Had new alternator installed. Now belt squeeks only when I start it once it's running it does not squeeks .
Truck Is 79 302. Would a lose belt cause this?

 

I have a belt problem too. Thanks Christmas.

You could be experiencing two issues. Loose belt, or worn out belt.

 

It could be loose. Put a straight edge across the two pulleys andthe belt should not deflect more than 1/2-inch when pushed or be manually turned 90° at its center.

The belt should also ride in the pulley groove rather than on protruding above the pulley's circumfrence.

Check!

 

Checked it. Seemed to go a Lil bit more then 1/2 inch when pushed down. Will try to tighten tomorrow. Could there be any other reasoning just so I can check that too.
Looks like mechanic put new belt so I know it's not worn out

 

Check the alignment and pulley width also . Likely just needs to be tightened .

 

In general, I've always understood the belt SHOULD ride up above the pulley...once they wear down (or are undersized) and ride down in the pulley groove they start slipping and should be replaced...

 

That is technically incorrect... that results in less contact surface and grip.

Belts are not supposed to wear down the sides as to eventually slide down the V-groove. Rather, belts lose tension by stretching over time.

Check your newest vehicle.. belts ride in the groove and not on top of them.

 

A v belt needs as much contact with the pulley as possible to properly transfer force and energy . Too deep is bad . Too high is bad . Look at the V . The belt should fit it properly . That is why you have different widths of belts . They match the pulleys .

 

nope, even a serpentine belt should only contact the pulley on the angled section of the belt...the v of the belt should not contact the bottom of the pulley and the top point of the pulley should not contact the bottom of the belt.

 

but the belt should always ride only on the sides of the pulley...as soon as it touches the bottom of the pulley, it actually decreases the wedging force.

 

Correct , somewhat . Depth is also an aspect to consider on a belt drive .Too tall of a belt leads to improper force applied as the belt wears down . You wind up with a ridge that effects in improper energy transfer .

 

That is a fair interpretation ....but I did not state or intend to imply that the V-belt touch the bottom of the pulley - just that the belt should not protrude above the circumference of the pulley.