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Belt speed ?

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  • Belt speed ?

    Problem - damper on the Tbird is going south - chunks of rubber flying everywhere. Thought at first the belt speeds were different on the new A/C set up but the pulley calc says no.
    May be the new flex fan is putting lots of resistance on the damper and causing it to separate since it is 50 years old? LOTS more air movement with that new fan so lots more resistance. The fan is driven off the water pump (no clutch) which is driven from 2 belts off the damper. The empty belt groove on the water pump is where the A/C belt will go when I install the compressor this summer. Don't want to change the belt config if I don't have to but don't want to ruin a new replacement damper either. Dang it.

    I used 7 inches as my crank pulley diameter and 5 inches for the PS pulley size (probably close). 800 rpm on the large pulley (crank speed at idle) - belt speed is 1466.1rpm. PS pulley running 1120 rpm.

    Next I used the same settings but 3 inches for the gen pulley (just for round numbers - probably close there too) Belt speed is still 1466.1rpm but the change is the gen pulley speed which is now around 1866.7 rpm.

    Pretty much like I had figured when I was putting it together - that the belt speed is constant and only the pulley speeds change. Not sure if the other 7 inch pulley on the water pump makes a difference - don't think it would since it is the same size as the crank pulley.
    Center measurement doesn't make any difference except on the belt length - not concerned about that.

    Am I missing something?


  • #2
    Are you sure the power steering belt goes around the water pump? All the A/C cars I've had only have the power steering belt on the crank pulley. All the parts books I have show the power steering belt w A/C as 37". That seems way too short to go around the water pump. I thought the generator with A/C has a double pulley. Maybe I'm wrong.
    John Pizzi - Squarebirds Administrator

    Thunderbird Registry #36223 856-779-9695


    • #3
      Pretty sure you are right. I have seen different set-ups with dealer or aftermarket air but the factory config was 2 belts to the wp and gen then another single belt off the crank to the ps pump (but not to the wp). Then AC driven off the wp pulley (I have the factory correct ac wp pulley on there).

      This set-up looked like it would work and the numbers were right on belt speed - so I went with it. I have the correct ac crank pulley with the additional grove for the ps pump but didn't install it because it would have meant moving the ps pump to the outside of the AC bracket using spacers (more work). Plus installing the 2 grove pulley on my generator. Ah well - I learn from my mistakes (so I must be a genius by now ).

      Was trying to wait and do the dual gen belt when I converted to an Alt. and move the PS pump belt at that time - guess I'll be dong it sooner than later.

      Thanks for the response!

      Last edited by DKheld; January 15th, 2012, 02:26 PM.


      • #4
        Hmmmm...if the damper pulleys are both the same diameter and the water-pump pulleys are both the same diameter then I cannot see you having any problem - let alone a problem of a damper being torn up.

        And even if there WAS a mis-match of pulley diameters I would say the resulting squeals of protest from the belts would let you know something was right.
        A Thunderbirder from the Land of the Long White Cloud.


        • #5
          Are you sure the dampner shives are the same dia?


          • #6
            A sheave (pronounced "shiv" or "shēv") is a wheel with a groove along its edge for holding a belt. When hung between two supports and equipped with a belt, one or more sheaves make up a pulley. The words sheave and pulley are sometimes used interchangeably. In automotive, both sheaves are fixed to their pulley and do not turn independly from each other.

            It is important to note that two different diameter (or width) sheaves can make up a pulley (like on your water pump). Y-Blocks with superchargers use this.

            If your system uses multi-sheaves on the same pulley and both belts share another multi-sheave pulley, each independent pulley needs to use same-diameter sheaves. In our case, the water pump pulley may have three sheaves but the two that are the same diameter will go to the crank pulley. The third (odd diameter) sheave will be used independently.

            I know some damper pulleys (on the crank) are different diameters. The fight starts and heat builds, melting urethane on the damper ring, when both belts are used with different diameter sheaves.

            But there is nothing wrong with using muliple belts on same diameter sheaves, even if the water pump diameter is different. Belt speed is determined by the damper pulley.

            Simply put, if your sheaves are all different diameters, they cannot be shared with the damper pulley. Only one belt can. - Dave
            My latest project:
            CLICK HERE to see my custom hydraulic roller 390 FE build.

            "We've got to pause and ask ourselves: How much clean air do we need?"
            --Lee Iacocca

            From: Royal Oak, Michigan


            • #7
              No loud squealing of belts so that's one thing that lead me to believe all was good.

              Even though I think there is not a problem with this config I'm not ready to go back with this set-up on the new damper - too expensive. I'll probably add the 2 groove pulley to the crank and gen and reconfig. the belts so that I have the factory style setup with 2 belts going to the gen and a separate one to the ps pump. I have all the pulleys just thought this would work.

              Haven't actually measured the pulleys on the crank but if they are different it's something you can distinguish by eyeballing it.

              Here's a pic with the belts off (and different fan spacer that didn't work) - the wp pulley has 2 grooves the same size behind the larger ac grove that line up with the crank grooves - cant see the first groove in the wp pulley very well.


              • #8
                Ah Ha !

                Apparently the set-up I used was not such a bad idea after all - seems this 428 FE Galaxie (found on the net) used much the same set-up. Big difference I see though is that the Galaxie damper does not have a belt groove.

                Ooo - ya' know - that motor would look pretty good in my Tbird....


                • #9
                  Later model dampers do not have a belt grove. They use a pulley that is bolted to them for the belt drive.