Hot rear rotors ?

Thom · #1 02-23-2009, 11:30 AM

Hi all.
I replaced my pads about 8 months ago on the rear. Now my rear rotors are getting very hot (cant keep your finger on them). The fronts are warm only.
I took the pads out and applied new anti seize and reinstalled them...same thing. After a short drive both rear rotors are hot. I backed off the parking brake shoes and its still hot !!!???
If the master cylinder fluid is low on the front resevoir will the backs come on first ?
Can two calipers seize at the same time. ?
Thanks for any help.

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01 BMW_X5 · #2 02-23-2009, 12:09 PM

I would 1st check if it is the parking brake or the brake pads causing the disc to heat up.
Could be caused by brake master cylinder. <<I am leaning towards this.
Also if the vent bore in the expansion tank is blocked .
Hand brake cables.
Corroded floating calipers.

fast4d · #3 02-23-2009, 12:10 PM

jack the rear off the ground and put trans in neutral. can you turn wheels by hand?

when you took pads off can you easily retract the caliper pistons back into the bore?

nra0707 · #4 02-23-2009, 12:25 PM

If water gets into the lines or condensations seeps through the caliper piston seals, it can corrode the piston to the point where it seizes it. I've had this happen on my other BMW. It might also indicate that it's time to flush and replace brake fluid in the lines.

Thom · #5 02-23-2009, 01:59 PM

What are the odds of both rear calipers going (or starting to go) at once ?

mrkbbd · #6 02-23-2009, 02:12 PM

You do realize brakes are supposed to get hot, very hot, that's how they stop the car by converting movement into heat...that being said you have to remember the rear brakes are smaller than the fronts, have a poorer cooling system, and have more rotating mass (the larger rear tires as compared to the fronts), which all translate into higher temps

01 BMW_X5 · #7 02-23-2009, 02:14 PM

Slim. But, I have seen strange things happen. Corrosion in your climate may quickly affect them.
Get the rear of the X in the air like another member said and start from there.

Thom · #8 02-23-2009, 03:44 PM

Thanks for the ideas. So, before I spend the $...how hot is hot ?
I know the rear rotors are solid metal (vs fronts that are "vented"). But how hot should they be ?
If I drive around in traffic, the fronts are warm but the backs you cant touch. There is no burning smell.

mrkbbd · #9 02-23-2009, 03:54 PM

If you've been using them in traffic, they should cause 3rd degree burns when you touch them

mrkbbd · #10 02-23-2009, 03:55 PM

think about this, if you've ever washed your car / rims after you've driven it and get water on the rotors, it instantly turns to steam, that means they are significantly hotter than 212 degrees

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