steering wheel shake is from bad wheel balance (most shops have issues getting it right, ive tried several and noticed there is a huge difference in how good they balance it, or maybe some of your wheel weights fell off), or it could be from slight imperfections in the rim or a bent part from road damage. if you have stock rims, im sure its just a wheel balance issue. altho ive also had bad or unevenly worn tires cause vibration.
vibration while braking would be related to a braking system part like pad/rotor.
yep, i say brakes...
i could have it bass akwards, but usually if the steering wheel vibrates its the front brakes (maybe rotors need turned), and if the brake pedal vibrates more, then its the back brakes (or drum needs turned).
? wouldnt missing wheel weights shake all the time? but it WOULD be more noticable while braking.
anyway just my .02$
__________________ 99 Civic EX
2dr, silver paint, stick shift
159,000 on the ticker
wheel balance issues usually only cause vibration between 60-75mph at high speeds. can be completely fine below or above that range. if its the tires, switching the rear to the front should change the amount of vibration. if it doesnt, tires are prolly not the cause. brakes would not have anything to do with it since you are not pressing the brake pedal.
Well if it's like your title says, "Vibration while braking at highway speeds", I would say it's the rotors. Replace or get turned if possible, along with the pads. Summit has a good deal on a slotted/dimpled rotor, ceramic pad combo. I've had these on my car for about 80,000mi, and the combo only costs about $150. The slots do make them a little noisy though if you step on them hard while at a high speed.
you can try to do some hard braking from 35mph and see if the pads get back into shape. usually "warped" rotors are just uneven pad material on the rotor. the rotor itself never changes shape. ive found that too much light braking can cause uneven buildup and usually hard braking can fix it. make sure the lug nuts are all torqued the same, otherwise you will always have problems.