‘66 Barracuda Brakes Suck — Proportioning Valve Maybe?

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clifftt

clifftt

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Formula S, KH discs front, 10” drums rear. Brakes were decent when I bought this car. While going through much of the car, I converted the single pot MC to a new (not rebuilt) dual pot 15/16”. The car does not stop well, no confidence if I have to make a panic stop.

Ever since then, I have a brake pedal that has normal travel, but then gets real hard. I’ve checked the calipers. They’re free. I’ve checked the rear brakes and compared to the factory service manual, all springs and adjusters are correct. I’ve rechecked my brake tube routings. I have slack in my parking brake.

My best guess is this old Kelsey Hayes proportioning valve may not be functioning or stuck. I’ve attached an image I found on the internet and two pictures of mine. I’m open to ideas and suggestions...

http://www.2040-parts.com/_content/items/images/22/411722/001.jpg

image.jpg


image.jpg
 
I'm in the process of changing to a KH brake setup on my 66....for the same reason, stopping sucks.

Well, no power brakes. Changing the MC as well, but with a standard modern proportioning valve. I've done the same process for my 66 Coronet, it seems fine. Perhaps replacing a 50 year old proportioning valve, is what you need. Cheap thing to do
 
clifftt said:
10” drums rear. Brakes were decent when I bought this car.
Click to expand...

clifftt said:
While going through much of the car, I converted the single pot MC to a new (not rebuilt) dual pot 15/16”. The car does not stop well, no confidence if I have to make a panic stop.
Click to expand...

Well the only thing changed was the master cylinder. Therefore if the swap was related to the problem, it must be the MC itself or something done during the swap. Was there also a change in linings? How are the MC lines connected to the prop valve?

The other possibility is that its not related to the swap.
clifftt said:
My best guess is this old Kelsey Hayes proportioning valve may not be functioning or stuck.
Click to expand...
Maybe. Are the rears locking up under hard braking at higher speeds?
In what way does it not stop well?
The prop valve only comes into play when the brake pressure is over 300 psi. At that point weight should have shift forward and the front brakes are doing most of the work.
see Disc Brakes (Session 219) from the Master Technician's Service Conference

Initial application and light to normal braking, none of the valves should be effecting the pressure or fluid flow from the master to any of the brake cylinders. Can you crack the bleeds on the rear cylinders and get fluid when someone presses the brake pedal? If not, then something is blocking flow.

Rear brakes do have a lot to do with initial braking. Check the adjustment, check the shoe placement (or post photos) and check the linings.

If the problem is more related to slowing down after the initial application, and the above all checks out, then focus on the front brakes.

Other possibilities
Linings can make a difference in feel.
Lining contamination will make a huge difference.
69 and up drum brake shoe adjuster work in the opposite direction the 68 and earlier.
Brake hose internal collapse

Lots of good info here on brakes. Look at 1966 to 69. Just beware about the change in drum hardware and shoes in 69.
Master Technician Service Conference - Chrysler's Training for Mechanics

Tandem master's rear outlet should feed the front brake Tee.
Tandem master's front outlet should feed the rear line. Only one residual valve is needed. Whether it's the one in the Master's outlet or the 66 in-line one from the single outlet master doesn't matter.
 
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“Was there also a change in linings? How are the MC lines connected to the prop valve?”
They are linings with good, dry material left, I didn’t need to change them. The front line from the MC goes into the factory check valve, then into the proportioning valve. (You can spot the check valve in the bottom of one of the pictures, it’s about the size of a small cigar.). Then it goes straight to the rear brakes.

“Are the rears locking up under hard braking at higher speeds?
In what way does it not stop well?”
The rears will not lock up at 25 or even 45 mph. It takes forever to haul this machine down, as bad or worse than my ‘64 did, and it had 9” drums all around!

“Can you crack the bleeds on the rear cylinders and get fluid when someone presses the brake pedal? If not, then something is blocking flow.”
Yes, fluid comes out when the rears are bled. They don’ appear blocked.

“Rear brakes do have a lot to do with initial braking. Check the adjustment, check the shoe placement (or post photos) and check the linings.”
I compared the rear brakes to the ‘66 FSM and they are identical. I wiggled the drums off no problem yesterday. The wheels spin with a slight drag like they’re supposed to.

“If the problem is more related to slowing down after the initial application, and the above all checks out, then focus on the front brakes.”
I’m not sure what to check in the fronts. With the front in the air, the wheels spin, then with the pedal down, the wheels stop spinning. Perhaps the pucks aren’t coming all the way out.

“Tandem master's front outlet should feed the rear line. Only one residual valve is needed. Whether it's the one in the Master's outlet or the 66 in-line one from the single outlet master doesn't matter.”
I bled and bolted in the MC, but did NOT mess with any residual valves.

Thanks for brainstorming for me, Mattax.
 
I don't have many more ideas right now.
To test the pressures would require access to a lift and at least one high pressure gage. Gage set used for testing automatic transmission pressure could be adapted. Not many shops do that, never mind checking brake pressures. But if you know of one, or someone who, that would be a great way to prove or disprove whether the problem is in the hydaulics.

Could try going over the surface of the drums and disks with a block and sandpaper or emery. And try different linings.
I'll say I found old Cycleweld Mopar pads were not very grippy at all - especially on initial application. Previous to them I had used a Raybestos lined pad that was really good, but now is long discontinued. I'm currently using Porterfield's street lining for both the pads and the shoes. They seem to have about the right balance, grip but not too grabby. But trying those Porterfields would be an expensive experiment just to see if the linings would make a difference.
 
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I wish I had an answer for you. I just put KH discs on the front of my Duster and I'm not impressed with the improvement over 9" drums. If someone installed the discs on the front while I was away and I came back and drove the car, I wouldn't even be able to tell there was a conversion done. Although mine has a soft pedal until about halfway down and then it starts to get firm and feel normal. Rear brakes are as tight as I can comfortably get them too.

Had a 67 Valiant years ago with drums all the way around with a rock hard pedal and only about 60% of the braking power my Duster had with the same size drums. I changed out every single thing other than the hard lines on that car and I could never figure it out, even with all the advice I got on here.

Your prop valve looks to be in bad shape but you said that the brakes were normal back with the old single pot MC. I know it sucks bleeding brakes but I'd swap the old MC back on and see if the brakes feel normal. At that point at least you'll know it's the MC and nothing else that's causing the problem.
 
Disk brakes always require more pedal effort than dua-servo drums.
Drum brakes of this design are self-assisting.

Disk advantage is mostly in repeated high speed stops and long downhill situations.

ps. Nothing on that prop valve's exterior looks anything more than surface patina. The body was always a -as cast- exterior.
 
Yea, Jim. Mattax said the same thing in post 3 and a spoke to a member on the phone. It might be that the caliper pistons are pushing out enough to slow down the wheels, but sticking some and not giving full bite. That’s my next move, won’t cost anything except some time.
 
UPDATE: Pulled left caliper off, one piston stuck. Got it out and found outer edge of bore rusted, but the inner bore and the piston are in nice shape. Will consider rebuilding both myself or just exchanging them with replacements. Thanks Mattax and all who chimed in!
 
Interesting. If the pistons chrome are good, I'd probably clean up the bore if its only the section above the dust boot.
IIRC There's two types of boots used. Ping or search for Jim Lusk and 71hemi can tell you more and also help through the tricks of getting the new seals in.
 
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