I recently replaced the motor in my PR3 Master Flow attic fan.

The fan with the the new motor vibrates significantly more than the old one. I may have been a little too aggressive trying to get the fan blade back up through the motor's suspension yoke. Some of the blades may have been tweaked...

I beliwve Master Flow doesn't make replacement blades for this model. (I've emailed them to verify.)

I could try a generic fan blade or try to straighten them - what would be the best approach?

If fixing the blade is best, what is a good way to straighten them as visually it is really hard to tell any blades are out of spec - the blades actually look fine.

If bending is just not practical, can I find 3rd party blades that will fit? I assume they usually attach with some kind of set screw?

Edit: Did get a response from manufacturer, they confirm PR3 series is discontinued, but say the closest blade they have is the X113873, so I'll need to call them and see if I can order that.


I bought a fan blade from their newer PG3 model that fits. It has 3 blades instead of five.

Since I took the other one back out anyway, I checked it on a table. Checking it was easier than I thought ... it was very obvious that one blade did not rest on the surface. I bent it back into place, but did not test it.

2 Answers 2


Take the fan blade assembly off the shaft and set it on a flat surface and verify that all the blades rest firmly on it. Tweak if needed. You can then check the angle of the blades by cutting a piece of cardboard to the angle 0f one of the blades and then checking it to the other blades to make sure they're all the same. Good luck/

  • 1
    I do the same but in place using a straight edge on each side or the leading then trailing edge of the blade.+
    – Ed Beal
    Commented Aug 14, 2019 at 17:57
  • I do that for ceiling fans.
    – JACK
    Commented Aug 14, 2019 at 18:24

That's a tough one without seeing it.. BUT I'd agree with your estimate that the fan blades "may" be tweaked some.

No belt, right ? Direct drive ?

The other thing is making certain that between where your new motor meets the fan frame mounting would be that make certain everything's tight...And "sometimes" there are rubber grommet washers that are required to be replaced if the old ones were with worn or gone...

One last ( but dumb ) thing is that the LOUVERS are sometimes noisy from the air flow... But if you are certain that is cool then ok then.

Maybe also check that the motor replaced is near or exactly the same rating and type as the original one... Check the nameplates, make certain they are minimum "close' and maximum exact.

👍Good luck, sir👍

  • No louvers, direct drive. The new motor was the one recommended and made by the manufacturer.
    – rrauenza
    Commented Aug 14, 2019 at 17:53
  • Wish I was there to see it ! I love working on stuff like that ! Commented Aug 15, 2019 at 2:12

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