The Ford Barn

rhpope · 02-03-2025, 02:09 PM

My questions are about the comparison between the 9" and the 9-1/2" clutches

The 9" clutch is just the typical clutch that was used for many years that used a standard Long style pressure plate. See the link.

https://fortwayneclutch.com/product/...ew-sku-kt5102/

For the 9-1/2" clutch, the pressure plate looks different than a standard Long pressure plate, but it still appears very similar. See the link.

https://fortwayneclutch.com/product/...t8594-1-375_r/

My questions are these:

Will the two interchange on the same flywheel or is there a difference in pressure plate bolt pattern?

What are the bolt circle dimensions on the two different pressure plates?

I have a 9-1/2" pressure plate that I measured the center line of the bolt circle to be approximately 10-7/8". I do not have a 9" pressure plate to measure the bolt circle. Is the 9" approximately 1/2" in diameter smaller?

Is it flywheel specific and would have to be redrilled if changing the size of the clutch and pressure plate between 9" and 9-1/2"?

Thanks for any help,
Roger

rotorwrench · 02-03-2025, 07:31 PM

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The standard 8BA type clutch was the 9.5" Long with a 1"-10-spline disk drive. Long type clutch covers all have three pairs of two bolts to secure them just like the other Longs and different diameter disks have different diameter bolt pattern centers with the pairs closer together than the distance between pairs. The 59A and earlier motors used the 9 and 10-inch Long types but they have the 1 3/8"-10-spline disk drive. Pickups, police cars, and station wagons in the 8BA era used the heavier duty 10" Long clutch but they also used the heavier duty drive spline.

Borg & Beck clutches were 10" but they have six equidistant bolt holes with the next size larger bolt size. They were used on the 1949 through early 1951 8CM Mercury cars which also use the 1 3/8" 10-spline disc drive. A lot of the modern diaphragm type clutches use the old Borg & Beck bolt pattern,

02-03-2025, 02:09 PM	#1
rhpope Junior Member Join Date: Aug 2010 Location: North Carolina Posts: 23	9" and 9-1/2" Clutch and Pressure Plate Questions My questions are about the comparison between the 9" and the 9-1/2" clutches The 9" clutch is just the typical clutch that was used for many years that used a standard Long style pressure plate. See the link. https://fortwayneclutch.com/product/...ew-sku-kt5102/ For the 9-1/2" clutch, the pressure plate looks different than a standard Long pressure plate, but it still appears very similar. See the link. https://fortwayneclutch.com/product/...t8594-1-375_r/ My questions are these: Will the two interchange on the same flywheel or is there a difference in pressure plate bolt pattern? What are the bolt circle dimensions on the two different pressure plates? I have a 9-1/2" pressure plate that I measured the center line of the bolt circle to be approximately 10-7/8". I do not have a 9" pressure plate to measure the bolt circle. Is the 9" approximately 1/2" in diameter smaller? Is it flywheel specific and would have to be redrilled if changing the size of the clutch and pressure plate between 9" and 9-1/2"? Thanks for any help, Roger

02-03-2025, 07:31 PM	#2
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 18,006	Re: 9" and 9-1/2" Clutch and Pressure Plate Questions Sponsored Links (Register now to hide all advertisements) The standard 8BA type clutch was the 9.5" Long with a 1"-10-spline disk drive. Long type clutch covers all have three pairs of two bolts to secure them just like the other Longs and different diameter disks have different diameter bolt pattern centers with the pairs closer together than the distance between pairs. The 59A and earlier motors used the 9 and 10-inch Long types but they have the 1 3/8"-10-spline disk drive. Pickups, police cars, and station wagons in the 8BA era used the heavier duty 10" Long clutch but they also used the heavier duty drive spline. Borg & Beck clutches were 10" but they have six equidistant bolt holes with the next size larger bolt size. They were used on the 1949 through early 1951 8CM Mercury cars which also use the 1 3/8" 10-spline disc drive. A lot of the modern diaphragm type clutches use the old Borg & Beck bolt pattern,