Coach Just Burned

[Mike Shumack]

It's fun to speculate -
I don't see anyway that the springs (both sides) got hot enough to loose tension. The springs would need to get red hot to loose tension. I think it is more likely the heat melted the back of the pressure housings (or center section) letting the springs "blow out".
We need a photo 

[Fred Brooks]

   You are right Mike, the springs thickness compared to the canaster stamped thickness validates your point. Fred

[Steve Huber Co-Admin]

The springs do not have to get red hot to fail. See https://www.osti.gov/servlets/purl/1241122 and select "View Conference".  Spring constant drops off due to heat at about 500C and accelerates as temperature increases (see fig 6 in ref). The temperatures of a normal fire (e.g campfire) are 700C in the fire, 585C in the middle of the campfire (coals but not flames), and 400C at the outer edge of the fire. Looking at the picture, it appears the coach got hot enough for the frame to fail. Tires melt at 600C.  Bottom line, IMHO, the heat was more than enough for the air brake springs to fail. Steel or iron must get to 900C to get red.
(Edit note: specified location of paper on web reference above)
Steve

[Dave Atherton]

Gentleman, air systems and spring brakes on rear axles. Think about this thought how spring brakes
operates. Air pressure release the spring brakes, or called maxi-brakes to move Motorhome down
the road for some reason rolling down the road you lose your air pressure. What happens after the
air pressure on motorhome dash gauge drops to 60 psi air warning buzzer sounds , when air pressure
drops to 50 psi the spring brake apply and lock up wheel and cannot be released . The only way to
release the spring brake or what called maxi-brake ( repair air leak or manual insert brake release
With a t bolt made to manual release spring brake.) the spring brake is used as a parking brake and
Applying air will release spring brake by pushing in yellow button. Last thought inside of brake drum
there are ( 2 ) small springs that keep brake shoes tension on rollers the movement apply and release
brake shoes. It would take very little heat around these springs to loose tension and would release
the brake shoes against brake drum and the coil inside the spring brakes did not release arm
movement on parking brake applied. Dave Atherton Retired Cat Mechanic

[Lee Welbanks]

I assume that a 08 would have disc brakes, I have to go look but I believe that the maxi brakes on my coach have stamped steel cans. If the fire got hot enough to melt the cans I would think that there would not be any tires left on the rear of that coach.
Norm do you know just how the coach ended up out in the street?

[Norm Green]

The build sheet indicates my coach had the Roadmaster S chassis and did have disc brakes on the drive axle.  The fire was obviously very hot and the rear tires were burnt down to the steel bands.  Here are a couple of pictures.