Rear brakes sticking lightly & Brake light comes on and off

[staminqia]

I have an issue when I drive that the brake light on dash comes on but when I press the brake pedal it goes off and sometimes when stopped and I let off the brake to press the clutch in I Feel the car does not drift back and its held by the brakes.

I took it to a local shop and he said the front brakes are fine and free spinning but the rear wheels have some resistance. He thinks its the HCU Hydraulic control unit HCU and he does not want to touch it. So before I take it to the dealership I wanted to get some insight from the group here to see if my local mechanic is on the right path or there could be another source to the problem?

Thoughts?

[TX '90 ZR1]

My first thought- Please do not take it to the dealership!!
Hard to diagnose long distance, but my first suspicion would be something going on with the parking/emergency brake.
:cheers:

[staminqia]

Thats what I thought but when I take it for a drive the sticking doesnt happen all the time almost live every second stop light I feel the resistance.

[TX '90 ZR1]

If the "Brake" light you are referring to is in the instrument cluster and not the ABS warning light I would still suspect adjustment of the parking/emergency brake.
FYI: The brake system is something any competent C4 mechanic should be able to address. Maybe someone can refer you to a good mechanic in your area.
:cheers:

[staminqia]

Yes you are correct, its on the instrument cluster not above the radio cluster. I agree I think my local mechanic doesnt want to deal with it or trouble shoot it.

[staminqia]

TX '90 is there a good video or document that demonstrates how to adjust the parking brake? is at the lever or at the rear caliper?

[32valvesftw]

I had that issue on mine when I first got it. The fluid level was fine the fluid was clean there were no leaks. What ended up fixing it for me was carefully disassembling and repairing the wiring harness to the switch on the master cylinder, I don't think it was making a good connection.

[Ccmano]

My first thought- Please do not take it to the dealership!!
Hard to diagnose long distance, but my first suspicion would be something going on with the parking/emergency brake.
:cheers:

Absolutely do not take it to a dealership! They will be even more clueless that the guy you brought it too in the first place. They will charge you an arm and a leg for the privilege.

Find a good corvette shop. The system is no different than any other C4 of the vintage.
H
:cheers:

[staminqia]

I had that issue on mine when I first got it. The fluid level was fine the fluid was clean there were no leaks. What ended up fixing it for me was carefully disassembling and repairing the wiring harness to the switch on the master cylinder, I don't think it was making a good connection.

What kind of a repair did you do to the wiring harness? were your brakes sticking or just the light came on and off?
any help here would be appreciated.

[secondchance]

?PARK? light indicates parking brake engaged. ?BRAKE? lights up when brake fluid is too low or an issue with brake hydraulics.
If ?BRAKE? light comes on intermittently, I would first check brake fluid level followed by perhaps checking wiring connector to sensor on the brake master cylinder. If both are ok, I would have a competent shop check master cylinder. HCU - hydraulic control unit? Never heard of this.
Rear brake sticking, I think, may be unrelated. Could be floating caliper binding and needing disassembly, clean and lube. Or, parking brake is not releasing fully.
How many miles on the car?

[32valvesftw]

What kind of a repair did you do to the wiring harness? were your brakes sticking or just the light came on and off?
any help here would be appreciated.
I pulled the harness apart disconnected the wires cut them and installed new ends then stuck them back into the harness. How bad are your brakes sticking? Did the shop check and record pad thicknesses. Normally if a caliper is stuck the pads will wear prematurely and one will wear more than the others. Disconnect the harness and see if the light stays on. It was several years ago, so details are sketchy.
As others have mentioned any competent shop can assess your braking system. These are not very complicated braking systems.
If the wiring is OK I would think you have an issue with master cylinder leaking internally and causing a temporary imbalance in the system when you apply the brakes.

[staminqia]

Car only has 19k miles. Brake fluid is filled just to the neck of the reservoir. It's a 92. I will disconnect the sensor that seems easy to do to see if light turns on or off.. Where is it located? I wish there was a good video on how to adjust emergency brake at caliper, can't find a good one.

[Ccmano]

Some information for you on the C4 ABS breaking system and how it's controlled.
H
:cheers:
https://www.corvetteactioncenter.com/specs/c4/1986-1996-corvette-abs-traction-control/

[TX '90 ZR1]

Go to the top of the technical postings page in this forum and select the sticky that is labeled "Solutions". Scroll down to section 5 and then to the section labeled "Brakes". Lots of info there.:cheers:

[staminqia]

I think I am going to try and diagnose this problem after sitting on it over night and reading a ton of posts. I am thinking to do the following tasks
1. remove rear wheels and inspect wheel spin
2. somehow remove any pressure from E brake (need to figure out how to do this) if this concluded that the wheels spin freely then I know where the problem lies. If this is the issue than I have to adjust the E brake tension. Might have to remove the driver seat to get to the e brake mechanism.
3. if E brake is not the issue than I need to check calipers sticking. may have to rebuild the calipers and flush the system fluids.

If this doesnt work than it has to be something with ABS components.

Thoughts?

[32valvesftw]

You can disconnect the ebrake at each wheel by unhooking the cable.

[staminqia]

You can disconnect the ebrake at each wheel by unhooking the cable.

Awesome, that could give me an idea if its an E brake issue. If its not, then I will go next to the calipers sticking.
Question how do I know if its a caliper that needs replaced or a bigger problem?
For an example with the E brake disconnected how do I know which caliper is causing the stick? - space between pads and rotor on each side? If I see one left Rear or right rear side pads touching rotors or not? what if both side pads are touching rotor, does that mean I have a bigger issue becuase its affecting each rear brake?

Lastly should I flush all of the brake fluid first before I do any of this diagnostic or after?

[32valvesftw]

Typically a caliper that is stuck will have a pad that is very worn compared to the others, if it has gone on for some time. Or the wheel will be noticeably harder to turn. I just went through this exercise on my daughters car. Three rear pads were almost new, one was down to the metal backing. Some amount of dragging is OK, I would not expect the wheel to spin freely like a bicycle wheel.

If I were in your shoes, I would flush the brake fluid first as that may clear up your issue, do not let the reservoir go dry, and plan on putting a liter or more of fluid through the system, you want clear fluid to come out of the bleeds.

Each rear wheel has an ebrake cable going to it. They can be disconnected individually.

[staminqia]

Typically a caliper that is stuck will have a pad that is very worn compared to the others, if it has gone on for some time. Or the wheel will be noticeably harder to turn. I just went through this exercise on my daughters car. Three rear pads were almost new, one was down to the metal backing. Some amount of dragging is OK, I would not expect the wheel to spin freely like a bicycle wheel.

If I were in your shoes, I would flush the brake fluid first as that may clear up your issue, do not let the reservoir go dry, and plan on putting a liter or more of fluid through the system, you want clear fluid to come out of the bleeds.

Each rear wheel has an ebrake cable going to it. They can be disconnected individually.


Thank you, good advice. I agree I will flush first with new clean fluid.

[Ccmano]

What year is your car?
H
:cheers:

[staminqia]

1992 zr1

[Ccmano]

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
:cheers:
https://farm66.staticflickr.com/65535/51116085549_7f627c0e74_c.jpg (https://flic.kr/p/2kSXinP)

https://farm66.staticflickr.com/65535/51116085539_70cca1d9fa_c.jpg (https://flic.kr/p/2kSXinD)

https://farm66.staticflickr.com/65535/51115770012_752ba8be98_c.jpg (https://flic.kr/p/2kSVFzw)

[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
:cheers:

[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.

[Ccmano]

When you look under the car just forward of the diff you'll see the cable for the emergency brake running cross the car. Follow the cable to the passenger side and you'll see a bracket that mounts it with a single bolt to the frame just ahead of the rear wheel. Undo that bolt completely and let the cable droop. This will take the emergency brake out of the equation. If the brakes still stick it either the master or something in the ABS system. Since you didn't get an ABS warning light its likely the master.
H
:cheers:

[staminqia]

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.

Ok this may be a bit too much but do you know which lines go to the rear? I dont have my service manuals yet. Also for the propostioning valve is it as simple as just unscrewing it from the front of the master cylinder? Will a bunch of fluid leak out when I do this?? This is a little out of my league.

[32valvesftw]

I would have to trace the lines from the rear caliper towards the front.
Have a look at this:
https://www.corvetteactioncenter.com/specs/c4/1986-1996-corvette-abs-traction-control/index.html
After reading through that I would pull the fuse that controls ABS and traction control and see if the wheels free up. The shop that said it was the hydraulic control unit, may not have been wrong he may have just used the wrong term.

[staminqia]

I would have to trace the lines from the rear caliper towards the front.
Have a look at this:
https://www.corvetteactioncenter.com/specs/c4/1986-1996-corvette-abs-traction-control/index.html
After reading through that I would pull the fuse that controls ABS and traction control and see if the wheels free up. The shop that said it was the hydraulic control unit, may not have been wrong he may have just used the wrong term.

Ok now I have to find the right fuse. Wouldn't the car off release that pressure though if it was ABS?

[Ccmano]

Forgot to ask, are both rear calipers locked or just one?
H
:cheers:

[staminqia]

Forgot to ask, are both rear calipers locked or just one?
H
:cheers:

they are both locked up.

[staminqia]

Well, I decided today to flush the old brake fluid and bleed all the lines. I did it. All new clean fluid. Then I put tires on started it and viola no light!. Took it for a spin and no sticking at a stop and no light. I hope this was the issue and it doesn't come back but for now I'm back to normal. Moral of the story here is when you get a 30 year old car flush the fluids first. That was the issue.

Thanks for everyone's help. I'll keep you all posted if it come back.

[Ccmano]

Well, I decided today to flush the old brake fluid and bleed all the lines. I did it. All new clean fluid. Then I put tires on started it and viola no light!. Took it for a spin and no sticking at a stop and no light. I hope this was the issue and it doesn't come back but for now I'm back to normal. Moral of the story here is when you get a 30 year old car flush the fluids first. That was the issue.

Thanks for everyone's help. I'll keep you all posted if it come back.

Glad you got it. Surprised that worked, but hey it's fixed!
H
:cheers:

[32valvesftw]

Good work! There was probably sludge fouling up something.

[staminqia]

Yes it was really dark and sludgy. Let's hope it doesn't come back. So if someone has this same problem bleed the system FIRST.

THANK YOU GUYS!