The Alcon Brakes are no use with street tyres as the brakes are so strong they will cause the ABS to activate. The only value is, if you are running slicks on a race track. You will find these brakes will squeal like crazy once they've done 10,000km as the scallops depth is reduced on the discs. They are fantastic brakes though.

 

i experienced this issue on another car. The culprit was a separated radial belt in one of the front tires. Easy fix, get new tires.

 

A GT car running the 24 hours of Le Mans might cover half that distance.

Depends on the driving of those miles if it needed brakes or not.

Even the weaker brakes on my XK can get the ABS to activate.
What is unique to the Alcon's on the car's that came equipped with them is they are a much more expensive fixed caliper design instead of floating caliper.
This is combined with three pistons per side each sized to the proper clamping force for that part of the pad.
The Alcon gives INCREDIBLE control and makes it much easier to get and hold the limit instead of over shooting or undershooting.

 

Im surprised no one has mentioned wheels.

Have you hit a pot hole recently? Bent or out of balance wheels will give you this issue.

I had the same thing, ended up buying new wheels and had them road force balanced - no more steering wheel shake.

Edit: never mind, I just saw the title says 'when braking'

 

Also consider a dodgy wheel bearing/s.
I had the experience after driving thru flood waters and about 1 week later same symptoms.
Thought it was brakes. Turned out to be mild rust forming on wheel bearing due to water penetration.
Not saying this is your cause, but who knows if your wheel bearings have a problem from another cause...
Worn tie rod or similar is the other place to look.

 

yes your rotors are warped just take a little bit of movement to move your steering wheel take them off and have them turned get new pads and enjoy your ride

 

The only way to warp a rotor is to bring it to it’s melting point which is nearly if not impossible to do with brake pads. What many including mechanics mean when the say warped is likely pad glazing on the rotor surface which can cause an uneven surface which in turn causes pulsation vibration.

 

I've been trying to work out the physics of a bushing in need of replacement causing steering wheel shake under braking(only?).
I would expect a weak bushing with play to reach the end of that play under force, no shake.
You'd just have an undesigned alignment change under braking.
Not a continuing shake

From long range, it is hard to tell.

A question, in a straight on level pavement that isn't crowned, if you are finger tip touch only on the steering wheel, is it still there?

 

I’ve had this “warped rotor” problem on my’08 XKR for three years and after much study and parts replacement I found that the unadjustable torque on the front wheel bearings caused the problem. I replaced both front wheel bearings and the shaking stopped which makes me believe that the preloaded bearings were too loose. I hate the fact that I cannot use a torque wrench to experiment with the preload because there is no large torqueable nut but a factory preset “rivet” design that is affected by brake rotor heat that loosens the bearings and caused the whole assembly to shake violently the hotter everything gets.
The smooth braking lasted about 5k miles then returned and I’m resigned to live with the shake. The car has only 50k miles on it but I’m ready to sell it. The non adjustable bearings are a DESIGN FLAW.
I haven’t heard of any way to resolve this problem but I wish the earlier design could be retrofitted.
Bill Schultz

 

Car has new tires. Less than 300 miles put on in June.

 

I drove my car yesterday. Some interesting things..the shake only happens under light/normal braking but goes away depending on the force demanded through the brake pedal. I don't think its my rotors/pads.

I plan to replace my lower control arms in the spring to see if this corrects my issue. I will report back.. next spring.

 

Last Mercedes I had came with brand new Conti's. The car shook all over the highway. I took it back to the dealership 3 times and finally one of the techs had a thought and swapped the wheels from another car, problem went away. They then checked the wheels (again) and finally put another new set of tires on and that solved that. The car pulled when I hit the brakes but didn't shake like you describe. Did the timing of the shake align at all (no pun intended) with the tire purchase?

 

Hi Sean,

No, my original tires (yes, I know how unsafe that was..) were doing the same thing. Funny thing..I did put Conti extreme contacts on!

 

Hi All,

Just a quick update. My front right wheel had a pretty big bend it it. Issue is mostly solved. I imagine the slight pulsating is now from the brakes and rotors (85% improved from before).

I didn’t suspect this. The tires were replaced last summer and road force balanced and the last shop didn’t mention the bend.

I will report back after the end of the summer.

 

Thanks for reporting back, brilliant news, and glad it's mostly sorted.

Weird that the tyre place didn't spot, unless damage was done since fitting?

Consolation is my alloy wheel refurb/repair specialist advises that jaguar wheels are soft alloy and easy to work on, unlike he says BMW, which are so brittle they shatter and most are not repairable.

 

Years ago I read a motoring article on the subject of warped discs , it was written by some American racing legend who said no such thing as a warped disc , can't remember his name . But it has stuck with me , after I get a bit of time today I shall look it up and post it

 

I've seen them, so I know they exist, and happen after they have already been used quite a lot. As in, a perfectly fine rotor turns into a rotor which ISN'T perfectly fine due to wobbliness and a machined surface which is no longer radially perpendicular to the turning axis of the hub.

 

Sorry CJ i must disagree , see the new thread on it . this guy knows more about cars than you or the rest of us will ever know

 

So you totally disagree with what I saw, in person, with my eyes, while I was not on any drugs whatsoever....... How could you with any brainpower tell me I'm wrong WHEN I SAW THE FRIKKIN' THINGS?!?!?!?!?
Geez, I cannot fathom how you could or would tell me that the facts are NOT the facts.................. Oh my gawd, if you were in the US you would be a Republican Trump Supporter.

 

The ONLY way a brake rotor can warp is if it heats up enough to soften the metal alloy. Different metals have different melting points. Carbon/iron alloy's is in excess of 1500 degrees, daily driving brings rotors to 300-400 degrees at the most and rotor track temps are usually around 500-1000 degrees depending on the track. Keep in mind street pads are designed for street temps no higher than 500-600 degrees before they'll fail which is far below any possibility of heating rotors to melting temps.

I reckon some thin, defective or inferior alloys brought to their melting point from excessive speeds and excessive continuous braking, perhaps coming down a mountain highway.

I believe the point's many "warp" diagnosis in fact's glazing or pad material melted to the rotor surface. OR the rotor was not seated to the hub correctly and wore unevenly.

Research lateral runout.