Master Cylinder or Brake Adjustment ?

[V269]

2 years ago I installed a new or maybe rebuilt master cylinder on the runner. I've noticed lately that when I get on the brakes firmly the brake light in the dash comes on and I seem to have to push on the pedal a little harder to stop. I re-blead the brakes and the pedal feels firm but when I went for cruise night on Wednesday the same thing was happening again. Should I try adjusting the brake pads up or do you think my master cylinder has crapped out on me. Everything is new from front to back, lines and all. Maybe a bad wheel cylinder ? Hoping I do not have to change out the master but this is what I'm thinking. :huh:

Ken.

 

[John69RR]

IIRC the light will come on due to low line pressure. If you are not losing fluid through a wheel cylinder or the back of the MC it sounds like the MC is leaking-by internally. Another possibility is a faulty switch.

 

[A31PKG]

X2

There is a plunger (which acts as a switch) in the metering block that relies on equal opposing hydraulic circuit pressures to keep it in the neutral position. If there is pressure loss (either through a leak or restriction) then the plunger moves from one position to the other, depending on which circuit is a fault, and thus completes the circuit to ground illuminating the dash lamp. Since you say that it takes more pedal effort to stop, I would suspect a restriction somewhere. I have seen rubber brake lines (even new ones) that appear ok, but collapse internally under pressure causing a restriction. Also kinked lines, frozen wheel cylinders, or perhaps an internal MC problem could be the cause. Keep us posted!

 

[V269]

Sorry guy's for not getting back sooner, been busy. Thank's for the good info. I'll try to get the wheels off this weekend and check everything out there first. When I blead the brakes I got good fluid coming at all 4 corners and no air. If there were a collapsed rubber line would the flow not be good when bleeding ? There are no external leaks anywhere and the fluid was right up in the master cylinder. Anyway's I'll check it out. Thank's again for the info and yes I'll keep you posted on what I find.
Ken.

 

[A31PKG]

Fluid will flow just fine when there is no resistance, such as when bleeding the system. It is when the hydraulic circuit is closed and under pressure, that the the hose can "close" up internally... If there is a hole or porosity in the inner main tube, fluid can leak out but stay trapped by the outer tube case. When pressurized, this fliud actually can constrict the inner tube causing an interuption of flow. Sometimes this can be observed as a swelling or ballooning of the brake hose, but not always. Hope that explains it a little better.

 

[Basketcase]

I had an '85 Power Wagon. The brakes acted like yours are. Bleed the brakes, and would get air from the back. Be OK for a few days, then it would do it again. no leakes anywhere. Then I finally noticed that the PO had run new lines on the back,and had one line sticking above the rearend husing. the muffler didn't have a tailpipe, and the heat from the exhaust was hitting the brake line, cooking it. In fact when I tried to move the line, it broke. Where the exhaust had been hitting it, it has caused the new line to rust. replaced the line, and ran it properly, problem solved.

 

[V269]

So I thought I would catch you guy's up on my brake issue. I know it's been a long time but I took all 4 wheels off and checked the wheel cylinder's and all were working fine. Had my son press on the pedal while I was holding 2 pry bars against the shoe's and they looked good. I noticed the shoe's had a little wear but not bad and the drum's come off easily so I thought I would just make an adjustment on all four. I took them up so the drum's just had a little resistance when they were on and presto changeo problem solved. Brake pedal is up full and never felt better and my e-brake work's great now. Took it for a drive and the light no longer comes on and this thing will stop on a dime and give a nickel change. Can't believe how a little adjustment made such a big difference. Very nice. They re-paved the highway out front of our house so I figured while I had the car out I'd give it a little extra black treatment. Sweet.

 

[69hemibeep]

So I thought I would catch you guy's up on my brake issue. I know it's been a long time but I took all 4 wheels off and checked the wheel cylinder's and all were working fine. Had my son press on the pedal while I was holding 2 pry bars against the shoe's and they looked good. I noticed the shoe's had a little wear but not bad and the drum's come off easily so I thought I would just make an adjustment on all four. I took them up so the drum's just had a little resistance when they were on and presto changeo problem solved. Brake pedal is up full and never felt better and my e-brake work's great now. Took it for a drive and the light no longer comes on and this thing will stop on a dime and give a nickel change. Can't believe how a little adjustment made such a big difference. Very nice. They re-paved the highway out front of our house so I figured while I had the car out I'd give it a little extra black treatment. Sweet.

Glad to help, Oh wait I didn't :leave: Glad it was an easy fix Ken

 

[Basketcase]

yeah when l first started messing w/ drum brakes l ran lnto the same thlng. amazlng how much dlfference a small adjustment makes