Mounting the Transmission into the 1929 Ford Model “A” Roadster Hot Rod
Now that the 1986 Corvette engine in positioned into the 1929 Ford Roadster hot rod, it is time to create the transmission cross member. The 1986 Corvette uses a prop shaft support or carrier support beam that connects from the rear of the transmission to the front of the carrier pod on the rear end. This beam has a “C” channel shape and is made of aluminum. To use this beam on the 1929 Ford Roadster does not make any sense. The chassis design I created for this hot rod, has two cross members. There will be one cross member for the rear of the transmission and a second for the carrier pod on the rear end. Both of these cross members are made of 2” x 3” x 0.1” rectangular steel tubing. When these cross members are welded in place, they will make the frame much more ridged. I used the 1986 Corvette 700R4 automatic transmission in my hot rod.
When setting up the transmission and rear end, the transmission output shaft must be parallel with the pinion shaft in the rear end. The angle of the transmission and rear end is critical. Normally the pinion shaft in the rear end will angle 3 degrees upward from the horizontal position and the transmission must angle 3 degrees downward from the horizontal position. This will produce a smooth ride and eliminate unnecessary u-joint wear. I set up a magnetic protractor to make this measurement on the yoke mounted on the pinion shaft for the rear end. Do not try to make the angle measurement on the output shaft of the transmission. It moves a bit without the driveshaft yoke installed. I actually use the mounting face for the carrier support beam on the transmission to make my measurement.
The transmission cross member has the wide part of the rectangular tubing facing up. On the top of the transmission cross member I needed to cut out a 1.5” x 2.5” hole. This hole will be used to insert and weld a ¼” plate with two nuts welded to it for the transmission mounting bolts. Once I determined that the transmission would bolt into place correctly, the 1.5” x 2.5” hole will be welded shut and ground clean. I used a similar method for 4 body mounts that will be located on the inside dimension of the frame rails and transmission cross member.
I used ½” thick metal spacers in between the transmission and the cross member position the transmission angle correctly and then welded the cross member to the frame rails. This positioned the transmission cross member with a 3 degree downward angle within the frame rails. Once the welding was completed the ½” thick metal spacer was replaced with a rubber one.
When I originally started on the design of the 1929 -31 Model “A” Ford hot rod chassis, I was intending to mount the 1931 Ford 5 window coupe body on the chassis. Everything worked out perfectly to the point that even the 1986 Corvette aluminum driveshaft could be used. With the project switching over to the 1929 Ford roadster body, the engine needed to be moved toward the front of the frame allowing the engine to clear the firewall. I ended up with about 2.5” of clearance between the firewall and the value cover of the Chevrolet Corvette 350 cubic inch engine. Using a small diameter distributer in the engine, I had about 2” clearance between the distributor and the firewall. If I knew some of these problems early on in the chassis design, I most likely would have made the chassis 3” to 6” longer. Then I could have place my front coil over shocks in between the frame rails just like some of the Indy race cars or the Plymouth Prowler. Oh well, version two on the chassis will be coming soon with several refinements.
Moving the engine forward now meant that I would need to have a drive shaft made. The 1986 Corvette driveshaft was too short. I did intend to cut and make my own driveshaft from one I salvaged from another car, but then thought better of the idea. It makes a lot of sense to have this job completed professionally. The driveshaft will be balanced correctly and will not cause any vibrations while driving the hot rod. Make sure you call the shop first to find out how they would like you to make the measurement for the driveshaft. This way you will not have any costly disappointments with the driveshaft. When you make the measurement for the driveshaft, make sure that the old driveshaft transmission yoke is inserted correctly on the transmission output shaft. I just used the wear marks on the old Corvette yoke to determine the correct position. It would be located exactly were the Corvette engineers wanted it in the transmission.
Come back next week for more interesting build information for my 1929 Ford Roadster hot rod.
Keep watching my Products Page for the AutoCAD drawings of the 1928 – 31 Model “A” Ford hot rod chassis / frame using C4 Corvette suspension components. They should be for sale shortly.