What actuates brake idiot light? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

avejoe · 06-01-2004, 11:37 AM

What actuates the idiot light for "BRAKE"? Is it fluid level, pressure, or what?

Thanks!

adamls · 06-01-2004, 11:41 AM

The "BRAKE" light comes on when you apply the e-brake. Should be a switch.

avejoe · 06-01-2004, 11:54 AM

Let me be a little more specific...

This morning as I came to the first interstection on my commute I made the turn without any brakes, yikes!. I pumped the pedal and I got a little brake back. Just then the brake idiot light came on. The emergency brake was not depressed. If the idiot light is related to the emergency brake (which makes sense as all cars have lights that say when the e-brake is on, duh), is it just a coincidence that it came on after I had brake problems?

68 Suburban · 06-01-2004, 11:57 AM

Quote:

Originally Posted by avejoe

Let me be a little more specific...

This morning as I came to the first interstection on my commute I made the turn without any brakes, yikes!. I pumped the pedal and I got a little brake back. Just then the brake idiot light came on. The emergency brake was not depressed. If the idiot light is related to the emergency brake (which makes sense as all cars have lights that say when the e-brake is on, duh), is it just a coincidence that it came on after I had brake problems?

I have always thought it was an e brake light. Try setting and releasing your e barake and see if it goes off.

LONGHAIR · 06-01-2004, 12:01 PM

It depends upon the year of the vehicle.
Most vehicles with a dual reservior master cylinder have a saftey valve that cuts off the fluid loss (and concentrates brake pressure) to the wheels that are still working in the event of a leak/line failure. Check for leaks/fluid level.

Jeepster376 · 06-01-2004, 12:11 PM

The light is activated by a loss of brake pressure, (pressure differential) between the front and rear brakes at the proportioning valve. Your light is functioning correctly, as you lost brake pressure somewhere. You need to check out your braking system, as you most likely have something that needs attention.

72gord · 06-01-2004, 01:01 PM

Sounds like you blew a brake line or wheel cylinder, better check underneath for leaks.
You can also look in the master cylinder and see if it is real low or empty in one end or the other.

**guyryan100** · 06-01-2004, 01:03 PM

The sensor for the light connects to the center of the proportioning valve on my '67 with manual brakes.

Crank · 06-01-2004, 01:37 PM

So what ur gonna wanna do, is fill ur reservoir and put your truck on a nice clean piece of concrete or road somewhere, then cycle the pedal a whole bunch... It'll spray fluid everywhere... It'll give u a round about idea of where the leak is. Then clean it, and have someone else do it, while it sprays fluid into your eyes. Ta daa. You've found ur leak. This is how my dumbass finds leaks anyway, feel free to use my method.

Brandon

smokekiki · 06-01-2004, 02:01 PM

Could also be an internal leak in the master cyl.You may not have any fluid loss,just pressure loss.Any time the pressure has a big enough difference between the front and rear side of the valve,the piston will move to block the side that is losing pressure and the light will come on.

Solver · 06-01-2004, 09:01 PM

On the same note then how do you reset the light to get it to go back off.

**JIMs70GMC** · 06-01-2004, 09:23 PM

solver, once the leak is fixed it'll reset it self after a good hard brake. At least mine did, had a bad wheel cylinder and replaced a brake line I figured after I bleed the drakes it would go out, it did noy but I went down the street and locked them up and ta da the light went out.

Also the e-brake lighting up the "brake idiot light is only on 71s and up, 70 and earlier did not come with the switch on the e-brake pedal. At least the 3 different 70 cabs I've had did not have it.(the 71 has a 70 chevy cab)

useRc10 · 06-02-2004, 12:19 AM

the light on my '72 goes off with loss of brake pressure...NOT e-brake ???

*1972C10* · 06-02-2004, 02:24 AM

Anytime my brake light light up it was from the pedal going down excessivly i had a sometime bad mastercylinder on my 85 once and when the pedal would go down generally after being stopped for awhile like at a red light the light would come on

The only way for me to get it to go off was to push the button on the prop valve that reseted it everytime its a black rubber button on one end of it and you can push it

LONGHAIR · 06-01-2004, 03:41 PM

flip66, only if there is no external leak. I have seen this dozens of times and it is rarely the master cylinder causing it. Not to say that they don't fail. I have seen more develop a leak down the firewall/booster than internally like that.

06-01-2004, 11:37 AM	#1
avejoe Custer had a plan too. Join Date: Dec 2003 Location: No. California Posts: 344	What actuates brake idiot light? What actuates the idiot light for "BRAKE"? Is it fluid level, pressure, or what? Thanks!

06-01-2004, 11:41 AM	#2
adamls Gotta Startem Early Join Date: Oct 2001 Location: Amarillo, TX, USA Posts: 364	The "BRAKE" light comes on when you apply the e-brake. Should be a switch. __________________ 67 SWB In Progress, one piece at a time, maybe 3 years I will be finished

06-01-2004, 12:11 PM	#6
Jeepster376 Registered User Join Date: Feb 2004 Location: Massachusetts Posts: 269	The light is activated by a loss of brake pressure, (pressure differential) between the front and rear brakes at the proportioning valve. Your light is functioning correctly, as you lost brake pressure somewhere. You need to check out your braking system, as you most likely have something that needs attention. __________________ 72 Cheyenne Super 4x4 SWB

06-01-2004, 02:01 PM	#10
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,473	Could also be an internal leak in the master cyl.You may not have any fluid loss,just pressure loss.Any time the pressure has a big enough difference between the front and rear side of the valve,the piston will move to block the side that is losing pressure and the light will come on. __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

06-01-2004, 09:01 PM	#11
Solver Registered User Join Date: May 2000 Location: Storm Lake, Ia Posts: 1,449	On the same note then how do you reset the light to get it to go back off. __________________ 1972 Cheyenne Super 20 LWB-Blue 1972 Cheyenne Super 10 LWB-Black 1972 Cheyenne Super 10 LWB-Red 1972 Cheyenne Super 10 LWB-green 1972 GMC 4x4 LWB-White 1971 Cheyenne 10 LWB-Ochre 1971 Cheyenne 20 Longhorn-Copper 1971 Cheyenne 20 Longhorn-Black 1969 Custom 10 LWB-lt blue 1968 GMC 3/4 ton-green 1968 1/2 ton swb stepside-silver 1967 Chevrolet CST 10 LWB-green 1967 Chevrolet custom 20 LWB-Maroon

06-01-2004, 11:54 AM	#3
avejoe Custer had a plan too. Join Date: Dec 2003 Location: No. California Posts: 344	Let me be a little more specific... This morning as I came to the first interstection on my commute I made the turn without any brakes, yikes!. I pumped the pedal and I got a little brake back. Just then the brake idiot light came on. The emergency brake was not depressed. If the idiot light is related to the emergency brake (which makes sense as all cars have lights that say when the e-brake is on, duh), is it just a coincidence that it came on after I had brake problems?

06-01-2004, 12:01 PM	#5
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	It depends upon the year of the vehicle. Most vehicles with a dual reservior master cylinder have a saftey valve that cuts off the fluid loss (and concentrates brake pressure) to the wheels that are still working in the event of a leak/line failure. Check for leaks/fluid level.

06-01-2004, 01:01 PM	#7
72gord Never enough time!! Join Date: Mar 2004 Location: sw Wisconsin Posts: 601	Sounds like you blew a brake line or wheel cylinder, better check underneath for leaks. You can also look in the master cylinder and see if it is real low or empty in one end or the other.

06-01-2004, 01:03 PM	#8
guyryan100 Registered User Join Date: Sep 2001 Location: Cumming, GA Posts: 483	The sensor for the light connects to the center of the proportioning valve on my '67 with manual brakes.

06-01-2004, 01:37 PM	#9
Crank Registered User Join Date: Aug 2002 Location: Crittenden, KY Posts: 1,965	So what ur gonna wanna do, is fill ur reservoir and put your truck on a nice clean piece of concrete or road somewhere, then cycle the pedal a whole bunch... It'll spray fluid everywhere... It'll give u a round about idea of where the leak is. Then clean it, and have someone else do it, while it sprays fluid into your eyes. Ta daa. You've found ur leak. This is how my dumbass finds leaks anyway, feel free to use my method. Brandon

06-01-2004, 09:23 PM	#12
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	solver, once the leak is fixed it'll reset it self after a good hard brake. At least mine did, had a bad wheel cylinder and replaced a brake line I figured after I bleed the drakes it would go out, it did noy but I went down the street and locked them up and ta da the light went out. Also the e-brake lighting up the "brake idiot light is only on 71s and up, 70 and earlier did not come with the switch on the e-brake pedal. At least the 3 different 70 cabs I've had did not have it.(the 71 has a 70 chevy cab) __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

06-02-2004, 12:19 AM	#13
useRc10 Registered User Join Date: Feb 2001 Location: Mechanicsville, VA, 23111 Posts: 1,138	the light on my '72 goes off with loss of brake pressure...NOT e-brake ??? __________________ -'02 Chevy Avalanche, 5.3L, 4x4... needing a small lift and bigger tires -'72 Chevy C-10(350, bored 60 over)dual flowmasters, 3 on the tree -'85 K5 Blazer,305 NO MORE...350 is in,2" lift,33" Mickey Thompson Baja Claw Radials -dads '70 burb (red, 5-7 drop, 350...) www.geocities.com/userc10/truckhome.html AIM: Auntjoedadda

06-02-2004, 02:24 AM	#14
1972C10 Account Suspended Join Date: Dec 2003 Location: Texas Posts: 2,686	Anytime my brake light light up it was from the pedal going down excessivly i had a sometime bad mastercylinder on my 85 once and when the pedal would go down generally after being stopped for awhile like at a red light the light would come on The only way for me to get it to go off was to push the button on the prop valve that reseted it everytime its a black rubber button on one end of it and you can push it

06-01-2004, 03:41 PM	#15
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	flip66, only if there is no external leak. I have seen this dozens of times and it is rarely the master cylinder causing it. Not to say that they don't fail. I have seen more develop a leak down the firewall/booster than internally like that.



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