Engine Belt Routing

Discussion in 'Fox 5.0 Mustang Tech' started by bertman, Sep 8, 2013.

  1. Can anybody tell me what belt i need. I have A/C eliminater kit and it moved the PS pump up to where the A/C was. Summit told me what belt to use, but its not right. I have no smog pump either. The belt is 84.5 inches and its to long
  2. Measure with a string..best way to figure it out
  3. The best method I've ever used -

    go to the parts store and get a cheap 1" or so wide ratcheting tie down. Use it to route in the belt config you would like and measure length. Reinstall, but ratchet it completely down (max the tensioner). choose a belt length that is as close to the median of those two numbers.
  4. stock or U/D pulleys. This normally works with stock pulleys however due to the poor tolerances and variances in pulleys and brackets, you could need as much as an inch shorter or longer belt.

    View attachment 124904
  5. 75 fit but not tight. Got a 74.5 going to try it tonight. Stock pulleys. Love those pics mikestang63
  6. those pics have helped countless times. There can still be variances due to aftermarket pulley configurations, hence the difference as you noticed. Still best to run a string on it
  7. If the 74.5 is too tight, try a larger aftermarket pulley on the idler and tensioner. Often times the aftermarket stock replacement ones from the parts store are a little bit bigger or smaller and can mess up what belt sizes should be.
  8. Check the appoximate length required using a piece of string along one of the routings shown in the diagram below:

  9. If you use the string method, then remember to "by-pass" the tensioner pulley to get your length.
  10. That's a good point. We often forget to take into account the initial effect of the tensioner and the later effect of belt stretch when selecting the belt size.
  11. example> On my car with a smog pump delete and U/D pulleys with the smalller overdrive alt pulley, it takes a 90" vs. stock 91" belt for sufficient tension.
  12. The 74.5 fit great. Started my car for the first time in 6.5 years. Been slowly putting it together. Runs great. Have a few things to finish up still before it road ready. I was pretty happy when it fired up
  13. So I've been having a belt issue. My setup stretches my belt, and I need a new one every ~3 months. Mine is set up like the smog pump bypass, but the AC is deleted, the powersteering was not relocated, and there is a tensioner bar, no belt tensioner.

    So it is alternator to PS, to crank and water pump....It was this way when I bought the car, I just replaced the brackets it had, since they were old and broken. It has the MARCH A/C delete and MARCH alternator bracket with tensioner bar.
  14. pics are worth a thousand words here
  15. How tight are you cranking down on the tensioner? You want some deflection of the belt.
  16. I tighten it until it doesn't squeal on startup.

    I know, I will take a picture soon.

    I put a new belt on at the end of August, and it already needs tightening...
  17. You want about 1/4 to 1/2" deflection on the belt normally.
  18. The automatic tensioner does compensate for belt stretch. It's why I'm very hesitant to convert to a system like what March uses that locks in a specific tension and requires some adjustment.

    One of my daily drivers has such a setup and I've had to readjust tension a few times to compensate for stretch..which does happen.

    On my Mustang, i've marked on the tensioner using the indicator arrow where a belt "sat" when i put it on fresh. A year or two later you can see it's moved quite a bit from that spot.
  19. I'll post a picture hopefully tonight. I might be able to just add a tensioner, if I'm lucky.
  20. Here are the pictures of my belt setup...

    The tensioner bar is underneath the coolant line going to the thermostat.

    As to refresh, my belt is stretching every couple weeks and needs to be tightened. I just tightened it yesterday to get rid of a start up squeal. The tensioner bar doesn't have much left in term of length, so after another adjustment or two I'll have to replace a perfectly good 25 dollar belt....

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