Brake Light (in dash) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

69halfton · 05-13-2009, 09:50 PM

so ive noticed the brakes on my truck starting to feel funny. if I stop at a stop light, i can firmly push the pedal, and have the pedal slowly just go to the floor. also with my foot on the brake at a light, the pressure will slowly bleed down, and the truck will start to creep forwars, and i have to apply more pedal pressure to hold the truck. so i just figured that it was time for a new master cylinder (it has started to leak a little since the problem developed)

today, the brake warning light on the dash came on, first time ive ever seen. its only on when i have alot of pedal pressure on during braking, and i can make it flicker with my foot at a stoplight.

my question is... a) confirm this sounds like a master cylinder issue?
b) what is the brake indicatior light measuring for? or what makes the light come on? (i.e high/low pressure in the resivoir or..?) ..just for my own curiosity

**LockDoc** · 05-13-2009, 10:11 PM

-
The light means there is unequal pressure in your brake system, front to back. I would check for a leaking brake line or wheel cylinder.... I would not drive it until you find the problem and correct it...

LockDoc

Putter · 05-13-2009, 10:14 PM

Not arguing, but I thought it came on when the fluid level dropped below a certain level.
If you are pushing hard enough on the pedal to use all the fluid (you did mention that it is LEAKING).....then that may cause it.

I only say this because my light has lit once ever...and the MC was dry as a bone.

sjarrett71 · 05-13-2009, 10:28 PM

If you have leaking I would definately replace the master cylinder. If the pedal slowly goes to the floor I would replace the booster too.

69halfton · 05-13-2009, 10:45 PM

i checked all the wheel cylinders and lines, and i cant find any wetness except the bottom on the MC. it went nearly dry on me once, and the light never came on, i filled it up a couple weeks ago, and it hasn't really used anymore, but it does still appear to be leaking

when i say pedal goes to the floor, i mean i have to push it pretty hard, and it feels like the fliud it getting around the piston and back to the MC, bleeding pressure down.

i think the booster is fine, it isn't leaking/hissing at me and holds vacuum...

Richard8971 · 05-13-2009, 11:04 PM

My truck is doing the same thing. Fluid level is full and has been. I figured it was time to have them adjusted.

D

*highperf4x4* · 05-13-2009, 11:18 PM

It's a master cylinder issue. When your brake pedal bleeds off while you're stopped it's fluid exiting somewhere. If it was at the wheels it would be all over the inside of the rim and tire. Your proportioning valve beneath the master cylinder is what's setting your light off. When your pedal moves far enough it fails to throw enough fluid to the rears and the pressure becomes unequalized.

If you're going to drive it without replacing the master cylinder keep a very close eye on your fluid level.

When you put the new master cylinder on be sure you bench bleed it before you hook it up to the brake lines. If the inner shaft moves more than 1" or so before the air has been evacuated from the shaft chamber it will damage the seals.

Longhorn321 · 05-13-2009, 11:21 PM

The M/C could have a leak internally causing your pedal to slowly go to the floor. This can happen and there may not be a visible sign outside....its just leaking by the seals on the piston, not the seal to the outside. If you hit 'em hard do you have a good firm pedal?

mixermike · 05-14-2009, 12:00 AM

Quote:

Originally Posted by Longhorn321

The M/C could have a leak internally causing your pedal to slowly go to the floor. This can happen and there may not be a visible sign outside....its just leaking by the seals on the piston, not the seal to the outside. If you hit 'em hard do you have a good firm pedal?

*highperf4x4* · 05-14-2009, 12:13 AM

Quote:

Originally Posted by Longhorn321

The M/C could have a leak internally causing your pedal to slowly go to the floor. This can happen and there may not be a visible sign outside....its just leaking by the seals on the piston, not the seal to the outside. If you hit 'em hard do you have a good firm pedal?

Right and he said he can actually see brake fluid leaking from the back of the master cylinder so it's a sure thing.

*highperf4x4* · 05-14-2009, 12:20 AM

Quote:

Originally Posted by Longhorn321

The M/C could have a leak internally causing your pedal to slowly go to the floor. This can happen and there may not be a visible sign outside....its just leaking by the seals on the piston, not the seal to the outside. If you hit 'em hard do you have a good firm pedal?

Wait, are you referring to Richard8971 or the original poster? In Richards case you could be right. It's a good possibility. My comments were directed at the original poster.

*highperf4x4* · 05-13-2009, 11:23 PM

If your booster is failing, the pedal will become much harder to push.

**CMACDONALD1** · 05-14-2009, 12:46 AM

I'am having these same symptoms with one of my trucks, if i hit the brakes real hard i have brakes but if i'am stoped at a light with minimal amount of pressure applied on the brake it will go to the floor and start to creep ahead but if i let off and hit it again i have brakes. I think it is the master cylinder myself but i guess i will soon find out as i just got another master to put in it. hopefuly within the next few days i can find time to get it installed and let you know.

*highperf4x4* · 05-14-2009, 01:01 AM

Quote:

Originally Posted by CMACDONALD1

I'am having these same symptoms with one of my trucks, if i hit the brakes real hard i have brakes but if i'am stoped at a light with minimal amount of pressure applied on the brake it will go to the floor and start to creep ahead but if i let off and hit it again i have brakes. I think it is the master cylinder myself but i guess i will soon find out as i just got another master to put in it. hopefuly within the next few days i can find time to get it installed and let you know.

Make sure you bench bleed it first!

Longhorn321 · 05-14-2009, 08:26 AM

Quote:

Originally Posted by highperf4x4

Wait, are you referring to Richard8971 or the original poster? In Richards case you could be right. It's a good possibility. My comments were directed at the original poster.

Either one. The OP said the M/C was a little wet but it had not gone dry recently.

Quote:

Originally Posted by CMACDONALD1

I'am having these same symptoms with one of my trucks, if i hit the brakes real hard i have brakes but if i'am stoped at a light with minimal amount of pressure applied on the brake it will go to the floor and start to creep ahead but if i let off and hit it again i have brakes. I think it is the master cylinder myself but i guess i will soon find out as i just got another master to put in it. hopefuly within the next few days i can find time to get it installed and let you know.

I would bet from your description that you will fix it with the M/C.

**bowtie72** · 05-14-2009, 09:33 AM

Normally you can pump the pedal with engine off or on. The pedal should hold firm. If not the master cylinder is likely bypassing internally. Cure replace master cylinder. Light comes on due to perportioning valve. When the valve senses a difference in pressure from front to back the valves moves and turnes the light on. This is cured by bleeding the brakes at the valve. But if the m/c is leaking internally it will cause the valve to move.

Hopefully I explained this so you can understand it. Good luck

**CMACDONALD1** · 05-14-2009, 11:57 AM

hey 69halfton I just replaced my master cylider this morning and problem went away hope this helps as my problem sounded very similar to yours. I love it when things work out!!

69halfton · 05-14-2009, 03:08 PM

pretty much what i figured. from all your responses im sure its the MC now. if i hit the pedal hard i have plenty of prssure, meaning it is by passing internally and cant escape fast enough...therefore i have plenty of brake pedal. im going to keep on trucking until the MC comes in and then make the swap. thanks for the help everyone...

*highperf4x4* · 05-14-2009, 05:37 PM

Quote:

Originally Posted by 69halfton

pretty much what i figured. from all your responses im sure its the MC now. if i hit the pedal hard i have plenty of prssure, meaning it is by passing internally and cant escape fast enough...therefore i have plenty of brake pedal. im going to keep on trucking until the MC comes in and then make the swap. thanks for the help everyone...

Don't thank me till you get the bill...........

I got that from Joe231!!

Richard8971 · 05-14-2009, 09:15 PM

I have a power brake booster from a newer S-10 pickup. No leakage that I can see... Fluid level is still good. They feel squishy and will lock the wheels if I need to stop quickly. It's getting scary to drive!

I just replaced the back cylinders and bled the system recently. The fluid level is the same now as it was then. Full.

D

Longhorn321 · 05-14-2009, 10:54 PM

Quote:

Originally Posted by Richard8971

I have a power brake booster from a newer S-10 pickup. No leakage that I can see... Fluid level is still good. They feel squishy and will lock the wheels if I need to stop quickly. It's getting scary to drive!

I just replaced the back cylinders and bled the system recently. The fluid level is the same now as it was then. Full.

D

Sounds like you need a M/C too. If there is no fluid leaking out, then it must be leaking internally. When you need to stop quickly, you stab the brakes and the seals flare out, you make pressure and either the front or the back lock. If you ease on the brakes on the other hand....squishy because the seal is not flaring out, it's letting fluid by.

tim21391 · 05-14-2009, 11:40 PM

mine came on in my 72 and so i took it to sears.. and they hooked it up and found out that my rear brakes needed adjusted... since they told me it would take half hour and it took them about 8 hrs i walked away with paying only fifteen bucks so i cant help you on the price it costs to hook it up to a scanner..

*highperf4x4* · 05-15-2009, 12:43 AM

What did they scan Tim? Your 72 doesn't have a computer, maybe they were pulling your leg.

*MonteSS454* · 05-15-2009, 01:25 AM

Quote:

Originally Posted by highperf4x4

What did they scan Tim? Your 72 doesn't have a computer, maybe they were pulling your leg.

My thoughts also.

Longhorn321 · 05-15-2009, 08:48 AM

Quote:

Originally Posted by highperf4x4

What did they scan Tim? Your 72 doesn't have a computer, maybe they were pulling your leg.

Quote:

Originally Posted by MonteSS454

My thoughts also.

Me too. I was gonna post last night but I was at a loss for words.

05-13-2009, 09:50 PM	#1
69halfton Registered User Join Date: Apr 2007 Location: King City, Ontario, Canada Posts: 974	Brake Light (in dash) so ive noticed the brakes on my truck starting to feel funny. if I stop at a stop light, i can firmly push the pedal, and have the pedal slowly just go to the floor. also with my foot on the brake at a light, the pressure will slowly bleed down, and the truck will start to creep forwars, and i have to apply more pedal pressure to hold the truck. so i just figured that it was time for a new master cylinder (it has started to leak a little since the problem developed) today, the brake warning light on the dash came on, first time ive ever seen. its only on when i have alot of pedal pressure on during braking, and i can make it flicker with my foot at a stoplight. my question is... a) confirm this sounds like a master cylinder issue? b) what is the brake indicatior light measuring for? or what makes the light come on? (i.e high/low pressure in the resivoir or..?) ..just for my own curiosity __________________ - Jason If you can turn, Youre not going fast enough. Favorite caption: first car to 200 mph in the 1/4 mile, no parachute, drum brakes all the way around.. ..back when men were men.

05-13-2009, 10:11 PM	#2
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,803	Re: Brake Light (in dash) - The light means there is unequal pressure in your brake system, front to back. I would check for a leaking brake line or wheel cylinder.... I would not drive it until you find the problem and correct it... LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - Last edited by LockDoc; 05-13-2009 at 10:12 PM.

05-13-2009, 10:14 PM	#3
Putter More Cowbell.... Join Date: Mar 2004 Location: Puckett, MS Posts: 3,569	Re: Brake Light (in dash) Not arguing, but I thought it came on when the fluid level dropped below a certain level. If you are pushing hard enough on the pedal to use all the fluid (you did mention that it is LEAKING).....then that may cause it. I only say this because my light has lit once ever...and the MC was dry as a bone. __________________ *There once was a member from Puckett.....Who ( fill in the blank blank blank* ) bucket** Last edited by Putter; 05-13-2009 at 10:14 PM.

05-13-2009, 10:28 PM	#4
sjarrett71 Registered User Join Date: Dec 2006 Location: Rolla, MO Posts: 2,463	Re: Brake Light (in dash) If you have leaking I would definately replace the master cylinder. If the pedal slowly goes to the floor I would replace the booster too. __________________ -Scott-

05-13-2009, 10:45 PM	#5
69halfton Registered User Join Date: Apr 2007 Location: King City, Ontario, Canada Posts: 974	Re: Brake Light (in dash) i checked all the wheel cylinders and lines, and i cant find any wetness except the bottom on the MC. it went nearly dry on me once, and the light never came on, i filled it up a couple weeks ago, and it hasn't really used anymore, but it does still appear to be leaking when i say pedal goes to the floor, i mean i have to push it pretty hard, and it feels like the fliud it getting around the piston and back to the MC, bleeding pressure down. i think the booster is fine, it isn't leaking/hissing at me and holds vacuum... __________________ - Jason If you can turn, Youre not going fast enough. Favorite caption: first car to 200 mph in the 1/4 mile, no parachute, drum brakes all the way around.. ..back when men were men.

05-13-2009, 11:04 PM	#6
Richard8971 Still livin the "dream" in '54 Join Date: Nov 2006 Location: Tucson, AZ Posts: 2,656	Re: Brake Light (in dash) My truck is doing the same thing. Fluid level is full and has been. I figured it was time to have them adjusted. D __________________ Current build. 1954 Chevrolet 3800 "Ella" SOLD! My '67 stepper "Tangerine Dream" "Anything worth doing is worth doing right" James Dean “When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.” Sherlock Holmes "There is no spoon." Neo

05-13-2009, 11:18 PM	#7
highperf4x4 Account Suspended Join Date: Apr 2009 Location: Oklahoma City Posts: 4,709	Re: Brake Light (in dash) It's a master cylinder issue. When your brake pedal bleeds off while you're stopped it's fluid exiting somewhere. If it was at the wheels it would be all over the inside of the rim and tire. Your proportioning valve beneath the master cylinder is what's setting your light off. When your pedal moves far enough it fails to throw enough fluid to the rears and the pressure becomes unequalized. If you're going to drive it without replacing the master cylinder keep a very close eye on your fluid level. When you put the new master cylinder on be sure you bench bleed it before you hook it up to the brake lines. If the inner shaft moves more than 1" or so before the air has been evacuated from the shaft chamber it will damage the seals.

05-13-2009, 11:21 PM	#8
Longhorn321 Size Matters Join Date: Aug 2007 Location: Lyman, SC Posts: 9,189	Re: Brake Light (in dash) The M/C could have a leak internally causing your pedal to slowly go to the floor. This can happen and there may not be a visible sign outside....its just leaking by the seals on the piston, not the seal to the outside. If you hit 'em hard do you have a good firm pedal? __________________ "Reading the owners manual is only for quitters." Jason Harper, Bloomberg News. ...WOOOO HOOOO!!!! Last edited by Longhorn321; 05-13-2009 at 11:23 PM.

05-13-2009, 11:23 PM	#12
highperf4x4 Account Suspended Join Date: Apr 2009 Location: Oklahoma City Posts: 4,709	Re: Brake Light (in dash) If your booster is failing, the pedal will become much harder to push.

05-14-2009, 12:46 AM	#13
CMACDONALD1 Senior Member Join Date: Jun 2007 Location: Red Deer Ab Canada Posts: 756	Re: Brake Light (in dash) I'am having these same symptoms with one of my trucks, if i hit the brakes real hard i have brakes but if i'am stoped at a light with minimal amount of pressure applied on the brake it will go to the floor and start to creep ahead but if i let off and hit it again i have brakes. I think it is the master cylinder myself but i guess i will soon find out as i just got another master to put in it. hopefuly within the next few days i can find time to get it installed and let you know. __________________ 1966 427 biscayne with a 5 spd tremec on old school torque thrusts. 1972 Cheyenne Short Bed 1958 Apache short fleet 1980 Chevy short bed http://67-72chevytrucks.com/vboard/s...d.php?t=761005 1959 "Henry" http://67-72chevytrucks.com/vboard/s...d.php?t=670461 1966 Biscayne http://67-72chevytrucks.com/vboard/s...d.php?t=444419 1972 Suburban http://67-72chevytrucks.com/vboard/s...d.php?t=478828

05-14-2009, 09:33 AM	#16
bowtie72 Registered User Join Date: Mar 2007 Location: Colorado Posts: 363	Re: Brake Light (in dash) Normally you can pump the pedal with engine off or on. The pedal should hold firm. If not the master cylinder is likely bypassing internally. Cure replace master cylinder. Light comes on due to perportioning valve. When the valve senses a difference in pressure from front to back the valves moves and turnes the light on. This is cured by bleeding the brakes at the valve. But if the m/c is leaking internally it will cause the valve to move. Hopefully I explained this so you can understand it. Good luck __________________ 1968 SWB "Little White Truck" 1972 LWB LS 4l80 "Plain Jane!!"

05-14-2009, 11:57 AM	#17
CMACDONALD1 Senior Member Join Date: Jun 2007 Location: Red Deer Ab Canada Posts: 756	Re: Brake Light (in dash) hey 69halfton I just replaced my master cylider this morning and problem went away hope this helps as my problem sounded very similar to yours. I love it when things work out!! __________________ 1966 427 biscayne with a 5 spd tremec on old school torque thrusts. 1972 Cheyenne Short Bed 1958 Apache short fleet 1980 Chevy short bed http://67-72chevytrucks.com/vboard/s...d.php?t=761005 1959 "Henry" http://67-72chevytrucks.com/vboard/s...d.php?t=670461 1966 Biscayne http://67-72chevytrucks.com/vboard/s...d.php?t=444419 1972 Suburban http://67-72chevytrucks.com/vboard/s...d.php?t=478828

05-14-2009, 03:08 PM	#18
69halfton Registered User Join Date: Apr 2007 Location: King City, Ontario, Canada Posts: 974	Re: Brake Light (in dash) pretty much what i figured. from all your responses im sure its the MC now. if i hit the pedal hard i have plenty of prssure, meaning it is by passing internally and cant escape fast enough...therefore i have plenty of brake pedal. im going to keep on trucking until the MC comes in and then make the swap. thanks for the help everyone... __________________ - Jason If you can turn, Youre not going fast enough. Favorite caption: first car to 200 mph in the 1/4 mile, no parachute, drum brakes all the way around.. ..back when men were men.

05-14-2009, 09:15 PM	#20
Richard8971 Still livin the "dream" in '54 Join Date: Nov 2006 Location: Tucson, AZ Posts: 2,656	Re: Brake Light (in dash) I have a power brake booster from a newer S-10 pickup. No leakage that I can see... Fluid level is still good. They feel squishy and will lock the wheels if I need to stop quickly. It's getting scary to drive! I just replaced the back cylinders and bled the system recently. The fluid level is the same now as it was then. Full. D __________________ Current build. 1954 Chevrolet 3800 "Ella" SOLD! My '67 stepper "Tangerine Dream" "Anything worth doing is worth doing right" James Dean “When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.” Sherlock Holmes "There is no spoon." Neo Last edited by Richard8971; 05-14-2009 at 09:19 PM.

05-14-2009, 11:40 PM	#22
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: Brake Light (in dash) mine came on in my 72 and so i took it to sears.. and they hooked it up and found out that my rear brakes needed adjusted... since they told me it would take half hour and it took them about 8 hrs i walked away with paying only fifteen bucks so i cant help you on the price it costs to hook it up to a scanner.. __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796



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05-15-2009, 12:43 AM	#23
highperf4x4 Account Suspended Join Date: Apr 2009 Location: Oklahoma City Posts: 4,709	Re: Brake Light (in dash) What did they scan Tim? Your 72 doesn't have a computer, maybe they were pulling your leg. Last edited by highperf4x4; 05-15-2009 at 12:44 AM.

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