Belt size question on 88

88mk_fox

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Dec 23, 2020
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Hi guys, I’ve searched around but can’t find any specific answer for my belt setup. I have an 88 notch that has factory ac delete and also am bypassing smog pump. Just put new underdrives on the car (has 3G alternator) and can’t seem to figure out belt size. Any help would be appreciated. Also wondering what routing would be correct.

thanks
 
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Mustang5L5

Put lubricant all over the balls
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It’s going to vary because unferdrives aren’t all the same diameter pullies. Best way to check is to get a string and measure it. Better yet, grab one of those tailors tape measure ropes and route it like the belt would go. Buy a couple belts, test fit, and write down the lenght.
 
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Rdub6

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After much trial and error with this myself, I found that the one that fit best was the most difficult to get on, almost seeming like it was too small. But after a few miles it stretched to the perfect fit. Just keep an eye on the pointer on your tensioner.
 
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88mk_fox

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Ended up finding the right belt size, 74” worked out well. After a few starts now I have a squeal just on startup, then goes away immediately. Belt stays aligned perfectly though. Hmm...
 

Mustang5L5

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Might not be tight enough. Is the tensioner towards the tighter end of the range? These belts stretch a bit after a while
 

88mk_fox

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Just checked my belt and seems slightly loose, good call. How to I gauge the tensioner? It’s almost completely vertical. I see the range gauge but what is the indicator and where would I want it to be at?
thanks
 

Mustang5L5

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Does it look like this? There usually is an indicator

8DA79731-6E46-4349-8E27-7E9BB1198293.jpeg
 
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88mk_fox

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Yea looks like that and I can read “range” but don’t see an indicator of where it should line up. The grayer metal piece that says “range” , the notch of it is all the way at the top, not anywhere towards the middle like this picture shows it
 

Rdub6

So while I wait to figure out my rear end issues
Dec 29, 2017
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Yea looks like that and I can read “range” but don’t see an indicator of where it should line up. The grayer metal piece that says “range” , the notch of it is all the way at the top, not anywhere towards the middle like this picture shows it
It doesn’t have the small raised arrow?
 

88mk_fox

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Nope. Not that I can read lol. The tensioner originally on the car when I bought it did not look like this and did not have the “range” or indicator. It was much thinner too. I stripped it out trying to install a steeda billet pulley and got this one from a mustang salvage yard online virtually free. So yea... lol

I assume the 90-93 had this tensioner and maybe earlier models looked different?
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Mine is an ‘88 and has it. Your tensioner has probably been replaced.

if you have a 74” belt now, a 73.0” or 73.5” belt might work a little better.
 

88mk_fox

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I got a gates 73 in the garage still from test fits, so I’ll give it a shot. Indicator should be near middle?
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Massachusetts
Middle to tighter end of the range. The belt will stretch a tad after some use
 
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Gs1987GT

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Sep 25, 2019
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The timing of this thread is great gents. My 87 GT is factory ac delete and I will be removing the smog pump next spring (bad)

Any idea what length belt I need for my car with the stock pullies?

Thanks
Greg