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Old 12/08/18, 04:37 PM   #1
Jfryjfry
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Brakes are lacking lockup

We recently bought a 72 and it has a handful of upgrades, including front disc brakes, and power brakes. It also has a body and suspension lift and large tires (33s I believe). It reportedly has sat for many years until we bought it.

I stripped it all down for paint but not before I had driven it a bit. The brakes are not great. They will not lock up the tires. The two kits (power brake kit and disc kit) are from wild horses I believe.

We bled the brakes to no avail. While it is down, Id like to solve this issue. The kits seem to use Chevy parts. Is anyone familiar with these kits? Id like to replace the master cylinder at least and hoping for options that might help.

Finally, the lines go to a block on the frame. Is this just the stock proportioning valve or a combo valve or ?? And should I get a new one or replace with something else?

Thanks for any ideas and info
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Old 12/08/18, 04:46 PM   #2
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I would also recommend looking at the power brake install. Make sure the pedal height is set correctly and the booster to master cylinder pushrod length is set correctly. IF those are off nothing downstream of the master cylinder will fix anything. And since those parts are aftermarket installed parts with no history, good place to look.

Another place to look is between the caliper and the knuckle. The knuckle must be ground for clearance. If the caliper touches the knuckle, you just lost half of your braking capacity. The caliper is on sliders and as the outer pad wears the whole caliper slides inward. Very common to not have enough clearance. Enough to install, not enough to work.

"She's built like a steakhouse but she handles like a bistro"-Zapp Brannigan
Why do people keep expecting "normal" from me?
Full throttle, it either solves the problem or ends the suspense.
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Old 12/08/18, 04:48 PM   #3
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Hey there. Quite a few things can keep the rears from locking up, but a few questions first.
Is the pedal soft and spongy?
Does it feel firm, but has a lot of travel?
Or is it firm and stops it's travel in a pretty short distance?

How many clicks do you have on your parking brake before it holds tight?
If the pedal is firm, but goes down more to the floor than you think it should, does applying the parking brake change how far the pedal goes?

And last, have you inspected the rear brakes? Perhaps they're a little oil soaked, or maybe worn pretty thin, or not oriented properly with the primary (shorter) shoe to the front.

Your '72 would have had the simple "H-block" version of the combination valve. Just a distribution block with the shuttle valve to activate the switch to turn on the dash warning lamp. No proportioning valve version until disc brakes were offered in '76.
Nothing wrong with keeping it, as a proportioning valve is there to reduce the pressure to the rear brakes even further!
Lots of us run disc brakes in the front with stock master cylinder and stock H-block and no problems. I'm running the Ford disc brakes along with stock manual master cylinder and things work perfectly.

Two other things that are possible are that the distance between the booster rod and the master piston was not set properly during installation, OR not enough material was ground off of the knuckles to clear the new GM-based calipers.

A few things to look into yet.

Good luck!

Paul

'71 Wagon, 3.5" WH, F150 disc brakes and steering, 4.11 33x11.50 Thornbirds, Kayline soft top, Hanson bumpers. "Built, not bought"

'68 LUBR, 2.5 + 1 WH, 31x10.50, 4.56, Explorer and 4R70w by EFI Guy, WH disc brakes, Hanson front bumper, Warn winch. "Bought, not built"

www.wildhorses4x4.com
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Old 12/08/18, 05:14 PM   #4
Jfryjfry
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Guys, those are great ideas. I don’t have the truck here but as soon as I get it back, I will check these items.

The pedal always felt good and the brakes felt fine for normal driving. But when I safely tested their ability, I learned they didn’t have much more stopping power than I had been using.

I replaced one of the axle seals and did not notice anything out of the ordinary. I am familiar with drum brakes, but with the leak in seal possibly contaminating the rear shoes on one side, even though they looked fine, I will replace them.


Any ideas on what vehicle the master would have been found on would be helpful but i imagine I will need some pics before anyone can id it.
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Old 12/08/18, 05:17 PM   #5
Jfryjfry
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And thanks for the info on the block. If it is just the valve to illuminate the warning light, I will likely leave it alone.

But curious if anyone has had issues with it leaking internally and thereby not isolating the two circuits?
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Old 12/08/18, 05:20 PM   #6
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Make sure the front brake plumbing goes to the rear masrer cylinder resorver closest to the firewall.

1974, stock 302, C4, BFG KM2 33x12.5x15, 8in rim, detroit rear, trutrac front 4.11 gearing, Warflairs,2.5" lift, chevy disc conversion, Hydraboost, owned since Christmas Eve 1977
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Old 12/08/18, 06:26 PM   #7
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I just want to check Paul's comments on one thing.
Is it just the rears that are lacking braking power, or all four corners? I read it as all four corners and I read Paul's comments regarding just the rear.

The brake imbalance switch (warning light) should not affect braking even if there is an internal leak. An external leak, that is a problem. But an internal leak both halves of the system should be running the same pressure so it is irrelevant for braking power. Now the loss of half the system, AND an internal leak, you are dealing with multiple simultaneous failures. The brake system is only engineered to handle a single failure. To be honest, I have never heard of the imbalance switch ever having an internal leak, ever. If anything they tend to just freeze and stick in place never moving even with an imbalance. Without a warning light it is nothing more than a convenient place to attach the lines from the frame to the master cylinder.

An adjustable proportioning valve can be used to dial back the rear brakes a little, but that is a fine tune adjustment once the overall braking package is working good. You don't need one now. Once you can lock all 4 tires, and the rears are just a little early, that is when one works. But you are working on a bigger problem right now.

You have plenty to look at now. pretty sure you will find something with the above checks.

"She's built like a steakhouse but she handles like a bistro"-Zapp Brannigan
Why do people keep expecting "normal" from me?
Full throttle, it either solves the problem or ends the suspense.
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Old 12/08/18, 07:05 PM   #8
Jfryjfry
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To clarify, I believe that I did not get lockup at either end. Because so much of this truck is an unknown, I do want to replace things that could be suspect, pertaining to safety especially.

I was thinking out loud about the leaky block. As in thinking ahead to if I were to need a proportioning valve, should I plumb it in after the block. Also, was wondering if they go bad and nullify the safety aspect of a split system.

But you’re right - I definitely have several things to check first!
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Old 12/08/18, 07:40 PM   #9
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all great advice here. I only have one thing to add, don't start adding new stuff (prop valve, etc) until you figure out what the issue is. Things 'should' be working as/is, so go ahead and find out what isn't.

One more, check your self adjusters. They should be pressing out until the shoe is pretty much on the drum. Mechanically you could be short of lockup if your wheel cylinders lack the juice to force your shoes out enough cause the bottoms are pressed out enough.
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Old 12/09/18, 01:25 PM   #10
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Quote:
Originally Posted by Jfryjfry View Post
...The pedal always felt good and the brakes felt fine for normal driving. But when I safely tested their ability, I learned they didn’t have much more stopping power than I had been using.
Then it's very unlikely you need to continue to bleed them. Air in the system will make the pedal more "soft" or "spongy" feeling. If it's full and firm, air is not the issue to my mind.
This could be due to a weak vacuum booster. Or maybe even a weak vacuum signal if you have a performance cam or leak or something like that.
But a weak booster is not uncommon. Is it new, used, older new, or original factory style?
Hard to tell probably if you didn't install it yourself, and they were not available on the actual truck until near '76 if I remember.

Quote:
Originally Posted by Jfryjfry View Post
I replaced one of the axle seals and did not notice anything out of the ordinary. I am familiar with drum brakes, but with the leak in seal possibly contaminating the rear shoes on one side, even though they looked fine, I will replace them.
I'm not sure I'd bother just yet. If they don't look contaminated (and you're familiar with how they should look) it seems a waste of time unless you think you can get a better friction material. Sometimes the compound alone can make or break how the system works.
Especially if your testing was done cold.

Quote:
Originally Posted by Jfryjfry View Post
Any ideas on what vehicle the master would have been found on would be helpful but i imagine I will need some pics before anyone can id it.
Correct. Way too many possibilities.
If it's got equal-sized reservoirs and two wire bails (the top clamps) then it's likely the aftermarket replacements like we sell, or perhaps a used GM-based setup.
The diameter of the piston is critical. I prefer 1" but you can go as large as 1 1/8" with these setups. But not larger until you get into hydro-boost systems.
If it's got an odd-shaped top, with one large reservoir in the back and a much smaller one in the front, with a single wire-bail that flips up from the sides, it's likely Ford-based.

But even the factory Ford drum brake master is perfectly fine for front discs. That's the setup I have and I can lock up both front and rear with 32" tires.
But that leads to another question. With 33's you really need as much performance as you can get. From shoe and pad material, to booster strength.

First thing I would do is peek over the tops of the front tires and make sure you see daylight (or the ground) between the calipers and the steering knuckle castings. If not, you need to do some grinding. If there is some, best to be at least 1/8" or so for pad wear. A little more might be even better.

The booster-to-master rod clearance sounds ok. If it was not, you would either have a longer pedal travel than normal (too much gap) or your brakes would start dragging after awhile (no clearance), but it sounds like you don't have either issue at this point.

Also, can you tell what size rear brakes you have? Small ones would be 10" or so, and the large ones were 11" or so. In '72 (assuming the rear end and brakes are still from the '72) a large brake would have meant a large bearing axle. If you remember the part number of the seal you bought, that can tell us whether you have large or small brakes.
If the small brakes, then maybe you're fighting more uphill with the heavy 33" tires as well.

So there are still some diagnostic tests you'll need to be doing to see where the weakness lies.

Paul

'71 Wagon, 3.5" WH, F150 disc brakes and steering, 4.11 33x11.50 Thornbirds, Kayline soft top, Hanson bumpers. "Built, not bought"

'68 LUBR, 2.5 + 1 WH, 31x10.50, 4.56, Explorer and 4R70w by EFI Guy, WH disc brakes, Hanson front bumper, Warn winch. "Bought, not built"

www.wildhorses4x4.com
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Old Yesterday, 11:11 PM   #11
broncnaz
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Id say pads may be a big factor in poor braking. High dollar fancy pad generally need a lot of heat before they start working good. Usually the old tried and true semi metallic pads are your best bet. Carbon or ceramic pads sound like the way to go with there claims but they both require lots of heat to work good.
Overall Id say your brakes are probably working ok. Wouldnt worry about the H block or adding a prop valve. The h block will still allow fluid movement even if its off center. and if it a seal leaks it will more than likely start leaking externally and you wont have a good pedal. The switch in it is mainly plastic and probably wouldnt take much pressure to blow it out.
Really the only time you'd want to add a valve to the brake system is if your brakes were locking up to easily. Even the so called metering/prop valve that ford used on its factory setups really does nothing the way its used other than provide a idiot light switch just like the H block. Master cylinders have a built in delay to the rear brakes so the fronts start to engauge first.
Another thing to look at is the MC bore size. You may be able to get a master cylinder with a slightly smaller bore size which will increase the PSI in the system but it may result in longer pedal travel. but the incrrease will provide a better chance for lockup.

Typically with 33in tires the brakes will be borderline in there operation they should still work decent but could stand to be improved. Remember both ford and ch#vy pretty much only set those brake systems for 28/29 in skinny tires not big fat 33in tires. back then 31 in tires were considered big

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Old Today, 10:32 AM   #12
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Also. Check to make sure the calipers are on the correct sides. It has been done many times on here that the calipers were installed on the wrong side. The bleeding zerk shoukd be facing up or near up. If it points down at all then you can not get a good bleed. I dont know if this is what is causing your problem but has given several on here a headache

Good luck. Hope it helps

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Old Today, 12:35 PM   #13
Jfryjfry
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I appreciate all of the advice and information guys! certainly some of it is super basic, but seeing as this is all-new to me, i can assume nothing and need to check things i otherwise might normally assume are ok.

I did find that the hubs weren't fully pressed together with the rotor and there was some wobble. I rectified that before I learned that the brakes aren't up to snuff.

I promise to keep you updated but it will be a little while until I get the truck back from the painters.
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