Ford Drive Shaft
The drive shaft I used turned out to be quite an oddball size from the normal Ford drive shafts in regards to U-joint dimensions. First of all, I was told the drive shaft came out of a Mustang of mid '80's vintage, but no other information was available. When I went to the salvage yard to get another one just like it, I found no Ford drive shaft to match the one I had bought earlier.
All the shafts I had looked at had smaller width U-joints than the one I had (the U-joints on my shaft were 3-9/16" across while the ones I looked at as replacement parts were about 3-3/8" across), some had bigger diameter tubes, but they all had the same bolt pattern on the propeller shaft yoke. Anyway, If I ever need to replace a yoke on my drive shaft, I will undoubtedly have to shorten another drive shaft for my Z.
The modification of the Ford drive shaft to fit the Z car starts with cutting (grinding) the front yoke off of the front of the Ford drive shaft. Then, after determining the amount that must be removed to shorten the Ford shaft to fit in the Datsun chassis, this same amount is then cut off of this same end (transmission end) of the drive shaft. The reason for modifying the front of the drive shaft is because inside of this drive shaft tube is another thick tube, of shorter length than the outer tube making up the drive shaft, that is vulcanized to the inner surface of the outer tube, to act as a vibration damper ( I think ). If you cut the outer tube from the other end (differential), then your job will be greatly complicated by having to cut into this damper and weld around it. Anyway, after the drive shaft tube has been cut on the original weld, and the yoke knocked out(which was pushed into the end of the tube prior to the factory weld), re-insert this yoke into new shorter tube cut earlier. After it is inserted, weld it back onto the tube, and your new shortened drive shaft is complete.
Next step is to make an adapter plate to mate the Ford propeller shaft yoke to the Datsun propeller shaft. This was done by having a aluminum plate turned on a lathe to a diameter of 4-1/2". Then eight holes were drilled into the plate, centered on the center point of the plate. The eight holes are in reality 2 groups of four holes. One group is for the Ford bolt pattern, and the second group is for the Datsun bolt pattern. The Datsun pattern holes consist of four 5/16" or 8mm threaded and countersunk holes that match the propeller shaft bolt pattern, and four, grade 8, 5/16" or 8mm flathead screws were installed into these adapter plate holes (to act as studs once they are torqued down) so that the plate can now be bolted onto the propeller shaft by inserting the four bolts into the four holes on the propeller shaft, and installing washers and nuts on the other side of propeller shaft flange. Flathead screws were used because the Ford drive shaft yoke was going to be bolted against the surface of these screw heads, thus they need to be countersunk and flush for a correct fit on the drive shaft side of the adapter plate after it is attached to the Datsun propeller shaft. The Datsun bolt pattern is approximately 1-3/4" X 2-1/8". The other grouping of four holes is for the four Ford drive shaft bolts (on a 3-1/2" diameter square bolt pattern) that will be used to then bolt the shortened drive shaft onto the already mounted adapter plate. Of course the Ford and Datsun bolt patterns are rotated 45 degrees from each other to spread out the holes. Also, the Ford pattern is of quite a bit larger radius than the Datsun pattern, so this worked out really quite well, and has proved to be quite strong too. The entire drive shaft, U-joint to U-joint is only 18-1/4" long. The power plant for this car is a mid 300hp small block Ford engine. Combined with 13" slicks in back (not a locking differential though). I was concerned that the small 5/16" bolts on the adapter plate might fail, but as of this writing, and after many completed races, I have had no failure at this location.
Note: Some time after I wrote the above information, I had to replace the differential in my street stock 280Z with another salvage one. I found out at this time that not all pilot shaft flanges are the same. The old differential had the same bolt pattern as the new replacement differential with the exception of the new differential used 10mm bolts instead of the old one having 8mm bolts. Upon further investigation, I found that most of the R200 differentials used the 10mm bolts. Being that I have had no failure to date with the smaller bolts (8mm or in the racing case- 5/16" flathead) I will leave as is. But I did want to warn you of the variations out there on salvage.