Rear brakes sticking lightly & Brake light comes on and off

[staminqia]

1992 zr1

[Ccmano]

Originally Posted by staminqia

1992 zr1

I don't have a 1992 Manual, however I believe the 1990-1992 cars are similar in function. In case you don't have the manual (you should absolutely get one if your doing this kind of stuff) the 1990 manual has the following to say on the subject. The "Brake" warning light has a dual function. It shows if the emergency brake is activated and it shows if the there is a hydraulic "proportioning" malfunction in the braking system. So first you need to eliminate the emergency brake as a source for the light. Make sure that the emergency brake lever isn't somehow hung up, the emergency brakes themselves aren't hung up or there is a malfunction in the emergency brake lever switch. Once your certain the emergency brake isn't the cause you can look into the hydraulic side of things. Generally this means either an external leak somewhere or (more likely) an internal leak in the master cylinder. If the binding rear brake story is to be believed the emergency brake may be the issue. It's a process of elimination. Here is what the 1990 manual has to say. But you should really get the 1992 manual. Brakes are a safety item, I would leave this to a professional if your not confident about this repair process.
H

[staminqia]

CCmano, thank you. Yes I need to get 92 service manual. Looking now to purchase one.
I agree with your statements. I am going to try all of this out on saturday. I am going to first change all of the fluid in the lines as it looks really dark. Then I will attack the emergency brake and try to disconnect the LR and RR linkages at the calipers. Then see if there is any binding after that.
If there is still binding then it may be the master cylinder.


Thanks

[staminqia]

So I started inspecting the rear brakes this morning. I am waiting for my pressure bleeding kit but I wanted to inspect the rear brakes first.
I jacked the rear. Car is in neutral, removed wheels. I could spin the rotors with one hand. I decided to use the parking brake and engaged it and they work good. I released the parking brake and i could move the rotor with one hand. So I am guessing that the parking brake is good. So i decided to remove calipers and inspect the sleeves. I did that and they moved freely but I lubed them all up while i had everything removed. Pads look good, they all look like they are wearing normal. I put everything back on both sides. See video. Thoughts??

https://youtu.be/5RcjrI6Qz50

[Ccmano]

Sounds normal. Now check the parking brake lever assembly, specifically the operation of the electric switch that sets the light. Test the ability of the switch to positively turn the light on a off. I doubt bleeding will resolve anything but it can't hurt. You most likely looking at an internal leak in the master cylinder.
H

[staminqia]

So I started the car, put it in neutral obviously. Car is still lifted and once I started it, brake light is on in cluster and when I try to turn rotors I cant. When I press the brake pedal light goes off. This leads me to believe its a master cylinder issue??

See videos
https://youtu.be/aYQ6NHhBfIc

https://youtu.be/wdZYpuSFJ3w

[32valvesftw]

Assuming the Ebrake is released or disconnected. I am puzzled, I did not think that could happen with a bad master cylinder. Maybe the proportioning valve?

[staminqia]

Not sure what it is. Once I turned the car off I still cannot turn the rotors. puzzling. I think it may be something to do with the proportioning valve.

[staminqia]

I did this check- key on, not running, parking brake OFF: disconnect pressure switch connector on inboard bottom of MC. Light does not go out. rotors still stuck from tuirning.

[32valvesftw]

You could try loosening the brake line connection at the master cylinder for the rear, see if that losses them up, then do the same with the proportioning valve. That may give you an idea of where the issue is.
In a previous life I worked with subsea hydraulics, if this happened I would suspect a bad non-return valve, or bad actuator. We had much more instrumentation to tell us where to look though.