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Elite Veteran
 
Location: Victoria, BC. Canada | So we have some confusion - my young mechanic friend who's helping me with the Cummins swap - as to the right way to confirm engine/trans alignment with the pinion on the diff.
I've measured the length of the drive shaft (stock original FMC type) from the trans yoke face to the diff yoke face and determined it's about 8". That's with the slip yoke about centered on it's slip range.
Made me a couple of metal spikes and centered them on a round disc that will bolt/clamp to each yoke. Each spike protrudes almost exactly 4" outward from each yoke (1/2 the total driveshaft length).
Good book says that when you are aligning the engine with the diff during install that these two points need only come within 1/16" of each other to be correct.
Can anyone chime-in and elaborate any more on this spec? My mechanic says that typically the pinion angle and the trans output shaft angle need to be the same regardless that they can be out of alignment, ie. one higher or lower than the other, but they have to be the same angle.
Does this same principle apply to the FMC set up? Or can you literally just make sure them two points are within 1/16" of an inch and that's that?
Any and all advice appreciated.
Thanks,
Terry
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Expert
 
Location: Cottage Grove, OR | Due to the angle of the engines install, what your friend says is normal in not correct in this case. It is not a normal install so normals don’t apply. |
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Elite Veteran
Location: Oceanside, CA | The other rule that doesn't apply is the clocking of the joints, standard install puts them "in phase", but, that only applies to shafts that are "equal and opposite" in angularity. For unequal angles the rule is just the opposite, you run the shaft at 90dgs out of phase. The problem with the stock FMC prop shaft is that the splines don't allow for 90dg clocking so they did the next best thing (two teeth off). The reason why none of the norms matter is because there is no "range of motion" with a fixed transmission and differential all you get is some slight flexing of the mounts for each, they don't move with the suspension travel so angularity is less critical..
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Engine install alignment.
