The Ford Barn

Fullraceflathead · 08-22-2023, 09:16 AM

It’s also on the four-speed bellhousing. I believe it’s a tooling point used for machining location.

alexiskai · 08-22-2023, 10:03 AM

Yeah I'm going with "contacting plane/datum" as the explanation. Notice that the flat face of the mystery bump is in the same plane as the flat face of the "cup" on the opposite side that provides room for the starter. There must have been a fixture in the factory that clamped at those two points to locate the housing for machining.

KenD · 08-22-2023, 01:39 PM

I work with castings a lot and this is fairly typical of a casting locator point. The machining center operator would place the rough casting into the fixture with fixed locations to orient the part in nearly the exact same place every time. The cast hole for the transmission input and perhaps the wishbone area hole would be for the X and Y locations. Then this mystery bump, the flat zone for the starter bendix, and the flat above the wishbone connection would be used to set the Z location. Then the housing would be probably internally clamped in the first station which would machine the surface to mate with the flywheel housing and likely all those mounting holes. Then they would use some of those 11 mounting holes in the second station for the remainder of the machining. I might be a little off base on this concept but I see Vintage Precision makes a bellhousing to adapt the T-5 transmission; would be interesting to see how their casting is machined.

08-22-2023, 10:03 AM	#22
alexiskai Senior Member Join Date: Apr 2018 Location: Mebane NC Posts: 2,355	Re: Mystery bump on bell housings Yeah I'm going with "contacting plane/datum" as the explanation. Notice that the flat face of the mystery bump is in the same plane as the flat face of the "cup" on the opposite side that provides room for the starter. There must have been a fixture in the factory that clamped at those two points to locate the housing for machining.

08-22-2023, 01:39 PM	#23
KenD Junior Member Join Date: Apr 2018 Posts: 7	Re: Mystery bump on bell housings I work with castings a lot and this is fairly typical of a casting locator point. The machining center operator would place the rough casting into the fixture with fixed locations to orient the part in nearly the exact same place every time. The cast hole for the transmission input and perhaps the wishbone area hole would be for the X and Y locations. Then this mystery bump, the flat zone for the starter bendix, and the flat above the wishbone connection would be used to set the Z location. Then the housing would be probably internally clamped in the first station which would machine the surface to mate with the flywheel housing and likely all those mounting holes. Then they would use some of those 11 mounting holes in the second station for the remainder of the machining. I might be a little off base on this concept but I see Vintage Precision makes a bellhousing to adapt the T-5 transmission; would be interesting to see how their casting is machined.