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I know this one at first would normally make no sense, but as my neighbor found out today, the worst possible time to find out your emergency brake isn't working is on a small incline while trying to change a flat tire. He has a 2005 dodge crew cab 4x4, and today, he got a flat on the rear, on a small uphill incline, so he pulled over, put his truck in park, set the e-brake, and proceeded to jack his truck up, but everytime the wheel would be just about off the ground, the truck would want to roll down the hill on him, so, he decided to drive very slowly on the side of the road, until he could get to a flat spot and change the tire.


After moving the truck, he realized the e-brake was on the whole time, from when he set it the first time, and seemed to not be doing anything at all to stop the truck. After changing the tire, he went to a local shop that does free brake inspections, and they informed him that his e-brake shoes were shot. After talking to him about it, i had a thought. Why not carry a short pair of 4x4 wood blocks, that way you have a backup to block the wheels, and not have to be worried about your vehicle rolling away on you. i know the best solution is always make sure the e-brake works, but, at least in NY and PA, they are supposed to check that at inspection time, so most people i know don't bother checking it themselves, myself included sometimes.


Another place i see where this would be useful, is an incident i witnessed about a year ago. I was on the highway, and there was a guy towing a rather large boat, and for some reason he was stopped about halfway up the side of an incline, that was maybe half a mile long, and was changing, or rather trying to change a flat on his truck, but, because either his e-brake didn't work properly, or the weight of the boat was too much for the e-brake, the truck wanted to slide itself down the hill. He ultimately had to drive almost a mile, to where he could safely change the tire, but even then, his wife was in the truck with her foot on the brake, just in case.



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Aside from the incident of a defective E-brake, there's also the issue of drum rear E-brakes not holding as well on upward inclines.  By its very nature, a self-energizing drum brake system (short leading shoe lining, long trailing shoe lining) will not be as effective going backward as forward.  I've shared this in other posts:  The self-energizing ("Bendix" or duo-servo type) brakes work very well going forward and less effectively backward. 


Even if the E-brakes work seemingly well overall, this weakness is inherent to the design.  Have you ever noticed that an E-brake set firmly on a drum brake system may seem "off" when you accidentally back the vehicle up without releasing the E-brakes?  You go forward, and the vehicle stops immediately.  This is the self-energizing effect and related to the lining length and effectiveness of the brakes in forward versus rearward drum rotation.  There are other designs (center plane, dual wheel cylinder and others, plus all disc brakes) where the direction of wheel rotation is not an issue. 


So, biggman100 has a good idea.  If you make an emergency stop, especially pointed uphill with a drum rear brake vehicle, use wheel chocks.  Actually, any emergency stop, especially wheel and tire changes, requires wheel chocks.  If you change a rear wheel and tire on any vehicle that has the E-brakes at the rear (virtually all vehicles except those with a driveline brake), jacking up one wheel will obviously decrease the braking capacity by 50%.  Add to that an incline upward or a heavy load, and you're really in an unsafe situation.  Quality wheel chocks would help here.



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