Those shimmying front wheels might indicate some warped rotors.

Dear Car Talk

Dear Car Talk | May 01, 1999

Dear Tom and Ray:

I drive a 1987 Acura Legend with 62,000 miles on it. It has an annoying problem. The front wheels shimmy when the brakes are applied. The brake rotors have been turned, the steering gearbox valve rack guide screw has been adjusted, and its spring has been replaced. Any other suggestions? -- Rex

RAY: Well, wobbly steering while braking is a classic sign of warped disc rotors, Rex. So even though your rotors have been refinished (also called "machined" or
"turned"), I think they bear further investigation here.

TOM: Ask a good mechanic to take off both front wheels and put a dial indicator on the rotors. The dial indicator will show if there's any "run out," i.e., if the discs are
warped, even very subtly.

RAY: If they are showing some warp, then find a shop that can machine them ON the car. By machining the discs on the car, you account for any slight imperfections in
the hubs and end up with a better result.

TOM: If you're not able to machine them flat on the car -- i.e., if the dial indicator still shows run out -- that suggests to me that you may have a bent hub. Hubs can bend
when you bang into curbs, hit serious potholes or try to run over portly in-laws. And a bent hub could mimic the symptoms of a warped disc rotor and cause a shimmy
on braking.

RAY: If the original dial indicator test shows that the discs are perfect, then you've got to look for something more unusual. And one thing I'd check is the rack itself. I
had a case recently where the steering rack itself was coming loose (there are bolts that hold it to the frame of the car). And if that's the case, any imperfections in the
tires could cause the rack to wobble. And yes, that IS dangerous, Rex, so get the car looked at soon.

Order Tom and Ray's best-selling pamphlet Ten Ways You May Be Ruining Your Car Without Even Knowing It! You?-re probably doing at least one of them! Send $3
and a stamped (55 cents), self-addressed, No. 10 envelope to Ruin, PO Box 6420, Riverton, NJ 08077-6420.

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

Distributed by King Features Syndicate, Inc.

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