RF brake locked up. Why?

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AJ/FormS said:
Ok then;
firstly, the driver's side is the left side
Brake fluid on the underside of the hood can only come from something in the engine compartment. If you have applied and released the brake with the M/C cover off,as you would do during the bleeding procedure, the returning fluid can easily gush thru the Compensating ports, and squirt up to the underside of the hood, even with the hood open.And then it drips down all over everything. Such a high fountain usually only occurs if the brakes were not yet properly adjusted.... or if there is air in the system. After you have stroked the pedal to make it hard, air in the system can be compressed to 800 or more psi. It has become a high pressure air-spring. Then when you lift off she unloads and forces all the fluid you just pumped down the line,back up into the M/C, with predictable results. Once the shoes are adjusted and the air is purged, very little fluid movement is required, and the returning fluid usually only roils in the bottom, with perhaps a lil fountain.

The photo appears to be of the passenger (right) side, and looks to be correct except the shoes should have two different length linings on them; a long and a short; the difference being about 2 inches; and the long one goes on the rear side or to the left when looking at that passenger side system.
Your self-adjuster cable appears to be a lil short. After it is installed, the blade should be resting on the star wheel, ready to crank it down, which should lengthen the adjuster. This event should only happen when backing up, as the entire shoe assembly is cranked around by the dragging drum. Since the cable is anchored at the top,the blade is forced to flick the starwheel. If the shoes are already properly adjusted,then there is insufficient cranking of the assembly to make an adjustment.

The pistons in the wc,have to retract after every application, to allow the linings to properly rest fully against that top anchorpin, so they cannot drag on the drum. If the fluid is not returning to the M/C, for whatever reason, then the linings may not retract far enough to not drag.
If, simultaneously, there was to be an air pocket trapped in the wc, the dragging shoes could, I suppose, heat that pocket enough to expand the air to act like an air-spring, and keep the shoes applied, maybe even increase the drag, in a vicious cycle.
If there was water in there, it would be even worse.
Silicon fluid is not hydroscopic, so any water in there will settle to the lowest point..... which is the wc.
Brakefluid should always be used from a sealed container.
I don't think any of these is your problem; just suggesting the possibility.

Next; as to points #1 and 2
You have to prove that the piston inside the M/C is properly parking, to the rear, so that the fluid can return. From the previous discussion, I think your C-ports are fine, but here is the procedure to prove it;
There are two ways to do this; directly and indirectly.
Since the drum is off, you can try the indirect method.
Make sure the reservoir cap is installed and clamped shut.
Make sure only one drum is off.
Have a helper step on the brake pedal, while you observe the shoes moving out. Ask your helper to stop about half-way down, and then lift off. Those two upper springs in the assembly; (OK WAIT! I don't see the lower spring in there. There should be a spring just above the star adjuster, holding the two shoes together. I assumed it was in the shadows, but I just can't see it; So make sure it's in there), should immediately start to smoothly retract the shoes, back onto the anchor. This proves the fluid is returning,and that the wc's are not sticking . Repeat several times. This also proves any valving in the system,or the distribution block, are also passing fluid... so yur done testing. This would indicate that hydraulically, the system is functioning properly. This does NOT prove the hoses are 100% as at this time, there is no pressure in the system with the one drum off.

As to mechanicals;
Make sure each side has a long and a short lining on it. and that the short one faces the front of the car on both sides. Drum brakes are self-energizing, and the rear shoe does most of the work, so needs to be longer. Well actually, the cheapazz manufactures can save some coin by making the fronts shorter,lol. If you don't have shorts, then as long as all 4 front linings are about the same length then it will be fine.
Make sure your wheel bearing endplay is properly adjusted. If it's loose, the the chassis will move down from it's normal attitude and could force the shoes into contact with the drum. I know it's only a couple of thou when properly adjusted, and then it's no big deal. IIRC endplay is maybe max .007. With drums I run them fairly close to zero.
Make sure the pads on the backing plates where the metal shoes rest are smooth, so the shoes slide smoothly over them. You can put a tiny dab of hi-temp grease on those flat pads to reduce wear. If the pads have ruts/ridges in/on them, grind the high part off. If deep, you can build it up.
Make sure the metal part of the shoes do not rub on the drum, or the step that often wears into the corner down in the bottom of the drum..
Make sure, on a dual-reservoir M/C that it is correctly plumbed. the front-most reservoir on the factory system should go to the rear wheels.
The first inch or less of pedal travel, can be non-functional, as the piston in the M/C is moving out and closing the compensating ports; this is normal.Make sure the pedal returns to the top of it's stroke by itself and rests on the stopper. If you flick your foot off the pedal in the first inch of it's travel, the pedal should sorta snap back to it's parked position and make a satisfying lil thud.

And above all, make sure you have a hard pedal, and that it gets hard in the first 50% or so of it's travel, and that it remains hard with modest pressure for at least 20 seconds, and that it never suddenly drops down.


IDK, that should cover it.
Happy Hunting
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AJ, thanks. I'm going to check all of that. I'll report the results. I'm travelling for 10 days, so it will take me a couple of weeks.
 
Okay riddle me this. On my numbers matching all stock 68 Dart GTS. I've been following this because I've been having the same problem with the right front brake locking down more than the left front and pulling strongly to the right.

That is until I drive a while and everything seems to warm up and presto... both the front brakes pretty much brake about the same. Maybe a little bit more on the left.

I've bled the brakes.

I have replaced the front rubber brake lines with stainless braided lines.

All hard brake lines and the front brake proportioning valve (wasn't sure the original would work after being on jack stands for 25 years) were replaced a few years ago and used copper gaskets on all fittings as suggested by someone I don't remember that does restorations because I used Dot4 synthetic.

Any ideas?
 
Does the opposite side have two shoes with a shorter lining? :rolleyes: You have two secondary shoes on one side.
 
markfh said:
Okay riddle me this. On my numbers matching all stock 68 Dart GTS. I've been following this because I've been having the same problem with the right front brake locking down more than the left front and pulling strongly to the right.

That is until I drive a while and everything seems to warm up and presto... both the front brakes pretty much brake about the same. Maybe a little bit more on the left.

I've bled the brakes.

I have replaced the front rubber brake lines with stainless braided lines.

All hard brake lines and the front brake proportioning valve (wasn't sure the original would work after being on jack stands for 25 years) were replaced a few years ago and used copper gaskets on all fittings as suggested by someone I don't remember that does restorations because I used Dot4 synthetic.

Any ideas?
Click to expand...
If every thing checks out as being good on both front wheels, your brake adjustment is off. It’s pulling to the right because that wheel is adjusted tighter than your left. So when you apply the brake it will apply slightly sooner than the left. Reason it gets better is your right brake is fading some what from the heat. This could be why it stops better as you drive it.
 
SGBARRACUDA said:
If every thing checks out as being good on both front wheels, your brake adjustment is off. It’s pulling to the right because that wheel is adjusted tighter than your left. So when you apply the brake it will apply slightly sooner than the left. Reason it gets better is your right brake is fading some what from the heat. This could be why it stops better as you drive it.
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I've adjusted the pads according to what was specified. After driving for a while I don't feel a difference in heat from one side to the other. Should I? Also, how about the auto adjusters. Can they fail to work properly and if so, how can I tell.

Thanks for the replies.
 
The heat probably evens out after you drive a while. But basically your right front is doing more work than your left. Try loosening the right side a little and see if that helps.
 
I know you said you bled the brakes, but the side that brakes less could still have a pocket of air in it, which acts like a spring, absorbing the fluid pressure without transmitting it to the shoes in equal fashion to the other side.
Your brake pedal should be hard and high. Any bounciness in it, is likely indicating air.
There is a way to absolutely prove there is air in the system. Have a helper pump the brake pedal about three times, full strokes and on the last stroke keep the pedal down about 1 inch. Now you pop the top off the M/C and observe the liquid. Ask your helper to slowly bring the pedal up, very slowly. When the piston uncovers the Compensating port, the brake fluid will want to rush back into the reservoir, forced to do so by the brake-shoe return springs.
In a normal system, the brake fluid will roil in the reservoir, like when water is on the verge of boiling in a pot on your stove.But if there is air in there under pressure,it will unload violently spewing fluid as high as the hood, which will then drip down onto everything. This is why your helper has to release very slowly, to try to contain the fountain in the reservoir.
If the fountain lasts a long time, it is because the shoes have a long way to go, to get back on the stops; ie one or more of them needs adjusting.
Caution; all non-silicon brake fluids eat paint so take precautions and have your cleaning supplies handy with running water; I will not buy you a new paint job.
 
AJ/FormS said:
I know you said you bled the brakes, but the side that brakes less could still have a pocket of air in it, which acts like a spring, absorbing the fluid pressure without transmitting it to the shoes in equal fashion to the other side.
Your brake pedal should be hard and high. Any bounciness in it, is likely indicating air.
There is a way to absolutely prove there is air in the system. Have a helper pump the brake pedal about three times, full strokes and on the last stroke keep the pedal down about 1 inch. Now you pop the top off the M/C and observe the liquid. Ask your helper to slowly bring the pedal up, very slowly. When the piston uncovers the Compensating port, the brake fluid will want to rush back into the reservoir, forced to do so by the brake-shoe return springs.
In a normal system, the brake fluid will roil in the reservoir, like when water is on the verge of boiling in a pot on your stove.But if there is air in there under pressure,it will unload violently spewing fluid as high as the hood, which will then drip down onto everything. This is why your helper has to release very slowly, to try to contain the fountain in the reservoir.
If the fountain lasts a long time, it is because the shoes have a long way to go, to get back on the stops; ie one or more of them needs adjusting.
Caution; all non-silicon brake fluids eat paint so take precautions and have your cleaning supplies handy with running water; I will not buy you a new paint job.
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Engine running or no?
 
Either way.
If you have a booster;
and engine off, your assistant will just have to press a lil harder.
And with engine running, the pedal has a slightly less hard feel to it. Try not to confuse less hard with spongy,lol.

BTW;
One time, as I was looking for the fountain; I lifted the reservoir cap just a lil, at a 45* angle, towards the drivers side fender where I was standing and promptly got sprayed in the face and eyes. Don't let that happen to you.

ALSO
the reason I said to pump the brake pedal three times is because each stroke will send fluid down the line.But when you lift, and press again, because of the air bubble, not all the fluid has time to return, so the shoes remain applied to some degree. By the third pump,a lot of fluid has gone out, and the shoes will be out probably about as far as they can go. And the return springs will be pulling hard. So the instant your assistant lifts the pedal, and the compensating port opens, that fluid is gonna try to make a mad-dash back into the reservoir, which can cause a geyser, 2 ft high! Any air in that system is gonna unload as well, making it worse.
If you have never done this before, maybe I shouldn't have said 3 pumps, lol. Try it with just the first pump, until you and your assistant get the hang of it. Mistakes will be made. With the engine off, your assistant can better hear your screams of panic..... Remember the emphasis on slowly relaxing the pedal; only the assistant can control the geyser by reapplying the pedal; the foot must stay on the pedal, and be prepared to reapply the brake to stop the fountain/geyser. With just one pump;Roiling is normal, a geyser is not. With each subsequent pump, the roiling will turn to an ever growing fountain. But if there is air in the line, anything can happen.......

I haven't tryed this but I suppose; To tame the fountain, you could cut and shape something to partially cover the floor above the C-ports. I seem to recall having seen some later model GMs with a floating closed cell foam patch in their reservoirs.
 
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Okay. Had my master pedal pusher help me out. Pedal is high and hard with engine off (power booster) a little lower with the engine running.

In both cases there was no roiling in the MC at all. I even had her let up the pedal quickly, with an appropriate guard over the MC, with the same result.






AJ/FormS said:
Either way.
If you have a booster;
and engine off, your assistant will just have to press a lil harder.
And with engine running, the pedal has a slightly less hard feel to it. Try not to confuse less hard with spongy,lol.

BTW;
One time, as I was looking for the fountain; I lifted the reservoir cap just a lil, at a 45* angle, towards the drivers side fender where I was standing and promptly got sprayed in the face and eyes. Don't let that happen to you.

ALSO
the reason I said to pump the brake pedal three times is because each stroke will send fluid down the line.But when you lift, and press again, because of the air bubble, not all the fluid has time to return, so the shoes remain applied to some degree. By the third pump,a lot of fluid has gone out, and the shoes will be out probably about as far as they can go. And the return springs will be pulling hard. So the instant your assistant lifts the pedal, and the compensating port opens, that fluid is gonna try to make a mad-dash back into the reservoir, which can cause a geyser, 2 ft high! Any air in that system is gonna unload as well, making it worse.
If you have never done this before, maybe I shouldn't have said 3 pumps, lol. Try it with just the first pump, until you and your assistant get the hang of it. Mistakes will be made. With the engine off, your assistant can better hear your screams of panic..... Remember the emphasis on slowly relaxing the pedal; only the assistant can control the geyser by reapplying the pedal; the foot must stay on the pedal, and be prepared to reapply the brake to stop the fountain/geyser. With just one pump;Roiling is normal, a geyser is not. With each subsequent pump, the roiling will turn to an ever growing fountain. But if there is air in the line, anything can happen.......

I haven't tryed this but I suppose; To tame the fountain, you could cut and shape something to partially cover the floor above the C-ports. I seem to recall having seen some later model GMs with a floating closed cell foam patch in their reservoirs.
Click to expand...
 
There has to be roiling. Stick your finger over the C-port, and feel the returning brake fluid.

To test you booster;
engine off, M/C lid on and clamped; pump the brake pedal to deplete the vacuum, about 5 or 6 times. On the last time, keep the pedal down and pushing moderately. Then start the engine. The pedal should drop down almost immediately as the vacuum chamber evacuates. How far depends on how hard you are pushing; I'll guess;more than one inch, less than about half way to the floor.
The first inch is taking up slack and closing the C-port.
You need the bottom half for emergency use, if one end (front or rear) catastrophically fails. When that happens, the pedal drops nearly to the floor, but, if the adjusters are correctly adjusted, you should still have enough pedal-travel left with which to stop the car.

If your pedal is hard within the first inch, you better check to make sure your C-port is still open! You can shine a light in there and maybe catch a reflection off it, but I just stick a wire in there, which should penetrate to the bottom of the bore which could be an inch plus the casting thickness. But the roiling is the proof that the fluid is returning.
If the piston inside the M/C is not parking all the way back, something is wrong.
 
Tested as in your first paragraph. The pedal came up high and hard. Held it down and started the engine and the pedal dropped about an inch.

Checked what I think is the C-ports in the MC with a wire (paper clip) and it doesn't go into the bore at all. Attached is a picture of what I see and I tried the wire in both holes and neither goes into the bore.

This is a new MC and I had the Booster restored by Booster Dave. Prior to that the brakes didn't work without superman pushing on the brakes.

AJ/FormS said:
There has to be roiling. Stick your finger over the C-port, and feel the returning brake fluid.

To test you booster;
engine off, M/C lid on and clamped; pump the brake pedal to deplete the vacuum, about 5 or 6 times. On the last time, keep the pedal down and pushing moderately. Then start the engine. The pedal should drop down almost immediately as the vacuum chamber evacuates. How far depends on how hard you are pushing; I'll guess;more than one inch, less than about half way to the floor.
The first inch is taking up slack and closing the C-port.
You need the bottom half for emergency use, if one end (front or rear) catastrophically fails. When that happens, the pedal drops nearly to the floor, but, if the adjusters are correctly adjusted, you should still have enough pedal-travel left with which to stop the car.

If your pedal is hard within the first inch, you better check to make sure your C-port is still open! You can shine a light in there and maybe catch a reflection off it, but I just stick a wire in there, which should penetrate to the bottom of the bore which could be an inch plus the casting thickness. But the roiling is the proof that the fluid is returning.
If the piston inside the M/C is not parking all the way back, something is wrong.
Click to expand...

Brake MC.jpg
 
To get to the bottom of the bore, you have to go around the interconnecting piston rod. You don't have to go that deep tho, just prove the hole is open. That opening you see at the top is not the orifice size at the bottom, rather just the counter bore. At the bottom is a tiny hole, perhaps .020 in diameter, perhaps smaller, I don't recall. I use a single strand of 14ga copper wire which is .011, I think.
If the all drum system is properly adjusted, then without air in the system, there may not be a lotta fluid movement in the lines so you might not get roiling.
All I'm asking is to prove the fluid is returning.
By your descriptions, I believe it is.
If nothing else time and miles will prove it.

however, fluid not returning, unless the shoes are dragging, is not your problem.

If your drums are new and your shoes are new, and if you did not get your shoes ground at a brake shop to fit the drums;
or if one drum is larger than the other;
then the new shoes are going to need a break-in period which could take hundreds of stops, until the shoes are making full contact. During this time if one side has more contact than the other, then you will have a pull.
If you take the drums off and inspect the lining wear, you should be able to see where the lining is glazed and where it is still new. I suppose you could compare one side to the other.IDK, I've never tried it.
The other thing you can do is remove a shoe and fit it to the drum and see how bad it is; if the shoe rocks in the drum, I would recommend to find a brake shop that has the tool to fit your shoes to your drums.
That should cure your pull.

But if a wheel locks up and stays locked-up, that is most likely a fluid-not-returning problem. And the usual culprit is a faulty brake hose. And that is easy to prove. While it is locked up, just crack the bleeder. If you get a stream and immediately the wheel turns, then replace the hose.
But if both sides are dragging, then you need to do some more detective work as it is highly improbable that both hoses fail at once.
 
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Neither of the wheels lock up completely so that's not a problem.

I'll pull the drums off and check the wear. I hadn't thought of that. It's been decades since I had a car with drum brakes on the road and I imagine back in the day my local buds handle that for me.

As to the fluid movement the only time I saw any was when the pedal is pushed down and I was sure to tell my master pedal presser to go slowly. :)

I do appreciate all the help you've given me. If you ever get down to Houston, when the world stops being crazy, let me know. It's not a tourist mecca but there are things to see here and (fairly) close by.

Mark



AJ/FormS said:
To get to the bottom of the bore, you have to go around the interconnecting piston rod. You don't have to go that deep tho, just prove the hole is open. That opening you see at the top is not the orifice size at the bottom, rather just the counter bore. At the bottom is a tiny hole, perhaps .020 in diameter, perhaps smaller, I don't recall. I use a single strand of 14ga copper wire which is .011, I think.
If the all drum system is properly adjusted, then without air in the system, there may not be a lotta fluid movement in the lines so you might not get roiling.
All I'm asking is to prove the fluid is returning.
By your descriptions, I believe it is.
If nothing else time and miles will prove it.

however, fluid not returning, unless the shoes are dragging, is not your problem.

If your drums are new and your shoes are new, and if you did not get your shoes ground at a brake shop to fit the drums;
or if one drum is larger than the other;
then the new shoes are going to need a break-in period which could take hundreds of stops, until the shoes are making full contact. During this time if one side has more contact than the other, then you will have a pull.
If you take the drums off and inspect the lining wear, you should be able to see where the lining is glazed and where it is still new. I suppose you could compare one side to the other.IDK, I've never tried it.
The other thing you can do is remove a shoe and fit it to the drum and see how bad it is; if the shoe rocks in the drum, I would recommend to find a brake shop that has the tool to fit your shoes to your drums.
That should cure your pull.

But if a wheel locks up and stays locked-up, that is most likely a fluid-not-returning problem. And the usual culprit is a faulty brake hose. And that is easy to prove. While it is locked up, just crack the bleeder. If you get a stream and immediately the wheel turns, then replace the hose.
But if both sides are dragging, then you need to do some more detective work as it is highly improbable that both hoses fail at once.
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markfh said:
As to the fluid movement the only time I saw any was when the pedal is pushed down and I was sure to tell my master pedal presser to go slowly.
Click to expand...
That is your proof right there! About the first inch of pedal travel is taken up by slack, and then the piston closes the C-port. That is when you get the little roiling or fountain.
So now we know absolutely that the port is working.
When the pedal returns, fluid moves down into the chamber ready for the next application.
The second thing this proves, since you did NOT get a geyser, is that your system seems to be free of air.
I would be confident at this point to say that you do NOT have a hydraukic problem.
markfh said:
Neither of the wheels lock up completely so that's not a problem.
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and this tells me your hoses are fine.
So now we are down to just three possibilities;
1) contact area,
2) contamination,
3) coefficient of friction.

#1 we already talked about, and
#2 that is to say grease,oil,or brakefluid on the linings,and
#3 is highly unlikely if you installed new shoes from the same box, with a reputable name on it.

As to #2,
In my younger years, I discovered that you can cook the contaminants out of the linings, in you mothers bake-oven; she'll never know I said. Hah! Mothers know everything......
markfh said:
I do appreciate all the help you've given me. If you ever get down to Houston, when the world stops being crazy, let me know. It's not a tourist mecca but there are things to see here and (fairly) close by. Mark
Click to expand...
I try to be as helpful as possible.
And thanks for the offer
 
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