Brakes lock up when car is on

[Dattebayo]

1991 Sentra w/ABS, American built...

I replaced all four pads and rotors, replaced two bad calipers, I bled all calipers in the order specified in the FSM, (LR, RF, RR, LF) and adjusted the emergency brake cable at the handle (because that seemed to be locking up the calipers in the rear a bit). Everything was fine until I started the car to test it. I hit the brakes a couple times and suddenly everything was locked up, just enough to let it move if I gassed it medium, but not enough to roll OR push the car. All brakes stay locked up when the the car is off.

This is frustrating. I need some answers soon and it seems like this forum is really fricken dead.

[elwesso]

So are you sure its the calipers that are locked up?

I think you're going to need to take the calipers off and make sure.. Did you lube the sliding pins properly and all that fun stuff? Usually when they lock up like that its because the caliper gets lodged somehow on the pins, maybe one is bent?

[Dattebayo]

So are you sure its the calipers that are locked up?

The rotors won't turn unless I release the pressure at the bleeder screw. All four. I thought I mentioned that, I guess not!

Did you lube the sliding pins properly and all that fun stuff? Usually when they lock up like that its because the caliper gets lodged somehow on the pins, maybe one is bent?

I did lube the pins, maybe with the wrong stuff tho now that I checked it out...
As I said, when the car is off, everything works just fine.

[IanS]

Are you sure all the brakes are staying locked up, or is it just one?

On older cars it is very common for the rubber brake hoses to collapse internally. Pushing the brake pedal creates enough force to push fluid into the caliper, but much of the pressure will stay there when the pedal is released. Often times, people replaced calipers, when in reality, the hose was the culprit all along.

If it is all of the brakes, then either you have an issue inside the ABS block internally, or possibly the master cylinder.

[Dattebayo]

I really don't think it's either the MC or the hoses because what I wrote up there... ^

[IanS]

I really don't think it's either the MC or the hoses because what I wrote up there... ^

If it only happens with engine on, then:

Try unplugging all the electrical connectors going to the ABS block. Start the car, and pump the pedal to see if the problem reoccurs. If it does not, then you may have an electrical fault, or a bad valve in the ABS

Try removing and plugging the brake booster line. Start the engine and see if the problem reoccurs. If it does not, then its related to the booster or MC.

[Dattebayo]

Booster and MC were checked, not the problem.

I don't see what valve would cause the problem in the ABS, the FSM shows a clear by-pass for when the system is not activated.

[IanS]

Booster and MC were checked, not the problem.

I don't see what valve would cause the problem in the ABS, the FSM shows a clear by-pass for when the system is not activated.

Did someone accidentally put some kind of petroleum product into the break fluid?

Even a small amount of something like power steering fluid will destroy everything rubber in the braking system, and it will cause all of the hoses to collapse. Not to mention all the seals get swollen.

I'll go take a look at the FSM, brb.

Edit: there is no 1991 FSM in the Nico repository.

[Dattebayo]

Upload these into the NICO database then:

VOLUME 1

VOLUME 2

[IanS]

Have you tried unplugging all the electrical connectors on the ABS block, then starting the car and testing the brakes?

The ABS system is capable of holding line pressure under certain situations. There may be a short causing the actuators to isolate the callipers once pressure builds.

[Dattebayo]

Not yet. I will do that in the morning tho. Keep checking in on me please! Thanks!

[IanS]

Will do. I have tomorrow off, so I wont be leaving the house till around 10:30 am. I will check in a few times before then.

[Dattebayo]

Sorry, I had things I had to take care of That I forgot about, so I'm on it right now. Back in a few with results...

[Dattebayo]

I just now disconnected the 20 and 30 amp ABS motor and cont. fuses in the engine compartment, I disconnected the motor relay and actuator relay as well. Anything else I should disconnect?

The brakes are still holding, but it's only been 10 minutes since I did all that. Where is this "ABS BLOCK" you speak of?

[IanS]

I just now disconnected the 20 and 30 amp ABS motor and cont. fuses in the engine compartment, I disconnected the motor relay and actuator relay as well. Anything else I should disconnect?

The brakes are still holding, but it's only been 10 minutes since I did all that. Where is this "ABS BLOCK" you speak of?

ABS block is a generic term for all the actuators, solenoids, and valves that make up the main part of the ABS system. They are usually all grouped together.

Pulling the fuses should have done it.

Ok, time to get tricky.

So some part of the system is holding pressure. The easiest way to figure out what, is to start at one end, and work your way to the other.

If I were you, I would pump the system up until the brakes stick. Then crack a line at the MC. If the wheels unlock, then the MC is likely the issue.

If they stay locked, crack the line AFTER the ABS actuator.

If they stay locked, crack a line after the proportioning valve.

Keep moving down the line till the brakes release. You may want to re pump the system up after every crack, just to make sure you dont get a false positive.

If you get all the way down, and the only thing that releases pressure is the bleeder screw, then Its likely the brake hoses.

[Dattebayo]

Okay, the rear e-brake cables seem to be hanging up independently of each other. If I apply the brake it does not make it lock up anymore when the e-brake is disconnected.

But the right rear one (which I replaced) is dragging slightly on the rotor. So that makes it the right rear and the front left that are hanging up.

I read in the FSM that the actuator controls things in pairs of opposite corners, so I wonder...

How long should the wheel roll when I spin it? I get about 3 seconds of spin on the rear left, same on the front right...

[Dattebayo]

Hey Ian, check this out:



See where the "solenoid valve" is? That's what I was talking about when I said "pairs of opposite corners"....

[IanS]

Okay, the rear e-brake cables seem to be hanging up independently of each other. If I apply the brake it does not make it lock up anymore when the e-brake is disconnected.

But the right rear one (which I replaced) is dragging slightly on the rotor. So that makes it the right rear and the front left that are hanging up.

I read in the FSM that the actuator controls things in pairs of opposite corners, so I wonder...

How long should the wheel roll when I spin it? I get about 3 seconds of spin on the rear left, same on the front right...

3 Seconds sounds about right for the rear, but Im surprised the front will spin at all. With all the axle and trans stuff, front wheels usually only make it a turn or two unless you really get them going.

IIRC you are right about the opposite corners thing, but I dont remember. I can try to look into it more tomorrow.

Are the ebrake cables themselves sticking, or is it the mechanism on the caliper?

In all honesty, do you really need ABS? It would not be all that hard to delete it.

Good luck, Im off to sleep.


Edit: just saw the diagram. From the looks of it, they can be triggered independently, which should mean they share a single valve. But if you unplugged the valve, then its not an electrical issue. It could be that the valve is backing up, and holding pressure in the accumulator. I dont recall what style valve these use, but you may be able to take it apart and see, or you could just replace it.

[Dattebayo]

No, I don't need ABS. I hate it. I drive much better without that crap.

I'm wondering what I would need to swap over tho, just the lines off another B13 and an MC? I don't have the luxury of a lift to get under the car, really.

BTW, it's the cables sticking. I can't tell if it's the center piece or the individual sides tho. Same issue about getting under the car...

[truckboy]

I am assuming your symptoms are somewhat off. If the car is carbureted then I suspect a carburetor float problem. Also it is possible that your fuel pump pickup may have a problem. These are, of course, just best guesses. I will be interested in others answers.

I do believe you are having a fuel delivery problem.

What happens when you drive down a steep street? Do some experimenting going up and down a steep grade.

When your engine stops the brakes no longer have power assist. Some brakes are very difficult to apply without assist.

[IanS]

I am assuming your symptoms are somewhat off. If the car is carbureted then I suspect a carburetor float problem. Also it is possible that your fuel pump pickup may have a problem. These are, of course, just best guesses. I will be interested in others answers.

I do believe you are having a fuel delivery problem.

What happens when you drive down a steep street? Do some experimenting going up and down a steep grade.

When your engine stops the brakes no longer have power assist. Some brakes are very difficult to apply without assist.

lol, wut?

[MaximA32]

I am assuming your symptoms are somewhat off. If the car is carbureted then I suspect a carburetor float problem. Also it is possible that your fuel pump pickup may have a problem. These are, of course, just best guesses. I will be interested in others answers.

I do believe you are having a fuel delivery problem.

What happens when you drive down a steep street? Do some experimenting going up and down a steep grade.

When your engine stops the brakes no longer have power assist. Some brakes are very difficult to apply without assist.

lol, wut?

Same thing I was wondering. He's been spouting random in all kinds of threads today.