Toyota Repair: 94 Previa Brakes, brake pad shims, oem pads

Question
I have a 94 Previa LE that seems to need the brakes replaced on every winter. I've had the van for 4 years and I love it, but the brakes are giving me fits! After replacing the mfgg brake pads, every set of new brake pads has squealed horribly, and within 6 months the grinding sound appears.I have used the expensive brake pads and the cheaper ones. Neither seems to fix the problem. It's being worked on again as I write this. This will be the 4th set of pads in as many years. Any solutions? Thanks!!

Answer
You didn't tell me how many miles you drive between the time the brakes need to be replaced, under normal driving conditions the brake pads should last between 25-30,000 miles, how fast they wear depends largely on driving conditions and vehicle weight, if you use the van for business and load it down with 1000 lbs of weight every day or constantly have a bunch of people in it and do a lot of city driving the brakes may only last 12-15,000 miles.
Have the repair shop measure the rotor thickness and make sure they are above the minimum thickness, if not replace them, use Toyota OEM pads and make sure the brake pad shims get installed, if they are not it can cause squeeking noises, that's the best advise I have for you at this time.