

I've owned this car a long time and the poor braking and strange pedal feel has been there the whole time, even as I have replaced the master, booster, and calipers.
 
With a booster, definately shouldn't require a lot of foot pressure.
Go to the Master Tech Series 1967-70 and read up on the brake system. It will make the trouble shooting much easier. There's even one on 69 up drums which is a big help these days since so few people really understand what it takes to make them work well.
Master Technician Service Conference - Chrysler's Training for Mechanics

For the booster, AFAIK the shop manual will be the only factory info. If you don't have one, Bishko is a retailer of reprints and sometimes originals.
free digital downloads are available at mymopar.com
 
Mattax said:
With a booster, definately shouldn't require a lot of foot pressure.
Go to the Master Tech Series 1967-70 and read up on the brake system. It will make the trouble shooting much easier. There's even one on 69 up drums which is a big help these days since so few people really understand what it takes to make them work well.
Master Technician Service Conference - Chrysler's Training for Mechanics

For the booster, AFAIK the shop manual will be the only factory info. If you don't have one, Bishko is a retailer of reprints and sometimes originals.
free digital downloads are available at mymopar.com
Click to expand...
Thanks Mattix, I fell into a rabbit hole watching those old Master Tech videos! They're awesome. But it just left me thinking the same thing I've been thinking for years and that the issue has to be the master cylinder. Even though I have already replaced the master cylinder.

So next on the list is the hard lines up front, only because I have them and it will be super easy with the engine out of the car right now. I think I will also replace the prop valve, since it will be so easy to do. But (I think) the core of my problem is the front brakes don't grab hard enough, so I'm not sure changing the prop valve will do anything. We'll see, I guess.
 
Hey, here's a thought. What would happen if the thickness of the rotors was under spec? Could it be difficult for the pads to put sufficient clamping force on the rotors?
 
trapster said:
THis is what I have View attachment 1715567764
Click to expand...

That is a combo valve for a disk/drum car. But looking at the lines and how it’s mounted it wasn’t stock. It also looks like the brake switch may be leaking.

autopar3000 said:
Hey, here's a thought. What would happen if the thickness of the rotors was under spec? Could it be difficult for the pads to put sufficient clamping force on the rotors?
Click to expand...

It would require more fluid in the system to move the pistons far enough to grab the rotor, yes. The clamp force would be the same as long as there was enough fluid though. And of course at some point you may lose the seal on the piston and have a leak.

And the fluid thing would just show up as a low level in the master cylinder, if you topped it off it would probably work fine as the rotors only knock back the pads so far, you wouldn’t be going from fully retracted with each brake application.
 
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