1996 Subaru Outback, 2.5L Automatic, drives fine - however it will sometimes vibrate when I'm holding down the brake pedal. The annoying thing is that it doesn't happen all the time, sometimes it's really loud. The car doesn't vibrate or shimmy whlle I'm driving.

The previous owner replaced the brakes (rotors, pads, control module).

 

The engine sounds good. It stops when I put the car in Neutral (of course). It seems it's more likely to be the brakes than anything but it being intermittent is weird.

Sounds like brake rotor(s) that are warped and out of round, even though you say previous owner replaced the rotors and pads. If you have a bad caliper that does not fully release the brake, the rotor can over heat and warp.

... vibrate when I'm holding down the brake pedal ... doesn't vibrate or shimmy whlle I'm driving...

 

Sounds like something is Wrong with the ABS control unit.

 

Have you tried to pull the ABS Fuse and check for said vibration?

Does it only do this when sitting still in drive (or other moving gear) with the brakes applied?

maybe I'm not following but, are you complaining about vibration when stopped in gear, that goes away when you shift to N or P ?

 

that is often poorly rebuilt (or worn ?) front axles. a 96 almost certainly does not have its original axles.

Edited February 19, 201412 yr by 1 Lucky Texan

maybe I'm not following but, are you complaining about vibration when stopped in gear, that goes away when you shift to N or P ? ...

 

A little bit Vibration while the car is Stopped and Engaged in Gear (Automatic Transmission) somehow is Normal, but as he said:

 

... sometimes it's really loud...

 

made me think that it is something that could Not be considered Normal.

If it occurs only when moving and you are pressing on the brake pedal, it could be the ABS activating when it does not need to, caused most often by a bad sensor or (more often) a cracked tone-ring.

 

When it seems to be prone to it happening, try removing the ABS fuse and see if it stops.