June 22, 2014

Car Talk

Engineers are up in arms about a recent column


Dear Tom and Ray:
Ooooh! Rarely do you guys make errors. But your recent comments about jacking up a Ford F-150 by the "pumpkin" were wrong. You said the "pumpkin is designed to take the full weight of the truck when the truck is on the ground," and that it carries the weight of stuff in the truck. That's not true. The weight of the truck and load are carried via the suspension to the axle tubes, just next to the wheels. The only reason the pumpkin/axle tube structure is required to carry the weight of the vehicle is because mechanics have historically used it as a jack point. And then it still doesn't carry the whole weight; half, or more, is carried on the front wheels or at other body jack points. So there! — Don

Tom:
I think we've heard from every engineer on the planet about this, Don.

Ray: And, by the way, if any entrepreneurial pocket-protector company would like the return address of every engineer known to man, we now have it.

Tom: Consider us corrected. The pumpkin (rear differential) does not carry the full weight of the truck, normally. The weight of the truck is spread out by the suspension system.

Ray: The pumpkin is subject to some very heavy forces. And since knuckle-scraper mechanics have, for eons, used it to jack up the back of the truck (ever since Julius Caesar first jacked up his 48 B.C. Chevus Silveradus), the engineers have made it tough enough to handle that job.

Tom: So, most of the engineers who wrote to us said that our bottom-line statement is correct: that you can get away with using the pumpkin to jack up the truck, but it's not recommended. So we will no longer recommend it to our readers.

Ray: Although we'll probably keep doing it ourselves!

Tom: Probably. But it turns out we had our heads up our rear differentials on the weight distribution. Sorry, guys! And thanks for the corrections.

(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)

Advertising

Partner video

Advertising