Brake Warning Light On?

jmoffo · #1 (**permalink**) 04-24-07, 07:20 AM

Went for a ride in my '76 Deville on Sunday in Jersey's gorgeous weather. Some DOPE cut me off and I had to brake relatively hard and quick to stop.

The BIG girl's brakes locked up, burned a bit of rubber but NO ACCIDENT. (The car is a show car and I RARELY get her out unless the weather is good). Since...the brake warning light on the dash is lit. No problems with the brakes...no problems with the E. Brake..what else can this indicate because of this event?

**jayoldschool** · #2 (**permalink**) 04-24-07, 09:09 AM

Simple. You burst a brake line when you made that hard stop. Common on older cars that have a bit of rust underneath. Maybe a hard line, maybe one of the flex hoses. Get it to a shop ASAP, because as of now, you are stopping with two wheels. If they are the rear wheels, you are going to run into trouble soon.

jmoffo · #3 (**permalink**) 04-24-07, 01:48 PM

Actually, I was looking through my 76 Repair Manual and it states that the Brake Combination Valve incorporates three functions: ".....2. The pressure differntial section monitors the front and rear brake systems to measure any difference in pressure from the master cylinder. If a sufficient pressure differential exists an electrical ground is made by energizing the BRAKES telltale light on the right side of the....The valve and switch are so designed that the switch will latch in the "warning" position once a failure has occurred. The only way the light can be turned off is to repair the failure and apply a pedal force as required to develop 450 psi line pressure."

Okay...now that I know why it is on...any suggestions as to where to begin the short but "confusing" process the manual states?

**jayoldschool** · #4 (**permalink**) 04-24-07, 02:25 PM

The "pressure differential" is from the leak. You have to find the leak, get it fixed, bleed the system, and step on the brakes hard to reset the switch. Any garage will have no problem taking care of it. If you want to find the leak yourself, just start at the master cylinder and follow the lines all the way to the wheels. I bet that it burst in one of three spots: along the frame rail to the rear, on the hard line on the rear axle, or one of the flex hoses.

I've been through this a couple of times over the years, btw

HTH
Jason.

kmagari · #5 (**permalink**) 04-25-07, 08:32 AM

Is it just me or does anyone agree it seems when we take our babies out (mine a 70 Deville Convertible), everyone wants to pass you, everyone wants to tailgate) Iam more or less doing the speed limit and notice on a regular basis that people have even less respect when they see a classic on the road).

Motorboat · #6 (**permalink**) 04-25-07, 04:19 PM

I think it is a question of more respect than less. Often in an effort to get a better look they forget about the task at hand, driving safely.

jmoffo · #7 (**permalink**) 04-26-07, 07:14 AM

Yesterday, I took the old girl to be repaired. My mechanic and I found NO leaks ANYWHERE. Nonetheless, the brakes needed some work. We found the rear shoes were the ORIGNALS!!! Never been replaced since '76! (50,065 miles) Needless to say, they are completely new now. The rotors were cut. I had to pick up the car before the warning light has been reset seeing that we were getting rain in NJ. (She has never been in the rain or snow). It is back today for the "finals." Let's see if that darn idiot light will go off. Speaking of idiots....ANOTHER dopey dude decided to cut me off as I was getting back home with her. Luckily, he sped up as he realized his mistake and I did not have to break hard. I hope it is a matter of what motorboat said..in that they are NOT paying attention to the road and are in wonderment of cars of yesteryear.

**jayoldschool** · #8 (**permalink**) 04-26-07, 09:20 AM

The rear shoes being very worn would cause the master to be low. Braking hard would cause all the fluid to slosh forward, allowing air to enter the rear chamber and get into the lines. This would cause the light to come on. Have your tech do a complete flush of the fluid (it will be bad after so long anyways), and do a complete bleed of the system. The light should go out after a thorough bleed.

Remember, brake fluid is hygroscopic - it will absorb moisture from the air. After a long time in a car, it should be changed. Your car will thank you.

jmoffo · #9 (**permalink**) 04-26-07, 10:09 AM

I am heading there now for that reason!

I will update this afternoon!

Red_October_7000 · #10 (**permalink**) 04-26-07, 02:29 PM

This exact thing happened to me when some dipship pedestrian bumbled into traffic a car in front of me. Except I burst ALL the power brake lines and barely had enough fluid to make it 1 mile to the shop.

The reason people tailgate and pass is that you are doing the speed limit. On a couple roads near me ten to twenty miles over is not uncommon and I've actually seen traffic cruise at 100 on a couple occasions. You gotta keep up!

z06bigbird · #11 (**permalink**) 04-26-07, 03:45 PM

Quote:

Originally Posted by jmoffo

Went for a ride in my '76 Deville on Sunday in Jersey's gorgeous weather. Some DOPE cut me off and I had to brake relatively hard and quick to stop.

The BIG girl's brakes locked up, burned a bit of rubber but NO ACCIDENT. (The car is a show car and I RARELY get her out unless the weather is good). Since...the brake warning light on the dash is lit. No problems with the brakes...no problems with the E. Brake..what else can this indicate because of this event?

I will put my money on the o ring on the piston in the bottom of the master cylinder. It deteriorates and allows fluid to go from one portion of master cyl to the other. Brakes will continue to work except under harsh conditions. Pumping will restore the brakes temporarily.

Replace master cyl with NEW one, not rebuilt. Also, get a brand name one. I think ICE???? used to be a good brand.

Your problem was fairly common on cars in the 70s.

jmoffo · #12 (**permalink**) 04-26-07, 08:00 PM

The brakes were bled and all new DOT 3 fluid installed. STILL the warning light is on. How can it be reset?

Old Fleetwood · #13 (**permalink**) 04-26-07, 09:44 PM

Oh Oh

Although we're talking GM vehicles and Cadillac - - -
Could it be that the PROPORTIONING VALVE is the culprit?
This was noted as a problem some time ago on the Allpar site with Mopars.
The answer was to find the "button" on the top of the Proportioning Valve (somewhere around the mid-point of the frame under the car) and depressing it.
I guess it equalizes the pressure or something.
I have no idea if this applies to the situation here or not, but it's worth a try since it's such a stinker, to end the problem.

jmoffo · #14 (**permalink**) 04-27-07, 06:33 AM

There is no button on ours, unfortunately. My mechanic has been servicing GM cars since 1971 and has concurred with most here that the light should have gone out once the system was bled, all new pads and shoes were installed, and the master cylinder filled with clean fresh brake fluid. USUALLY the light should go out once this happens and you step on the pedal to bleed the sysytem. Our light is still Glowing

**jayoldschool** · #15 (**permalink**) 04-27-07, 09:00 AM

Yes, it should have gone out if all the air is out of the system. The day I got my 71 Ponitac, I tried the brakes hard. The line to the rear brakes burst right under the driver's door. I replaced the line, bled the system, and made a few hard stops - and the light went out.

I can only think that there is still air in there...