Hyundai Repair: 2004 Hyundai sante fe, hyundai sante fe, caliper pistons

Question
Hi Our car just started doing very strange noises.  No lights have come on except the brake light comes on & stays on when driving or if starting to stop quickly it pops on & will go off or just be on.  However, that isn't the issue, we are currently experiencing at lower speed a throbbing of the brake petal and a very loud grinding sound (or like a separate motor) trying to turn. Motor appears to idle fine, transmission appears ok altho fluid is dirty and brown.  No burnt smell. Oil is at this moment a quart low - no leaking on ground and brake fluid has been filled today - it was half empty.  Can this be cause by air in the line? TCS going bad? Or what?  Any help would be great.

Answer
Hi, Christy.  

Your brake lamp coming on and going back off suggests that your brake fluid is at the minimum level in the master cylinder.

There are primarily two potential issues causing the pulsation and grinding:

1.  On at least one of your brake pads, the friction material is worn completely away, causing the metal backing for the pad to rub against the brake rotor.  This scenario is consistent with low brake fluid; as the pads wear, the caliper pistons are more extended to take up this space, causing more fluid to reside in the brake calipers and a lower fluid level in the reservoir.

2.  There is a problem causing the ABS to activate as you slow to a stop.  This is the less likely scenario as the ABS/TCS computer would typically notice a problem and turn on the ABS and/or TCS warning lamps.

You should inspect your brakes immediately.  If you're unable to do this yourself, you should have someone qualified do it for you, paying them to do it if necessary.  If case 1 is indeed the issue you have, continuing to drive the vehicle will eventually wear the rotor and brake pad backing plate to the point where the backing plate will drop out.  Not only will this significantly increase the cost of repair, but you run the risk of the brake system potentially failing.  If the piston comes too far out of the caliper, your brake fluid will completely leak out and your brakes will stop functioning.