Posted by Paul Cook in Kempner, Texas on Monday, September 18, 2006 at 11:33AM :
In Reply to: Drive shaft emergency brake question. posted by Bruce on Sunday, September 17, 2006 at 5:21PM :
A parking brake on the drive line only prevents the drive shaft from turning. If one rear wheel looses traction, the differential will let that wheel turn while the wheel with traction will roll.
I learned this back in 1956 when I parked my '49 Chrysler New Yorker on a hill when the streets were covered with ice. I parked at the side of a high crowned road. The wheel on the lower (ditch) side had traction from the weight transfer and the presence of gravel. The wheel on the high (street) side was on smooth ice. The car rolled forward with the high side rear wheel spinning backward. I was able to jump back in and apply ALL 4 wheel barkes and then move the car and park it at a level spot.
This is a serious safety issue when someone is changing a rear wheel. Once the weight is off the wheel being jacked up, that wheel may turn and the car can fall off the jack.
Also, when one rear wheel is jacked up, weight is also removed from the other rear wheel and there is a possibility that the rear end may slide to one side when on a high crowned road.
The books say chock the wheel opposite the one being changed, but in a situation where the rear end might slide to one side, both front wheels should be chocked front and rear to reduce the twisting motion that might result.
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