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Dash brake light on after replacing rear brakes

184 Views 1 Reply 2 Participants Last post by  Gluckmysock
'96 XJ here and I've just replaced everything you can on my rear drum brakes, and now that they're done the red 'BRAKE' dash light is constantly on. I have sort of an idea as to why but no idea how to go about fixing it. This happened on both sides btw... When I had finished replacing everything and was fitting the new drum around the new pads neither drum on either side would slide on. Somehow the shoes were too far apart by just a hair. Looking back, I now know what happened to cause this, just wish I had realized it then. When I began installing the new parts the first thing I put in on both sides was the new wheel cylinder and attached the brake lines. I think when I attached the brake lines it kept some pressure in the cylinder and they wouldn't let the top of the brake shoes retract in as much as they should've. To correct this I should've cracked the bleeder valve and left it open until everything was fit back together.

So what does my dumb a$$ I take the adjuster wheels back out (where the bottom of the brake shoes rest) and dremel grind both ends down some so the shoes can come together a bit more. This was enough for the drums to go on and voila! job done. Yep, not so much.

How do I go about adjusting things so my dash brake light goes off? Only thing I know to do is to get new adjuster wheels and redo the build steps again with the brake fluid bleeder valve cracked open, close it all up, bleed the lines and see if that gets the light off.

One thing I should mention that could be a factor here is that when I took off both drums there was the same piece broken in each one...the odd cable part that hooks onto the thick top anchor point where the top two shoe springs attach, does a 90 deg turn around another piece to the side then continues down to hook into the odd J looking piece close to the bottom adjustment wheel. I think this part has something to do with the emergency brake but I'm not entirely sure. The green line in pic below shows where each of these pieces/cables were broken. The pic isn't of my brakes, just one I pulled off the net.

Wood Motor vehicle Automotive tire Gas Auto part
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umm I have never had to grind down any parts of a drum brake setup. I have had to wiggle and bang the shoes together and wiggle them side to side and eventually they went together.
are your wheel cylinder bleeders on top? Sorry, but I have seen them installed upside down.
Did you clean all the rust off the backing plates. I have seen small lips from wear cause them to hang up. I am going to assume you replaced all the hardware. It's not necessary every brake job, but these things do rust and stop working normally. OK, picking over.
The wheel cylinder at the top is what applies the brake when you press the pedal. If you left the lines off for any length of time. or the master cylinder ran dry, you have air in your lines. The reservoir at the master cylinder has 2 chambers. one for the front and one for the rear. the rear can run dry and you still have brakes because the lines from the MC connect to a proportioning valve, which shuts off fluid to the rear if it senses a major loss of fluid, so for obvious safety reasons, you can still have partial braking. if you don't properly pressurize your rear brakes, the proportioning valve won't reset and the system will still think you have a leak and turn on the dash light. Also, your parking brake handle will cause this light to illuminate, so make sure that is not your cause. You can also have air in the Prop valve which will set the light. Here is a link to upgrading a prop valve for disc brakes, but gives a lot of info about the system and how to bleed the prop valve. Jeep XJ prop valve mod.

Back the the rear drums. the two top springs are used to return the brake shoes after application, They are very heavy, and are easily overcome by the hydraulic pressure in the wheel cylinder. The cable piece that attaches to the pin at the top and runs down to the adjuster is part of the auto adjuster system. Which functions during a brake application or the application of the parking brake. it pulls on the lever which is pressed against the adjuster wheel teeth which rotates the adjuster, pushing the bottom of the shoes out, "automatically adjusting the brakes". The brakes have to have enough wear so that when the adjuster moves back to it's resting position it can click onto another tooth.
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