i had the spark plugs replaced about 300 miles ago. i have 118000 miles on it. what else would i check.
Did it do this before changing the spark plugs? What spark plugs were installed? If its while you're still moving and pushing the brake, it could be warped brakes. The regen would make it more difficult to detect at higher speeds compared to most cars. If its after you stop, it could just be the ICE shutting down, especially if its still warming up.
This could easily be normal behavior associated with the engine turning off, but it could also be something wrong. Without being able to compare it to another Prius, you're going to have to give us more information. Is there a sound associated with the shaking (and if so what, can you tell where it seems to come from)? You said it is only during braking, not after you're fully stopped? If you suspect the rotors, it might help to get to ~35 mph (NOT exceeding 42, stay lower) and put the car into Neutral and come to a stop. Do this preferably on an empty street, as the braking characteristics will be different than you are used to. It will only be using the physical brakes, and no regen. I'm not sure (someone else will have to chime in) but this might also keep the ICE from turning off/on while you're in Neutral. Don't leave the car in neutral after this test, and basically never use neutral because the battery cannot be charged in neutral, and the car's electrical motors can be damaged by going too fast (I think it's 42mph+ causes MG1 to exceed its rev limit).
