Partial to no front braking

[75GmcJimmy4x4]

Ok heres my issue when i am driving and i go to stop my 75 dont want to .......


the pedal is not hard and not spongy just seems like the rears are doing all the work and the front seems to not have any braking affect i have bled the front brakes numorus times and it doesnt get any better, i have cleaned and lubed the caliper hardware and checked the lines , all good, .... am i missing something

 

[Capt.D]

proportional valve....or master cylinder

 

[75GmcJimmy4x4]

proportional valve....or master cylinder

so its possible the master cylinder would cause this ?? how can i check it

 

[dyeager535]

If the master or proportioning valve has failed, then your dash light for "brake" SHOULD be on. Test to see if it works. Unplug from the proportioning valve, and ground the wire with the key in "run".

No way to really test your master, except that the proportioning valve should trigger the light as pressure bleeds past the piston seal in the master cylinder.

 

[75GmcJimmy4x4]

If the master or proportioning valve has failed, then your dash light for "brake" SHOULD be on. Test to see if it works. Unplug from the proportioning valve, and ground the wire with the key in "run".

No way to really test your master, except that the proportioning valve should trigger the light as pressure bleeds past the piston seal in the master cylinder.

ok i checked the light and guess whats not there ....... the bulb and socket ... however i used my volt meter on the wire for the light and there was voltage . so this makes me think i need a new master cylinder

 

[dyeager535]

Good idea to replace that, it WILL give you warning of impending brake failure.

You might try driving around with the voltmeter hooked up, when my master failed the light would stay off until I was doing something like using the brakes at a stop light, where the pressure had time to bleed off, triggering the valve. AND I could make the light go off by pumping the brakes.