excessive shaking when applying brakes points to brake rotars being out of round, cracked or warped. have rotors machined
Most common cause is warped rotors.
Stepping on the brakes of a moving car is an example of
Is stepping on the brakes of a car acceleration. That would be deceleration.
YES !
he he he
Check the brakes. You may need new rotors. You didnt say how hard you stand on the brakes because if you are heavy on them it could be the abs unit working properly
warped rotors
Have the front rotors turned on a lathe at a dealership. check brakes and rotors
You probably have rusty/scored brake rotors.
Bad ground in brake light circuit
If its shaking side to side could be a tire out of balance or maybe a mechanical issue (wheel bearing, alignment, etc). Probably not a safety issue, but it can wear the tires out prematurely which can be expensive. Warped brake rotors are the most likely cause if the steering wheel only shakes when applying the brakes.
Sounds like a vacuum leak.