I'm planning to replace the manual tranny in my 66 F100 with a C4 automatic. The truck has a cross-member running under the bell housing that has to be removed to make room for the swap. I guess the cab was dropped onto the frame and drivetrain at the factory. I plan to grind of the rivets and remove it, and my question is whether it is necessary to replace it. As you know, this truck has a pretty substantial engine crossmember and of course a tranny cross-member under the tail of the tranny. Any thoughts?

 

I can't see why; to convert from manual to auto you have to remove the crossmember. What year is the truck? I've had to change trans hump before but not cross member. gong from a 3spd to C-4 in a 65 F100

 

It's a 1966. I've never seen any reference to having to modify the trans hump to do this swap. If I'm not mistaken, Ford put the C4 in some F100s starting in 1965. I doubt they had different cab designs for manual and automatic. I wonder if your cab was built prior to the intoduction of the C4 and that's why it had to be modified?

 

It is absolutely necessary to replace it! It serves as a stiffener to prevent excessive flexing of the frame. If you notice, it supports the I-beam stabilizing points on the frame.
Trucks with factory manual transmissions had the crossmember riveted to the I-beam supports, but these crossmembers in factory automatics were bolted. The crossmember MUST be removed in order to R&R the entire transmission and engine as a pair, as well as just the transmission itself. Use grade 8 bolts to reattach it and you will be fine.
I understand the the COM had the bellhousing bolted to the transmission case much like a manual transmission. If so, it may be possible to remove it without removing the crossmember if the case and the bellhousing are removed separately from the truck.
Additionally, the automatic cabs had an inspection plate on the side of the hump, on the passenger side of the cab. This plate was used to adjust the COM bands, since they could not be accessed from below. The inspection plate is not necessary for adjusting a C6, but I do not know about other transmissions.

 

That's very helpful. Thanks. It did occur to me in looking at it yesterday that the I-beam supports are attached to the cross member as well as to the chassis rails, and the cross member would therefore provide additional support. So, given the work involved I'll just reattach it. Thanks again, and thanks Custom Cab too.