Braking Woes

I have a 2007 Toyota Matrix with 110,000 miles. I take very good care of this car. Recently I had new tires along with new front brakes installed at a local National brand tire dealership. They did work to front rotors along with adjusting the rear brakes. The first time I got on the interstate and drove it at 65+, I noticed a slight shimmy every ten seconds. I took it back and they rebalanced all four tires. It still did it so I took it back. They said I had a bent rim and put the tire on the rear. Everything seemed to be fine except—when I brake while driving at about 45+; I get a hard shimmy for a brief moment. Recently I had the tires rotated and what I assumed was the bent rim is back on the front. I no longer get the brief shimmy at 65+ but now I get more shimmy when braking. What’s going on? Is it the bent rim or a warped rotor? Please help!

“They did work to front rotors”

I am going to assume that this “work” consisted of machining the rotors, rather than replacing them.
In my opinion, this is “penny-wise and dollar-foolish”, as new rotors cost only a little bit more than machining the old ones. Most brake rotors nowadays have so little mass that machining them can make them thin enough to warp very easily, thus leading to problems soon after the machining process.

But, whether one opts for new rotors or for machining the old ones, your rotors can be warped by a ham-handed mechanic who fails to use a torque wrench when tightening the lug nuts. Over-tightening and/or using different torque on adjoining lug nuts (both of which are the result of failure to use a torque wrench or failure to adjust the wrench to the proper torque specs for that particular vehicle) has ruined many a rotor.

I think that you may have no option other than replacing the warped rotors. And, in the future, make sure that anyone who changes or rotates your tires uses a torque wrench and that it is set for the correct-spec torque! Your Owner’s Manual should list the correct torque spec.