Dear Tom and Ray:
My Ford F-150 owner's manual points out that there are certain "jack points" for the front and rear axles. I had a puncture in the sidewall of a rear tire, so the tire needed to be replaced. The local tire dealer jacked up the rear of the truck by the pumpkin — the rear differential. I pointed out that the owner's manual says not to jack the vehicle by the rear differential. The dealer said they "do it all the time, and it does not make any difference." Please clarify for me. I would think that Ford's recommendation is more valid, but what is the reason? Thanks. — Mike
Tom: My guess is that Ford's advice is geared toward you, Mike, the owner of the vehicle. And it assumes you'll be using the jack that came with the truck to change a tire.
Ray: That jack is small, and really is for emergency use only. It's designed to lift up only one corner of the vehicle, because that's all it needs to do to allow you to swap out a tire.
Tom: So Ford, and every other manufacturer, creates jack points near each of the wheels. Those are reinforced spots that can handle the full weight of that corner of the car when you raise it up in the air.
Ray: They don't want you to jack up the car using some other point that's not reinforced, because if your improvised jack point fails and the top of the jack punctures the vehicle, the truck could come down on top of you. And that's no fun.
Tom: But if you have a hydraulic floor jack that's capable of lifting the whole truck, then there are other points you can use, if you know what you're doing.
Ray: This dealer did know what he was doing. The "pumpkin" (the rear differential that looks kind of like a pumpkin, that sits in the middle of the rear axle) is designed to carry the full weight of the truck when the truck is on the ground. If it couldn't, the axle tube would break. So we know it can carry the weight of the truck when it's in the air, too.
Tom: And, in fact, that pumpkin and axle are designed to carry much more than just the weight of the truck. Since you have a pickup, chances are you're also going to be doing what? Picking stuff up with it!
Ray: So with a proper jack, the pumpkin is a perfectly acceptable jack point. We do it all the time, too.
(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)