Brakes pushing back?

I just had my front passenger driveaxle replaced, the CV boot tore and I didn't notice until it gave me a lovely grinding sound while braking and started leaking tranny fluid.

On the ride back I noticed while braking at low speeds the pedal was bouncing up and down and making a buzzing noise. I checked the rotor and there doesn't seem to be anything scratching it. I tried braking at higher speeds and the sound keeps returning, and on occasion the pedal hardly moves at first but the brakes still engage. Brake fluid level is the same as when I brought it in, I was thinking of topping it up to the max line and giving that a shot. Any ideas?

Sounds like you are activating the ABS .....
It pushes back on the pedal and the actuator will buzz when working (if
I remember right). Does the car have ABS ? Possible that installer
damaged the ring on the axle so the sensor cannot read it (or misinstalled
the axle)

It does indeed have ABS. I had a feeling that was it, I was thinking of pulling the fuse and seeing if it kept happening. I'll give that a shot first. It's funny that it does it without pushing hard on the pedal.

I pulled the fuse and sure enough the problem vanished. I took a closer look at the axle they installed and looks like they had gotten one that isn't equipped for ABS. Apparantly their supplier is notorious for forgetting little details like that.

Isnt saying much for the shop that installed your axle either if they didnt
notice and didnt figure it out after installing it