bad_idea

The issue: When I start the Jeep the brake warning light slowly illuminates and then stays on. I mean the light is off at start up then dimly illuminated then gets brighter. It takes approximately 5 seconds for this to happen. I don't touch the brakes at all while this happens. Shut the Jeep off and immediately turn it back on the light is steady on. Light stays on entire time I drive the vehicle. Shut the vehicle off for a while and the issue starts all over. The brakes work great.

1990, 4 door, 4wd, 4.0l, auto, non-abs, 8.8 rear axle with disc brakes from explorer, zj prop valve guts, wj booster and master cylinder, new driver's side front caliper, new pads at all four corners, new brake hoses.

The brakes worked good yesterday with all of the above done with exception of the booster had a massive vacuum leak. I replaced the booster yesterday. I was able to swap the booster out w/o disconnecting the master cylinder due to the flex hose section in the WJ brake lines. During the swap I did have to disconnect the switch from the proportioning valve.

My troubleshooting so far includes disconnecting the switch on the prop valve with the ignition on, the brake light goes out. I have the FSM, but it doesn't include the wiring schematics. I don't understand why there are two wires going to the switch, most I have dealt with only have one wire. I assume when the switch closes the two wires are connected, turning the light on. Thoughts?

Turbo X_J

That is humorous.

It may just be a glitch in the wiring or the proportioning valve (air in the system) but until you know for sure I wouldn't drive that freakin' thang.

bad_idea

It's parked now until I figure it out. I didn't notice the light on before I left the house. I was most of the way to the grocery store (only a mile or so from the house) before I noticed. I pulled the Jeep over and did a visual inspection, didn't notice anything out of the ordinary. This Jeep is my second vehicle, I don't NEED it for daily driver status.

Air in the line occurred to me this morning. When I pulled the master cylinder from the old booster, I tipped it forward for a few minutes. I'm thinking the rear port within the master was uncovered and air was allowed to get into the line. The brakes do not feel spongy, but the scenario makes sense. I find it hard to believe I had component failure overnight immediately following a repair. To bleed air from the master cylinder/ prop valve, should I bleed at the wheels or somewhere else?

Turbo X_J

cruiser54

Bleed the whole system at this point.

bad_idea

So you think I should bench bleed the master cylinder Turbo? I would love to just bleed at the four corners if I can get away with that. I'm willing to pull the master if I must.

cruiser54

Try bleeding the calipers first.

bad_idea

Will do. Hopefully I get some time tonight to get out there. I will report back afterwards.

bad_idea

Problem solved. Bled the brakes at all four corners. No more light. Slammed on brakes at 35 mph and left skid marks for 10'. Very controllable. Not too bad for 33s. All in all, happy with the setup. Thanks for the help guys.

Turbo X_J

cruiser54

Yay. We like giving good ideas to a guy named bad idea.......