Im sorta new at this but I have a 97 F150 and while coming to a stop the pedal dropped, started to shutter a bit then the pedal got hard. Had to put alot of pressure to stop it. I put a new master cyl and is doing the same thing. Stops great till it does what it's doing. Any help would be appreciated.

 

Could be the ABS module or the sensor in the rear axle.

 

Thanks but how would I find that out

 

Has rear drum brakes. ABS lights up on dash when key is turned on. goes off after it's started. Where would the abs sensor be?

 

On my 1997 the sensor is on top of rear differential. Be careful removing because sensor on my truck came apart and half of it dropped back into rear end. Had to take rear cover off to get it.

 

Get someone to check for abs codes.