brakes stopped working, what can be wrong? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

SnS C10 · 08-21-2004, 12:55 PM

on my way home last night my 72 gmc with disc and drums brakes wouldnt stop anymore. the pedal started to go all the way to the floor and if i pumped the pedal it made no difference and still went to the floor with barely any resistance. So i let it sit last night and checked it this morning. i checked the fluid and it is fine. then i did a vacuum leak test. i turned the engine on and let it idle for a minute or 2. then i shut it off. waited another minute and pressed the brakes pedal about 5 or 6 times. each time was the same and the pedal went to the floor. this is the procedure my manual said to do. so i guess there is a vacuum leak in the system. the hose for the power brake booster is perfectly fine. what can i check to fix this, what do u guys think the problem is? thanks

69ride · 08-21-2004, 01:12 PM

could it be the master cylinder bypassing inside? if the vacuum is fine I would crack a bleeder and see if the wheel cylinders are getting fluid.

Tx Firefighter · 08-21-2004, 02:30 PM

Master cylinder leaking internally.

under 25 bucks at any parts store.

ckhd · 08-21-2004, 02:47 PM

pedal to the floor with little to no braking is typically the master cylinder. Typically, if you pump it fast, it will pump up a little and slow you down. Went through it twice...

First on my '68, manual brakes, It would slow it down, a little. I intalled a new MC, and now when I stomp on the brakes, I can almost make the passenger hit his head on the dash... remember MANUAL brakes!

I went through the same thing on my '99 Suburban. The wife tells me that the brakes aren't working very good, so I go test it. Scared the crap out of me! Pedal hit the floor and I wasn't slowing down! Changed the MC and they work great.

walker · 08-21-2004, 03:12 PM

Ditto, MC, $15.

ryan68 · 08-21-2004, 03:29 PM

Last time mine did that, both rear wheel cylinders were blown apart. Something to check, but most likely is the MC.

68w/sbc406 · 08-21-2004, 04:17 PM

i just had that same problem, so i changed my master. went for a test, couldnt stop coming out of my driveway. bleed the front brakes and they still went to the floor. so then i changed all fluid front to rear with a niffty bleeder that hooks to your air compressor and sucked evey thing out. went down the road and was getting a 4 tire lock up.

72C203503ONTHETREE · 08-21-2004, 04:31 PM

Ever lose a master cylinder with the suicide single cylinder single line versions the pre 67 cars had? LOL, I had a 66 Malibu that did that and I about wrecked on the highway. Had to pump the pedal as fast and as hard as I could to stop, the piston had corroded enough to let some fluid go around it and would produce almost zero fluid pressure.

08-21-2004, 12:55 PM	#1
SnS C10 Registered User Join Date: Jul 2004 Location: Lomita, Ca Posts: 1,225	brakes stopped working, what can be wrong? on my way home last night my 72 gmc with disc and drums brakes wouldnt stop anymore. the pedal started to go all the way to the floor and if i pumped the pedal it made no difference and still went to the floor with barely any resistance. So i let it sit last night and checked it this morning. i checked the fluid and it is fine. then i did a vacuum leak test. i turned the engine on and let it idle for a minute or 2. then i shut it off. waited another minute and pressed the brakes pedal about 5 or 6 times. each time was the same and the pedal went to the floor. this is the procedure my manual said to do. so i guess there is a vacuum leak in the system. the hose for the power brake booster is perfectly fine. what can i check to fix this, what do u guys think the problem is? thanks

08-21-2004, 01:12 PM	#2
69ride All Go, No Show Join Date: Jul 2003 Location: Creighton SK Posts: 286	could it be the master cylinder bypassing inside? if the vacuum is fine I would crack a bleeder and see if the wheel cylinders are getting fluid. __________________ 69 LWB Rebuilt 283, aluminum intake, edelbrock carb, Mild Melling Cam, HEI.

08-21-2004, 02:30 PM	#3
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Master cylinder leaking internally. under 25 bucks at any parts store. __________________ I'm on the Instagram- @Gearhead_Kevin

08-21-2004, 02:47 PM	#4
ckhd Registered User Join Date: Oct 2000 Location: St. Johns, Arizona Posts: 2,660	pedal to the floor with little to no braking is typically the master cylinder. Typically, if you pump it fast, it will pump up a little and slow you down. Went through it twice... First on my '68, manual brakes, It would slow it down, a little. I intalled a new MC, and now when I stomp on the brakes, I can almost make the passenger hit his head on the dash... remember MANUAL brakes! I went through the same thing on my '99 Suburban. The wife tells me that the brakes aren't working very good, so I go test it. Scared the crap out of me! Pedal hit the floor and I wasn't slowing down! Changed the MC and they work great. __________________ my 2¢ - t.i.o.l.i. Bowen 1968 K20 fleet 1969 K10 swb fleet 1972 K10 Suburban 1972 C10 lwb step 1992 K1500 'burb 1995 K2500 'burb 1997 C1500 'burb 1999 K1500 2000 K1500 'burb Why do I own so many Suburbans?

08-21-2004, 03:12 PM	#5
walker Registered User Join Date: Jul 2003 Location: north of Phx AZ about 30 miles Posts: 698	Ditto, MC, $15. __________________ Andy,Phx AZ '67 C-10 (Ahhh, done at last. Well there is that disk front end I want to put in and...) "23 C-Cab-sold '48 Ford 8N tractor(still working) '67 Scout(Now on the road) '70 MG B.-sold

08-21-2004, 03:29 PM	#6
ryan68 Certified Chevy Man Join Date: Jan 2000 Location: Tucson, Arizona, United States Posts: 2,053	Last time mine did that, both rear wheel cylinders were blown apart. Something to check, but most likely is the MC. __________________ 68 Chevy CST (327,TH400) 3/5 drop lots of fun stuff 71 Suburban 4x4 (350,TH350) 7" lift 37's, D44/14 bolt and other sorts of goodies, lockers front and rear, flexes 40", 895 RTI score Check out my web site!!! http://www.geocities.com/cst68chevy/

08-21-2004, 04:17 PM	#7
68w/sbc406 Got Light Emitting Diode? Join Date: Apr 2004 Location: Newberg, OR Posts: 2,485	i just had that same problem, so i changed my master. went for a test, couldnt stop coming out of my driveway. bleed the front brakes and they still went to the floor. so then i changed all fluid front to rear with a niffty bleeder that hooks to your air compressor and sucked evey thing out. went down the road and was getting a 4 tire lock up. __________________ 1968 1/2 ton 2wd lwb 6 lug disc and bags up front. Next c notch and rear bags '02 Chevy Silverado LT ext cab short bed 2WD 5/7 drop on 22's(the family car) 1993 Cherokee work ride/weekend wheeler

08-21-2004, 04:31 PM	#8
72C203503ONTHETREE Registered User Join Date: Apr 2004 Location: Grant, Alabama Posts: 504	Ever lose a master cylinder with the suicide single cylinder single line versions the pre 67 cars had? LOL, I had a 66 Malibu that did that and I about wrecked on the highway. Had to pump the pedal as fast and as hard as I could to stop, the piston had corroded enough to let some fluid go around it and would produce almost zero fluid pressure. __________________ 72 Chevy C20, SOLD (Dang it.) 09 Challanger RT six speed in all black. 74 Datsun 710 wagon, all 1.8 liters of screaming Datsun power. 73 C10 long bed, 350/350 combo, nice shape.



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