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#1 |
Not a bad nut after all..
Join Date: Dec 2000
Location: ND
Posts: 1,756
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Brake Light On, Pedal Feel not Right, Front Brakes not Bleeding Anymore
When I bought my '72 Chevy 4x4 the brake pedal went to the floor and both the rear reservoir on the master cylinder and the rear wheel cylinders leaked. I replacing those and the rear hard lines from the rubber Y to the wheel cylinders (they were rusty and I damaged them disconnecting them front the wheel cylinders). After bench bleeding the master cylinder and vacuum bleeding the lines the brake pedal felt okay so I took it out on my gravel road and sneaked out on the highway. Brakes still didn't feel 100% so I went home and looked things over closer. There were some burned out lights in the cluster (one being the brake light) so I replaced them and now the brake light is on.
I vacuum bled some more and couldn't get the light to go out, so I had my wife help while I opened and closed the bleeders. The rear brakes seam okay and push out lots of fluid. The front brakes don't push out much fluid and the pedal has gone soft again. Now with the vacuum pump I can't get any fluid out the driver's front and very little out the passenger's front. I pulled out the front bleeder screws and verified they aren't plugged. I don't have enough courage to drive it until I get the pedal feel back. What should I check next?
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'05 Chevy 2500HD 4x4 '72 GMC LWB 4x2 driver '72 Chevy LWB 4x4 plow truck '71 Blazer 4x4 driver '70 GMC LWB trailer |
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#2 |
Registered User
Join Date: Aug 2010
Location: Harrison Arkansas
Posts: 164
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Re: Brake Light On, Pedal Feel not Right, Front Brakes not Bleeding Anymore
I'd change the rubber flex lines. I've encountered several over the last 10 years that have collapsed internally. When that happens little or no pressure makes it to the calipers/wheel cylinders.
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#3 |
Registered User
Join Date: Feb 2006
Location: Smyrna, Ga
Posts: 1,647
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Re: Brake Light On, Pedal Feel not Right, Front Brakes not Bleeding Anymore
Your proportioning valve has tripped. Its a safety feature. when you loose either the front or rear brakes, the valve will trip to stop brake fluid from flowing to the side that is experienceing lower pressure.
Some of them you can reset and some wont. I have heard of a special tool you can buy or make. I have read of people hitting thier brake pedal with a hammer. It may require a new proportioning valve. |
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#4 |
Registered User
Join Date: Jun 2006
Location: Indiana
Posts: 4,859
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Re: Brake Light On, Pedal Feel not Right, Front Brakes not Bleeding Anymore
If the proportioning valve does not reset, it is broken. Pretty rare event though.
Go to http://www.mpbrakes.com/. They have a tech suport page that details the reset proceedure. No extra tools required, only the line wrench you are using to loosen/tight the tube nuts. Oh, and your foot on the pedal. Basicly, you open the oposite line a bit and stomp the pedal. The pin will move. The centering valve is made to shut off the flow of fuid in the case of major failure thereby stopping all the fluid from draining.This is to retain the braking power of the "good" side. While you are at MPbrakes, you might want to read the rest of the tech sheets. Loads of information about brake systems. Stuff like when you need residual valves and when you do not. How a vacuum booster works and how to tell if it is broken.
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'70 GMC C1500 LWB Power disc brakes. WooHoo! Posi 6 Lug Dana 60 |
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#5 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,591
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Re: Brake Light On, Pedal Feel not Right, Front Brakes not Bleeding Anymore
Assuming it's the prop. valve, they can sometimes be re-centered by pushing the brake pedal very hard several times.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#6 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: Brake Light On, Pedal Feel not Right, Front Brakes not Bleeding Anymore
reading the GM factory service manual allows you to learn how to bleed the brakes properly on these trucks
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71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY |
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#7 | |
Registered User
Join Date: Jun 2010
Location: San Diego Co.
Posts: 1,160
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Re: Brake Light On, Pedal Feel not Right, Front Brakes not Bleeding Anymore
Quote:
This is how I got mine to recenter after a complete brake system overhaul. I did it with the help of the booster....started the truck with the booster hooked up, and pressed hard on the pedal...light went out. Bleeding procedure calls for clamping the pin of the combination valve open when bleeding the brakes. |
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#8 |
Not a bad nut after all..
Join Date: Dec 2000
Location: ND
Posts: 1,756
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Re: Brake Light On, Pedal Feel not Right, Front Brakes not Bleeding Anymore
I ordered new rubber flex lines for the front today.
__________________
'05 Chevy 2500HD 4x4 '72 GMC LWB 4x2 driver '72 Chevy LWB 4x4 plow truck '71 Blazer 4x4 driver '70 GMC LWB trailer |
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#9 |
Not a bad nut after all..
Join Date: Dec 2000
Location: ND
Posts: 1,756
|
Re: Brake Light On, Pedal Feel not Right, Front Brakes not Bleeding Anymore
Fixed!
The rear brake shoes (which were on the truck when I bought it) were either defective or the incorrect part number because some of the holes were off slightly causing insufficient contact with the star wheel adjuster.
__________________
'05 Chevy 2500HD 4x4 '72 GMC LWB 4x2 driver '72 Chevy LWB 4x4 plow truck '71 Blazer 4x4 driver '70 GMC LWB trailer |
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