Brand new serpentine belt (Conti-Tech) 6 rib X 2415mm is squeaking and beginning to fray 1/8th inch all the way around from the side closest to the block. Rebuilt the power steering pump (new seals) and thought I'd be good and replace the serpentine at the same time about 2,000 miles ago.

1) New belt appeared to ride higher on the pulleys and squeaked when cold right after start up, stops after warm up in 4 minutes or higher rpms.

2) Other items have all been rebuilt or renewed as well within the last 9,000 miles (water pump, idler pulley, a/c compressor, fan, smog pump, tensioner)

3) Alternator is the only exception and it was fine when I checked with the belt off.

What could be the problem here?

Some posts say Alignment? Whats to align? Everything bolts right up, no missing spacers etc. I ordered a new belt (Dayco) and have the old belt (Dayco) which never squealed.
I tensioned the belt as described in the manual, started up the car, squeak and squeal when the A/C compressor came on. Tightened another 1/2 turn and the squeal stopped from the compressor slippage but the squeak continues.
Bad belt? Too tight to loose?

Thoughts

Forgot to list model, w124 1990 300ce

I use Gates belts

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

Clean your pulleys with a wire brush and solvent. On my Ferd(TM) I had the same problem, I ended up machining the alternator pulley.

__________________
$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

Did you remove the radiator? If so you may have splashed some coolant on a pulley.

Once mine was squeaking for several weeks. I took a closer look and found that I hadn't routed the overflow hose properly. The alternator pulley was slowly eating into it. I'm lucky it didn't make it all the way through.

I think I will clean the pulleys with wire brush and re-install the old belt, which still looks new. It did not squeak, ever. If the squeaking returns, I'll know it was something else.

+ make sure the tensioner bearing is not going bad (not the pulley bearing, but the bolt that attaches the assembly to the front of the motor)

__________________
2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900

On my two cars with serpentine belts I have a gatorback on my OM601 diesel which is smooth and silent, and an OEM MB belt on my M112 gasser....no sounds from either.

Fraying could be caused by pulley alignment issues...you said you rebuilt the P/S pump, that could be the culprit if the pulley is not seated on the shaft perfectly...

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Something not installed right, or wrong part somewhere.

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Kudos to connerm and mpolli. After digging into things several more problems arose.
1. Tensioner bearing frozen (the attachment bolt), why don't know its a Febi/Bilstein new 15,000 miles ago. Forced some new grease into it along with some WD-40 and its functional again, but bit the bullet and bought new from the stealership, yikes!
2. Tensioner shock very weak, also only 15,000 miles on it, bought new from the stealership.
3. Wrong belt length! According to my VIN, and engine number from the data card, I ordered and installed the correct belt, but its too short. Which makes me wonder at this point if this is not the original engine, and some parts have been cobbled together from another engine.
4. Installed the old belt which is a 2440 mm Dayco, the 2415 mm Dayco is to short. Also the old belt is 4.3mm thick and the new one is 5.0mm thick. The old belt is almost more like a smooth and very flexible silicone compound as opposed to the new Conti and Dayco belts which are stiffer, thicker and have a textured back, not smooth like the old one.
5. Even with the new tensioner and shock installed the tensioner pulley (where belt runs over) has minimal clearance with the water pump pulley. I mean cigarette paper clearance with thinner old belt. This lack of clearance destroyed the new Conti belt because the inner lip of the water pump pulley was making contact with the belt. It eventually pushed the belt over and carved a .1mm groove into inner running edge of the plastic tensioner pulley, side loaded and chewed up the belt, hence the perceived alignment problems.
6. Also cleaned all pulleys with wire brush, lacquer thinner, and compressed air.
Result is totally quiet and my daughter's car is back in business! However I am still not pleased with the lack of clearance between the water pump and tensioner pulleys.
I am wondering if a belt 5mm longer (some are now sold as 2445mm) would provide more clearance? Someday in the near future I will have to purchase a new belt and the 5mm thick belt will once again impede with the water pump pulley. Thoughts.