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#1 |
Barrito Loco Diablo
Join Date: May 2008
Location: Cherry Valley, Illinois
Posts: 636
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brake question (pedal to the floor)
I'm pulling my 72' GMC C/2500 into the gas station when my brake pedal goes to the floor and my brake light pops on. I swerved to miss the parked car at the other side of the pump and wiped out a few cones laying around before i was able to coax the 3/4 ton beast to a stop. I looked under at all the wheels and around the lines and saw nothing. I popped the hood to check the fluid level and there was a bunch of brake fluid that spewed from under the master cap. The levels were still full. I dried off the master top and put it back on. Still had no pressure. I have a front disc rear drum truck. Does this sound like a bad proportioning valve? I replaced my right rear wheel cylinder a few months ago but haven't checked the left, but haven't seen any fluid around the drum.
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#2 |
sharp as a marble
![]() Join Date: Jan 2007
Location: atlantic beach,florida
Posts: 1,082
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Re: brake question (pedal to the floor)
The brakes had been working fine until then? If the pedal went all the way to the floor, and you see no leak my guess would be the master cylinder?????
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#3 |
Barrito Loco Diablo
Join Date: May 2008
Location: Cherry Valley, Illinois
Posts: 636
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Re: brake question (pedal to the floor)
That was my first thought after seeing all the fluid coming out of the top of the master. I've never run into this problem before though. Although, it's only like 15 bucks for a master. Shouldn't i be losing fluid though? i drove the truck around town earlier today and after a few stops, i lost the brakes again and the light came back on. But yeah, before this happened the other day, the brakes were working fine.
Last edited by exmonkeypunk; 10-25-2009 at 03:10 PM. |
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#4 | |
Registered User
Join Date: Aug 2005
Location: Pasadena,Tx /Pto Pta DR
Posts: 5,415
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Re: brake question (pedal to the floor)
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#5 |
Nothing to see here.....
![]() Join Date: Jun 2007
Location: Shawnee, KS
Posts: 4,625
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Re: brake question (pedal to the floor)
hummm. wonder if one of the rear wheel cylinders blew a seal? however you said that you checked that.
I'm with everyone else, sounds like a mc.
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Doug ![]() ![]() The democracy will cease to exist when you take away from those who are willing to work and give to those who would not. Thomas Jefferson Last edited by tcb-1; 10-25-2009 at 03:25 PM. |
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#6 |
Registered User
![]() Join Date: Nov 2007
Location: Turlock California 95380
Posts: 2,075
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Re: brake question (pedal to the floor)
I would check the other wheel cylinder as well. I had leaking wheel cylinders in my C20 but they were just soaking the brake linings so no brake fluid loss was evident. I however was losing some fluid in the rear chamber of the m/c, and the brake light would come on. When you replaced the wheel cylinder, did you bleed your lines afterwards ? I agree with mbgmike, try that out.
I think if your proportioning valve was bad, your rear brakes would lock up during your hard braking.
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72 C20 Longbed 05 1500 Z71 |
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#7 |
Son of a gun
Join Date: Jan 2007
Location: Hot Springs, Arkansas
Posts: 1,636
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Re: brake question (pedal to the floor)
bad master cylinder.
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Bill BEATERS ARE NEATER |
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#8 |
Barrito Loco Diablo
Join Date: May 2008
Location: Cherry Valley, Illinois
Posts: 636
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Re: brake question (pedal to the floor)
I'm glad so many agree with the master cylinder probably being the cause of this issue. I've never replaced one before, but by looking at it, as long as all the old lines come off smooth, then it looks like a piece of cake. What bleeding procedure do i need to run through after replacing the master? There's a bleeder on the proportioning valve isn't there? Should i flush all the lines when i replace the master?
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#9 | |
Barrito Loco Diablo
Join Date: May 2008
Location: Cherry Valley, Illinois
Posts: 636
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Re: brake question (pedal to the floor)
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#10 | |
Registered User
Join Date: Aug 2005
Location: Pasadena,Tx /Pto Pta DR
Posts: 5,415
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Re: brake question (pedal to the floor)
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#11 |
Barrito Loco Diablo
Join Date: May 2008
Location: Cherry Valley, Illinois
Posts: 636
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Re: brake question (pedal to the floor)
Yeah, the fluid is dirty looking, probably rusty. I know the longer the fluid is in the system, the higher acidic it gets. I'm sure i'll end up replacing a few more lines before this is done.
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#12 |
Registered User
![]() Join Date: Mar 2003
Location: Asheville, N.C
Posts: 952
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Check on the back side of the MC to see if the MC leaked into the booster.It might have destroyed the booster .Check all 4 wheels to see if there is any leaks (with wheels off). Bench bleed new MC ,put it on the truck ,bleed all 4 wheels, You should be good to go.
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#13 |
Barrito Loco Diablo
Join Date: May 2008
Location: Cherry Valley, Illinois
Posts: 636
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Re: brake question (pedal to the floor)
Okay. I've been pretty busy lately. Lost my job and all that. But i finally got around to replacing my master cylinder. I now have pedal pressure, but am hearing a loud hissing whenever the truck is running. I can get it to stop by pulling the vacuum line out of the booster and plugging it with my thumb. Does this sound like my booster is junk? The truck has great pedal pressure but stops kind of lame. I won't be able to buy a booster until next year sometime, so if there's a way i might be able to rebuild it or whatever. let me know.
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#14 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: brake question (pedal to the floor)
Your booster is junk
Did you have to fight the pushrod in there at all? I've done that one myself on a friend's truck. you can remove the booster and bolt the master cylinder directly to the firewall. You'll need a new pedal to master cylinder pushrod. |
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#15 |
Barrito Loco Diablo
Join Date: May 2008
Location: Cherry Valley, Illinois
Posts: 636
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Re: brake question (pedal to the floor)
where can i find a new pedal to master cylinder pushrod at? didn't know i could do that. do i just block off the hose then? The new master bolted on with no issues.
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#16 |
Barrito Loco Diablo
Join Date: May 2008
Location: Cherry Valley, Illinois
Posts: 636
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Re: brake question (pedal to the floor)
Is this pedal to master pushrod something i need to make? i haven't found anything so far online.
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#17 |
Registered User
Join Date: Mar 2007
Location: San Pedro River, SE Arizona
Posts: 734
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Re: brake question (pedal to the floor)
Sometimes getting the correct length pushrod can be a pain, and I have found the length to be critical to correct operation. You probably could make one with rounded ends just fine, but what exact length.? Without a model to work from it could be tough. A good brake shop (find an older guy) should be able to advise easliy - and maybe reach into a box of used ones and hand you the correct one. I save every one I find.
Actually, IMO you may not be ahead by removing the booster and bolting the MC directly to the firewall. In my slipping memory, seems like braking action through a non-functioning booster is about the same as non-power brakes. Maybe not? If so, save yourself the pushrod problem and drive as is (with caution) until you get a working booster. There is an outfit in the nearest big city here that rebuilds them in an hour or two for about $100. And, they appear on this site every so often in good used condition for much less Make sure you get the correct one for a 3/4 ton - different from the 1/2 ton and better action - and the booster for the 1 ton is different yet (even better IMO) and might fit your 3/4. The advice from Daves72 and others here is very good. Best wishes, CCCC
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CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp |
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#18 | |
Barrito Loco Diablo
Join Date: May 2008
Location: Cherry Valley, Illinois
Posts: 636
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Re: brake question (pedal to the floor)
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#19 | |
Registered User
Join Date: Aug 2005
Location: Pasadena,Tx /Pto Pta DR
Posts: 5,415
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Re: brake question (pedal to the floor)
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