brake light STILL on:why?

I just finished completely rebuilding my back brakes. new shoes,hardware kit,wheel cylinders both sides,hard lines,you name it. bled the brakes this afternoon,twice,absolutely no air in the back brakes. fired the jeep up to see if the brake light on the dash went out,nope still on. the pedal is more firm then before I did the back brakes,but it still isn't as hard as it should be. It wasn't like the back brakes didn't need rebuilt,one wheel cylinder was frozen open and leaking,brake fluid had destroyed the shoes on that side,so no money loss there. I just need to know what else might make the light stay on? front brakes seemed to work fine,no pulling to one side like a caliper is hung up or something. thanks for the ideas. deer season is almost here,been spending way to much time on the jeep instead of in the woods scouting,and I need the jeep for deer season

Check the amount of fluid in the master. If its low the light will go on. Also make shure the ebrake isnt on at all. That will turn the light on.

Mine did that too. Then I (for unrelated reason) unhooked the battery. When I hooked the battery back up, the light was not on and has not come on since. I don't know why, nor do I care. Just some food for thought.

e brake isn't on,fluid is full in both reservoirs, will try disconnecting the battery. thanks for the ideas!! sorry this is for my 92 5 speed 4.0 dana 35 rear 180,000 miles.

The brake light comes on because of one of two reasons:
one--there is an imbalance between the front and rear circuits. The switch in the combination valve is held in the center position when the brakes are in balance. If one side has less pressure than the other, the switch moves and turns on the light.
Bleed the fronts as well, and/or bleed the combination valve as well.
Two, the E-brake has a switch that also turns on the SAME brake light. Insure that's not the problem, by removing the wires from the combination valve; if the light is still on, it's the E-brake, or a short to ground in one of the systems.
I think you need to bleed all of your brakes.

Like he said, it is probably the imbalance in the front and rear. You will need to bleed all the brakes in the sequence shown in your manual.

Hoss

xjbubba said:

The brake light comes on because of one of two reasons:
one--there is an imbalance between the front and rear circuits. The switch in the combination valve is held in the center position when the brakes are in balance. If one side has less pressure than the other, the switch moves and turns on the light.
Bleed the fronts as well, and/or bleed the combination valve as well.
Two, the E-brake has a switch that also turns on the SAME brake light. Insure that's not the problem, by removing the wires from the combination valve; if the light is still on, it's the E-brake, or a short to ground in one of the systems.
I think you need to bleed all of your brakes.

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Here is what happened that made the brake light come on in the 1st place. I had to get on the brakes hard when somebody using their car as a phonebooth instead of a mode of transportation decided it would be a good idea to change lanes without looking. I got on the brakes hard,and the light came on and the pedal was more soft than before,so I inspected the brakes and that's when I found the back brakes as messed up as they were. I thought the back brakes were the reason the light was on.I will bleed the fronts in the morning when I get off work. where is the combination valve located,and how do I bleed it? thanks!!

When you first checked your master cylinder, was there ample fluid in both reservoirs? Could be fluid got low enough for you to have pumped air into one, or both circuits.
So check out the front brakes as well.
The combination valve, on an '88 at least, is located below the MC, and towards the engine. To bleed it, you need to loosen each line in turn, as someone holds pressure on the pedal. And before the pedal is released, tighten the fitting; very similar to bleeding the calipers and wheel cylinders. Bleed until no air is present.

Check e-brake again and make sure it's not pulled taut. If it is (due to lift or excess screwiness from the earlier condition of the brakes), the light coming on isn't uncommon.

Jim www.yuccaman.com

Any leaks anywhere? Inpect all of the brake lines.

Getting on the brakes hard and getting a light might indicate your burst something. Or something small. Not sure what kind of brake leak would be small enough to not see.

But it comes to mind.

Blaine B. said:

Any leaks anywhere? Inpect all of the brake lines.

Getting on the brakes hard and getting a light might indicate your burst something. Or something small. Not sure what kind of brake leak would be small enough to not see.

But it comes to mind.

Click to expand...

a leak is what I was thinking i would find after the brake light came on,thinking i might have caused a line or hose to bust after stomping on the brakes so hard. the only leak I found was the driver's side wheel cylinder,and it was more a slow seep than a major leak. it looked like it had been seeping for awhile and the level wasn't down that much. I didn't find any other leaks anywhere in the lines.I will bleed the fronts here in a little while. thanks for the all the ideas!!

try disconnecting the wiring harness for the light, which is on the top of the proportioning valve and reconnect.

i believe the light can also be rest by apply pressure to the brake pedal. im not sure how much pressure, but off the top of my head its something light 250ft/lbs. maybe someone with a FSM can look up the procedure.

hopefully this is not a sign of the master cylinder failing.

brake light is off and I have good brakes I think 89xj had the right answer,I did this when I was working on it just for giggles,and the light went out. I bled the front brakes,started the jeep and the light was still on. setting there all dejected in the jeep,thinking about what to do next,I started the jeep up and just pumped the brake pedal really hard one time. I felt the pedal "bounce" a little bit,and the light went off. went for a drive,brakes work good!! all is good in jeep land again!! until next week when I have a new problem LOL. thanks for all the ideas and patience!!

I had the exact same thing happen to my 89 when I came to a panic stop....ended up being busted self adjusters.Fixed that and brakes were fine for awhile untill recently I came to another sudden stop and what do you know?brake light

I'm starting to suspect proportioning valve because all other parts are new.I got that same "pop" in the brake pedal then the light went out awhile back...theres something about that pop that makes me think sticky/failing proportioning valve in our case....however I don't think they fail very often.