Danny76

Hi all,

So about 6 months ago my brake light began to stay on all the time. I have only had my 76 about 11 months now, so I haven't driven it a whole lot (been working on it a lot more than driving it. I'm sure you all know.) But the light won't go off. I bled the crap out of the brakes. I've stomped on the pedal to make it go off. One day it actually went off, but came right back on and has stayed ever since.

I have also noticed the pedal goes nearly to the floor when braking. It does stop hard, but only after the pedal goes down quite a bit.

I have tried the following:
Stomp on brake to reset brake light-didn't work
Bleed all 4 brakes approx. 4 quarts
After driving, pulled vacuum line from brake booster-no sound of any suction, however when I pump the brake and start the engine with my foot on the pedal, it does go down. So I don't know if the booster has anything to do with it.
I don't see any leaks in the calipers. I believe they are pretty new from the previous owner.
Oh, and it does seem to pull somewhat to the left when braking.

Before I start replacing anything and wasting more money, any suggestions on where to start? I'm basically trying to figure out the constant brake light (oh, and I did pull the plug on the distribution/proportioning valve which did make the light go off, which tells me this is part of that issue?)
And trying to figure out why I have the soft pedal.

I have used a lot of suggestions from this forum to diagnose this, but I just don't' know where to go from here. I don't want to start replacing everything until I have a better idea of what might be wrong.

Help!!!

Thanks for any and all assistance!!

SteveG75

You have a leak. Probably on the right side of the car since it pulls to the left on braking. Could be a caliper (that was mine) or flex line. Maybe even hard line if it has a pinhole.

Either way, do not drive the car and fix the leak. The light is coming on because the front and rear pressures are not matching.

Danny76

Thanks for the quick reply.

Ok, I'll start investigating. One thing I did notice when I was bleeding was when I opened the bleeder valve on the right, it immediately began leaking from the threads. It doesn't seem to have any leak there when it is tightened up, but wasn't sure if that had anything to do with anything. I'll start looking, but so far I never saw any fluid leaks anywhere and the master cylinder doesn't seem to go down.

Thanks again.

HeadsU.P.

Ok, now we're getting some where. No fluid on ground and master is full. The MC is likely shot. The piston seals have done their time and its time to move on, new master.

One way to double check the master is: Buy one foot lengths of premade brakelines with the correct diameter and correct thread pitch fittings on one end. (front & rear fittings on the master are different) Remove both brakelines from master. Install your temporary short lines in master. Next, pinch, plug, cap, do whatever to close the end of lines. Now pump the pedal. Firm pedal? Master is good, leak elsewhere. Pedal to the floor? Master is toast.

The Punisher

Master cylinder

Danny76

Thanks so much guys. HeadsU.P. that sounds like a pretty easy test. I'm assuming once I hook the short lines up, start the engine up when I test the pedal? Also, will it be easy to find the correct connections on the lines? Do you think I can get them at any auto parts store?

HeadsU.P.

Actually it was a local NAPA that fixed me up with "test" lines. I think I have $15 into it. The front is smaller fitting maybe? than the rear? I can't remember. Different dia, different thread pitch. You may have to Google that info for a C3 or someone might chime in here with brass fitting size needed.

No need to start the engine. You are not testing the power part, just the manual brake system. Once the (deadend) test lines are installed that pedal should not budge! (maybe a pinch)
Here is the bad part; you just introduced air so you know what to do next. But at least you have isolated any MC issues for now.

Danny76

Yeah, I figured I'd have to bleed again. Still cheap insurance if I find out that the MC is what is causing my problems. I'll try to get to this later this week. I really hope I can figure it out soon. Is changing the MC very difficult? Doesn't appear to be too bad.

BTW, what should my brake pedal be doing right now when the engine is off? Is there anything I can do now to kind of get a better idea as well?

HeadsU.P.

First thing on changing a MC. Cover fenders, front bumper, around windshield. Brake fluid eats paint. Put an old towel under the master for drips. Two nuts on MC, I believe a 9/16 boxend wrench works well. Keep the lid on the MC with one bail. Pretty straight forward removal. Spillage is your enemy, be careful.
You will need a brake bleeder kit; (two plastic hoses & fittings) for your new MC to bench bleed.
Why are some MC $30 and others $200? Do some research, compare. Some are "date coded", some are for manual brakes, some for power brakes, some are new, some are rebuilt, some aluminum.

Danny76

Awesome. Great info! Thanks again. I'll try to do some test later in the week and update. If I have any more questions, I'll be sure to drop them on here.

Thanks again. This forum makes me not feel helpless!

HeadsU.P.

Your welcome.
When my MC gave out on me in July I checked around for prices. I ended up calling Corvette Central because they had one for $75 and one for $130. The difference? Rebuilt & new. I chose new so as not to have to mess with system again. A rebuilt unit is only as good as the person who honed out the bore, correctly. They also sell the bleeder kit for $8 a must have. Your old core does not have to go back with them.

Danny76

Good to know. I've ordered from them before. I would definitely go new. I just went to O'Reilly and they didn't have any lines. I'll probably go to NAPA in the next few days.

san

Everything sounds normal for pressing brake and starting car.. But...pulling to one side when brake pedal is pressed may not even be the brakes, it can be caused by worn suspension parts as well. If you cant find a leak when light cam on to begin with AND..VERY IMPORTANT, fluid doesnt go down, it is master cylinder. They can be hard to bleed when new, but if you watch a couple youtube videos you will learn almost all the tricks to.getting it done fast.
Another way to check master cylinder is to lock brake pedal down with a painters pole or broom stick, immediately crack a line somewhere amd notice the pressure, tighen it back up, reset pole or broom stick to lock brake pedal down again, now go for coffee...wait an hour or two...and crack the same line...same pressure?? I always crack them at cylinder...much quicker. Also....you dont need a line to go from front side of master to back. Use nylon or brass bolts. It wont hurt anything, and you can add some plumbing tape if you cant get them to seal tight. Once sealed tight....your brake pedal should go down a little, no more than a 1/4 of travel, and holding hard with leg, should stay solid.

HeadsU.P.

You misunderstood about "test lines". I said nothing about a steel line from front to back of the master. That would accomplish nothing. One test line off the front port plugged on the end. One test line off the rear port plugged on the end. This eliminates any issues past the MC. CAREFUL! Using bolts in those MC ports could damage the thread and / or the flare inside. Not a good idea.
If you own a tubeing bender tool, those test lines can double as a MC bleeder kit, bending the line right back towards and into the reservoir so the fluid is circulated, bubbles removed. And that is exactly what a MC bleeder kit does but with plastic hoses.
Trouble with the broomstick method is, once a bleeder is opened, the stick falls to the floor, pedal comes up, introduces air.

Danny76

Thanks again guys for all of the tips. When I get a chance this week I'll be getting the test lines to see what I can find. At this point, I hope it's just the MC. Doesn't seem like too much of a pain to replace/bench bleed and bleed the system. I just want my car to run without problems......for a little while at least!! Lol.

HeadsU.P.

Quote:
"doesn't seem like too much a pain to bleed". . . . Your nightmare has only begun. Suicide rates have occured for the following:

1. Huge debts
2. Loss of loved one
3. Job loss
4. Bleeding C3 brakes

Maybe not.

Danny76

Hahaha. Ok, I won't speak again. I have already bled them about 4 quarts worth, so I do know it isn't "easy." I guess I'm just trying to look at the bright side of things. I really just want to drive this car for more than 2 weeks without having an issue.

HeadsU.P.

If the day ever comes where our C3 is just perfect every single day, then and only then would we become bored with it and likely sell it. But until that day, the maintance issues forces us to hang on to it, challenging us for perfection and becoming part of our lives.

(what a line of crap, but it sounds good)

Danny76

Lol. That sure did SOUND good.

Danny76

So I went to NAPA and got some short brake lines, however when I got home saw that the threads are incorrect. So, I just bought a MC bleeder kit, used the plastic fittings to find the correct sizes and unfortunately, NAPA doesn't have the lines I need. So, I think I'm just going to buy a new damn MC. The consensus so far is that it's bad, so why not just spend a few more dollars and buy a new one. NAPA has a new one for $43, and while I'm at it, even though I'm not the biggest fan of buying parts that I don't know if I need, I'm thinking of just tacking the brake booster as well. Something tells me it is bad. When I pull the vacuum line, I never hear anything and the videos I've watched, when that hose is pulled you can hear a suction which mine doesn't do. Both the booster and MC are the original ones, and there must be issues with diaphrams, etc. Also, aesthetically it looks horrible. So maybe I'll just do it all and at that point, I would certainly hope my brakes are like new (so-to-speak.) Thoughts?