Brake Light...Out of the blue! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

KP1972 · 11-29-2004, 03:22 PM

The other day, I start up the truck. Sure, it has been sitting there for a bit but it cranked right up but out of the blue the Brake Light on the instrument panel comes on. I have checked the master cylinder and there is plenty of brake fluid. So, what gives?????

Fred T · 11-29-2004, 03:37 PM

With disc/drums it usually means something is out of balance on the pressure between the fronts and rears. Can be a fluid leak or crud in the proportioning valve or master cylinder. Start with a leak check by inspecting the calipers on the front and the wheel cylinders on the rear. Also check all the brake lines.

Super Duck · 11-29-2004, 03:37 PM

the ebrake may be setting it off, or the master cylender may be going bad

Gordo · 11-29-2004, 10:01 PM

Yep, pull up on the e-brake pedal to make sure it's not that before you go nuts.

texnician01 · 11-30-2004, 04:19 AM

I don't recall that I have ever see the brake light come on in my truck when i set the e-brake. I've never see that light come on except for when i start it. is something wrong with my truck? or where is the swith to turn it on with the e-brake?
Sorry don't mean to intrude on your thread but i figured they were on the same lines.

Nathan

Tx Firefighter · 11-30-2004, 08:31 AM

I don't remember there being an electrical switch on the e-brake pedal for the light.

texnician01 · 11-30-2004, 10:44 AM

good neither do I

Nathan

Gordo · 11-30-2004, 05:42 PM

ooops! You guys are right, I'm wrong. I musta had a brain fart.

chickenwing · 11-30-2004, 06:03 PM

Sometimes if you pump your brakes hard the valve will equalize and the light will go out for a moment. I guess it could be crud. I would be looking real hard for fluid leaks.

tom hand · 11-30-2004, 08:15 PM

I know for a fact 71/72 trucks have a switch that will turn the light on..as well as brake problems...they are wired parallel...here's a pic of the switch

chickenwing · 11-30-2004, 08:25 PM

I had to go out and triple check but my 72 C20 Super doesn't got it. Nor holes for it.

Sweet72 · 11-30-2004, 08:39 PM

Nope, mine don't have that parking brake switch either. Rare option or add on?

franko72 · 12-02-2004, 07:14 PM

my 72 doesnt have it either. Sound like the proportioner valve stuck. you'll find out when you try to bleed the brakes.One of the wheels wont get any brake fluid if the valve sticks.got to start with an inspection first.wheel cylinders or a brake line could be the problem.look under the rear end for fluid at the inside wheel rims at the bottom of the rim .

tjhooker125 · 12-03-2004, 02:18 AM

Check this website, scroll 3/4's of the way down, you'll find a way to check your proportioing valve. Also, the shop manual for these trucks spells it out. TJ

http://www.classicperform.com/TechBo...t.htm#testprop

11-29-2004, 03:22 PM	#1
KP1972 Registered User Join Date: Dec 2001 Location: Mansfield Texas Posts: 645	Brake Light...Out of the blue! The other day, I start up the truck. Sure, it has been sitting there for a bit but it cranked right up but out of the blue the Brake Light on the instrument panel comes on. I have checked the master cylinder and there is plenty of brake fluid. So, what gives????? __________________ 1972 Chevy Custom/10 www.PictureTrail.com/KP1972 Metroplex Muscle Car Club www.PictureTrail.com/DreamCarArt

11-29-2004, 03:37 PM	#2
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	With disc/drums it usually means something is out of balance on the pressure between the fronts and rears. Can be a fluid leak or crud in the proportioning valve or master cylinder. Start with a leak check by inspecting the calipers on the front and the wheel cylinders on the rear. Also check all the brake lines. __________________ Fred There is no such thing as too much cam...just not enough engine.

11-29-2004, 03:37 PM	#3
Super Duck Chevy Nuttttt Join Date: Sep 2004 Location: Santa Maria Ca. Posts: 568	the ebrake may be setting it off, or the master cylender may be going bad __________________ 67' Chev swb step side 69' SS elky 03' Chev ext cab 4X4 hey who lernt me to spell is there anything else?

11-29-2004, 10:01 PM	#4
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	Yep, pull up on the e-brake pedal to make sure it's not that before you go nuts. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

11-30-2004, 04:19 AM	#5
texnician01 Senior Member Join Date: Mar 2002 Location: 12 Miles South of Des Moines, Iowa Posts: 359	I don't recall that I have ever see the brake light come on in my truck when i set the e-brake. I've never see that light come on except for when i start it. is something wrong with my truck? or where is the swith to turn it on with the e-brake? Sorry don't mean to intrude on your thread but i figured they were on the same lines. Nathan __________________ 69 C-10, 340HP 327 55 chevy 4 door 150 47 Willys CJ-2A 05 Harley Night Train 06 1200 Sportster (Wife's bike) 70 Honda CL350 OIF2 & OIF7 Veteran Nathan & Tiffany

11-30-2004, 08:31 AM	#6
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	I don't remember there being an electrical switch on the e-brake pedal for the light. __________________ I'm on the Instagram- @Gearhead_Kevin

11-30-2004, 10:44 AM	#7
texnician01 Senior Member Join Date: Mar 2002 Location: 12 Miles South of Des Moines, Iowa Posts: 359	good neither do I Nathan __________________ 69 C-10, 340HP 327 55 chevy 4 door 150 47 Willys CJ-2A 05 Harley Night Train 06 1200 Sportster (Wife's bike) 70 Honda CL350 OIF2 & OIF7 Veteran Nathan & Tiffany

11-30-2004, 05:42 PM	#8
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	ooops! You guys are right, I'm wrong. I musta had a brain fart. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

11-30-2004, 06:03 PM	#9
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	Sometimes if you pump your brakes hard the valve will equalize and the light will go out for a moment. I guess it could be crud. I would be looking real hard for fluid leaks. __________________ The truck... you hear that? No really, you did hear that?!!!

11-30-2004, 08:15 PM	#10
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	I know for a fact 71/72 trucks have a switch that will turn the light on..as well as brake problems...they are wired parallel...here's a pic of the switch Attached Images __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

11-30-2004, 08:25 PM	#11
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	I had to go out and triple check but my 72 C20 Super doesn't got it. Nor holes for it. __________________ The truck... you hear that? No really, you did hear that?!!!

11-30-2004, 08:39 PM	#12
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Nope, mine don't have that parking brake switch either. Rare option or add on? __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.

12-02-2004, 07:14 PM	#13
franko72 Franko72 Join Date: May 2004 Location: Cincinnati,Ohio Posts: 471	my 72 doesnt have it either. Sound like the proportioner valve stuck. you'll find out when you try to bleed the brakes.One of the wheels wont get any brake fluid if the valve sticks.got to start with an inspection first.wheel cylinders or a brake line could be the problem.look under the rear end for fluid at the inside wheel rims at the bottom of the rim . __________________ 1972 C20 cheyenne Super 402 BB/400 turbo LWB A/C Tilt, Cruise Control, Saddle tanks, Tach My Home Page Better to burn out than it is to rust

12-03-2004, 02:18 AM	#14
tjhooker125 Registered User Join Date: Oct 2004 Location: SSF CA Posts: 34	Check this website, scroll 3/4's of the way down, you'll find a way to check your proportioing valve. Also, the shop manual for these trucks spells it out. TJ http://www.classicperform.com/TechBo...t.htm#testprop



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