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Loud thumping

I have a 2000 Mercury Sable sedan with 150k miles on it. Recently (as in today) I noticed that, whenever I turn left, there is a loud thump coming from around the front driver’s side wheel area. What could this be? And does anyone know how much it runs to get something like this fixed?

First stab at the cat(sorry KAT) is a bad cv joint, I don’t know pricing but $700 would not surprise me.

could it also be the boot?

The cv joint failure is usually related to a boot failure as the boot failure lets water dust and debris into a sealed system that leads to failure. Typical cv joint repair includes a new boot.

I suspect waterboy is right. It all fits.

If the boot has been cracked for an extended period of time, then the boot is likely to be the reason for the apparently failing CV joint.

By itself, a cracked boot is not a problem unless the owner defers replacement of the boot long enough so that dirt and grit contaminate the CV joint, thus eventually destroying the joint. Personally, if I discovered that one of my CV boots was cracked, I would not drive the car for more than a couple of weeks before replacing the boot.

Could be any of several things – some fairly trivial, some dangerous. It could be a Constant Velocity joint which will cost a number of hundred dollars to fix, but won’t kill you. At worst it will leave you stranded with no way to get power to the wheels. But the classic symptom of a bad CV joint is a “card in the bicycle spokes” sound, not a thunk.

It could be a bad ball joint, tie-rod end, or wheel bearing. Those could kill you when the wheel falls off or the steering fails.

It could be something else. A broken strut maybe. A broken strut mount. A broken motor mount. Even a loose brake caliper or loose lug nuts if anyone has had a reason to remove the tire recently and forgot to tighten the nuts.

Anyway, I’d drive (slowly) to a mechanic and get it diagnosed. Once you know what is wrong, you can worry about cost and whether you need to fix it immediately.