C3 Brake problem...

**Patrick H.** · September 15, 2002, 08:52 PM

Re: C3 Brake problem...

Brake warning light on the tach? Isn't that for the emergency brake? Mine comes on if I bump the brake handle just wrong.

Try jiggling the e-brake handle. It may have popped up just enough.

Patrick

**Duke W.** · September 15, 2002, 09:36 PM

Re: C3 Brake problem...

I don't think your car has a proportioning valve. That was only part of the J-56 pakage. Your car just has a "switch" that detects differential pressure between the two circuits.

If you get the light and the brake pedal pedal height is lower than normal when the brakes are applied, you have a circuit that won't hold pressure.

If you can't find signs of leakage at the calipers or lines, it's probably the master cylinder.

Duke

**Gary Schisler** · September 15, 2002, 09:45 PM

Re: C3 Brake problem...

I am relying on my memory here but there is an electrical connector to the brake valve. This is on the driver's side of the car, just below the master cylinder and forward of it. I think there is a technique for getting the light to go out, that says to remove the electrical connection for a few seconds and then reconnect it. This is a short term correction, a band aid if you will. You will need to find and correct the problem.

The system is telling you that something in the system isn't right: air in one line, air in the MC, or one side of the system not working properly. I had an intermitant brake light (no, it isn't in the tach but right by it) and I solved my problem by rebuilding the MC. You said you have a rebuilt unit with SS brakes. How are the flexible brake lines? Is there any indication of a leak from the MC?

Gary

**Patrick H.** · September 16, 2002, 11:46 AM

Re: C3 Brake problem...

Hi again,

I drove my 71 to work today as usual. We're all discussing the same light.

To date, on all the cars I've worked on or maintained, despite bad MC's, boosters, leaking lines, calipers, etc. I have yet to see the light go one because of one of these items. I agree with Gary that there's a connector on the rear of the brake block below the MC, but I'm just sharing my experience. I'd at least a) wiggle the e-brake handle ot check it out. Its a cheap fix. Then b) I'd check that connector on the back of the brake block below the MC. Look for corrosion at the connection, too.

In other words, check the easy stuff first before you spend time and effort on the big ones.

Patrick

**Joe L.** · September 16, 2002, 03:35 PM

Re: C3 Brake problem...

Patrick------

The "brake" warning light is actually a "dual function" light. Its most common and recognized function is to warn of engagement of the parking brake. It does this via a switch mounted on the parking brake lever mechanism.

The second function of the light is warn of a pressure differential in the front-to-rear braking circuits. It does this via the switch located in the brake distribution block. Basically, this switch is an internal "toggle switch". It remains centered when the front and rear brake systems are operating at equal pressure (as the should be). When one circuit or the other loses pressure (due to air in the lines, a major fluid leak, etc.), the pressure in the normal circuit deflects the "toggle switch" to the side with lesser pressure. At this point, the switch activates the light on the dash.

This same system is used on all 67-82 Corvettes.

**Patrick H.** · September 16, 2002, 04:27 PM

Re: C3 Brake problem...

Joe,

I assumed as much. I was just commenting that in my experience, even despite having a brake line failure, it has yet to go on due to one of those reasons. It FREQUENTLY comes on if the e-brake is jarred.

Just giving advice based on personal observations and odds-of-occurrence.

Patrick

**Joe L.** · September 16, 2002, 04:57 PM

Re: C3 Brake problem...

Patrick-----

Do you know if your brake differential pressure switch is working or if the wire to it is connected on both ends? That could be the reason that you've never had it illuminate the dash light under brake hydraulic system abnormalities.

**Patrick H.** · September 16, 2002, 06:58 PM

Re: C3 Brake problem...

Joe,

I'm also talking about my experience with more than one Corvette. I have yet to see the light illuminate for a reason other than emergency brake usage. Period. On any Corvette, mine or not. In fact, before this thread I'd never ever HEARD of anyone having it go off for another reason, but its function as a dual purpose light still didn't surprise me.

And I've never verified whether the switch on the brake block works because I wouldn't even know how to begin doing so. And, of course, the switch was likely discontinued by GM 20 years ago, so it's a moot point, right? If it doesn't work, the light will never be able to illuminate anyway. The switch is likely not able to be tested when at your local swap meet, so...the current switches on our cars stay in place and life goes on.

Patrick

**Gary Schisler** · September 16, 2002, 08:18 PM

Re: C3 Brake problem...

The reason I know that my brake light works both as a parking brake light and a pressure differential light, is that my master cylinder failed, causing the light to come on. I also got a very slightly spongy brake pedal.

Gary

**Joe L.** · September 16, 2002, 08:27 PM

Re: C3 Brake problem...

Patrick-----

I've had mine illuminate several times when I was having "air pumping" problems. In fact, with mine, even if there was a slight pressure differential it would illuminate.

The switch for your 71 and 72 is discontinued. However, Dr. Vette of New Philadelphia, OH used to rebuild these units. I don't know if they still do, or not. I don't know how one would easily test the switch on the car. However, making sure that the electrical connections are making good contact should not be too difficult.

Actually, this switch is an important safety device since it alerts one to a problem with one of the 2 braking systems. Of course, if there were a complete failure of one of the 2 circuits, one would know that without the aid of a warning light. However, the presence of an impending problem might not be so obvious to the driver.

**Patrick H.** · September 16, 2002, 09:13 PM

Re: C3 Brake problem...

Thanks Joe and Gary. It's interesting that you've both had the light go on for relatively minor occurrences, as far as you could tell.

Learned something new today. I'll have to check sometime and see if Dr. Vette still rebuilds and/or tests the switches.

Patrick

**Grant M.** · September 17, 2002, 06:56 AM

Re: C3 Brake problem...

Patrick,

Add me to the list of those who've had it light for 'minor' occurrences. On two separate occasions (with different wheels) I had caliper seals begin to leak (prior to stainless steel sleeving). In each case, along with a 'spongy' feel to the brake pedal, I had the light illuminate (1978).

**Jim T.** · September 17, 2002, 09:35 AM

Re: C3 Brake problem...

I can attest that the pressure switchs on my 68 and 70 work just like they were designed to do. Have had them illuminate when there was a problem.

**bruce11495** · September 18, 2002, 12:35 AM

Re: C3 Brake problem...THANKS

Hi Guys....Thanks very much for all the input. Re-bled the brakes the other day and drove it 150 miles with no problem. Me thinks....that it is the master for sure. I'm making some inquiries now to have it tested off the car. Everything else checks out fine....Thanks Again

C3 Brake problem...

C3 Brake problem...

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