Is This a Master Cylinder?

[Bob Chadwick]

I was driving home today and the brake light came on and stayed on. Checked the fluid and it was a little low so I added some. Now the light only comes on when I press the pedal hard.

No sign of external leaks. Had all four caliper and rotors replaced last year.

Seems to stop like it always has.

If it is a master cylinder is there anything to look for when purchasing a new one and how difficult is it to replace?

Thoughts anyone?

Bob

 

[67HEAVEN]

Over time, air will enter your brake system. How does the pedal feel?

Likely all you have to do is bleed the lines. If you've never done it before, get some knowledgeable help and watch closely for next time.

:bang

 

[c4ever]

Master usually shows up as a pedal which when steady pressure applied goes to the floor. Car will stop but piston continues to travel in master therefor pedal continues to slowly drop to the floor. seems like you may just need to bleed. Changing master is a snap. Just be sure to bench bleed the unit prior to install and you won't even have to bleed the brakes.

Carlo

 

[Bob Chadwick]

Pedal is not mushy and doesn't pump up. Was bled just last year when I had the brakes done.

What is the procedure for bleeding brakes? As I recall you started with the back right, back left, front right and then front left. Also, aren't there two bleeders on each caliper? Which do I do first?

Bob

 

[ChuckG]

There are 2 bleeders on each rear caliper, inner and outer. There's only 1 on each front. Regarding the sequence...that's a can of worms Conventional wisdom says go from the farthest from the MC to the closest. That, to me, would be RR, LR, LF, RF, but the shop manual tells you differently.

Sounds like you have pumped some air into the system. Bleeding should take care of this. Rotor runout is the most common culprit, but it could be front/rear wheel bearings, which allow the wheels to "wobble" with each rotation, causing air pumping back through the calipers. Chuck

 

[Bob Chadwick]

Replaced the master cylinder (it was on the list anyway) and bled the brakes. The light went away for awhile but came back. Took it to the shop that did my brakes last year. Let them hassle with it. Bleeding the brakes is not so bad, it's getting the car up in the air and the wheels off so you can access the bleeder screws.

Mine actually had three bleeder screws in the rear. Two on the outside half and one in the front on the inside.

 

[JohnZ]

Have you checked the switch for the parking brake lever? It's on the same circuit and uses the same bulb as the differential pressure switch.

 

[Bob Chadwick]

Got it back from the shop. Air in the lines. They bled them out and everything is fine for the time being. I'll have to see if it resurfaces.