Brake pedal goes to floor - The 1947 - Present Chevrolet & GMC Truck Message Board Network

70 shorty · 10-16-2014, 05:21 PM

I have a 70 4 wheel manual drum truck, and the pedal goes to the floor. Upon investigation, the back of the master cylinder is empty, and the front is down a little, (although the front may have been what spilled when I took the cap off). My question is, does the back of the master cylinder feed the back brakes, or is it separated? I see the line from the back of the master goes into the distribution block, but does it stay separate from the front? I pulled both back drums and didn't see any obvious leaks on the wheel cylinders. Since the truck sits a lot though, could it be possible that if a wheel cylinder was leaking, the fluid could have dried up? If nothing else, I'll dump more fluid in the master, and see if I can see where it's leaking, but I figured I'd start here, and see if anyone had any tips.

Xeen · 10-16-2014, 05:38 PM

If one half of the reservoir is dry then there is definitely a leak somewhere.
The front half goes to the front and the back half goes to the back.
The leak could be from a loose fitting, a rusted line, a bad rear brake hose, or a bad drum brake cylinder.
Time to do some trouble shooting.

70 shorty · 10-16-2014, 05:42 PM

Thanks Brian. I wasn't sure whether something changed as it went through the distribution block. I'll fill the master and see what happens.

Xeen · 10-16-2014, 05:55 PM

Quote:

Originally Posted by 70 shorty

Thanks Brian. I wasn't sure whether something changed as it went through the distribution block. I'll fill the master and see what happens.

If you have never replaced the drum brake wheel cylinders then I would replace them just to replace them unless of course you get in there and they still look new.

luvbowties · 10-16-2014, 08:10 PM

Quote:

Originally Posted by Xeen

If you have never replaced the drum brake wheel cylinders then I would replace them just to replace them unless of course you get in there and they still look new.

I double this idea, esp. considering the mild expense of new ones. And, even if they look new, you may find leaking if you "peel" back the rubber boots & inspect behind them.
sam

frank69 · 10-17-2014, 02:51 AM

Check and make sure it's not leaking out back of mc into booster

70 shorty · 10-17-2014, 07:42 AM

No booster Frank, so that eliminates that problem. I will check to make sure its not leaking out of the m/c onto the firewall though. Thanks!

stomper · 11-11-2015, 04:59 PM

Did you ever determine the cause of this problem? I have the same situation.

57larry · 11-11-2015, 05:57 PM

maybe a good time to add disc brakes to the front, new rear wheel cyls, & a new master cyl combo. overhaul your whole brake system

Ken B · 11-11-2015, 06:29 PM

Pull the mat or carpet back on the upper drivers side. I bet the master cylinder is leaking.. That was probably the original posters problem also...

stomper · 11-11-2015, 09:05 PM

I'm considering that too but a new MC is so cheap. I did find a complete power disc conversion kit for $575.

10-16-2014, 05:21 PM	#1
70 shorty Where's my beer? Join Date: Oct 2004 Location: Glen Allen, VA Posts: 1,772	Brake pedal goes to floor I have a 70 4 wheel manual drum truck, and the pedal goes to the floor. Upon investigation, the back of the master cylinder is empty, and the front is down a little, (although the front may have been what spilled when I took the cap off). My question is, does the back of the master cylinder feed the back brakes, or is it separated? I see the line from the back of the master goes into the distribution block, but does it stay separate from the front? I pulled both back drums and didn't see any obvious leaks on the wheel cylinders. Since the truck sits a lot though, could it be possible that if a wheel cylinder was leaking, the fluid could have dried up? If nothing else, I'll dump more fluid in the master, and see if I can see where it's leaking, but I figured I'd start here, and see if anyone had any tips. __________________ 70 C10, shortstep, .30 over 250,Hurst shifted 3 spd parts hauler. Holley 390, Clifford Intake, Header, ported cylinder head, unknown bigger cam. 79 Corvette L82, 4 spd, black, red interior, headers, flowmasters, and unkown bigger cam. '03 Grand Cherokee Laredo, 4.0 4x4 daily driver. 165K miles, and runs great '08 Tahoe LTZ 4x4 155K

10-16-2014, 05:38 PM	#2
Xeen Registered User Join Date: Aug 2012 Location: Topeka Kansas Posts: 2,655	Re: Brake pedal goes to floor If one half of the reservoir is dry then there is definitely a leak somewhere. The front half goes to the front and the back half goes to the back. The leak could be from a loose fitting, a rusted line, a bad rear brake hose, or a bad drum brake cylinder. Time to do some trouble shooting. __________________ Please call me Brian. Check out My 1972 SWB Fleetside 5.3L Vortec Restomod Build Last edited by Xeen; 10-16-2014 at 05:46 PM.

10-16-2014, 05:42 PM	#3
70 shorty Where's my beer? Join Date: Oct 2004 Location: Glen Allen, VA Posts: 1,772	Re: Brake pedal goes to floor Thanks Brian. I wasn't sure whether something changed as it went through the distribution block. I'll fill the master and see what happens. __________________ 70 C10, shortstep, .30 over 250,Hurst shifted 3 spd parts hauler. Holley 390, Clifford Intake, Header, ported cylinder head, unknown bigger cam. 79 Corvette L82, 4 spd, black, red interior, headers, flowmasters, and unkown bigger cam. '03 Grand Cherokee Laredo, 4.0 4x4 daily driver. 165K miles, and runs great '08 Tahoe LTZ 4x4 155K

10-17-2014, 02:51 AM	#6
frank69 Registered User Join Date: Feb 2007 Location: Laughlin,Nv Posts: 141	Re: Brake pedal goes to floor Check and make sure it's not leaking out back of mc into booster

10-17-2014, 07:42 AM	#7
70 shorty Where's my beer? Join Date: Oct 2004 Location: Glen Allen, VA Posts: 1,772	Re: Brake pedal goes to floor No booster Frank, so that eliminates that problem. I will check to make sure its not leaking out of the m/c onto the firewall though. Thanks! __________________ 70 C10, shortstep, .30 over 250,Hurst shifted 3 spd parts hauler. Holley 390, Clifford Intake, Header, ported cylinder head, unknown bigger cam. 79 Corvette L82, 4 spd, black, red interior, headers, flowmasters, and unkown bigger cam. '03 Grand Cherokee Laredo, 4.0 4x4 daily driver. 165K miles, and runs great '08 Tahoe LTZ 4x4 155K

11-11-2015, 04:59 PM	#8
stomper Junior Member Join Date: Jul 2002 Location: Scottsdale, AZ Posts: 1,702	Re: Brake pedal goes to floor Did you ever determine the cause of this problem? I have the same situation. __________________ "I was patina when patina wasn't cool." 1973 Cheyenne SWB Sunset Gold / Frost White / Saddle

11-11-2015, 05:57 PM	#9
57larry Registered User Join Date: Nov 2007 Location: Indianapolis Posts: 1,161	Re: Brake pedal goes to floor maybe a good time to add disc brakes to the front, new rear wheel cyls, & a new master cyl combo. overhaul your whole brake system

11-11-2015, 06:29 PM	#10
Ken B Registered User Join Date: Sep 2015 Location: danbury, ct. Posts: 568	Re: Brake pedal goes to floor Pull the mat or carpet back on the upper drivers side. I bet the master cylinder is leaking.. That was probably the original posters problem also...

11-11-2015, 09:05 PM	#11
stomper Junior Member Join Date: Jul 2002 Location: Scottsdale, AZ Posts: 1,702	Re: Brake pedal goes to floor I'm considering that too but a new MC is so cheap. I did find a complete power disc conversion kit for $575. __________________ "I was patina when patina wasn't cool." 1973 Cheyenne SWB Sunset Gold / Frost White / Saddle

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