I have an 07 Chevy Impala and I'm trying to pinpoint the shaking that occurs when braking. Only shakes when braking slowly on highway. The whole car does shake pretty badly. I just put in a new set of tires also so it can't be that. Rotors or alignment?
There are a number of possibilities here, including:
- bad tire
- bent rim
- unbalanced wheel
- bad shock absorber mount
- other suspension parts loose/worn/missing
- steering rack
- faulty wheel bearing
- warped brake rotors
- alignment problem
Although you have just put on new tires, there is still a possibility that they weren't properly balanced or that they were, but a wheel weight has come off since then. Since most vibration issues stem from tire and wheel imbalance, check the first three on the above list first.
Because the problem only happens under braking at highway speeds (if I understand your description correctly), suspension parts are another good thing to check. Worn or missing bushings, failing ball joints, etc. can all cause annoying vibrations. Do a good visual inspection of the suspension, especially in the front.
Steering rack problems and wheel bearing failures usually make noises in addition to vibration, and they're both relatively easy to check.
Finally, warped rotors and alignment problems can cause this, but are, in my opinion, much less likely to be the culprit here. If you have the equipment, it's not hard to check the runout on the rotors and determine if they're warped or not.
I'd suggest checking things in about the order I've listed.
This seems to be more of the problem on warped brake rotors or brake cylinders itself (had the shakiness once from the 2nd one as brake caliper had gone and cylinder was touching the rotor).
I do not think this can be unbalanced wheel as you would feel the effect of unbalanced wheel without braking on highway speeds.
Also, there was suggestion that shock absorbers are defective, but I would rule that out too, as I have driven car which had faulty shock absorbers and you couldn't feel it as shaking when braking, moreof feeling like being on a boat that goes up and down alot.
My prime candidate would be shock absorbers being defective. Without the damping effect of shock absorbers you are basically bouncing on your springs. Every little bump or roadway imperfection would be felt. It would be very noticeable when braking for the simple reason of your tires having intermittent with the road. One of the things that shock absorbers do help the tires maintain contact with the road surface for improved cornering, braking effectiveness, and overall vehicle stability.