GMC Repair: alternater problems, gmc vandura, careful eye

Question
We have a 1978 GMC VanDura Motor Home with a 350 motor. We were on a trip and the alternator went out (we thought).  We replaced it and the belt. Since then we can not keep a belt on it. We can drive it even short distances, and it will break or throw the belt.  The problem is worse at night when the lights are running.  We have changed pulley, that did'nt help. Any ideas what to do next?

Answer
Without actually seeing the problem first hand you have several possibilities:

1. The new alternator is not aligned correctly with the other pulleys. It may be to far FORWARD or to far BACKWARD thus being out of alignment.

2. The pulley on the new alternator is SMALLER in WIDTH than your old alternator's pulley.

3. The WRONG belt (smaller in WIDTH ) may be being installed so it fits deeper into the NEW alternators pulley thus being to SMALL in width to fit securely into the other components pulleys thus causing the belt to slip and or break.

I have seen this many times and it takes a careful eye to spot these small descrepencies.

Look real close.

let me know.


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