xg300 brakes

recently replaced left rear caliper. at that time replaced all pads and turned all rotors. all has been fine up until the last two weeks. after a few moments of engine on time, my brake pedal starts getting hard (no
evidence of travel) after a short period when i need to slow down i don't need to depress the brake pedal as the car will come to a stop on it's own. this problem is itermitent. i have told that it could be the abs pump. anyone have any ideas???
Thanks,
Larry
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I'd seriously doubt it's the ABS pump. You'll need to check to see if it's a hydraulic issue or a mechanical issue. Once you get the condition to occur, place the car on a rack or jack wheels until you find one that doesn't want to turn. Then open the brake bleeder on that wheel. If the wheel is then able to turn, you have a hydraulic issue. If not, then you're looking at something causing the caliper/pads to bind.
If you determine it's a hydraulic issue, then you need to isolate where the cause is. Once again, with the problem occurring, begin loosening fittings approaching the wheel in question, starting at the master cylinder and working toward the wheel. If loosening the master cylinder fitting allows the wheel to turn, then the problem is in the master cylinder. If not, then it's still between there and the wheel-- move to the next fitting to determine whether it's on the master cylinder side or wheel side. Simply continue doing this until the location of the issue is narrowed to one segment of the system. You'll also need to do this procedure for each wheel displaying the problem (unless loosening fitting(s) in one location solves the issue).
I've seen some (but not very many) Hyundai master cylinders cause this issue. And although I haven't seen it on Hyundai, it's a frequent occurrence on GM vehicles for a brake hose to become restricted causing the same problem.
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