Front disk brake(s) sticking- where to start toubleshooting?

-

MRGTX

Well-Known Member
Joined
Sep 24, 2007
Messages
2,198
Reaction score
728
Location
CT, USA
My project has been subject to long starts and stops. A couple years back, I replaced the calipers, rotors, wheel bearings and flexible lines on my Dart's front brakes. I used OEM replacement parts.

There's honestly not a lot that can go wrong with this job...but I didn't get around to bleeding the brakes until very recently. They sat for a long time.

Now that the car is back on the road, I find that the pedal will feel normal (pretty damn good, actually), then the brake doesn't release entirely, and the brake predictably gets super hot. Fortunately, I haven't driven too far!

The change is detectable through the pedal...it loses travel and feels harder. Usually, it doesn't happen right way...but when I jacked up the car yesterday, the wheel was clearly being held by the brake, even when cold.

First thought is that the pistons corroded and aren't sliding back into the caliper. What would this look like? Could I see this without taking the caliper off?

Is there any way to fix this (lubricant?) without replacing the calipers?
 
If it is the calipers you cannot see it without pulling the pistons. My first question is did you put another master cylinder on and is there a chance it is a drum brake master? If so that may have a residual valve in it holding the brakes on.
 
First thing to do is determine if it's hydraulic. "Get the problem to show" and be prepared in advance. That is, have tools, rags, cardboard to lay on, a handy jack, etc, plan it out. When the pedal gives you the "feel" you describe, immediately go out and get some rags in there and crack the tubing fittings at the master and see if there is pressure holding.

If it still sticks and the above did not "show," then next time crack the bleeder on the caliper. If one side seems to heat worse, crack that side.

If you have the time, you can jack up that wheel and confirm "you gained" be rotating the tire and feeling for "looser" after cracking the bleeder, that is, if there's any question.
 
I converted my manual drum brake car to power discs using all new parts except for the spindles. I had the same issue that you have. My problem ended up being that the booster to master push rod was out of adjustment. I'm not sure if your dealing with power brakes or not. But it's something to check.
 
I converted my manual drum brake car to power discs using all new parts except for the spindles. I had the same issue that you have. My problem ended up being that the booster to master push rod was out of adjustment. I'm not sure if your dealing with power brakes or not. But it's something to check.

^^THIS^^ amoung other things. Some members have reported problems with hoses swelling shut. Personally, I've never seen one. There can be problems in the prop valve / warning switch.

As old as these girls are, could even be something stuck / rusted up in the pedal hanger "stuff"
 
If the "hang" can be felt through the pedal, I suspect the problem is between the pedal and the master cylinder. I can't feel hanging problems through the pedal is the issue is at the caliper.

My usual experience is for a single, sliding caliper to hang. This happens when the pins or the ways that the caliper uses to slide are not straight and smooth. I've never had a piston seize in a caliper, but I know it can happen. When something of this nature happens at the caliper, pad wear is uneven between the sides and sometimes even the pad itself develops a significant "ramp".
 
Thanks, guys!
Some great suggestions on how to get started...

This car is an original disk brake/non power car. Master cylinder is original as far as I know.

The pedal hang feels more like fluid pressure than linkage. It loses travel and feels harder under foot.
 
I am going with rusted up caliper. You say you replaced all that grocery list of stuff and the let it sit for a couple of years without bleeding.

Moisture has set up in the system and the calipers have probably paid the price.
 
I am going with rusted up caliper. You say you replaced all that grocery list of stuff and the let it sit for a couple of years without bleeding.

Moisture has set up in the system and the calipers have probably paid the price.
x2 ALL of my problems with brakes in the 70's back in the day when I was driving them just a few years old were with the caliper pistons sticking the bores. I rebuilt quite a few of them, and when I was lees young and less poor, I just bought rebuilt calipers.
 
Compensating port.Do you know about these?
-There is a wee small hole in the bottom of the M/C,that goes into the hydraulic circuit. That's how the brake fluid gets into the lines. This port has another purpose. As the pads wear the piston continuously moves out of it's bore, dragging the fluid with it, all the way from the M/C. And it has another purpose; Every time you step on the brake, the fluid is forced into the system at one end, and at the other end the pistons are forced out. Well, it works backwards too.When the pedal returns to it's parking spot, that fluid returns to the M/C;all but a wee tiny smidgen that is compensating for the worn pads. That's how it's supposed to work.
-Now, if it should happen that the fluid did not or could not return to the M/C, what do you think might happen?And what would be the symptom? That's right; the brakeS;plural, would stay on, and things would heat up.Now the guys talked about other stuff, which are all valid helps.Especially if the M/C cover was not sealed. But,I just wanna talk about this. You cannot diagnose a non-functioning C-port, if the pistons are hanging up, or the piston seals are not retracting, or a hose is checking.(Well you can but you have to crack open the system.)So what to do? Easy.If ALL the brakes are stuck on, it's almost guaranteed to be the C-port. If just one sticks, it ain't the C-port.Or at least extremely unlikely.
-Now what to do about it. Well guys already mentioned about cracking bleeders. This will let the fluid go somewhere and it's business as usual until the very next application;when they stick on again.And if they are all stuck on, you can crack any bleeder and they will all release. It's that easy.
-So you wanna fix it.Well that port is as far to the back as it can be in the pressure chamber, so that as soon as the brake pedal moves,it closes the port and begins the braking action.If the pedal does not park where it is supposed to, or if the pushrod that connects the pedal to the piston is too long, then the piston inside the M/C will also not return to its parked position and it will fail to open the port. Did you get that?Read it again.These two stops have to be synchronized.
-Easy check. Having proved all brakes are sticking on(or at least both fronts), and therefore that the C-port is not opening,here is what to do. Get the front wheels into the air, and get the brakes locked.Then loosen the M/C from its mount and move it towards the rad. That will allow the piston inside to move to its stop,and open the port, releasing the brakes. Shazzam!
-But perchance it does not release the brakes, then the port could be plugged. How to prove it? With the M/C still loose, crack the line going to the front wheels. If the brakes release, there you have it; the port is plugged. Be it debris, or rust or an incorrectly parked piston; that would be for you to determine.
-But let's say it did release right away, as you loosened the mounts.That would indicate that the pushrod is incorrectly seated in the M/C piston,or incorrectly adjusted.Fix it.
-Now I couldof told you just to loosen the M/C in my opening statement, but you wouldn't have learned a single thing except what size wrench to use.Plus now every person that reads this post between now and eternity, will learn a little bit about brakes too.
- 'course your problem might not be at all related to the Cport, but in less than 5 minutes you can prove it and hardly get dirty, cuz you don't really need to jack it up.
Awrighty then, beer-break!
 
Again, thanks to all.
AJ, that's a brilliant write-up...awesome stuff.

:cool:
 
-
Back
Top