Mechanical brake light upgrade

[Von]

I'll try to remember to take some pics this evening... try to get the mounting clear.

Well that didn't happen. I'll try again tonight..

[Barrman]

To answer the question about which is best. I think the pedal switch is better for several reasons.

Driving through tall grass and brush won't pull the plug off the switch leaving you with no brake lights. Like happened to me last month in my M715.

That same brush and or small trees won't break the switch off the T leaving you with no brake lights and no brakes at all.

If the pedal switch breaks then all you are missing is no brake lights. Not so with the pressure switch. If it breaks then you might not be able to stop and not be aware of the issue until the pedal hits the floor.

I think the pressure switch being on the M715 is a function of Kaiser Jeep having them in inventory for the M38A1 contract as well. My 1952 and 1953 REO M35 Gasser trucks have the exact same switch as the M715. I have had two failed switches in the past 10 years on that truck.

The military actually has a kit to convert the fluid activated switch to an air activated one for the M35 trucks. They had all 1964 and newer M35 trucks built with the air activated switch. The best way to describe why is to tell a story.

I get calls all the time from people who have green things. Sometimes those calls are from the side of the road. A few years ago I got one of those calls from the middle of the road during a parade. A M35A2 which had started life as a M35 Gasser but converted by the military to multifuel had started throwing sparks under the truck during the parade every time the brakes were applied. The driver thought all the pointed fingers and yelling was just people appreciating his truck. Once he started smelling and seeing smoke he shut it off and got out. Blocking the parade of course. The sparks and smoke stopped with the engine because he wasn't using the brakes, not because he turned it off. Firing it back up had him thinking all was good until he applied the brakes to get rolling again. Then it repeated.

He called me at this point I think. He had gone through years of his brakes getting air into them and always having to bleed them if the truck sat for more than a week or so. I had helped a few times with that process. When he was describing what the truck was doing I had no clue what the problem was until he said instead of just having to bleed the brakes that morning, the master cylinder was totally dry and took forever to get a good pedal. I suggested he turn off the light 3 lever switch and see what happens. (I love reading the old PS magazine cartoon repair articles the military put out for decades. One of those cartoons is about this exact situation. Which is probably why I thought of the solution.) He was able to let the parade go by and get on home. He ordered the hydraulic to air conversion kit and has good brakes for a few years now.

Since wire 75 and wire 75A are the two that go to the brake switch and one of them is always hot if the 3 lever is in any position except off. Fluid getting into the contact point area of the switch could be worse than what happened to him during the parade.

Just to finish the thought. The replacement air switch for the M35 trucks isn't all that great either. I have had two of them fail on my Whistler in the past 8 years. Also, why did every vehicle manufacturer in the known world switch away from pressure switches to pedal switches? I think the VW bug was the last one sold that had it.

[Barrman]

Oh, a disclaimer. The M35A2 parade driver is not a member of the forum and as far as I know has never been on here.

[Von]

I remembered to take pics of the rotary switch mounting.




Looks like I might need to upgrade the electrical tape...

[brycer1968]

Those pics and ideas helped a lot and thanks for the stories Barrman. . .

I picked out a micro switch from a military aviation parts seller on eBay with a metal lever arm and metal roller tip and I'll try that mounted to a smaller but similar custom bracket like Von is using.

I'm looking forward to finally be able to drive my truck. Brakes are the last thing to finish

[Mikel]

My setup is just like Von's, but with a regular arm-microswitch.

[brycer1968]

I got the micro switch I ordered and had some time tonight so I TIG welded up a bracket out of some stainless steel scraps I had here. I think it turned out fine and should last longer than any hydraulic brake light switch.
I'll post some pics once I get it wired up later this week.
Bryce

[brycer1968]

Some pics of what I built using several of the ideas on here.
The bracket is stainless steel only because those are the materials I have on hand here:





http://i1108.photobucket.com/albums/...pspwdrhuo4.jpg

http://i1108.photobucket.com/albums/...psvmhhiko9.jpg

Thanks for the ideas and help.
Bryce

[brycer1968]

[Mikel]

Very nice. Just like mine, but much better executed