Float-A-Motor Mount on 28 roadster with fixed front mount

[Ian Crawford]

Originally Posted by rotorwrench

The rear axle pushes on the back of the transmission through the torque tube when moving forward and the pulls on it when braking. Add that to the twisting movements of the frame and road vibration and the original AR type fixed mountings started to have cracking issues. Ford came up with the semi-rigid mountings to give enough flex as to slow the cracking problem a good bit. They redesigned the rear engine to frame mounts and used the rubber pads with bushings. They put out service bulletins for this stuff that included the modification to the front cross member and addition of the coil & leaf spring set up for the front. Eventually, the front cross member was changed again to open up the yoke stud hole for the front mount since they were having problems with cracks in the smaller hole they punched in those that came equipped with the more flexible front mount.

The front cross members went through a LOT of changes in the first year of production alone. After they finally got it the way that they wanted it for the 1930 model year, very few changes happened till the end of production in 1931.

I feel fortunate to have the later 1929 model that is fully equipped with the semi-flexible mounting since it functions about as well as Ford ever made it to. This set up was used through the end of production for the most part. Those that have the early cars and want them to be factory original are pretty much stuck with the rigid mount. Apply all engine balance procedures and add a counter balanced crankshaft and that will smooth that part out without showing much to the Judges at model A show events.

I agree with rotorwrench and would like to add the following. All of these changes to the crossmember are due to the stresses that were induced into the engine by the continious torsional twisting of the chassis. The cracks were caused by the resistance of the engine to "torsionaly twist". Having said that, we only need to distort the tunnel bore by 0.001 to 0.002 to create a problem of interference in the main bearings. It seems unreasonable that judges would take points away from what was a Ford production rectification. Just remember that a three legged chair will always sit even on an uneven floor. The engine should not be subject to any external torsional forces if you want it to last.