Brake Bedding ? or time for new rotors ?

was out of town for a week, so i washed the car and parked it indoors for the time i was away, when it came time to driving it, it made a big thud (pads and rotors seemed to break away from each other), took it for a drive on the highway, that's when i discovered the shaking of the pedal and steering wheel while braking...

when i look at the rotors (all, front and back) i can clearly see an imprint of the pads (pads and rotors are original BMW)

so i followed the bedding/conditioning procedure as per the E46 Wiki link. after 3 cycles of bedding, the brakes dont shudder as much (but they still do), and the imprint on the rotors is almost gone but not fully wiped off... i'm guessing it's just a matter of time before the brake materials starts building up again against the rotor imprints and causing the shudder to increase with time....

the bedding procedure suggests 8-10 times of near stops from 60 MPH while not locking in the brakes... i did that the first 2 times (which reduced the braking vibration, but not significantly) so for the third time, i did 12 near stops (i waited for the rotors to completely cool off between attempts).

any advice ?? should i give it another shot ?? i'm i harming anything else (CABs, links, suspension) by doing these repetitions?? or should it just bite the bullet and get another set of rotors/pads ??

pads are less than 10000miles old (16000Km) and the rotors thickness was within spec when i replaced the pads...

Did you replace the rotors and the pads at the same time or just the pads?

I replaced only the pads and replaced the brake fluid, but did not do a bedding procedure,
they were fine, until the above happened

What's the condition of the rotors...?

Your caliper cylinders/pistons may need a good cleaning if rotors are ok as the pistons may be sticking. A symptom of what you described.

Since you obviously have a pad imprint issue and attempts at bedding the pads of yet to work..... Take the rotors off the cars. Get some 120 grit garnet (garnet only please) paper. I like to get the self adhesive round one that stick to a pad that I use on my drill or air angle grinder. Go over both sides and remove all pad material. put back on and clean with brake cleaner. At this point it would be wise to check for axial and radial runout but in your case, I would imagine they will be fine (although I would still check!). Go and bed them again. That should do it for you. Do check the other components again while in there, particuarly the slides for smooth easy movement.

Thanks New Kid.... I cleaned the guide pins twice (once when a replaced the pads, and another time to eliminate a sticking calliper) and checked the calliper pistons for movement inwards and outwards...


Rdorman, do you mean lightly scratching the surface of the rotor to aid the bedding process (like the cross scratches found in new rotors) ??

Originally Posted by sannouni

Thanks New Kid.... I cleaned the guide pins twice (once when a replaced the pads, and another time to eliminate a sticking calliper) and checked the calliper pistons for movement inwards and outwards...


Rdorman, do you mean lightly scratching the surface of the rotor to aid the bedding process (like the cross scratches found in new rotors) ??

What you are looking to do is remove all pad material. You will see it coming off the same color as brake dust. When no more comes off, it is clean! By using a disc is does give it a bit of a cross hatch type of look. But that from the factory on news rotors is from blanchard grinding (the right way to surface rotors!). Max runout is .002". Oh, and if your pads are glazed, take the sand paper to them as well (remember, garnet only). Heck, you might as well just do them any ways!

Originally Posted by rdorman

Since you obviously have a pad imprint issue and attempts at bedding the pads of yet to work..... Take the rotors off the cars. Get some 120 grit garnet (garnet only please) paper. I like to get the self adhesive round one that stick to a pad that I use on my drill or air angle grinder. Go over both sides and remove all pad material. put back on and clean with brake cleaner. At this point it would be wise to check for axial and radial runout but in your case, I would imagine they will be fine (although I would still check!). Go and bed them again. That should do it for you. Do check the other components again while in there, particuarly the slides for smooth easy movement.

I think rdorman is sending you in the right direction, although I disagree with the problem being solved. Your imprints are not transferred pad material, as occurs when you park the car with very hot brakes. Your imprints are simply rust from parking the car for a long time after a car wash, so water was trapped between the pads and rotors. You only need to remove the rust imprints from the rotors.

Originally Posted by rdorman

What you are looking to do is remove all pad material. You will see it coming off the same color as brake dust. When no more comes off, it is clean!

Please wear protective gears, such Respirators and Safety Goggles during this process. Brake dust can be hazardous to your health.

Both valid points above this post. While I would think that simply a rust imprint would certainly be gone by now, stranger things have happened. Even if they where just rust imprints, I would still recommend removing pad deposits from the entire rotor because if you just remove it from the rust area you have in effect, the opposite issue! The whole rotor except one area has a transfer layer deposited. Either way, the sanding will take care of the remaining. Yes, do use appropriate safety equipment! For this all I use is safety glasses and a particle filter.

Just drive it for a while, and you should be fine. Next time you wash the car, run it up and down the street before you park it to dry the rotors.

See also this thread for photos of pad imprints and lots more:
Rotor Refinishing does that stuff work?

Thanks guys, bluebee, that's exactly what i have on the rotors...
I got the sandpaper last night (120 Grit Garnet), all i have missing is a mask and some gloves.... i'll give it a go this weekend to see how it turns out.... i'm also thinking of sanding the pad materials off of the rear rotors as well since i'm at it ...

I say just keep driving it. It happens to some of my cars regulary, and after awhile it will go away.

I'm trying to figure out what 'really' causes brake judder ... by reading these papers:

*******>********>

	analysis_of_the_vehicle_brake_judder_problem_by_em ploying_a_simplified_sourcepathreceiver_model.pdf (548.7 KB)
	A-Parametric-Study-Brake-Roughness.pdf (132.9 KB)
	Judder-Diagnosis-Prevention.pdf (126.2 KB)
	Improved_mathematical_models_of_vehicle_brake_judd er_and_experimental_observations.pdf (5.23 MB)
	Judder_vibration_in_disc_brakes_excited_by_thermoe lastic_instability.pdf (925.9 KB)
	Aspects_of_Disc_Brake_Judder.pdf (342.7 KB)
	Braking_Process_in_Automobiles_Investigation_of_th e_Thermoelastic_Instability_Phenomenon.pdf (1.07 MB)
	Brake_Vibration_and_Noise-A_Review_and_Discussion.pdf (592.0 KB, 2 views)
	Hitachi_NVH_Simulation_Technology_for_Disc_Brake_C alipers.pdf (323.3 KB, 3 views)
	Experimental_Analysis_of_Disc_Thickness_Variation_ Development_in_Motor_Vehicle_Brakes_1of3.pdf (6.98 MB, 4 views)
	Experimental_Analysis_of_Disc_Thickness_Variation_ Development_in_Motor_Vehicle_Brakes_2of3.pdf (6.98 MB, 2 views)
	Experimental_Analysis_of_Disc_Thickness_Variation_ Development_in_Motor_Vehicle_Brakes_3of3.pdf (1.13 MB, 2 views)
	Thermal_Brake_Judder_Investigations_Using_a_High_S peed_Dynamometer_1of2.pdf (6.04 MB, 7 views)
	Thermal_Brake_Judder_Investigations_Using_a_High_S peed_Dynamometer_2of2.pdf (3.39 MB, 2 views)
	surface_temperature_distribution_in_a_composite_br ake_rotor.pdf (531.1 KB, 2 views)
	discussion_of_the_characteristic_of_brake_judder_a nd_the_necessary_data_acquisition_system_for_c.pdf (314.0 KB)
	Order_domain_analysis_of_speed-dependent_friction-induced_torque_in_a_brake_experiment.pdf (2.08 MB)