Flaming Brake Lines

I got a phone call yesterday afternoon from a M35A2 owner 60 miles away. He had been hauling Scouts in some kind of parade and his brake pedal went to the floor. He coasted to a stop, unloaded the Boys, waited for the parade to go by and then started home in 1st low. He said he kept pumping the brakes trying to get pedal and a few blocks into the drive he smelled smoke. Then he saw filckering under the cab floor.

He doesn't know all the parts of a brake system and explained to me that "the big long thing under the pedal, but under the thing the pedal hooks to was on fire. I was able to use my gloves and put it out."

He asked me what the parts where and if they caught on fire often. I told him I had never heard, seen or read about a brake master cylinder or air pack catching on fire before.

Here is why I am posting this on the Zone. The more I talked to him, the more I found out. His brake lights had never worked and he never investigated why for almost 3 years. He had also been losing brake fluid a little each time he drove it. The older M35 trucks have the exact same brake light switch as the M715 trucks.

What probably happened was his switch was bad all along and seeping fluid. Somehow yesterday he was using the brakes enough to push fluid into the electrical portion of the switch, a spark happened and whoosh, he had fire. I told him to turn off the master light switch to off and continue crawling home. Then, I told him to print out a -20P manual, look at the pictures of all the parts and learn the names. Then, print out a -20 for that truck and follow the steps to replace it.

The military had trouble with our style brake light switches on the M35 trucks so much that they re did the system. Most of the trucks should have been swapped over to a switch that was on the air side instead of the fluid side. I guess his never got swappeed.

Just wanted to pass on what could happen if the brake light switch on a M715 has a particular failure. Since it is basically below the fuel hose on the M715. A fire there would be a bad thing. Also wanted to pass on how the military wiring and the ability to turn off everything is so cool.

If you have a brake fluid leak, find it, fix it or don't drive the truck.

Oh, I know all brake fluid will burn at some point. However, I think if he had kept using BFS instead of DOT3. He probably wouldn't have had a fire. The military switched over to the Brake Fluid Silcone for a reason. Buy it in gallons over the internet and it is cheaper than DOT 3 too.

Wow...would have never thought of it...thats a good one to keep in mind!

Thanks for the comprehensive heads up!!

Had the same thing happen last year on my M715. Went outside about 2200 hrs looking for my cat and smelled rubber burning, opened up the door of my truck and got hit in the face with a cloud of smoke. It hadn't caught fire yet I was able to disconnect the battery before that happened. Investigated the next morning what was burning and it was the brake light switch leaking through to the connectors. Put on a new one and did a rewire so all the power goes off when I turn off the master switch.

Good catch...wow.

I have seen this before but on newer fords cruise control, they had a big recall.
Wonder how long till some one makes this same mistake again like ford did.