redwoodwalker

I recently replaced the master cylinder on my 91 Runner. Before I did this, I had no brake warning light issues. Matter of fact, I had no brake issues at all except for the tell-tale signs that the MC was going bad. Afterwards, it comes on intermittently, and not at full glow. It's like whatever is tripping the light is not quite tripping it all the way. My first thought was the fluid level sensor on the top of the master cylinder reservoir, but that's not it. And fluid level is good. I checked fuses, and found that the previous owner had removed the rear wheel antilock fuse, so I replaced it, but the light stayed. I had already bled the brakes, so I bled them again, and the proportioning valve at the rear axle. All seemed well, yet still I have the light. The pads are not glazed, the rotors are clean, and the emergency brake works as it should. I've also checked for vacuum leaks leading to the vacuum booster, and there are none.

The 2 odd things about it are 1) that the light is intermittent. I haven't been able to isolate for sure any environmental or driving time issues that could affect it, but it seems that when it's driven for a while, it goes away, and it seems to go away on warmer days. This is not always law, but it seems to be a rough general rule. The second thing is that when the light is on, the brakes are not as reliable. The pedal seems to stop a little lower and feels like it's hitting a wall. It'll stop, but you'd better not be tailgating anyone. When the light goes away, it stops as good as my wife's new Corolla.

I've done more than my fair share of brake jobs and MC replacements, but this is the first time I've dealt with RW anti locks only and it's the first time I've seen this type of event. Anyone have any ideas?

redwoodwalker

Really? Nobody has a clue?

yoterr

my only guess would be to check the FSM and see how the rear anti-lock system works and check the parts accordingly, seems like a faulty sensor, good luck

isaac338

The red parking brake light is independent of the antilock system. A problem with the antilock system will light the REAR ABS light.

The only reason that light will come on is a low fluid level or the pin on the side of the parking brake handle not pressing the parking brake switch.

Make sure the switch is firmly attached to the handle bracket and the pin is still in place in the handle (they do fall out).

Sloshing brake fluid will also cause an intermittent light; it doesn't necessarily have to be at the min level in the reservoir to do this. Fill it right to the top.

Other than that, try unplugging the sensor at the reservoir next time the light's on to see if it goes off - I'm not sure how that switch turns on the light (by either making or breaking a connection) but if you can figure it out, replicate the continuity it should have with a full reservoir by leaving it unplugged and shorting the harness with a piece of wire (if needed), and see if the problem goes away. If it does and your fluid is definitely all the way to the top it might be a faulty sensor.

redwoodwalker

I think I still need to rebleed the brakes to firm them up, but I disconnected the reservoir sender and the brake warning light went out. It's irritating that it's such a small issue, but at the same time I'm greatly relieved. I appreciate the input......