What are the likely causes of steering wheel shake / vibration when breaking? My car is an 04 seat leon with 50k miles on it.
ETA: I’ve just done a search, and it seems the answer could be warped brake rotors. If this is indeed the case, and given that the rotors on my car were replaced at the last service 6 months ago, any thoughts on what might be wrong with the rotor set-up that’s causing the shake? Or could it be something else?
The rotors may have been cheap ones, and they’ve warped from use
The brake caliper could be sticking, leaving the brakes slightly engaged, which will heat up the rotors, causing them to warp.
There may have been a lump of rust or whatever on the hub, preventing the rotor from seating properly, and the rotor is simply “wobbling” rather than being warped.
If the rotor wasn’t seated properly, that’s probably fixable by cleaning its mounting surface, but for the other causes, warped is warped, and you need to address why they warped - eg: use better ones, or check the caliper to see why it’s sticking.
It’s braking, not breaking, unless the brakes are broken. 
Last time I had severe steering wheel shake, I took it in to have the tires balanced and they found a big wad of mud stuck in one of the wheels casuing the balance to be off. Something to check out.
Out of balance shows when when ever the speed of the car is right. Brake vibrations only show up while braking.
You could argue that if the steering is shaking the brakes are broken, but you of course are correct. It’s braking.
Is it only when braking ? And not while doing say highway speed.
Declan
Sorry I read “steering wheel shake / vibration when breaking” not as steering wheel shake/vibration while braking but rather as two separate issues 1)steering wheel shake and 2) vibration when braking. The spaces on either side of the slash through me.
Have you had any service on the front end that required the wheels removed? If the lug nuts/bolts were over-tightened in the wrong sequence, it could cause rotor warpage
Between Busy Scissors breaking his/her car, and the slash through Joey P, this is an unexpectedly violent thread! :eek: 
Thks all for the replies. It sounds like one of those car jobs that I could do myself - I’ve been thinking of making a start at basic car mechanics. I suggested this to my wife last night (it’s our only car, but she drives it almost exclusively), I was working on my mountain bike and told her that the brakes were probably just the same between the 2 vehicles. She said 'Don’t you 'king dare start messing round with my car!
So I guess it’s back to the garage.
Between the bike and the car? There actually is a similarity in the basic design principle (caliper pressing braking material against a rotating part associated with the wheel). There are a few noticeable differences in the details, however. 