DEAR CAR TALK: I have a 2006 Buick Rendezvous. The rear end is completely gone, so I’ve been told. I am a 65-year-old, single woman. I don’t have a lot of money. What does that mean? – Ava

RAY: Not to worry, Ava. My wife tells me my rear end is completely gone, too. But she’s still sticking with me.

The “rear end” is your mechanic’s shorthand for the differential. The differential is essentially a complex box of gears that allows the wheels to turn at different speeds when you take turns. Without it, you’d be dragging your outside wheel along the pavement whenever you turn.

Typically, when the gears wear out – or the bearings fail – the differential will start to howl. You’ll hear something that sounds like a deep whistling sound that goes up and down in pitch as you go faster and slower.

Sometimes it’ll go away when you step on the gas. Sometimes it’ll go away when you take your foot off the gas. The only symptom that’s absolutely consistent is that, over time, it’ll drive you cuckoo.

My late brother had a bad differential in his Chevy Suburban, and until he figured it out, he was convinced the cops were following him around everywhere. And that they knew about the plastic coffee urn he stole from an International House of Pancakes in 1967.

If you’re short on funds and want to keep this car for a while, your best bet is a used differential. Differentials will often last the life of the car. If you found a Rendezvous in a junkyard, chances are its rear differential would be fine.

Now, we don’t want you climbing around piles of wrecked cars in a junkyard, Ava. You need to find a mechanic who’s willing to work with you and help you out.

Your mechanic probably has a junkyard or two he works with. He can call them and track down the right part for you. Then he can install it.

It’s not cheap. It’ll probably cost you between $500-$1,000 including labor, depending on how much the part costs. But you can’t continue to drive with a bad differential forever. There’s a chance that it’ll seize up on you, and that can be dangerous, especially if it happens at higher speed.

So, if the alternative is to get rid of this car, spending $500 or $1,000 bucks probably makes sense, assuming the Rendezvous is otherwise in good shape. Get a mechanic to work with you, and good luck with your new rear end, Ava.

Got a question about cars? Email Car Talk’s Ray Magliozzi by visiting the Car Talk website, www.cartalk.com.