52K 2010 AWD Touring..........Rears pulsate noticeably at lower speeds, not so much at higher speeds or at all. Had them checked and was told rotors and brakes look good. Checked them myself and found nothing unusual. I saw that there was a recall/assessment about vacuum boosters leaking, or similiar.

Have no idiot lights on. Problem is isolated to rear only. It feels like your riding a bike w/a rear bent rim when you apply the brakes.The "uneveness" of the rotor when the brake rides along it. Help appreciated!!

 

How do you know the problem exists in the rear?

Rule of thumb: Feeling a pulse in the steering wheel when braking means front rotors are warped. Feeling the pulse in the seat of your pants (when braking,) rear rotors are warped.
Either way, they should be turned to true them up again. You will not "see" the problem, but it can be measured with a caliper and careful measuring along the entire surface(s) of the rotor.
If you are not using the brakes when this occurs, it is not in the braking system. The problem could be elsewhere, such as: Tires that are out of round or balance; or a rotating problem like an axle bearing, axle or stub shaft.

 

It only happens when applying the brakes and the steering wheel does not shutter or anything. It is coming from the rear because I can feel it happening........the "bent rim on a bike" feel. You know which one it is. Are these cheapo rotors they put on this? I've never owned a new vehicle that did this whether the rotors needed to be replaced or not. I've read similiar problems w/other years to 08. Front is fine like it should be, which puzzles me as to why the back is acting the way it is.
Rotors IMO shouldn't do this at these miles or 10K earlier w/90% highway driving and easy to moderate braking. And the pads still have 50-60% left to boot.

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No offence is intended in this post so don't take it that way. Just because it is of your opinion that the rotor shouldn't be bad at that mileage doesn't mean that the laws of physics will change. I have ONLY 26k miles on my 3 and ALL my rotors need to be replaced cause they are worn out. First thing I would do is rotate my tires to remove that possibility, if it feels like a bent rim rule that out by swapping the rear tires to the front. Second (while the tires are off maybe) I would closely inspect the rear calipers for any signs of being grabby (not releasing), spin the rotor and see if it catches at any point, look at the surface of the rotor for signs of heat/cracking/uneven wear/rust. Always look at your car's problems through a strangers eyes with no bias, just cause you think it's good doesn't mean it is. Highway driving is VERY tough on brakes due to the heat generated during braking, city driving can in some cases be MUCH easier on brake parts than highway driving but usually only in cases of heat generation whereas city driving just eats the pads and rotors. Also "easy" braking can be WORSE for your brakes than moderate to hard braking because it can glaze over the rotors making braking "eventful" at times or at best very noisy.

 

I have a short video on brake problems/solutions. There's a Mazda in the Video!

Video: How to Diagnose a Brake Problem | eHow.com

This is a good general video.

52,000 miles? is a lot. I have 58,000 km and am well in to my 2nd set.

 

A common cause of rotor warpage is not torquing the wheel lugs, or using a "Zip" gun instead. This is more true now than ever before: If you or your tire shop does not use a torque wrench or torque bar when tightening the lugs of a modern car, you riskl the possibility of warping the rotors.
Rotors/Disk brakes are not like drum brakes and with more vehicles now coming with 4 wheel disks, this is a problem.
Are the rotors cheaply made? Maybe. Are the rear pads harder than the front? I can tell you from my own experience that they are, and my rear rotors had a fairly deep groove in the outer edge before I hit 50k miles.

 

Just checking, Does the vibration occur all the time when driving or just when applying the brakes?

 

Only when the brakes are applied...........thanks

 

Another cause of that "bent wheel" sensation is "thickness variation". That is different from warped rotors. The remedy is the same though: have them turned on a lathe.
New brakes have to be properly cleaned, any waxy residue will cause thickness variation in short order.

Virgin1 is correct: always use a torque wrench in a cross pattern to torque the wheel nuts. And if you have alloy wheels re-torque them after 100miles of driving!
I also avoid using the parking brake when the brakes are hot. The contact with the shoes could make the brakes cool off unevenly and cause warping.
When braking from high speed to a stop I have made it a habit to do this in stages: brake semi hard, release the brake and brake once more to come to a stop. I have no scientific proof but I feel that this pause avoids extreme high temperatures because it allows the rotors to cool off while there is still air movement around the wheels.

 

That's some "out of the box" thinking. I'm impressed. It's like going above and beyond the call of duty!
Virgin's thought was real good too!