Brakes! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

smokekiki · 05-28-2003, 11:48 AM

Do my brakes need bled again,or could it be something else?I have a good firm pedal,the truck stops fine,but while sitting with my foot on the pedal,it slowly goes to the floor.The previous owner put on new wheel cylinders and master cylinder.I put on new rotors,calipers and hoses for inspection.The power booster has been replaced and will hold vacume overnight.This is the first I got the truck out this year.I flushed out all the old fluid.The fluid level does not go down.Thanks Mike

ckenwright · 05-28-2003, 12:13 PM

Sounds like you have an internal leak in your master cylinder.

Old Chevy · 05-28-2003, 12:28 PM

Yep, first place I would look would be the master cylinder!

tommie · 05-28-2003, 03:54 PM

same as above,
master cylinder

smokekiki · 05-28-2003, 04:17 PM

Anyone use rebuilt master cyl from autozone?they have them for 17.00 with a lifetime warrenty.At least that's what the counter guy said on the phone.79.00 new at pep boys

tommie · 05-28-2003, 04:35 PM

i've used the ones from auto zone before.

they work...
a new one would be better,
but i don't have the money for a new one either.

tommie

**nightmare** · 05-28-2003, 05:47 PM

try looking to see if you have any leaks in the lines anywhere, i had that problem.

jimfulco · 05-29-2003, 12:51 AM

I've used AutoZone rebuilt ones & they last maybe a couple of years. No more for me. This was before they had lifetime warranties though.

smokekiki · 05-29-2003, 03:16 PM

Put on a new master cyl. this morning.Took care of the problems.Thanks for the replies!

Mike Culpepper · 05-29-2003, 08:30 PM

Just curious.....
Where does the fluid that's leaking go?
Mine does the same thing but the pedal doesn't go to the floor. If I sit at a stop light for a while, I have to apply a bit more pressure, to prevent rolling foreward, though. Maybey my leak isn't as bad yet?
Mike

cableguy0 · 05-29-2003, 08:32 PM

mike your problem sounds like the booster isnt holding vacumm is the pedal getting hard to push as u sit the or is it sinking

**old Rusty C10** · 05-29-2003, 09:37 PM

i didnt read the whole thing but MASTER CYLINDER

Mike Culpepper · 05-29-2003, 11:27 PM

The pedal gets firm as I stop. If I put NO more pressure on the pedal, the truck starts to edge forward VERY slowly. I then put a little more pressure to stop the truck and it doesn't do it again. The truck stops very well when I need it to, (no sponginess or difficulty in stopping). I'll be honest, it hasn't been that big a deal that I've wanted to look into it yet, but when I saw this post it got me to thinking...................
Mike

smokekiki · 05-30-2003, 10:00 AM

On another post about brakes someone said to run the truck,shut it off,and wait 5 min. then pull the vacume line to the booster. you should hear the vacume release if not it is leaking.My master cyl had an internal leak.The pressure would bleed off.

ckenwright · 05-30-2003, 11:14 AM

Basically what happens when you have an internal leak in your Master Cylinder, is you have a worn o-ring on your piston so when you press on the brake pedal as pressure increases fluid slowly leaks past the o-ring or through groves in the cylinder and goes back to the resorvoir. Then when you release the pedal a vacuum is created in the system and fluid is sucked into the piston as the o-ring passes the pickup hole for the resorvoir. It is hard to explain it, but if you take one apart it is really simple. Everything is held together with a snapring.

05-28-2003, 11:48 AM	#1
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,473	Brakes! Do my brakes need bled again,or could it be something else?I have a good firm pedal,the truck stops fine,but while sitting with my foot on the pedal,it slowly goes to the floor.The previous owner put on new wheel cylinders and master cylinder.I put on new rotors,calipers and hoses for inspection.The power booster has been replaced and will hold vacume overnight.This is the first I got the truck out this year.I flushed out all the old fluid.The fluid level does not go down.Thanks Mike __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

05-28-2003, 12:28 PM	#3
Old Chevy Registered User Join Date: Jan 2000 Location: Tulsa, Oklahoma Posts: 498	Yep, first place I would look would be the master cylinder! __________________ Broken Arrow, OK. 1977 Corvette, ZZ4 Crate, new interior, new suspension, new driveline, you get the picture, (new project / daily driver)

05-28-2003, 04:17 PM	#5
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,473	Anyone use rebuilt master cyl from autozone?they have them for 17.00 with a lifetime warrenty.At least that's what the counter guy said on the phone.79.00 new at pep boys __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

05-29-2003, 03:16 PM	#9
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,473	Put on a new master cyl. this morning.Took care of the problems.Thanks for the replies! __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

05-29-2003, 08:30 PM	#10
Mike Culpepper Red Join Date: Feb 2003 Location: Llano... Texas Hill Country Posts: 448	Just curious..... Where does the fluid that's leaking go? Mine does the same thing but the pedal doesn't go to the floor. If I sit at a stop light for a while, I have to apply a bit more pressure, to prevent rolling foreward, though. Maybey my leak isn't as bad yet? Mike __________________ '72 Cheyenne LWB 350/350 "The sun don't shine on the same dog's ass all the time." - Catfish Hunter (commenting on why he was not able to pitch another perfect game).

05-28-2003, 12:13 PM	#2
ckenwright Registered User Join Date: May 2003 Location: Phoenix, AZ Posts: 104	Sounds like you have an internal leak in your master cylinder.

05-28-2003, 03:54 PM	#4
tommie 97' Tahoe 2dr/2wd Join Date: Jul 2002 Location: Huffman,TX Posts: 1,168	same as above, master cylinder

05-28-2003, 04:35 PM	#6
tommie 97' Tahoe 2dr/2wd Join Date: Jul 2002 Location: Huffman,TX Posts: 1,168	i've used the ones from auto zone before. they work... a new one would be better, but i don't have the money for a new one either. tommie

05-29-2003, 12:51 AM	#8
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	I've used AutoZone rebuilt ones & they last maybe a couple of years. No more for me. This was before they had lifetime warranties though.

05-29-2003, 08:32 PM	#11
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	mike your problem sounds like the booster isnt holding vacumm is the pedal getting hard to push as u sit the or is it sinking __________________ 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.

05-29-2003, 09:37 PM	#12
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,313	i didnt read the whole thing but MASTER CYLINDER __________________ 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!!

05-29-2003, 11:27 PM	#13
Mike Culpepper Red Join Date: Feb 2003 Location: Llano... Texas Hill Country Posts: 448	The pedal gets firm as I stop. If I put NO more pressure on the pedal, the truck starts to edge forward VERY slowly. I then put a little more pressure to stop the truck and it doesn't do it again. The truck stops very well when I need it to, (no sponginess or difficulty in stopping). I'll be honest, it hasn't been that big a deal that I've wanted to look into it yet, but when I saw this post it got me to thinking................... Mike __________________ '72 Cheyenne LWB 350/350 "The sun don't shine on the same dog's ass all the time." - Catfish Hunter (commenting on why he was not able to pitch another perfect game).

05-30-2003, 10:00 AM	#14
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,473	On another post about brakes someone said to run the truck,shut it off,and wait 5 min. then pull the vacume line to the booster. you should hear the vacume release if not it is leaking.My master cyl had an internal leak.The pressure would bleed off. __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

05-30-2003, 11:14 AM	#15
ckenwright Registered User Join Date: May 2003 Location: Phoenix, AZ Posts: 104	Basically what happens when you have an internal leak in your Master Cylinder, is you have a worn o-ring on your piston so when you press on the brake pedal as pressure increases fluid slowly leaks past the o-ring or through groves in the cylinder and goes back to the resorvoir. Then when you release the pedal a vacuum is created in the system and fluid is sucked into the piston as the o-ring passes the pickup hole for the resorvoir. It is hard to explain it, but if you take one apart it is really simple. Everything is held together with a snapring.



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