Long ago, as a green undergrad, I decided to take my car out after a heavy snow – simply to see what it was like to drive in bad winter conditions, as I had never driven in snow before.I didn’t get far. Turns out, our parking lot was covered with ice. When I tried backing my car out on the slightly sloping parking lot, my car slid over and gently contacted an old car parked next to me. Luckily, no damage, but now I had a new problem. The elderly man who owned that car came outside and happily reassured me not to worry about his car, then offered an idea as to how I could free my car.
“Jack up your car about 12 to 16 inches,” he said, “then push your car off the jack, away from my car. Do this a few times and you’ll be fine.”
My father warned that the jack would be carrying a lot of weight and might “kick out” and shatter my leg. My neighbor whispered to me that no such thing would happen. After mulling my options, I followed my neighbor’s advice, which admittedly sounded a bit risky.
It actually worked. By jacking up my car 5 times and each time pushing it off the jack (it was an old school jack–not a scissors jack or bottle jack), I managed to separate the two cars. Interestingly, there was no kickout or kickback at all. Zero. My car simply fell off the jack, with no recoil. Kerplop!
Was I lucky or is this simple physics? Please explain.
All I can offer is that I’m better at controlling a car than a jack. If I couldn’t control a car on the ice, I’d have serious doubts about my ability to control a jack on the ice.
Point #1-- All 4 tires combined have a much larger contact area than the jackstand does.
Point #2-- From the description, it sounds like you would have had to push uphill in order to push your car in the correct direction. The slope had to have been VERY gentle, or you would not have had the strength to do that. Cars are heavy. Any significant slope would have sent your car downhill.
I would say that you got lucky. There are multiple ways that you could have been injured. The old man’s advice was more suited to a FLAT surface.
I assume the OP is talking about a bumper jack, one that hooks under the bumper and lifts the car by the bumper (these were much faster and easier to use then scissors but went the way of the dodo).
ETA: I can see this working if the OP chipped the ice away from under the jack first, and if it was indeed a bumper jack.
I was indeed using a big bumper jack, which I had positioned on an ice-free patch of pavement and attached to the rear bumper of my car. The parking lot was very very gently sloped, with the downhill portion on the driver’s side of my car. The left/driver side of my car was touching the next car’s right/passenger side. The ice was indeed very slick. Once I raised the car with the jack, I placed my hands on the car’s left rear corner and pushed it hard, right off the jack. I was a strong kid and recall a good, hard shove toppling the weighted jack right over, causing the car to move farther “uphill” about 10-12 inches each time.
I also vaguely recall my clearing the ice away from the uphill landing path of my car, to avert Saint-Cad’s scenario. Once I had separated the two cars, my elderly neighbor chuckled and congratulated me. My father, ever the hard ass, ended that episode by telling me how foolish I had been to drive a car with ice/snow on the ground – and he hailed from upstate Michigan!
I have several old cars from the 50s/60s and yes, this would work as these style of jacks are quite “tippy”. Now did this constant tipping the car off the jack damage the jack’s tang that inserts into the bumper or bend the jack stem or base? I would have inspected it before the next use. Would be safe if one was standing off to one side if the jack did “kick out” while tipping it off the jack.
These style jacks are very dangerous and I would not change a tire with them and I would NEVER get under the car while using one. Screw jacks from more modern cars/trucks under the axle won’t work with my old cars as the body needs to be lifted up (lifting from the bumper) for the fender lip to get high enough for the the tire to clear. I use an aftermarket jack from that era that is a tripod type with 3 legs stabilizing the jack. Even then I am nervous when changing a tire. Luckily with the limited miles I drive these cars (and during nice sunny summer weather) I have only needed to change a tire once in 30 years. Plus, if going on a longer old car tour I put a set of quality jack stands in the trunk just in case I need to crawl under the car to do repairs.
My question: How likely is it that a loaded bumper jack will violently or dangerously
“kick out,” if things go awry? I noticed no worrisome action at all. The jack simply fell over when I shoved my car off the jack. Given how much weight the jack was supporting, my tipping action looked so benign that it was a bit surreal. It didn’t make sense to me but I finally decided to end my physics field experiment instead of capping it with a trip to the ER.
BTW, small bottle jacks do not strike me as very safe either.