I know, there is no such thing…except I did manage to potatoe chip the front rotor on a zx11 with a power stop from 170mph+

Back to my 2008 xk. When I received the car last fall I replaced all rotors and pads along with other sundry pieces. The brakes were then smooth and reasonably effective. I’ve put 8K miles on this car, at 6k miles I noticed the steering wheel shaking during braking…it had gotten worse and I actually thought that maybe I had a bent wheel but since the shaking was only on braking I attributed it to the rotors.

So, getting ready to order another set of rotors but thought what the heck, pulled the wheels off and block sanded the outer surface of the rotors with 180 grit sand paper. I figured that if it helped I’d pull the rotors off and sand both sides and if not I’d go ahead and order new rotors.

Great news for me…sanding just the outer surface has eliminated the shaking!



wj

 

Likely pad material. I’ve never had this problem, ever, until recently. On the Disco I replaced all 4 discs and all new pads. I’m d been quite frustrated with the OEM pads as the wheels would be completely brown after just a day of driving. I’d heard great things about Brembo’s NAO red ceramic pads. Well I will say their stopping power’s actually better than OEM BUT surprisingly they produce a LOT of dust AND they have a bad habit of leaving brown streaks across all 4 discs. Along with the unsightly streaks comes horrific shaking in light to moderate braking which goes away with heavy braking. Repeated hard heavy braking temporarily rids the shaking but it eventually returns.

Point is I reckon pad material’s likely the culprit in most cases like this.

 

Pad glazing, pulsing pedal, and damaged rotors are often due to one or more dragging calipers.
The (square cross section) caliper piston sealing ring(s) normally retract the piston sufficiently to prevent dragging. Dirt and age reduce this retraction.
Calipers rarely leak, but old ones often drag.
Good news is that caliper kits are generally cheap, and the job is pretty easy. Usually no need for new calipers unless you're working flat rate. I also recommend new pin bushings/caps on sliding calipers; again cheap and easy. Ditto new hardware kits. Brake flex lines if the car is more than 10 years old. Suggest always use OE parts (eg, ATE, Girling, Brembo, etc). FCP Euro, Autohaus, and others carry these parts.
Finally, make sure your brake pedal is retracting 100%. Master cyl pushrod should be a little loose... Flush your brakes once every two years; use a full quart of good DOT 4. Do not manually pump and bleed - high chance of ruining the master cyl seals. Use vacuum or pressure bleeder, and never let fluid get below res min level while bleeding (or you may create ABS system issues). Cap your lines after removing calipers.
Note that faulty calipers often only drag when they get hot, which makes 'em get hotter, and so on. Often you can feel this by placing a hand on wheel centers after freeway driving. Always rebuild both calipers on an axle (not just the hot one).

(Hope this helps...)

 

All good stuff but I have been manually bleeding brakes for over 50 years and have never once ruined any cylinder seals. 🙂

I have also changed rotors several times during that period due to warping although that is much less of a problem these days as commercial garages replace the rotors on a regular basis and at least every second pad change.

Richard