Brake lamp in dash? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

70c10 · 07-04-2005, 12:50 PM

On my dads 70' the brake lamp keeps coming on. He has new wheel cylinders,shoes,drums and booster. The cylinders are all dry with no leaks. Recently the rear master cylinder resevoir was really low. Filled it but the light still comes on. The brakes work great. Any ideas what would trigger the lamp???

**68 Stepside** · 07-04-2005, 01:18 PM

It probably has something to do with the proportioning valve, as that's where the low pressure switch is (I'm pretty sure). There's a way to reset the valve, by stomping hard on the brake pedal, but I've never tried it. I know others on the board have, and I"m sure someone will chime in and tell you exactly how that's done.

Good luck.

Longhorn Man · 07-04-2005, 02:01 PM

if the master cylinder was really low, then you need to find where the fluid went. (there is a leak somewhere)

LONGHAIR · 07-04-2005, 02:01 PM

I would try bleeding the brakes, since you said thay they were very low recently. But I would also be on the look-out for "why"? That fluid had to go somewhere. Look at the back of the master cylinder where it meets the firewall/booster. If the cylinder is leaking there you will see it or at least bubbling paint. If it is non-power brakes it could leak down the inside of the firewall into the cab. You could also have a line leak where the rubber lines meet the steel.

Back to the original answer, the light may be coming on because of the imbalance of pressure.........air in the line from the low reservior. The light can also come on because of the E-brake switch. Make sure that it is totally off.

**Green Machine** · 07-04-2005, 02:13 PM

My money is on a bad master cylinder.

70c10 · 07-04-2005, 02:52 PM

Thanks for al the replies so far. We'll have to check for leaks again. The proportioning block and master cylinder are original. I was thinking maybe the proportioning block went up but how would I know for sure?

BowTieMan · 07-04-2005, 03:59 PM

I thought the brake light ment the parking brake was on?

**Stocker** · 07-04-2005, 04:22 PM

Quote:

Originally Posted by 68 Stepside

It probably has something to do with the proportioning valve, as that's where the low pressure switch is (I'm pretty sure). There's a way to reset the valve, by stomping hard on the brake pedal, but I've never tried it. Good luck.

This gets my vote, though I am also unsure how to reset it.

Had the same thing happen when I replaced my master cylinder. Took it to a shop and they reset it and didn't charge me, so I know it was easy - but I failed to ask them what they did!

Longhorn Man · 07-04-2005, 04:32 PM

Most of these trucks didn't have a switch to turn on the brake light with the parking brake.

LONGHAIR · 07-04-2005, 04:55 PM

Quote:

Took it to a shop and they reset it and didn't charge me, so I know it was easy - but I failed to ask them what they did!

I'd be willing to bet that they just bled the brakes.........this happens when the pressure is greater on one side (front/rear) and the valve closes off that side...and turns on the light to tell you that there is a problem.

cableguy0 · 07-04-2005, 05:24 PM

look around on the firewall inside the cab for any wetness on a non power brake truck the fluid can leak out of the master cylinder and into the truck and you will never see it. and if you have power brakes unbolt the master cylinder and look for wetness. the fluid went somewhere

4x4Poet · 07-04-2005, 05:55 PM

Look to see if you can unscrew the switch from the proportioning valve. Look in side and see if the rear system has shifted the hole that the switch lever rides in due to an imbalance.

A.P. · 07-04-2005, 08:13 PM

I have the some problem about the brake light not turning off. I replaced the master cylinder, rotors, and calipers. I also bleed the entire system. There gots to be a way to reset the prop valve? I tried the hard braking and that did not work either. My brakes work great.

**Green Machine** · 07-04-2005, 08:30 PM

To reset(center) valve, turn on switch, and bleed one end. No more than 1 pump should be needed. If that doesn't turn off light, go and bleed 1 pump from other end. It depends which end works, as to which way the valve is off center. Ususally light will go off within 1/2 stroke. If that doesn't work, then the valve is stuck or the MC is bad.

70c10 · 07-04-2005, 09:35 PM

Thanks for all the replies. Will start checking all these things out.

matthufham · 07-05-2005, 12:36 PM

in my sister's 90' 4runner, she had a tripped wire so the brake warning light came on. there was no mechanical problems so we never bothered to find the bad wire, and the problem fixed itself somehow.

jtminton · 07-05-2005, 12:45 PM

I had the same problem with disappearing fluid. I'm pretty sure it was leaking back into the booster from the bad M/C. Changed the M/C and it fixed the problem. Also helped my braking.

A.P. · 07-05-2005, 07:14 PM

Here is some info that might help with the brake warning light.

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

**Stocker** · 07-05-2005, 08:09 PM

Bookmarked! Thank you thank you thank you!

1STtimePRo'71 · 07-05-2005, 10:57 PM

Good Info A.P. Maybe this will help my light go bye, bye.

07-04-2005, 12:50 PM	#1
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,857	Brake lamp in dash? On my dads 70' the brake lamp keeps coming on. He has new wheel cylinders,shoes,drums and booster. The cylinders are all dry with no leaks. Recently the rear master cylinder resevoir was really low. Filled it but the light still comes on. The brakes work great. Any ideas what would trigger the lamp??? __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

07-04-2005, 01:18 PM	#2
68 Stepside huh? Join Date: May 2000 Location: Washington, Illinois Posts: 5,692	It probably has something to do with the proportioning valve, as that's where the low pressure switch is (I'm pretty sure). There's a way to reset the valve, by stomping hard on the brake pedal, but I've never tried it. I know others on the board have, and I"m sure someone will chime in and tell you exactly how that's done. Good luck. __________________ Someday when I'm lonely, Wishing you weren't so far away, Then I will remember Things we said today. RIP El Jay

07-04-2005, 02:13 PM	#5
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	My money is on a bad master cylinder. __________________ 1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0

07-04-2005, 02:52 PM	#6
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,857	Thanks for al the replies so far. We'll have to check for leaks again. The proportioning block and master cylinder are original. I was thinking maybe the proportioning block went up but how would I know for sure? __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

07-04-2005, 03:59 PM	#7
BowTieMan Registered User Join Date: Dec 2003 Location: Glendale Arizona Posts: 747	I thought the brake light ment the parking brake was on? __________________ "A true hotrodder wouldn't be content untill he had created a car so violent, so hairy, so totally sick that the very act of dropping the hammer would result in instant death. Anything less results in the need to go faster." - Tony DeFeo

07-04-2005, 02:01 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	if the master cylinder was really low, then you need to find where the fluid went. (there is a leak somewhere)

07-04-2005, 02:01 PM	#4
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	I would try bleeding the brakes, since you said thay they were very low recently. But I would also be on the look-out for "why"? That fluid had to go somewhere. Look at the back of the master cylinder where it meets the firewall/booster. If the cylinder is leaking there you will see it or at least bubbling paint. If it is non-power brakes it could leak down the inside of the firewall into the cab. You could also have a line leak where the rubber lines meet the steel. Back to the original answer, the light may be coming on because of the imbalance of pressure.........air in the line from the low reservior. The light can also come on because of the E-brake switch. Make sure that it is totally off.

07-04-2005, 04:32 PM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Most of these trucks didn't have a switch to turn on the brake light with the parking brake.

07-04-2005, 05:24 PM	#11
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	look around on the firewall inside the cab for any wetness on a non power brake truck the fluid can leak out of the master cylinder and into the truck and you will never see it. and if you have power brakes unbolt the master cylinder and look for wetness. the fluid went somewhere __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

07-04-2005, 05:55 PM	#12
4x4Poet Registered User Join Date: Nov 2004 Location: "Under Montana skies." Posts: 1,836	Look to see if you can unscrew the switch from the proportioning valve. Look in side and see if the rear system has shifted the hole that the switch lever rides in due to an imbalance. __________________ '71 GMC K20 Suburban, '71 GMC K10 Suburban, '72 Chevy C10 CST Suburban, '72 Chevy K20 clunker pickup.

07-04-2005, 08:13 PM	#13
A.P. Black 72 Chevy Join Date: May 2002 Location: Los Angeles, California Posts: 662	I have the some problem about the brake light not turning off. I replaced the master cylinder, rotors, and calipers. I also bleed the entire system. There gots to be a way to reset the prop valve? I tried the hard braking and that did not work either. My brakes work great.

07-04-2005, 08:30 PM	#14
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	To reset(center) valve, turn on switch, and bleed one end. No more than 1 pump should be needed. If that doesn't turn off light, go and bleed 1 pump from other end. It depends which end works, as to which way the valve is off center. Ususally light will go off within 1/2 stroke. If that doesn't work, then the valve is stuck or the MC is bad.

07-04-2005, 09:35 PM	#15
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,857	Thanks for all the replies. Will start checking all these things out. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

07-05-2005, 12:36 PM	#16
matthufham Registered User Join Date: Feb 2005 Location: Carl Junction, Missouri Posts: 2,061	in my sister's 90' 4runner, she had a tripped wire so the brake warning light came on. there was no mechanical problems so we never bothered to find the bad wire, and the problem fixed itself somehow.

07-05-2005, 12:45 PM	#17
jtminton II Timothy 4:2 Join Date: Mar 2005 Location: Fort Worth Posts: 361	I had the same problem with disappearing fluid. I'm pretty sure it was leaking back into the booster from the bad M/C. Changed the M/C and it fixed the problem. Also helped my braking. __________________ 72 C-20 2WD LWB Custom Camper Deluxe 350 4 Speed "Project Lazarus" MY TRUE PRIDE AND JOY "Dangit, Bobby, people will see that oil stain and think I'm a drunk."



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07-05-2005, 07:14 PM	#18
A.P. Black 72 Chevy Join Date: May 2002 Location: Los Angeles, California Posts: 662	Here is some info that might help with the brake warning light. http://www.classicperform.com/TechBo...t.htm#testprop

07-05-2005, 08:09 PM	#19
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,593	Bookmarked! Thank you thank you thank you! __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

07-05-2005, 10:57 PM	#20
1STtimePRo'71 Registered User Join Date: Feb 2005 Location: Lake Crystal, MN Posts: 656	Good Info A.P. Maybe this will help my light go bye, bye. __________________ -Cory 1967 2 Wheel Chevy

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