Brake switch mystery... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**HIGHWAY BY THE SEA** · 12-07-2018, 07:15 PM

I was told when I bought my 67 GMC 3500 by the Previous Owner that the Previous Previous Owner had installed a different engine in it. I also noticed that the steering wheel is a 1970s one, but the steering column looks 67ish to me.
But the brake light switch that was installed in it has "shaved" sides, right on top of the threads for the retention nut. So I bought a new switch today, and when I went to install it I found that the hole for the switch to mount in is SQUARE, and will not accept the factory-correct round one. What The Hell?!?!?!
Now I know why the old one was shaved. But what type of switch fits a square mount hole? Was there some weird type of square-shaped brake light switch for these back in 1967?

Andy4639 · 12-07-2018, 07:21 PM

Not that I have ever herd of. My 67 has the round one like my 71.

**michael bustamante** · 12-07-2018, 07:27 PM

my 67 is round as well. but mines a chevy not GMC
does you 3500 have a power brake system?

ray_mcavoy · 12-07-2018, 07:28 PM

It sounds like a previous owner may have mounted the brake light switch in the hole that's normally used for the rubber bumper that the pedal arm hits against at the upper limit of it's travel. If I remember correctly, those rubber bumpers fit into a square / rectangular shaped hole.

**HIGHWAY BY THE SEA** · 12-07-2018, 08:20 PM

Quote:

Originally Posted by ray_mcavoy

It sounds like a previous owner may have mounted the brake light switch in the hole that's normally used for the rubber bumper that the pedal arm hits against at the upper limit of it's travel. If I remember correctly, those rubber bumpers fit into a square / rectangular shaped hole.

Mystery solved!!! After I read your post I went outside and checked, and it appears that this is EXACTLY what he did! The shaved switch fits perfectly into that square hole (missing it's rubber stopper). I have never installed a brake light switch into a 67 - 72 GM before, but I thought that the setup looked strange. Good call Ray! And thanks to all who responded!

**Steeveedee** · 12-07-2018, 08:31 PM

So what stops the brake pedal lever when it comes back up? That might be why the switch needs to be replaced, if the switch is doing it.

Andy4639 · 12-07-2018, 08:52 PM

Ha! You got to love people who improvise!
That would explain the square and yes thats why the switch has stopped working taking the hit everytime you let off the pedal.

The switch is up over top of the column and is a hassel to get out and back in. I have a 1x1 about 1ft long I wedge in between the pedal and seat bracket. This holds the brake down until I get the switch out and the new one back in. Then I release it and adjust the switch. Then I set it again to tighten down.

**Steeveedee** · 12-07-2018, 11:36 PM

Quote:

Originally Posted by Andy4639

Ha! You got to love people who improvise!
That would explain the square and yes thats why the switch has stopped working taking the hit everytime you let off the pedal.

The switch is up over top of the column and is a hassel to get out and back in. I have a 1x1 about 1ft long I wedge in between the pedal and seat bracket. This holds the brake down until I get the switch out and the new one back in. Then I release it and adjust the switch. Then I set it again to tighten down.

Yes, I've replaced the switch in the past and I'll agree that it is a real "sweetheart" to replace.

12-07-2018, 07:15 PM	#1
HIGHWAY BY THE SEA Senior Member Join Date: Nov 2012 Location: BY THE CAROLINA SEA Posts: 922	Brake switch mystery... I was told when I bought my 67 GMC 3500 by the Previous Owner that the Previous Previous Owner had installed a different engine in it. I also noticed that the steering wheel is a 1970s one, but the steering column looks 67ish to me. But the brake light switch that was installed in it has "shaved" sides, right on top of the threads for the retention nut. So I bought a new switch today, and when I went to install it I found that the hole for the switch to mount in is SQUARE, and will not accept the factory-correct round one. What The Hell?!?!?! Now I know why the old one was shaved. But what type of switch fits a square mount hole? Was there some weird type of square-shaped brake light switch for these back in 1967? __________________ FRANKENTRUCK 1981 Chevrolet C10 Shortbed Stepside GRANDTRUCK 1968 Chevrolet C10 Stepside Longbed http://67-72chevytrucks.com/vboard/s...d.php?t=584617 PROJECT JIGSAW 1967 GMC C3500 GREAT WHITE 1986 Blazer M1009 454 engine w/700R4 transmission gas conversion

12-07-2018, 07:21 PM	#2
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Brake switch mystery... Not that I have ever herd of. My 67 has the round one like my 71. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

12-07-2018, 07:27 PM	#3
michael bustamante Senior Member Join Date: Sep 2007 Location: Albuquerque NM Posts: 7,862	Re: Brake switch mystery... my 67 is round as well. but mines a chevy not GMC does you 3500 have a power brake system? __________________ 1967custom

12-07-2018, 07:28 PM	#4
ray_mcavoy Registered User Join Date: Nov 2009 Location: Sherman, ME Posts: 2,366	Re: Brake switch mystery... It sounds like a previous owner may have mounted the brake light switch in the hole that's normally used for the rubber bumper that the pedal arm hits against at the upper limit of it's travel. If I remember correctly, those rubber bumpers fit into a square / rectangular shaped hole.

12-07-2018, 08:31 PM	#6
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,676	Re: Brake switch mystery... So what stops the brake pedal lever when it comes back up? That might be why the switch needs to be replaced, if the switch is doing it. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

12-07-2018, 08:52 PM	#7
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Brake switch mystery... Ha! You got to love people who improvise! That would explain the square and yes thats why the switch has stopped working taking the hit everytime you let off the pedal. The switch is up over top of the column and is a hassel to get out and back in. I have a 1x1 about 1ft long I wedge in between the pedal and seat bracket. This holds the brake down until I get the switch out and the new one back in. Then I release it and adjust the switch. Then I set it again to tighten down. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.



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