Screeching from engine when downshifting

When I downshift at high RPM, the engine screeches. This is one hell of a loud screech.
Almost sounds like the tires, but it's not.
Any clues?
Kinda sounds like a fan belt, but the belt isn't that old..maybe 9 months old...

It probably is a slipping fan belt. It has probably worn(not stretched) into the pulleys over the past few months and the more it slips the quicker it wears out the belt. You can adjust it by pulling out one shim from between the pulley half and the fan and putting it to the outer side of the half. DON'T DISCARD THE SHIM. It is needed to properly hold the pulley half on.

That should end the squeal. You could probably do a search and find the correct spec. Warren could probably tell you as well but you better ask nice He's been incredibly helpful to me and probably everyone else on this BB. Thanks again Warren.

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'76 911S

'80 924 M471

There is not much of a chance it is anything but the fan belt. Did you adjust the shims after the belt had 100 miles or so of wear on it? New belts always stretch or wear-in, and need to be compensated for after a week or so of use. If you can turn the alternator pulley by hand or by wrench, and the belt slips, then you have found the culprit, and it needs to be readjusted.

Chances are that the hotter weather of summer has caused the belt to grow/stretch a bit, and it is 'glazed' from the slippage. If the belt 'gives' more than 1/2" at the midpoint between the pulleys, then it is too loose ... about 3/8" to 1/2" is the optimum tightness, but you don't want it much tighter, or it causes bearing problems for the alternator!

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Warren Hall
1973 911S Targa

Right. You know, after I posted it, I saw the other post on fan belts...never thought to check them so frequently.

I'll go see if I can find this shim and
tighten the belt down. Once again, Gary, Warren.

What about a PBS show: "Ask Warren about your 911" ?
We could have contests to find questions he can't answer.