DEAR CAR TALK: I have a delicate question.
In a late-1960s/early-'70s round-headlight Ford van, how possible is it for two people in the back of this van to actually get the van visually moving up and down?
I have a sister who says she saw a van that I was in reacting this very way in an apartment parking lot close to 5-5:30 p.m. I know this did not happen because, while I was in this older van, I was sitting in the front passenger seat. If you need this for your calculation, I weigh about 120 pounds, and the man in the driver's seat weighs at most 160-170.
OK, if this scenario did take place ... as far as two people in back of the van ... my thoughts are that no way are they going to be able to get that older van to visually move up and down so that someone on the outside could see it.
My sister said it was moving. She said, "Very much visually up and down." This was a generic work van for upholstery type work. Again, this did not take place. I would just like to put to rest the inconceivable thought that it's even possible that my sister saw what she says she saw.
— Calli
DEAR READER: Upholstery, huh? So I bet it was nice and comfortable in back.
I'm afraid it's more than possible. It's so possible that a "rockin' van" is a cliche. When we test shocks on a customer's car, the way we do it is by simply pushing down on each corner of the car. And if the shocks are worn out, with each push, the movement of the car increases, until it's bouncing up and down. That's called simple harmonic motion.
Think about a swing set at the park. You push it once, and it goes out and comes back. And if you catch it at its farthest point and push it again, you add to that momentum, and it goes farther out and comes farther back the next time. Shocks can behave the same way. Even more so when they're worn out.
I know I can create that "up and down" motion on the corner of a car all by myself. So certainly, two people can do it. In fact, if you really want to entertain your sister, Calli, you can also get the van moving side to side.
If you want a plausible defense, if you were laughing and moving around in your seats in an older van with worn-out shocks, you could probably make the van move that way, too. So maybe tell your sister that Upton the Upholsterer has a particularly keen sense of humor.
And then suggest he may want to get his shocks checked and replaced if necessary. Newer shocks might provide more cover next time.
DEAR CAR TALK: I have a strange question about my old 2006 Saab SportCombi Wagon. Every morning, I drive over a very steep and windy mountain road. The start of the road is about three miles from my house, and it's typically cold in the morning, so the heat is on.
As I drive up the mountain, I'll make hairpin turns (rather quickly, which is why I bought the Saab). That causes the vents to stop blowing heat and blow cold outside air. I'll straighten out of the turn, and the vents return to heat then go into another chilly turn.
I'm curious what causes this.
— Connor
DEAR READER: You have a vacuum problem.
Have you tried changing the bag? It might be full of cat hair. Actually, the blend doors inside the ventilation system — the flaps that direct warm or cool air into the cabin — are controlled by vacuum motors.
Vacuum is produced naturally by the engine when the piston draws down. You create the greatest amount of vacuum when your engine is idling and the throttle is closed, and the least amount of vacuum when the throttle is wide open and you're accelerating hard.
And you say you're accelerating through those uphill turns. That means you're creating a low-vacuum situation.
Normally, that shouldn't be a problem. Most cars use check valves and vacuum reservoirs to maintain enough vacuum during hard acceleration to keep things working. But there's obviously something wrong in your car.
You might have a bad check valve or a cracked or leaky vacuum reservoir. Or you might have a small vacuum leak somewhere else in the engine that's draining enough vacuum so the reservoir can't do its job.
So take it to your Saab dealer, Connor. Sorry, that was unnecessarily cruel. I'm sure you have a mechanic who has kept the thing running for the past decade and a half. Ask him to check it out and see if he can figure out why the vacuum is dropping too low. He can check for vacuum leaks using something called a "smoke test." That test does not involve any fire, Connor. So don't get your hopes up about getting a new car with the insurance money.
Ray Magliozzi dispenses advice about cars in Car Talk every Saturday. Email him by visiting
cartalk.com