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Brake lights come on when driving and when parked
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joehadams
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PostPosted: Sun Aug 30, 2015 8:23 pm    Post subject: Brake lights come on when driving and when parked Reply with quote

I have been fighting this issue for quite a while now and I just can't seem to figure it out...

On my 67 Sandwinder when I'm driving around, the brake lights come on. (I am not touching the brake pedal.) I notice the lights are on, I tap the brakes, the lights go out. They stay out for a while but then come on again. Occasionally they pulse on and off too. When I am done driving and park the car, they may be off; but will eventually come on by themselves. (And kill my battery if I don't get back in time, or remember to pull the brake light fuse).

Important Notes:
-Single master cylinder purchased from JC Whitney a few years ago.
-All new lines (hard and soft) within the last 5 years.
-Tried a half dozen switches thinking they may have been bad.
-The brakes are not applied or dragging any more than normal while the lights are on.
-I have adjusted both the pedal stop on the floor, and the pushrod distance according to the book and information I have gathered from this forum.
-In a last ditch effort we added a 90* elbow on the master cylinder to elevate the brake light switch hoping the fluid level would fall down and away from the switch.
-Lights go out when wire is pulled off the switch, the fuse is removed, or the pedal is pressed and released.


Thank you in advance for any and all help with this issue!!

My Sandwinder (with running lights on):
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Letterman7
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PostPosted: Mon Aug 31, 2015 5:24 am    Post subject: Reply with quote

Sounds like something is heating up the fluid and causing it to expand just enough to trip the switch. Or there is still air in the system causing a lockup at the switch. Really, you should probably have a dual master in there from a known reputable supplier anyway.. if you lose a circuit with the one you have, you will have no brakes.
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Q-Dog
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PostPosted: Mon Aug 31, 2015 6:11 am    Post subject: Reply with quote

I wonder if the brake pedal push rod doesn't have enough free play? (rod is too long?)
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Dale M.
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PostPosted: Mon Aug 31, 2015 6:17 am    Post subject: Reply with quote

Check the free play in pedal adjustment... IF pushrod from pedal is adjusted incorrectly (to long) it will not allow the fluid port in MC to open and you get excessive build of fluid in system, it can just cause your problem with lights or is can eventual block port to a point you over heat brakes and it will lock them up and you can hardly move buggy under power...

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Nice looking buggy but do you always park it diagonally under freeway over pass...

Dale
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porkey
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PostPosted: Mon Aug 31, 2015 12:25 pm    Post subject: Reply with quote

My buddy had the same problem. We adjusted the push rod untill the lights stayed out when the pedal was relaxed. I didn't use the service manual spec's for the adjustment. Probem solved.
Good luck !
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joehadams
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PostPosted: Mon Aug 31, 2015 3:03 pm    Post subject: Reply with quote

Thanks for the replies everyone. I have adjusted the pushrod play multiple times at different lengths trying to find the "sweet spot" where the lights stay off. No luck.

To reply to the fluid heating up statement: The lights will come on if the car is sitting in a parking lot without any shade. I would assume the black top parking lot, and the black chassis play a part in this. Are there different brake fluid's that react differently to heat?

I will have to bleed the brakes again just to confirm there is no air in the system.

Also, are there different diameters or lengths of MC pushrods? Maybe the one in my car is incorrect for the year. If that is even a thing...


PS. I only park like a jerk between the hours of 12 and 3am
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jsturtlebuggy
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PostPosted: Mon Aug 31, 2015 5:07 pm    Post subject: Reply with quote

There are early and late style push rod for the M/C. Both work without problems with any stock M/C.

A single M/C has the rubber grommet in the top inlet where the steel tube goes into. To keep the rubber grommet from stopping up the ports which it can. There a small steel washer that set in a recess just below the grommet to keep it from happening.
It is plugging up the holes it would not let the expanding fluid out of M/C back toward the reservoir. This could cause the problem. I seen it many many years ago.
In the blue Bentley manual 1966-1969 years. Is show the washer in a parts break down and it also gives a warning about the rubber grommet/plug covering the ports and causing brakes to drag.
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Dale M.
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PostPosted: Mon Aug 31, 2015 6:08 pm    Post subject: Reply with quote

Might be marginal brake light switch....

Dale
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joehadams
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PostPosted: Thu Sep 03, 2015 8:31 am    Post subject: Reply with quote

jsturtlebuggy wrote:

A single M/C has the rubber grommet in the top inlet where the steel tube goes into. To keep the rubber grommet from stopping up the ports which it can. There a small steel washer that set in a recess just below the grommet to keep it from happening.
It is plugging up the holes it would not let the expanding fluid out of M/C back toward the reservoir. This could cause the problem. I seen it many many years ago.
In the blue Bentley manual 1966-1969 years. Is show the washer in a parts break down and it also gives a warning about the rubber grommet/plug covering the ports and causing brakes to drag.


Thank you for this tip, I will have to do some investigating on my next day off and try to get the master cylinder out of the car to check on this!

Dale M. wrote:

Might be marginal brake light switch....


I have tried a number of switches from different parts stores in town. Is there a specific one I should try instead of whatever they give me at the store?


Thanks guys!
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BL3Manx
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PostPosted: Thu Sep 03, 2015 9:27 am    Post subject: Reply with quote

Last year Unique Parts made a mechanical brake light switch which was much superior to the slower and failure prone hydraulic switch. For some reason they quit selling them. I hope its just to make improvements or something. Also, I'm not sure their unit would clear the body flange on a buggy, but if they don't make a new version that would fit a buggy, I'd be tempted to make something similar myself.

https://www.youtube.com/watch?v=Lg8ixpQodgU

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joehadams
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PostPosted: Sun Jul 08, 2018 6:23 pm    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

So, I'd like to revisit this thread. Thought I had found a solution but I guess not. The car sat for most of 2017, but this year I noticed very often that the brake lights would be on when the car was parked after driving even a short distance. This also means that they are illuminated while I am driving weather I am pressing the brake pedal or not. In addition If the car is parked in the garage or a parking lot, the will lights come on. When driving at night, I can see the light spill on the ground coming on and going off while driving too. Pulsing almost.

Yesterday, my dad and I put the car on jack stands so no one of the wheels were touching the ground. I adjusted the pedal stop and pushrod free-play according to information found throughout the forum. We found a leaking front-driver wheel cylinder and replaced it. Adjusted all the shoes to dragging, then turned the adjusters back 4 clicks. Then bled the brakes.

Lights were still coming on by themselves after maybe 30 - 45 minutes of sitting. Sometimes a shorter amount of time.

Also noticed that when pumping the brakes the driver-front drum (even after the new cylinder) wouldn't release pressure and kept the drum from turning even when the pedal was released. So, I've got new rubber hoses on order thinking that they'e collapsing internally.

In the mean time, we installed a new brake light switch in the master cylinder. I read a lot about how there are some crappy switches out there so we tried a new one. The car sat in the driveway, on the jack-stands from 4:30pm yesterday to 1pm today without the lights coming on. Came back home today at 5pm and the brake lights were illuminated. Pulled the fuse and admitted defeat.

Once the rubber hoses come in, I also plan to install a new, single circuit master cylinder from CIP1 into the car. I am hoping that this will finally help solve this mystery of why the lights continually come on and pressure is built up in the system even when the car is parked.

Does anyone have any other ideas what may be causing this? The lights are on because of some built up pressure in the system, triggering the switch, but what is causing it?? Is the synthetic DOT 4 fluid I am using incorrect for the application? Any and all help is greatly appreciated.

-Joe
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Dale M.
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PostPosted: Sun Jul 08, 2018 6:44 pm    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

Do you have single switch or dual switches to warn of brake system failure...

Remove the wire from brake light switch to lamps and let it sit..... IF brake lights come on, you have some funky wiring some place.... IF it sits disconnected and no lights then it has to be switch...

Switch has pressure operated diaphragm (same style as oil pressure switch) and over time it could have gone bad and makes marginal contact at most any time...

Dale
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Last edited by Dale M. on Sun Jul 08, 2018 6:54 pm; edited 1 time in total
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joehadams
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PostPosted: Sun Jul 08, 2018 6:53 pm    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

Single switch. I typically pull the fuse to keep the lights off. Never thought about pulling the leads off the switch. Will try and report back.

The switch I installed was brand new off the shelf yesterday and the lights came on today. Could be a faulty switch but I wouldn’t hope not. Could always try another..

Thank you!
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Dale M.
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PostPosted: Sun Jul 08, 2018 6:55 pm    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

joehadams wrote:
Single switch. I typically pull the fuse to keep the lights off. Never thought about pulling the leads off the switch. Will try and report back. Thank you.


Any other devices wired on same fuse as brake lights? Is brake light bulb filament also used as turnsignal?

Dale
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"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
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joehadams
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PostPosted: Sun Jul 08, 2018 7:20 pm    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

The same bulb is used for running light but not blinker. No other accessories tied to that circuit as far as I can remember. I will have to find the diagram for the simple buggy harness we installed to confirm.
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EVfun
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PostPosted: Sun Jul 08, 2018 9:55 pm    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

A new master cylinder might fix it because the older single circuit type have a built in residual pressure valve. If that valve was holding a little too much pressure it could be right at the switch trip pressure. I would also try to source a good 2 terminal switch because they where used in single circuit applications where a residual pressure valve is normal. Most VW dual circuit brake systems don't use a residual pressure valve, and use 2 of the 3 terminal brake light switches.
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joehadams
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PostPosted: Mon Jul 09, 2018 4:39 am    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

There is a single circuit MC in the car now, and we’ve only used 2 prong switches since installed. That MC is from JC Whitney, this new one (also single circuit) that we plan to install is from CIP1. I’m hoping it might be a build quality issue and the new one solves it.
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PostPosted: Wed Jul 11, 2018 6:45 am    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

Installed new rubber hoses on the front, and a new single circuit MC last night. Drained the whole system and bled with DOT 5 fluid. Took the car for a ride and it feel pretty good. Doesn't pull to either side under heavy braking. So far the lights have come on only when the pedal is pressed. Fingers crossed it stays that way.
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Wanderlost_Overland
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PostPosted: Sun Nov 26, 2023 9:15 am    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

I know this is an old thread, but I'm experiencing the same thing. Hopefully someone has had the same issue and found a fix.
*new(ish) dual master cylinder.
*new calipers in front, wheel cylinders in rear.
*new three prong sending units.
*My Bug has ALL aftermarket wiring and everything else works perfectly.
I wanted a low pressure warning light, that's why I went with the three prongs
The system works; the rear brake lights come on when the pedal is pressed, go off when pedal is released. The warning light comes on when we bleed the brakes (when loosening the bleeder). Lately when driving the brake warning light flickers and I'm assuming, due to the times I've almost been rear ended, the brake lights are acting up too.
After being parked the rear brake lights will come on all by themselves. Touching the pedal turns them off, for the time being. The low pressure light doesn't come on.
I've disconnected the wires from the senders that operate the warning light, brake lights still come on all by themselves.
Any suggestions on what we can do to solve this dilemma?
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EVfun
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PostPosted: Sun Nov 26, 2023 12:19 pm    Post subject: Re: Brake lights come on when driving and when parked Reply with quote

I recommend 2 checks. The first one must be done before the second one because it’s not correct the second test may give inaccurate results.

1. Check the free play as noted above. The point is that the master cylinder has to return all the way until the back of the piston is against the top ring in the back of the master cylinder. Mine is not the 1mm that it is supposed to be, it's more like 0.1mm. That works because anything greater than zero is enough. If the piston is pushed forward at all it will block the ports that relieve residual pressure in the system.

2. Temporarily disconnect the brake failure warning connections from the brake light switches. Wait until the brake lights are on when they should be off. Check the brake light warning terminals on the brake light switches with a test light or volt meter. Most likely one will read voltage to ground and the other one will not. The one that reads voltage to ground is good, the one no longer reading voltage to ground should show voltage on both connected terminals. Most likely you have found a bad brake light switch. It could instead be a bad master cylinder or blocked brake fluid line.
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Last edited by EVfun on Sun Nov 26, 2023 3:07 pm; edited 1 time in total
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