First I bought a Broan BP27 replacement motor elsewhere. The installation instructions sheet and the Broan web site say it's compatible with my Broan ventilator 678-B. The BP27 motor shaft is 1-11/16", 1/4" longer than my original. It butts up so tightly against the fan housing ceiling that the shaft won't turn. Contacted Broan, agent said the correct replacement is this part#, S97012038, available at Home Depot. I ordered it. It arrived open box, no instruction sheet. The shaft length on this item is also 1/4" longer than my original. I didn't bother trying to install it. I'm going to return it. Mine is not the only review that notes the S97012038 motor shaft is too long. Broan needs to correct their product information.
This may be a fine motor, but it is NOT compatible with 678-B.
After all this I did a very careful inspection of my original motor and found nearly invisible faded print on the motor: "MODEL 57F2M". Broan customer service, before you write me a dismissive reply, do your homework, and provide the real 'correct' replacement, if there is one. At this point I'm considering replacing the whole unit with a another brand.
Thank you for your review on the BP27 replacement motor and wheel. The information you were provided is directly from the parts list for this model. Unfortunately, there is no alternate Motor or Assembly recommended for the Broan 678-B. The 57F2M you have provided from your motor is showing in our system as used in a Range Hood. Please contact our Technical Team directly at 800-637-1453 to allow us to assist you further.