Brakes

[mygtsissweet]

My 69 dart gts has power front disc and 10 inch rear drums. I got a hard pedal but the car won't stop. No response. Slows but really no brakes. Any ideas
Thanks in advance.

 

[junkyardhero]

i'd suspect a bad booster to start. but i'd bet there's other forces at play here...

after that we'd need more info: has it been sitting, when was the last time the brakes were serviced (flush & bleed), has any work been recently done-- specifically brakes, but other things apply as well, is everything bone stock, what else can you tell us: have you had the car a long time? did you just buy it? is this a new problem that just suddenly cropped up or an ongoing issue?

 

[Dana67Dart]

Start at the beginning...

Did the brakes work good at some time?
What changed between then and now?

 

[65TerrorCuda]

Did someone wd40 your pads?
I did that to our Jeep as a kid bc the brakes squeaked.
I got in a lot of trouble

 

[Bewy]

Booster or booster related; check booster hose, not blocked, or collapsing under vacuum; booster check valve.

 

[AJ/FormS]

My opinion of the KH 4-pots and 10 x 2 rear brakes, is very high. If the C-valve is plumbed correctly, you should easily be able to lock the front brakes at 20 or even at 30 mph. I've never tried it on purpose, but I think mine would lock even at 40mph.
As to the C-valve the frontmost reservoir goes to the rear brakes. Therefore the reservoir closest to the firewall is for the Front brakes. Those lines are size-coded from the factory, so that they cannot be reversed. The line that feeds the front brakes, goes to the Top of the valve, then splits into two directions, to feed the front calipers. The line to the rear brakes enter the valve near the bottom, then it comes out of the Proportioning valve and continues to the rear.
Between the two lines, inside the housing, is a shuttle valve that responds to a pressure loss on either side of the system, by shuttling to one side, which turns on the dash-mounted brake warning light.
Is your warning lamp on?
Here's where it get interesting;
That light is also turned on whenever the Park-brake is set. So then, if your dash-light is on, you HAVE to figure out why, and if it's not the Parkbrake, then you gotta pull the connector off the Safety Switch. If that turns the light off, then the shuttle valve is grounded.
When the shuttle valve turns on the light, it simultaneously shuts off fluid to the supposedly leaking side. But the valve does not know if the system is leaking, it only knows about a pressure imbalance.
Thus it is easy to suppose that Nothing is leaking, and, as in your case, maybe the front brakes have been shut off, leaving you with just the pitiful rear brakes working.
That shuttle, is supposed to be self-centering, but if it's 55 years old, it might not be happy about moving. So, to get it to move, if the light is on, you are gonna have to create a pressure imbalance the other way;
like
crack the rear line and push hard on the pedal until the light goes out. Then close the crack. Roadtest!
But
if your brake warning lamp is NOT on, and it works, and it is connected, then it is reasonably safe to assume that the shuttle valve is NOT your problem.

Part-2
To check your booster do this;
With the engine off, pump the brakes several times. Then press it the pedal with modest force; keep the pedal down and start the engine. As soon as the engine starts, the pedal should fall towards the floor as the vacuum chamber gets evacuated. say about an inch.
Now,
if, at this time, your pedal is hard, then chances are very good that the hydraulic portion of your brakes is fine. release the pedal.
After the pedal has returned, step on it again. If it drops only about an inch, and then gets hard, I would NOT expect a hydraulic problem.

Finally, with the engine still idling, pump the pedal rapidly about four times.
If the pedal comes up higher, that is normal. Now release the pedal and wait a few seconds, then step on it one more time. If the pedal has returned to it's former height, then the pushrod length is, at least, not too long.
Thus we have proved that the hydraulics are most likely, working correctly.

Part-3
From here, I would chase down a mechanical issue or faulty friction materials and/or surfaces. If I couldn't find an obvious source, then;

I would jack the car up, remove all the calipers and all the rear stuff, then C-clamp each piston into the bottom of it's caliper and C-clamp each wheel-cylinder into it's bore. At this point you have created a hydraulic lock situation, and the pedal with engine idling, should be high and rock-hard with as good as no movement, other than a little springiness in the booster, and a lil springiness in the soft lines.
This is absolute proof that the hydraulics are working.

At this point, I would have to believe that the problem is mechanical; and the first place I would look is for foreign fluids on the pads the shoes, and/or the friction surfaces.
Next, I would look for the pistons not being frozen in the bores.
Next, to the pads being able to sit flat on the rotors, and parallel to eachother..
Next, that the pads fit properly in/on their holders, without getting up.
And finally, that all the front hardware is useable, and nothing compressible is installed between the pads and their running positions.
Now it's time to reassemble the fronts and move to the back.
At the back, the big deal is that the shoes and the drums having matching rubbing surfaces. Look at the shoes. If there is only a tiny patch that is shiny, set the shoe into the drum, on the wear surface, and make sure that firstly it is the right width for it, that it does not sit on an unworn area, and that it does NOT rock in the drum. If it does; The drums and the shoes will need to be matched, and only a brake shop can do this, and not all shops have the tool.
Once that is done, notice that each side has one shoe that is longer than the other, and it goes in, facing the REAR of the car. Then button it up, then adjust the shoes up tight. Then step on the pedal to center the shoes, and again, adjust it up tight. Finally back off each side adjuster, about the same, until the drums can be rotated, with effort, showing that the shoes are still dragging a lil.. Leave like that for break in.
And finally, have a helper step on the brakes while you watch each caliper doing it's thing, and put a bar between the wheelstuds and make sure the system is well able to clamp the rotor. and then move to the back, and with just one drum off check to see that the WCs are working, on both sides, then reinstall the drums..... and all the wheels; jack it down, torque the wheelnuts, and go for a roadtest.

 

[toolmanmike]

Thread moved to brakes forum.

 

[mygtsissweet]

i'd suspect a bad booster to start. but i'd bet there's other forces at play here...

after that we'd need more info: has it been sitting, when was the last time the brakes were serviced (flush & bleed), has any work been recently done-- specifically brakes, but other things apply as well, is everything bone stock, what else can you tell us: have you had the car a long time? did you just buy it? is this a new problem that just suddenly cropped up or an ongoing issue?

Good questions. The place I had doing work on it skipped over all the diagnosis stuff and install a booster vacuum now I'm putting the pedal to the floor every time I come to a stop and then I have to keep on pumping the pedal to maintain breaks. So the car set for years and I don't think anybody put any attention into brakes I pulled off all Wheels and brand new stuff is in the rear and front. I'm guessing that they may have just put the stuff in and never bled the lines. Thanks for your response let me know what you think

 

[junkyardhero]

Good questions. The place I had doing work on it skipped over all the diagnosis stuff and install a booster vacuum now I'm putting the pedal to the floor every time I come to a stop and then I have to keep on pumping the pedal to maintain breaks. So the car set for years and I don't think anybody put any attention into brakes I pulled off all Wheels and brand new stuff is in the rear and front. I'm guessing that they may have just put the stuff in and never bled the lines. Thanks for your response let me know what you think

in your first post, you cite that the pedal is hard. but now, you cite that it goes to the floor.

but in between there, a shop installed a booster.

you probably have several things going on here, in addition to the likelihood that there was just some flat out wrong, poor, or half *** work done.

but let's start with what you currently have: a pedal that goes to the floor and you have to pump. that means that you're either leaking fluid or sucking air-- or both. the booster could contribute to this, exacerbating the issue, but pedal travel starts with the master and what the fluid is or is not doing.

i'm *guessing* they just knocked on a booster and master cylinder, called that done and shipped it. which if that's the case besides needing to investigate that, you're in for a comprehensive flush and bleed. and by the sound of it (having set for years) the whole system needs attention.

repeat after me: new does not mean correct, correct does not mean good quality, good quality does not mean that it was installed and adjusted properly.

so looping back. my suggestion is to take it back and have them fix the brakes. you probably paid them a decent chunk of change to fix them in the first place and they should make right by that.

but if you're uncomfortable with that scenario, then let's boogie down. post up some pics of what you have so we can all be on the same page. familiarize yourself with the brake system and the terminology so we can all know what we're discussing. get your grubbies on and be ready to work.

i would start with looking for leaks, inspecting the master, pulling the rear drums and making sure that the shoes are adjusted properly. that's the easy stuff. from there, it gets more involved.

 

[mygtsissweet]

in your first post, you cite that the pedal is hard. but now, you cite that it goes to the floor.

but in between there, a shop installed a booster.

you probably have several things going on here, in addition to the likelihood that there was just some flat out wrong, poor, or half *** work done.

but let's start with what you currently have: a pedal that goes to the floor and you have to pump. that means that you're either leaking fluid or sucking air-- or both. the booster could contribute to this, exacerbating the issue, but pedal travel starts with the master and what the fluid is or is not doing.

i'm *guessing* they just knocked on a booster and master cylinder, called that done and shipped it. which if that's the case besides needing to investigate that, you're in for a comprehensive flush and bleed. and by the sound of it (having set for years) the whole system needs attention.

repeat after me: new does not mean correct, correct does not mean good quality, good quality does not mean that it was installed and adjusted properly.

so looping back. my suggestion is to take it back and have them fix the brakes. you probably paid them a decent chunk of change to fix them in the first place and they should make right by that.

but if you're uncomfortable with that scenario, then let's boogie down. post up some pics of what you have so we can all be on the same page. familiarize yourself with the brake system and the terminology so we can all know what we're discussing. get your grubbies on and be ready to work.

i would start with looking for leaks, inspecting the master, pulling the rear drums and making sure that the shoes are adjusted properly. that's the easy stuff. from there, it gets more involved.

Okay I pulled the rear drums. Everything looks brand new. I looked at the wheel cylinders and they look fine no leaks. I adjusted the brakes and put the drums back on. So the rears are good the front shoes are good. Check the master cylinder fluid level is good. So the vacuum pump has a fuse on it I pulled the fuse out and the car had virtually no breaks whatsoever it was like putting your foot into a brick wall to get any results. So I put the vacuum assist pump fuse back in and that's when the problem starts when I come to a light I throw it in neutral put my foot on the brake and the pedal is spongy. Have to pump them up a little bit. I got brakes but just don't seem right. Maybe the vacuum assist pump is too strong maybe I could get away with one it does half of the vacuum? But anyways thanks for your detailed description of what's going on. Thanks again Jeff

 

[Dana67Dart]

Thought.

The pushrod in the power brake booster needs to be adjusted correctly.

There is a procedure in the FSM.

But in a nutshell, measure the depth of the hole in the MC measure, how far out the rod is from the booster. The rod should stick out slightly less then the depth of the hole in the MC.

Also check that the MC does not have the retainer in the hole. I'm 99.99% sure it is not necessary on power brakes and might interfere

 

[Inertia]

I think I'd be checking the front calipers to see if the are seized.
Try pushing the caliper pistons back into the caliper, see if you can get them to move.
Mopar had a real issue with plastic caliper pucks/pistons seizing, especially sitting for long periods no use.
Good luck.