[19652plus2]

I picked up a 7 blade '65 Big Car 19" fan that has a 1 3/4" pitch. Hayden only recommends a Heavy duty(2747) or a severe duty(2797) clutch for a fan with a 2 1/2" pitch. Which fan clutch should I get? Should I go with the Heavy duty anyway or buy a "standard duty" clutch? Thanks for your advice.

[70pontiaction]

Got these (2797s) on several of my Pontiacs with whatever pitch fans they came with - very happy with the clutch performance on every one.

[HWYSTR455]

I too say the 2797, BUT, keep in mind, it kicks in at a lower RPM (which provides better cooling), and can make more noise pulling away from a stop light. On that same note, your pulleys and belts need to be in order to ensure they don't slip, there will be more resistance from the clutch. That gets amplified at higher RPMs, like in the 4500-6000 range.

.

[77 TRASHCAN]

Originally Posted by HWYSTR455

I too say the 2797, BUT, keep in mind, it kicks in at a lower RPM (which provides better cooling), and can make more noise pulling away from a stop light. On that same note, your pulleys and belts need to be in order to ensure they don't slip, there will be more resistance from the clutch. That gets amplified at higher RPMs, like in the 4500-6000 range.

.

X2
I've tried the severe duty clutches, They start pulling air too much, for what I needed. I went back to a standard duty thermal clutch, it does the job. A thermal clutch has the bimetal coil in front of it. Some fan clutches are viscous only (have no thermostatic switching, lacking the bimetal coil in front), I wouldn't use one of those...

[19652plus2]

Did anyone even consider blade pitch when selecting a clutch? Thanks.

[68 Firebird]

Honestly when I changed over from a 5 blade direct drive to the 7 blade style
I never even measured. The one I purchased was from a 76 Transam with
Auto and AC. Figured being and AC car it would be an improvement.
That and a Hayden HD(2747) clutch and no issues.
Pulls ALOT of air.
How do you measure? From where to where, I will chk and post finding.

Gerry

[19652plus2]

I think "pitch" is measured in the following way. As the fan is lying on a flat surface, you measure up from the surface to the highest point of the blade.

[67GTONUT]

I have been using the Heavy Duty for years with great success

[72LuxuryLeMansLa.]

Originally Posted by 19652plus2

I think "pitch" is measured in the following way. As the fan is lying on a flat surface, you measure up from the surface to the highest point of the blade.

This isn't a way to measure but....... My 1972 Pontiac Service Manual has a chart for all '72 models. It shows which fan they should have with the number of blades and the pitch listed. So if you have a manual look it up. On my car it is as easy as counting the blades then looking at the chart to get the pitch then buying the clutch for that pitch............