I hope this saves someone some time and frustration. As a fore note, replace both idler pulley bearings as well if you're going this far, it's another $12 each...small price to save another on road failure IMO



So I was down in AZ and my wife was driving my f250 when the tensioner pulley grenaded...

I fought a red eye home and stopped at Oreilleys and picked up the replacement, and a new belt...that's where it started...

The new belt was an 8 rib, my belt is a 7 rib...

The new tensioner was obviously longer...

Had I read up before proceeding I would have found my answers, but I didn't, AND I tried pulling just the pulley off because I didn't have the T50 tore bit to remove the original tensioner, and snapped the bolt off the pulley because I didn't realize it was left hand threads...DOH!!!

So I went to napa and found a tensioner that looked similar to mine and a T50 bit

When I got home and removed the tensioner, the nipples on the back didn't match the one that was similar in size and also the similar sized replacement was about 1/2" thinner from front to back...


Then I read up and found my mistake, the longer one is the correct replacement. The original belt still fits, although I did use my new spare from my road side kit.

Here's pics of what I found





This is my original tensioner from the back side, note: the nipple configuration





This is the longer replacement from Oreilleys from the back





This is the similar sized replacement from napa from the back





This shows the depth difference between the original and the incorrect replacement that just so happens to look more similar than what is the correct replacement





This is the correct replacement part #





This is the incorrect part from napa that looks more similar but the nipples on the back are different and it's different depth wise