Underdrive Pulleys & Belt Question (searched)

criticman · Jul 6, 2005

Underdrive Pulleys & Belt Length Question (searched)

Okay, so I searched for this and no luck.

I have MAC underdrive pulleys (crank, water pump, alt). My battery is having some serious charging issues (yeah, I know...50/50 chance that it would happen from what others have said).

I was thinking of putting the stock alternator pulley back on until I get a PA Performance 3G alt.

So, with the crank and water pump MAC underdrives....and the stock alternator pulley...what size belt do I need to do it?

Thanks!

marine_2003 · Jul 6, 2005

If you cant use the same belt then you are going to have to go to your local parts store and go through the belts until you find one that fits.

bullitstang1313 · Jul 6, 2005

Do you have the A/C delete kit or is your power steering pump in the lower mounted position? You'll probably have to go to the auto parts store and just try belts that are a little smaller than the one you have. Just a note, when I bought an auto-parts 3G the pulley on it was the same size as my bbk underdrive pulley.

dstanggt50 · Jul 6, 2005

If you didn't need to change belt sizes ( I didn't w/my underdrives) then I would just use the stock one

criticman · Jul 6, 2005

Okay...when I added the u-drives, I maintained stock belt. Putting the stock alt pulley back on means the size will change, so I will HAVE to get a different belt...unless I am missing something? Would the auto-belt tensioner take care of that small size change?

If no one has an exact size, I will do as suggested and do trial and error at the parts store.

WantaGT · Jul 6, 2005

subscribing

criticman · Jul 7, 2005

Don't expect a reply from anyone else. I think that was the response I am going to get. I will however post up whether or not the stock belt works still with the pulley swapped and if not, I will post what size I end up using.

Daniel50 · Jul 7, 2005

same belt size

Scorcher2005 · Jul 7, 2005

criticman said:
Okay...when I added the u-drives, I maintained stock belt. Putting the stock alt pulley back on means the size will change, so I will HAVE to get a different belt...unless I am missing something? Would the auto-belt tensioner take care of that small size change?

If no one has an exact size, I will do as suggested and do trial and error at the parts store.

if you are still using the stock belt, i dont know why you are confused as to which belt to use when you are putting a STOCK pulley back on.

mustangibew · Jul 7, 2005

I always just take a string and wrap it around the pulleys like it is a belt and then measure it to see what size.

criticman · Jul 7, 2005

Scorcher2005 said:
if you are still using the stock belt, i dont know why you are confused as to which belt to use when you are putting a STOCK pulley back on.

Putting ONE stock pulley back on....meaning TWO aftermarket pulleys remain. Make sense now?

Car RamRod · Jul 7, 2005

ok, what belt are you using now with all three u-drive pulleys? The stocker?

criticman · Jul 7, 2005

Yep - lets make this simple....

I bought MAC underdrive pulleys: crank, water pump, alternator.

I removed the stock pulleys and installed the above.

I maintained the stock belt size.

I am going to be removing the MAC alternator underdrive pulley and replacing it with the stock pulley.

I will attempt to use the same belt (stock) since others above said it should work. If not, I will do the "string method" to get a size and run to the parts store.

93tealstang · Jul 7, 2005

Your putting back on the stock alternator pulley so your belt will have to be smaller by maybe an inch or so from a stock belt. Somewhere around an 88-89 size belt, I'm guessing.

8950HO · Jul 7, 2005

My car has ASP street underdrive pulleys on the crank and waterpump,and a ASP 1-7/8" overdrive alternator pulley for better charging.

I`m using a Dayco 5060895 belt with this setup,which also worked with the stock alternator pulley.Car has AC too.

So basically you would need the next belt size down from stock to run the stock or overdrive alternator pulley,with the underdrive crank and WP pulleys.
The parts store should let you try out a different size or two to get the ideal one.The store had to order the 5060895 size for me because they didn`t stock it,as it`s probably a not too common oddball size maybe.

Scorcher2005 · Jul 7, 2005

you somehow arent understanding here. You had the same belt with stock pullies. The stock pullies are smaller than the overdrives. Lets just call that the minimum belt size. You now have 3 larger pullies. Lets call this the maximum belt size. Now, you are only replacing 1 of 3 pullies back to stock size. This new belt size is bigger than the min, but less than the max. Therefor it will work.

Car RamRod · Jul 7, 2005

so look picute it like a number line. Stock you were a 1, then with all the u-drives you were a 3, and your stock belt worked for both. Now, by removing one of the u-drives your a 2. I couldnt see a feasable reason why a belt would work on the two extremes (full mod and stock) and not work in between.

criticman · Jul 7, 2005

Scorcher2005 said:
you somehow arent understanding here. You had the same belt with stock pullies. The stock pullies are smaller than the overdrives. Lets just call that the minimum belt size. You now have 3 larger pullies. Lets call this the maximum belt size. Now, you are only replacing 1 of 3 pullies back to stock size. This new belt size is bigger than the min, but less than the max. Therefor it will work.

You somehow aren't understanding ANYTHING. The crank pulley is smaller in underdrive pulleys. The water pump and alt are larger (larger the diameter, longer time to rotate, so slows the components down). The crank is smaller because less diameter means less mechanical effort to rotate it.

So, dropping a LARGER pulley to go back to the SMALLER stock pulley of VERY little difference means what everyone else is saying is accurate - the stock belt MAY work - if not a slightly smaller belt will be required.

EDIT: Here is a diagram I just created that shows the size variances (not to scale obviously).

srothfuss · Jul 7, 2005

Have you put the stock belt back on and looked at the tensioner? There is a range on the tensioner (Max / Min) If your stock belt falls within that zone than you are fine. If not, well just go get a shorter belt

criticman · Jul 7, 2005

Yeah - that is what I had said I am going to try. Thanks for the tip though. Thankfully the tensioner is self adjusting...I believe based on the Haynes manual, early Fox bodies had a manually adjusted tensioner where you had to check the tension using a gauge.

Underdrive Pulleys & Belt Question (searched)

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