greg of kurst

I've got some issue with my belt tensioner (it's spring-loaded) on my
2000 3.8L mustang...

The old fan belt started squeaking incredibly and it had been
stretched I think... I bought a new one, it doesn't just have the pure
longitudinal ribs but has additional cross-hatching... anyway compared
the two, the new one seemed about an inch shorter in circumference,
put it on and it's quite a bit tighter. The range indicator for the
tensioner seems like it's ok; it's not pulled somewhat not too little
and not to the max.

My system looks like Figure 11 in
http://www.autozone.com/az/cds/en_us...rInfoPages.htm
(or google
ford mustang belt tensioner
and pick the autozone link)

when the car first turns on, it goes through a series of RPM changes,
it revs up and down as it idles. in the lower RPM state things are
fine, but in the higher RPM idling state, the tensioner arm becomes
unstable, and it goes back and forth and the whole system makes a "tic
tic tic" sound, about 3 tic's per second. The instability in the belt
runs all the way around the alternator (?? upper-left, with the
triangle--it kicks on and off), and the two pulleys on the upper
right. The smaller pulley on the upper right, which has no grooves
(touches the back of the belt) and may have no real function, has the
belt sort of move forward (toward the front of the car) and back. if
the belt moved forward too much, it would slip off.

the pulley on the tensioner arm, i found out, had a hard ball-like
mass inside one of the grooves that was large enough to possibly cause
a problem. i picked it out and the system seemed to be a little bit
smoother, but still did the tic-tic-tic.

I revved the engine and things seemed OK. the system doesn't squeak
BTW, apart from the tic.

in the lower RPM state, things are very smooth. there is no tic sound
or visible instability.

any idea what causes the instability? I assume a back-and-forth on
the tensioner arm can stretch out whatever serpentine belt is placed
there and could have been the cause of the previous belt's
deterioration?

i am worried about difficulty in replacing the belt tensioner, the T50
(?) nut keyhole wasn't budging, I tried hard to turn it and it started
stripping.

probably I will trust it enough to drive it in town to the shop but
maybe there is some insight.

greg