Author Topic: brake light switch  (Read 3884 times)

Offline David Anderson

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brake light switch
« on: November 26, 2007, 06:12:51 PM »
My brake light switch leaks around the terminals when I release the parking brake.  This is the switch that engages the brake lights when the parking brake is on.  It is a N.C switch.  I took it apart and the little rubber washer is old and is what is leaking.  I flipped the washer 180 deg. and it slowed the air leak some, but still can feel air blowing on my hand.   

I went to NAPA and a standard 60 psi switch is $47.  Wow,  a lot of $$ because of a .60c washer.  Unfortunately, there is no brand name on the switch.  Anyone know of a better source to replace the switch?

David

Dallas

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Re: brake light switch
« Reply #1 on: November 26, 2007, 08:08:11 PM »
David,

Go to your local wallyworld and buy yourself a $5 silicone baking/cutting mat in the household section. Make yourself a new diapragm/gasket with that. It should last another 50 or 60 years, if you don't abuse it.

Dallas

cody

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Re: brake light switch
« Reply #2 on: November 26, 2007, 08:26:46 PM »
I'm just amazed at the amount of usefull information dallas has stored in the dismal swamp, I had heard at one point that useless trivia that gets remembered outnumbers all other thoughts by a ratio of 10 to 1, and that really scares me because it doesn't seem to matter what the topic or question is, the right answer or at least a version that will help seems to pop out, now if only he could remember where he left the remote. lol  The silicon baking mat does work tho, I've cut gaskets, washers etc out of them and they do hold up well lol. 

Offline David Anderson

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Re: brake light switch
« Reply #3 on: November 27, 2007, 07:47:13 AM »
Brilliant.

The best minds in the world dwell in this bus-nuthouse. ;D ;D ;D

Dallas

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Re: brake light switch
« Reply #4 on: November 27, 2007, 08:12:39 AM »
This is an air pressure regulator I rebuilt as an exercise to show how to make a quick roadside repair

Dallas

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Re: brake light switch
« Reply #5 on: November 27, 2007, 08:14:11 AM »
In Progress

Offline David Anderson

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Re: brake light switch
« Reply #6 on: November 28, 2007, 05:55:32 PM »
Rats, it didn't work.  I cannot cut a perfect circle on the pad and this washer has to be perfect to hold that air.  It is a bit smaller than a dime in diameter.  Back to searching for a switch.  Anyone know of one less than the $47 at Napa?

David

Offline TomCat

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Re: brake light switch
« Reply #7 on: November 28, 2007, 06:17:18 PM »
David,

Try a leather shop, and ask them to punch one out for you with a hole punch (not the plier kind) and hammer.
A parachute rigger should be able to do the same.

Jay
87 SaftLiner
On The High Plains of Colorado

Offline akroyaleagle

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Re: brake light switch
« Reply #8 on: November 28, 2007, 08:30:17 PM »
David, Are we talking about the one below the driver in the lower access?

I got mine from Hector at CHF some years ago. I think it was less than $20. I could probably look up the receipt for it or you could just call his son. He tried to talk me out of by suggesting I jus tgo to a truck parts store and get one but I wanted his Eagle one.

Have you tried Jefferson or Eagle?

Joe Laird
'78 Eagle
Sioux Falls, South Dakota

Offline David Anderson

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Re: brake light switch
« Reply #9 on: November 29, 2007, 05:03:05 PM »
David, Are we talking about the one below the driver in the lower access?

I got mine from Hector at CHF some years ago. I think it was less than $20. I could probably look up the receipt for it or you could just call his son. He tried to talk me out of by suggesting I jus tgo to a truck parts store and get one but I wanted his Eagle one.

Have you tried Jefferson or Eagle?


No I haven't tried them. 

Yes it is below the Eagle wiring panel where all the air switches are.  It is a NC switch that sends 12v to the brake light relay coil when the parking brake is engaged.  When the parking brake is released the air line is loaded and disconnects the switch.  This is when it leaks which would make it leak all the time the bus is rolling down the road.

David

Offline gmbusguy1

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Re: brake light switch
« Reply #10 on: November 29, 2007, 05:18:26 PM »
I know that I had one of these switches purchased for an 4104 and was the wrong pressure, I am almost sure it is a 60 psi normally closed

THE SEARCH IS ON ..........when I find it i'll let you know

chris

Offline JackConrad

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Re: brake light switch
« Reply #11 on: November 30, 2007, 04:35:08 AM »
    On our MC-8 we installed a brake application pressure gauge. Normal braking is 10-20 PSI. A 60 PSI switch not not activate the brake lights except in a hard panic stop. We do have a 60 PSI N.C. switch for the LOW AIR warning. Our brake light switch is about 3-5 PSI N.O. (confirmed by watching brake application pressure gaue and brake light telltale). Hope this helps, Jack
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Offline David Anderson

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Re: brake light switch
« Reply #12 on: November 30, 2007, 02:46:47 PM »
    On our MC-8 we installed a brake application pressure gauge. Normal braking is 10-20 PSI. A 60 PSI switch not not activate the brake lights except in a hard panic stop. We do have a 60 PSI N.C. switch for the LOW AIR warning. Our brake light switch is about 3-5 PSI N.O. (confirmed by watching brake application pressure gaue and brake light telltale). Hope this helps, Jack
You kind of have me thinking now.  This is on the parking brake circuit and I think when the parking brake is disengaged it blows full tank pressure on the switch.  I'm not sure if the brake pedal actuation while driving affects this switch.  However, I'm not sure.   I think I will put a pressure gauge on the circuit and see what happens with a service brake application, so I can find out what pressure this switch really is.

Thanks for the heads up Jack.

David

Offline FloridaCliff

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Re: brake light switch
« Reply #13 on: November 30, 2007, 03:18:00 PM »
David,

Different bus, but same problem.

Your post reminded me that I need a diaphram for a small, but annoying air leak on mine.

Called Mike at US coach and after a little research, he found me the rebulid parts, $5.00 for my 4905's.

If anybody can get you yours, I bet Mike or Luke can!

He told me most just order a new one(not as cheap as me  ;D) but I like to tear things apart.

Best of luck on your fix

Cliff

 

1975 GMC  P8M4905A-1160    North Central Florida

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Offline David Anderson

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Re: brake light switch
« Reply #14 on: December 02, 2007, 07:04:19 AM »
I put a gauge on it and it is 100+/-psi when the parking brake is off and 0 psi when the brake is engaged.  No proportional change when the service brake pedal is pushed.  So, it is just an on/off switch.

David
« Last Edit: December 02, 2007, 07:32:21 PM by David Anderson »