Drilled, Slotted, and/or Dimpled Brake Rotors


Rick Norwood
07-07-2013, 11:06 PM
I have an issue with another vehicle (not a Blazer or Jimmy) with warping brake rotors. Does anyone have any experience with drilled, slotted, and/or dimpled Rotors good or bad?

I know motorcycles have been using them for years, but have never seen them on a Truck or car.

Any input would be most appreciated including sources.

Thanks,

Rick

old_master
07-09-2013, 08:37 PM
The term "warped", when referring to a rotor, covers two different problems. As a warped, or bent rotor rotates, it oscillates back and forth horizontally. The calipers and pads "float" on the guide pins, so they follow the oscillations. It might make some noise if the guide pins are not well lubricated, or you might hear or feel the calipers vibrate back and forth, but no pulsation in the pedal or surging sensation when applying the brakes. Brake pulsation on the otherhand, occurs when the two surfaces of the rotor are out of parallelism, which is caused by poor quality casting or overheating. By far, the most common reason for rotors to overheat, is the opposite set of brakes are not doing their job. ie if the fronts overheat, the rears are slacking, and vice versa. Other causes would be seized guide pins, restricted flex hose, binding or seized caliper piston, worn or faulty hardware kit causing the pads to bind or seize. If the rear brakes are drum style, they might just need to be adjusted.

Unless you're doing some serious road racing in a high performance vehicle, drilled, slotted, or dimpled rotors aren't necessary. Without repairing the root cause, the same thing will happen to the new stuff too. Substantially less cost involved to repair the problem ;)

Rick Norwood
07-10-2013, 08:59 AM
The problem is very noticible on downhill grades, but almost undetectable on flat streets. On my last trip, we had to take my 2008 Dodge Grand Cavavan SXT 4.0L into a dealership where they turned all 4 rotors. I could be mistaken, but after 3 or 4 trips to 2 different dealerships, this is the first time they actually serviced the rear brakes. This is the 3rd or 4th time we have taken this vehicle in for brake service with only 47k total miles. This is actually the 3rd set of rotors on the front. I replaced the stock brake pads and Rotors with Premium NAPA Ceramic Rotors last year, and in approximately 7k miles I am back to the same issue again with bad shuddering that you can feel and see in the steering wheel when braking on a downhill grade.

old_master
07-10-2013, 03:27 PM
Hi Rick,
Sure sounds like there's a problem with the rears not doing as much as they should. A clue might be if the rear pads still look like new. With 47K miles, they should be approximately 50% to 60% worn. There might be a problem with the proportioning valve, or even the master cylinder, not allowing the proper pressure to the rear brakes. Might even be air in the rear hydraulic circuit: Air compresses, fluid does not: air acts like a "shock absorber" reducing and/or dampening the hydraulic pressure. Just a couple of thoughts....

Rick Norwood
07-10-2013, 11:29 PM
Is there a way to test the Proportioning valve? Is the valve adjustable? Any chance there is a TSB I could refer them to? I fully believe this could be my problem.

This Vehicle having Antilock Brakes, I know it takes a special scanner to bleed the system, but I don't know if this has ever been done.

I couldn't tell you how much the rear pads are worn as the Dealership reportedly "Re-surfaced" the pads. I can tell you that they checked and lubed all of the sliders, Turned all 4 rotors, and claimed to have gone over the entire brake system. After that, the brakes worked flawlessly.

Here is one more tiny tidbit of information, last week while literely on my way to the Dealership, the Red "Brake" light lit up on the dash, then went out after a few seconds. The emergency brake was not engaged, even slightly. I told the Service Advisor at the Dealership thinking it threw a code, but He told me that the brake system doesn't set codes.

old_master
07-10-2013, 11:54 PM
The proportioning valve is not adjustable: It meters fluid through orifices. As for TSB's, gotta check with the dealer, (might wanna find a new dealer). The brake light coming on is a clue, and the proportioning valve can turn on the red brake light. The ABS system most definitely sets codes, and stores them in memory, but the ABS light might not come on depending on the problem detected, (it may go straight to the pending file). Same holds true with the check engine light for the powertrain. An ABS capable scan tool is required to retrieve the DTC's, I'd be real surprised if the dealer doesn't have one... if they don't, find a new dealer ;) Powertrain DTC's start with "P", ABS DTC's start with "C".

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