Q. Dear Tom and Ray:

My friend Sammie has been nursing along a 1989 Pontiac Bonneville with a 3.8-liter engine that has what her mechanics call a "bad harmonic balancer." As I understand it, these devices are counterweights, designed to cancel engine vibration and reduce noise. Does she have to replace the harmonic balancer? Or can it simply be disconnected, with some sacrifice of driver comfort? Thanks.

-- Bob

A. TOM: "Some sacrifice of driver comfort" would be putting it mildly, Bob. The harmonic balancer is essentially part of the crankshaft pulley. And since the belts that go around the crankshaft pulley run all of the car's accessories, without the harmonic balancer you'd have no air conditioning, no power steering, no alternator and no water pump.

RAY: Plus, it does have a role in "balancing" the crankshaft. And without it you can do damage to the crankshaft and the engine bearings. So you really do have to replace it.

TOM: A new harmonic balancer costs somewhere around $150 or $200, Bob. But you can buy a used one at a junkyard, and that'll balance your harmonics just fine.

RAY: And it's an easy repair to do. There's one bolt that holds it onto the crankshaft. Even my brother could handle this, Bob. So tell Sammie to get it fixed.

Dear Tom and Ray:

I just bought a 1996 Subaru Legacy Outback Wagon. This is an all-wheel-drive wagon that comes with one of those stupid little Dunkin' Donuts mini-spares instead of a full-size spare tire. I've heard that if you have to use the mini-spare, you're supposed to disengage the all-wheel drive so you don't mess it up. Is there any reason (besides money) that I shouldn't just buy another 15-inch rim and stow a full-size spare in the back?

-- Dave

TOM: There's no reason you can't do that, Dave. But personally, I don't think it's necessary.

RAY: You do want to avoid using a mini-spare in all-wheel-drive mode, because using one smaller tire could damage the center differential. But taking this car out of AWD mode is a piece of cake.

TOM: To put the car in "front-wheel drive only" mode, all you have to do is insert a fuse. The procedure is described in your owner's manual, and it's really very simple.

RAY: Plus, the mini-spare is not stupid, in my opinion. It may look flimsy (okay, it is flimsy), but it's really quite adequate for emergencies. It's good for about 50 miles, which is enough to get most people home, or to a gas station, or both.

TOM: If you live out in the boonies and often find yourself more than 50 miles from civilization, then it makes sense to have a full-size spare. But for most people, it's just not necessary. And besides, flat tires are becoming rarer and rarer these days, because of significant improvements in tire quality.

RAY: Then there's the issue of room. While many cars have room for a full-size spare, some do not. I don't remember whether the '96 Legacy has a full-size well for a spare tire, but check before you buy one or you may wind up with a permanent tire-sculpture-art installation in your cargo area.

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(C) 1999 by Tom and Ray Magliozzi and Doug Berman