Im on belt #3 in about 3 or 4 months. The first belt was old and broke on the wya home from buying it, the next belt after just another 3 weeks. This last belt has lasted several months and still looks ok. The car is an 87' T2, w/o p/s or a/c at the moment. All thats hooked up is waterp ump, alt. and air pump, which isnt being used and will be removed one day. The pullies are alligned correctly from what I can see. Its a good belt and everything else seems to be in shape, yet the belt loosens every week or 2. Tighten it up, in several weeks its squeeking again, retighten and the same thing. Ive done this probably 5 times with this belt. Is this probably just caused by belt slippage under hard accel. and fixable by installing a double sheeve pulley? Or do you think it might be something else? The belt isnt eating away very much, but I guess any slippage will result in black residue on everything near the alt.

 

Sounds like you are overtightening the belt. When you have the tension right, there should be a half inch of deflection when you push on it.

 

Ive done every tension I can. Ive tried 1/4'' deflection, 1/2'', 1'', still no matter how it ends up slowely getting loose again. Anything at or more than 1/2'' deflection ends up making it slip and squeel under hard accel.

Im guessing a double sheeve pulley will help or cure this problem. I hope anyway

 

Ive run into this before and the best fix Ive found is an OEM belt and a pulley inspection/replacement.

I find that in the cases where no tension seems to work (too little and it slips, too much and it stretches quickly) that the belt isn't seating 100%.

The orientation of the main - water pump - alternator pulleys isn't ideal for traction on the pulleys themselves and any irregularities in the pulley groove or difference in bevel of the belt itself can result in rapid breakdown of the belt.

So just check your pulleys out for any incosistensies (sp?) on the belt surface of the pulley(s) and try an OEM belt for good measure. The alt. belt from Mazda is about 20bucks IIRC, nothing extravagent.

Also when the belts off, make sure that none of the pulley(s) are tight at all, the water pump and alt. should spin relatively freely.