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Changing out the C6 auto trans for a ZF S-42 five speed. This is part of a gas to diesel conversion for a 1989 F250 4WD. Gas engine was a 351 with a C6 auto trans and now is a 7.3 IDI with a ZF S42. I have heard and read about the auto to manual transmission change over is pretty uneventful. However the question remains as to the transmission support crossmember to the frame. Some say one has to lengthen the transmission mount holes to the frame crossmember by approximately 1/2 inch due to the difference in length from the C6 to the ZF. But, when comparing the frame transmission cross member that came with the ZF to that of the C6 it appears that the lengthening the trans mount holes would not be needed. Please see the photos. I know some will say just use the ZF crossmember however I do not have the gussets which are different from the C6 gussets so I must use the C6 mount. In the photo with the two crossmembers side by side the one on the left is from the C6 and the one on the right is from the ZF. The mark on each crossmember shows where the transmission mount sat and when lining up the two crossmembers' bolt holes it appears that the C6 crossmember can accommodate the ZF without modification. I am looking not the modify the C6 crossmember. Has anyone done the C6 to Zf swap without making the transmission mount holes longer on the C6? All replies are greatly appricicated.
Well I haven't done a C6 to ZF swap, it was an M5OD to a ZF. I DID need to modify the transmission mount holes by about 1/2 on my crossmember. I lengthened them with a dremel. I ended up using the same transmission crossmember from the M5OD (manual 5 speed behind the 302) for my ZF5. I'd say if everything bolts up and the holes line up on your C6 crossmember, you'd be fine in leaving it alone!
Now I see you say you are comparing the holes between the crossmembers, but the lengthening of the holes is due to the position the transmission sits in the vehicle after everything is mounted up. If, when you bolt the 7.3 and ZF5 in there, the crossmember lines up with the mount on the ZF, then you won't need to cut any holes. If the crossmember doesn't line up with the transmission mount (attached to the transmission), then you'll need to elongate the holes in the crossmember.
