I have bought a set of underdrive pulleys and the stock belt does not fit Help
Did you install all 3 pulleys? are you routing the belt properly?
You might just need a shorter belt...
I installed only the crank and water pump pulleys, and my belt didn't fit, nowhere close. I had to go to autozone like 6 times, I'd get the belt, drive home, see that it didn't fit, put the original on, go back, repeat.
I'm yet to see a set of underdrives that did not require a shorter belt. If the mfg did not include belt reccomendations, do this. Use a string to wrap the pulleys(go under the tensioner) and then mark where they overlap. Remove the string and measure between the two marks, subtract approx 1.5" to get the tensioner in the proper range.
Only subtract 1.5" for the tensioner? I would assume the belt would stretch and it would still be loose. I don't know that much though. I'm running everthing stock and something must be worn because I need an 0.6 inch shorter belt just to keep from slipping. It was an incredible pain to install myself, especially with the really short 18mm wrench I had.
yeah, the pully belt shuffle is a pain, i remember going thru that , the string idea will save you the trial and error you have to go thru..
but make sure the belt isnt extremely tight this will cause some stress which is not good,the reading on the pully tensioner should tell you the safe zone as well... there is a standard size for pully set ups... but also it all depends what your set up is as well....i forgot what size that was....
If you look at the front of the tensioner there is a RANGE marked, and an arrow. Basically you want the tension to be right in the middle of that range according to the arrow. Getting there...heh, that's the trick. But if it's too loose you'll throw the belt, and if it's too tight you'll start locking up pumps.
FYI:
Stock Cougar/T-Bird 5.0 w/air pump and a/c: 93.0"
Stock Mustang w/air pump and a/c: 91.5"
If I remember right, the u/d pulleys on the Mustang setup netted a 90.0" belt. But I can't say for sure since I've had, oh 6 or 7 different belt combinations on this motor.
Eric is right about the being in the proper range but...... I had a belt on my Bird for five years that allowed the tensinor to completely bottom out, and did not have any problem even with several visits to the drag strip and 6000 rpm shifts.
Just last week revised my setup(ditched the smog pump), so I needed a shorter belt. Found a new one in my stash that was 83.5" which was approx 1.5" too short(I could get it on but the tensioner extremly tight. What did I do??? Drilled a new locating hole for the tensioner pin approx 7/8" lower on the mounting bracket... bingo tensioner is now in middle of travel. Must be OK, stayed on last night for
8-9 passes at the drag strip.