i wonder if they did there pre trip or just started up and left. all in all that was a good save and i don't think the truck could have landed any closer to the pump

Originally Posted by Pedigreed Bulldog

Brakes can go out without warning, without dumping your air, and without providing any indication of a looming problem. I had it happen to me this past Friday when a relay valve malfunctioned. The brakes worked flawlessly all day for 495 miles. Then, 8 miles from home a light changed ahead of me, and when I stepped on the brakes to stop the trailer locked up as though I had grabbed a handful of the trailer brake valve without touching the foot pedal. Needless to say, I was lucky there was nobody ahead of me because I was able to roll through the intersection unscathed.

When I got home, I dropped the trailer and test drove the truck in the driveway...and it was taking 40 psi of pressure to feel like it should with only 10 psi of pressure applied. I grabbed the creeper and rolled under the truck...plenty of pad on the shoes, drums not cracked, no oil or grease contamination....I couldn't see any reason why the brakes weren't working, but they weren't. I took it down to the Mack dealer on Saturday and on the diagnostic test drive, it was taking 50 psi to stop the bobtail rig. Ordinarily, that would put you through the windshield. They couldn't dig too deep on Saturday, so I had to leave it 'til today. They found the malfunctioning valve and changed it out...so I have brakes again for tomorrow.

Point is, no matter HOW thorough your pretrip inspection might be, you probably aren't going to catch a relay valve that will malfunction before the end of the day if it was working properly at the start of your day.

The thing is you were able to stop. A service brake relay valve just compensates the long travel to the trailer brakes along with a series of check valves. Without it the tractor brakes would come on and with a delay the trailer brakes would come on. When it's stuck open is exactly like you described and requires much more pedal pressure because of the long lines you now have to push air through instead of in stages.

This guy come off the interstate wide open with intentions of a soccer mom stop. Too late! But good reactions for what he had left.

Had he caught it earlier he could of used his trolly brake if he had one or even popped his emergency brake. He might of jacked knifed if popped the red button, but with a little luck and good steering he could of kept it up right.

I'm sure the age of his tractor had nothing to do with it! If you did do a brake bleed down test you would probably catch it. How many drivers do you see doing that?

I bet everyone involved is counting their blessings.