Finally got my trans all straightened out and now I have the legendary Ford belt squeak not only at WOT but at half throttle and above! My Gates belt is only a year old with less than 10k so I installed a brand new idle pulley and tensioner today from Ford and it still does it. Heard gator back belts would help but I was told by two performance shops that I should install a 1" smaller belt than stock that's what they do on Fords that have this issue or install a manual tensioner from a mustang/Ford lightning

 

Gatorback belt is what I'd try and all I'd use.

 

Stock length gator back didn't help, exchanged it for a 1" smaller gator back and that didn't help! So I put a 1" shorter Gates belt on and my squeak at full throttle shifts are almost now completely gone. So what should I do to get it gone completely? Was told by a shop that's works on mustangs and lightning that my next option is too install a manual tensioner...

 

Hmm can't help. I had a squeak issue only once, it was on my '99 7.3 and even though the belt was newer I replaced it with a Gatorback and the squeak was gone. Since then whenever I replace a serpentine I use a Gatorback and I've never had a belt squeak. That's why I had recommended trying one.

 

I know you said you replaced the idler and tensioner but have you inspected and spun all the pulleys too?

 

Brand new Ford tensioner and idler, and I spun all the pulleys and the rest are not wobbly and spin fine not loose or too tight. I also simple greened all the pullies and scrubbed them with a tooth brush and flushed them with water and then dried them with my air compressor

 

And I know I'm not the only one with this problem. If you go on any Ford website Wethersfield it's a truck or Mustang site this is a normal problem. Mustang and lightning fixs are 1" smaller belts and in high hp motors manual tensioner. On pickup sites no one seemed to find a fix from what I've read so far

 

Interesting, was going to guess the pulley's were dirty but sounds like you were very thorough in cleaning them.

 

I soaked them with simply green and scrubbed them, rinsed and dried and then redid them a second time. Checked all the pullies, brand new idler and tensioner and 1" smaller belt and it's almost gone but under WOT it still squeaks just not nearly as bad as it was. This has me so annoyed and literally about to go mud bogging after work and dunk this truck a couple dozen times and teach her if she messes with me I'm gonna do it right back LOL

 

But in all honesty I know people with Fords that have this problem and I went to performance shops and they told me it'sa Ford thing and to wash the pullies, add a 1" smaller belt, if that fails think about a manual tensioner.... its stupid really