Brake Pedal SOMETIMES goes to the floor - The 1947 - Present Chevrolet & GMC Truck Message Board Network

kcackler · 01-07-2010, 07:49 PM

I've got a 76 C10 with a problem. The brakes work perfectly all of the time (They are brand new) and stop me in an instant. However, recently, if I'm sitting at a stop light and sort of let up on the brake to creep forward, when I go to press the brake again, I have no brakes and it goes to the floor. But then all I have to do is let up all the way on the pedal and push it and it's as solid as it always has been.

So what could my problem be? The most I know about brake systems is changing the pads and bleeding the lines.

cableguy0 · 01-07-2010, 07:56 PM

check all the rubber lines,the calipers,wheel cylinders and check for leaks. also unbolt the master cylinder and check for fluid seeping out behind it. after your done with that. bleeding the lines one more time might also help.

fixit-p · 01-07-2010, 08:06 PM

Sounds like a bad MC. if your at a stop and maintain the brake pedal (no more or less effort) will it creep forward?

ironroad9c1 · 01-07-2010, 08:30 PM

Master cyl is bad, that is the sure sign right there, if you sit there with your foot on the pedal, just apply light pressure and it will sink to the floor. Go ahead and replace it and then do a good bleed and flush of your lines.

kcackler · 01-07-2010, 09:54 PM

I'll go start it up tomorrow and see if it creeps forward when I maintain a steady pressure on the pedal.

So if the MC was bad, braking would work fine all of the time, except at a stop?

Also, how big of a job is the replacement and how long does it take?

cableguy0 · 01-07-2010, 09:57 PM

The symptoms your experiencing are one of the first signs of the master going bad. not the end all be all but just a sign. master cylinders going bad can do all sorts of different things. it will come to a point it wont work at all

msgross · 01-07-2010, 10:02 PM

I had a master cylinder work fine when I left the parking lot, then go to the floor at the next light...

cheap part, easy fix, just have to bench bleed the MC and then bleed all four wheels... Takes 1-2 hours and $30 but I would spray some PB blaster on your bleed valves right now and let them soak. Get a buddy to help you, plenty of info on the net...

ToughBowtieTruck · 01-07-2010, 10:37 PM

Look at the brake booster behind the master cylinder. 80% of the time it will be wet. What happens is the seal gets worn in the master cylinder...if you use the brakes normally the seal swells up and won't leak, but then if you push it real light or slow; or hold the brake pedal down, the seal deflates and leaks the pressure out.

Happens on a lot of older trucks.

kcackler · 01-07-2010, 11:11 PM

Quote:

Look at the brake booster behind the master cylinder. 80% of the time it will be wet.

That confirmed it. The booster is soaked.

I love this place

Thanks everyone.

**old Rusty C10** · 01-07-2010, 11:40 PM

just make sure you search and read thoroughly the part about bleeding the master when you install a new one or it wont work right either... masters are easy to do

01-07-2010, 07:49 PM	#1
kcackler Registered User Join Date: Feb 2009 Location: Russellville, AR Posts: 164	Brake Pedal SOMETIMES goes to the floor I've got a 76 C10 with a problem. The brakes work perfectly all of the time (They are brand new) and stop me in an instant. However, recently, if I'm sitting at a stop light and sort of let up on the brake to creep forward, when I go to press the brake again, I have no brakes and it goes to the floor. But then all I have to do is let up all the way on the pedal and push it and it's as solid as it always has been. So what could my problem be? The most I know about brake systems is changing the pads and bleeding the lines. __________________ Blue - 77 Chevy Scottsdale

01-07-2010, 07:56 PM	#2
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	Re: Brake Pedal SOMETIMES goes to the floor check all the rubber lines,the calipers,wheel cylinders and check for leaks. also unbolt the master cylinder and check for fluid seeping out behind it. after your done with that. bleeding the lines one more time might also help. __________________ 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.

01-07-2010, 08:30 PM	#4
ironroad9c1 Master Hater Join Date: Apr 2006 Location: Temple,Tx. Posts: 402	Re: Brake Pedal SOMETIMES goes to the floor Master cyl is bad, that is the sure sign right there, if you sit there with your foot on the pedal, just apply light pressure and it will sink to the floor. Go ahead and replace it and then do a good bleed and flush of your lines.

01-07-2010, 09:54 PM	#5
kcackler Registered User Join Date: Feb 2009 Location: Russellville, AR Posts: 164	Re: Brake Pedal SOMETIMES goes to the floor I'll go start it up tomorrow and see if it creeps forward when I maintain a steady pressure on the pedal. So if the MC was bad, braking would work fine all of the time, except at a stop? Also, how big of a job is the replacement and how long does it take? __________________ Blue - 77 Chevy Scottsdale

01-07-2010, 09:57 PM	#6
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	Re: Brake Pedal SOMETIMES goes to the floor The symptoms your experiencing are one of the first signs of the master going bad. not the end all be all but just a sign. master cylinders going bad can do all sorts of different things. it will come to a point it wont work at all __________________ 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.

01-07-2010, 10:02 PM	#7
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: Brake Pedal SOMETIMES goes to the floor I had a master cylinder work fine when I left the parking lot, then go to the floor at the next light... cheap part, easy fix, just have to bench bleed the MC and then bleed all four wheels... Takes 1-2 hours and $30 but I would spray some PB blaster on your bleed valves right now and let them soak. Get a buddy to help you, plenty of info on the net... __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer"

01-07-2010, 10:37 PM	#8
ToughBowtieTruck Registered User Join Date: Dec 2009 Location: MI Posts: 111	Re: Brake Pedal SOMETIMES goes to the floor Look at the brake booster behind the master cylinder. 80% of the time it will be wet. What happens is the seal gets worn in the master cylinder...if you use the brakes normally the seal swells up and won't leak, but then if you push it real light or slow; or hold the brake pedal down, the seal deflates and leaks the pressure out. Happens on a lot of older trucks. __________________ -Josh "Mr. Simpson, there are thousands of people like you with no discernible talent." Duff World Records Division "Yeah, they're called Congress!!" -Homer Simpson

01-07-2010, 11:40 PM	#10
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,310	Re: Brake Pedal SOMETIMES goes to the floor just make sure you search and read thoroughly the part about bleeding the master when you install a new one or it wont work right either... masters are easy to do __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

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