Air bubbles shouldn't cause a violent shaking, it would just make the brake lines ABSORB the pressure instead of transmitting it to the brake pads. IE: The brake pedal will become very mushy and "spongey". What usually required 5 lbs of thrust can require 13lb or more to get the same hydraulic force because air and water compress easially, hydraulic fluid is designed not to compress.
Go ahead and bleed your brakes anyways since it's nice to have fresh fluids at the calipers. Better yet is to do a brake fluid flush. More of a pain but at least you know that the fluid won't be causing the shaking.
Bleeding them isn't too hard. Get a cup and take the wheels off (helps to have the car jacked up on jackstands) and a buddy to step on the brake to push the fluid out. That's about it. Read an article about it first.
warped rotors, alignment, loose->cracked\worn bushings, (lower control arm bushings most notibly) ball joints.
If your bushings are worn and you replace them, be sure they re-align your car unless you go to the dealership where they should do that anyways.
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