mbyers

I have a weird issue with the brake lights staying on.

Realize this does have the pressure switch that is screwed into the master cylinder; so I can't just adjust a swtich at the pedal :-(

Another note: I recently bought the car, just as its restoration was being completed. All the brakes are new and the swtich looks new (definitely not 40 years old).

This is what is happening: I go out to a cold car, I start it up, and the lights are off. Press pedal, lights go on. Release pedal, lights go out. After driving a little bit, I notice the lights stay on. If I lift up on the pedal I can get them go out (most of the time), but they come back on once I release the pedal. I bled the brakes (and the swtich) and that didn't help. The other day I noticed that if I just start the car and let it run and get warmed up, the lights come on (without ever pressing the pedal). Of course, if I disconnect a wire at the switch the lights go out.

Before I throw a switch at it, I figured I'd give this forum a try. Maybe this is something someone has experienced, and can maybe recommend a particular brand of switch?

Not sure if this matter, but I figure more info is better, when I bled the swtich it was very hard to get out; like it was screwed in too far.

Thanks in advance...

Epic2112

Could your master cylinder pushrod be misadjusted? A lot of master cylinders have a little little hole that will let brake fluid back into the reservior. As the fluid heats up from braking it will expand, if it has no way to get out of the brake lines it will apply the brakes. The hole in the master cylinder allows the fluid to go back into the reservior when you aren't pushing on the pedal, in order to stop this from happening.

It's a little bit strange that the lights will come on without you driving at all, but maybe the switch is sensitive enough to pick up even the slight expansion from just engine bay heat. Have you taken it on a decently long drive? If not, try it and see if the brakes lock up after a while. If they don't, the pushrod might still need to be adjusted, or it could be something else. But if the brakes do lock up, I'll bet money that is your problem.

mbyers

I had previously looked at were the rod connects to the pedal and I didn't see a way to adjust it. I thought I could maybe 'back it out' or something, but I didn't see an adjustment. Are you thinking of that type of adjustment, or some other way? If you hae specifics, that would be great.

On one of the 'long' rides it did seem that the brakes were harder to press. That is when I pulled all of them to make sure they were adjusted ok (i.e. not hanging up) and to bleed them. I did find one wheel that was too tight and another that had an air bubble. Since then, I haven't had the hard braking issue.

Thanks for input...

Epic2112

There could be an adjustment on the rod in the master cylinder, on/near the pedal, or any number of places, or there may not be one at all. It may need to be cut, or replaced all together. Unfortunately I'm not as much of an expert with these cars as others here, maybe they will chime in.

For what it's worth, on a longer drive I'd expect the brakes to lock up and stop the car by themselves, while pedal stiffness may or may not change, or it may not be as immediately noticeable as the brakes locking up. Take it out for a good long drive (even an hour maybe?), see what happens, just give yourself some time in case the brakes do lock up and you have to wait by the side of the road for them to cool off .

mbyers

I just wanted to follow up with what happen. I don't like it when I read a thread and it doesn't say how it turned out. Plus I wanted to thank Epic2112 for his help. Thanks!

I tried swapping the brake light switch and that didn't help (I didn't think it would, but it was the cheap & easy thing to try).

After driving back from a show, one day, which was about 30 minutes and I did some hard braking, I pulled into the garage. After a few minutes I went to pull the car back out and the brakes were locked up :-(

A couple weeks later, I pulled the car out of the garage in the morning and had it idling for a while in the driveway; while looking things over and showing off the car to my brother. After a while, and some tinkering, we got ready to go from a ride. We ended up going nowhere because the brakes were locked up!

So that was it, time to try the master cylinder. Since it was less than $50, I just went for a new one. Put that in, spent the time bleeding the system (thats was fun). And tada, the problem is now gone!!!

The interesting thing is that the pedal travels down farther (than it use to) before the brakes kick in. At first I thought maybe I still have air, so a re-bleed, but got nothing. I also re-checked the adjustment of the brakes, which was still good. The pedal never hits the floor and they are not spongy. So it just shows how screwed up the master must have been. Anyway, I'm adjusted to the new pedal feel and all is ok; at least with the brakes lights and locking up.

coupleofbridges

A year and half later I'm having a similar issue. 64.5 Mustang, but I have a new master cylinder and new brake switch. The lights comeon after it warms up, and there's no apparent adjustment in the pedal or rod. I'm cutting down the rubber bumper on the brake pedal arm so it can maybe travel back further easier. We'll see. I haven't found that my brakes lock up though.

mbyers

I do not think adjusting the rubber bumper will help. It was one of things I wasthinking about at thetime, but it just didn't seem like it would help. Since the brake switch is pressure based, I don't think the little bit you can do with the rubber bumper will help :-(

My suggestion to test it before cutting anything. Whenlifting up on the pedal, do the lights go out? If so, leave it like that for a little longer while the car continues to warm-up. While warming up make sure to leave the hood closed, as it will keep the heat in the engine compartment. These made sound a little strange, but it threw me off when I was testing things. With the hood open, the engine heat would escape and it wouldn't get as hot as when I drove. And lifting the pedal aleviated pressure for a moment, then it would build up some more.

I know you said you got a new master and switch. However, I've heard the switches are made cheap these days, so it isn't unheard off to get a bad one. Also, I've read different things about bench bleeding the master or not. If the bench bleeding is not done carfully, or during the install the rod gets pulled just right, it can screw-up the seal on the rod and you end up with a bad master :-(

Just thought I'd share these other things.

I am interested in how things work out, so please post your results.

jlg2002

The springs on the brake shoes are the main thing that controls the return of the pedal back to the off position. This along with the internal master cyl spring and the wheel cyl's. If you are having problems with the pedal not returning, replace these brake shoe springs (all 4 wheels if you can)and lube the shoe pivots on the backing plates. You also want to make sure your wheel cylinders are not sticking also, so while you have the shoes off, pull the WC boots back and look for crud and push them to make sure they move freely. I think this will help.

coupleofbridges

I actually redid the whole 4 brakes a couple months ago, new cylinders, springs, adjusters, turned the drums, and the master cylinder and brake switch.

Maybe a clue here: the brakes feel pretty good, no pull to one side or the other, BUT sometimes braking while making a left/right turn on another roadI hear a light screech. I haven't pinned it down, but it sounds slightly like a wheel locking up... although I can't feel it. Maybe a belt? Don't know yet.

So, this evening I pulled of the back drums and checked my springs, etc etc. Everything looks good. I put some more lithium grease on the rub points for good measure. I'll try to check the front soon.

Yea, the lights go out when you pull up on the pedal. I haven't gotten to drive the car enough to tell if it get harder and harder to turn offthe lights after longer and longer driving times, by pulling the pedal, eluding to heat making it worse and worse. They do come right back on when I quit pulling the pedal.

Next time the lights are staying on I'll jack up the back and see if the wheels are hard to turn by hand. Hey, I do remember when putting on the master cylinder it seemed awful hard to tighten up the bolts that pulled the MC to the firewall. That stinks, probably going to have to pull it back off and see if something didn't line up, I don't know.

coupleofbridges

Hmmm, the left rear shoe was glazed over some. I thought maybe from before I redid the brakes, since I didn't change the shoes. But maybe from now, meaning the brake is staying on some??? The rub points did look a little drier than the right ones, maybe that's it? I'll drive again this week and see.