Ok I'm about to throw the drivetrain back in the Plymouth. Its a 350/350TH combo w/a 9" rear in a 47 Plymouth coupe. I'm going to throw an angle finder on everything when I get it back in to see if its all aligned properly. I never really had any vibrations or noises (which is amazing since the trans mount bolts were completely stripped out). The Engine is off set nearly an inch or more to the passenger side to clear the steering gear box. I'm not sure if this was all taken into account when it was built the first time. I need to know the maximum allowable drive shaft angle both side to side and top to bottom. I suppose I should check the pinion angle while I'm at it. Any pointers for checking these angles and any other angles I need to check will be appreciated. -N8
The most important thing is that the engine center line is perpendicular to the rear axle and that the inclination of the engine/transmission assembly is equal to the pinion angle. There is of course a maximum angle that the joints are designed to work at but that's not usually as much of a concern as having the other angles correct. In the case of the engine, You will notice that the carb mounting plane is not parallel to the top of the block but is higher at the back of the engine so that the carb sits more or less level with the car on the ground. This angle should also be your pinion angle. The reason for these angles being important is that a typical cross type u joint is not a constant velocity device and the lack of vibration in the driveline depends on the angles of the joints at the front and rear of the shaft being the same so that the vibration will be cancelled within the driveshaft. A web search of U joint applications may give you some insight into the maximum allowable operating angles.
As the illustrations from mgtstumpy show, you want the engine down about 3 and the rear pinion up 3. Or, 4 and 4. It isn't rocket science, but you want those angles so the u joints will "work" as the driveshaft spins around. If you were to aim the trans tailshaft straight at the pinion the u jonts would not last as long and you would probably have some vibration. Just buy a $10 angle finder at someplace like Home Depot, put it on the tailshaft flat spot and get your degrees set, then do the same on the rear axle housing, except aiming the pinion up instead of down. Don't sweat the rear axle pinion being offset to one side and not in line with the transmission tailshaft, most cars that come off the assembly line are like that and they work fine. Don