Car: The car is a 1987 300D turbo.

Problem: When braking, the pads squeal, and when I am about to stop, the abs kicks in or something and the petal gets spongy.

I changed the master cylinder and power blead the brakes with Ate brake fluid. That didnt help.

I got the mercedes cleaning pads with sand paper and I sanded the rotors in the front. It fixed the squeeling problem and the spongy problem for two weeks. Now the brakes become spongy. The pads are fairly new (2k miles) they are jurid. I didnt replace the rotors when I did the pads, but the rotors seemed good. After I cleaned the rotors, I put the Jurid pads back in, and put some Anti-squeal compound on, and now its back again.

Would the squeeling cause the abs sensor to rattle and then make the abs pump turn on?

What should I do considering I replaced the master cylinder already?

Thank you for your help,

Austin