Brake lights stay on.

Scott21 · Post by **Scott21** » Sun Oct 16, 2011 6:47 pm

Before I pull the master cylinder an rebuild, my brake lights stay on once my 38 is driven. If you put the brakes on cold the work properly. Once the jeep warms up they stay on. I have bleed the brakes and have cleaned the switch. Like I said, it works fine when cold. Any input? I also have lots of new pictures in the members album.

http://www.willysmjeeps.com/v2/modules. ... _album.php

Scott

donthedickens · Post by **donthedickens** » Sun Oct 16, 2011 6:59 pm

I had the problem on my 3B. I had to put a heat shield between the exhaust pipe and the master cylinder. I've had no trouble since I did that.

Post by **wesk** » Sun Oct 16, 2011 11:45 pm

Don is probably right on since the heat will cause the fluid in the cylinder to expand and apply pressure to the switch. Also an improperly adjusted push rod can cause that simply because you are just a wee bit too long but the effect only shows up with the cylinder warmed up. So check for a heat shield and if you have a heat shield get the book out and adjust the pushrod.

artificer · Post by **artificer** » Mon Oct 17, 2011 4:46 am

Also an improperly adjusted push rod can cause that simply because you are just a wee bit too long but the effect only shows up with the cylinder warmed up.

This is the most likely problem, not enough push rod free travel, not allowing the piston to fully return, keeping enough pressure in the lines to keep the brake lights on.
If you let sit for a few minutes the light/s will probably extinguish.
I think the heat shield is unlikely the problem.

Scott21 · Post by **Scott21** » Mon Oct 17, 2011 4:47 pm

Thanks guys, will be adjusting the pushrod tonight will let everyone know.

Scott

Bill_F · Post by **Bill_F** » Mon Oct 17, 2011 5:34 pm

could also be a faulty switch mine did the same thing and turned out to be the switch on the master.

Scott21 · Post by **Scott21** » Mon Oct 17, 2011 7:31 pm

Not the pushrod.

artificer · Post by **artificer** » Mon Oct 17, 2011 8:06 pm

Next check that the piston is fully returning to the circlip in the master cylinder bore & if it is, there is a possibility that the primary cup rubber [in front of the piston] is swollen impeding the fluid return through the by pass or compensating port [the small port in front of the piston].

Check if your brakes are dragging when the brake light is on by jacking up one wheel, as we don't want to be spending money yet.

If it were the switch it should be faulty whether hot or cold.

Scott21 · Post by **Scott21** » Mon Oct 17, 2011 8:50 pm

Thanks John,
Brakes sometimes drag for a moment, then release. They do not lock up, a slight drag. I will check and clean out where the pushrod meets the piston. The boot was not on corect.

WESTCOMVIC · Post by **WESTCOMVIC** » Thu Oct 20, 2011 3:25 pm

Had a similar problem, not just brake lites, but brake dragging...check the small return hole in the bottom of the master cyl. Mine was gunked up and after clean up...no more problems.

Scott21 · Post by **Scott21** » Tue Oct 25, 2011 4:48 pm

Cleaned out and rebuit the Master. Removed a lot of sediment. No more hangup but light comes on after warmup. Going to try a civvi switch from NAPA for $6.oo and a heat shield.

wilfreeman · Post by **wilfreeman** » Thu Nov 17, 2011 3:55 am

What did you come up with scott? I'm sortof having the same problem, although I havent started troubleshooting yet. My brake lights stay on - period. I adjusted the rod out until I had alot of play - still on. New m/c, lines and wheel cylinders. I'm guessing my switch is bad since it's the only old part left in the system. I think the one on my parts jeep still has good wires on it, so I'll prob try it next week when I'm off.

Post by **wesk** » Thu Nov 17, 2011 10:49 am

There are a simple set of checks to make with an ohm meter for brake lites stay on.
1-disconnect the wires.
2-ohm out the switch. (0 ohms the switch is stuck closed.)
3-Remove the switch. (still 0 ohms switch is stuck or bad.) (You can try cleaning and actuating with air pressure but generally once they stick or fail they'll do it again. So a new one is in order) If the switch was open when removed then you have too much residual pressure inside the cylinder.

For no brake lites use the volt meter or a test lamp

1-Check for power to the switch on one of the two wires with no pedal applied.
2-Connect the hot wire to the switch. Connect test lite to switch's remaining terminal.
3-Apply the brake pedal. Power to the bare terminal means switch is good. No power means bad switch or air behind switch.
4-Bleed switch and repeat 2/3.

That's all you need to do with the switch. You've either found the problem or now know the problem is not the switch.

wilfreeman · Post by **wilfreeman** » Thu Nov 17, 2011 2:34 pm

Thanks Wes - I'm starting a list of things for next week when I get off

Scott21 · Post by **Scott21** » Fri Nov 18, 2011 6:57 pm

Will

Haven't had time in the garage since the snow storm at the end of october. Will keep you informed.

Scott