Update - This swap is much easier and better for other reasons if you use the Modern Motorsports "Z CV Halfshaft Adaptor Kit". When you purchase this kit, you send Modern Motorsports LTD. companion flanges that match your stub axles (either the 25 spline 240Z/early-260Z version, or the 27 spline late-260Z/280Z version).
The information below is still presented to show how the conversion was initially done on my Z. I recommend the Modern Motorsports CV Halfshaft Adapter Kit for any 240Z through 280Z with significant power increases over stock.
After discussing things with Jim Biondo, I decided to buy his custom 280ZX Turbo CV halfshaft -to-240Z stub axle companion flanges and custom stub axle inner seals. The price was reasonable and the cost of these and used CV halfshafts were less than buying 4 new NISSAN U-joints for the halfshafts. Of course, I couldn't resist the temptation to send them out to Raxles (tell Mardy I sent you ;) to have them rebuilt. Mardy cannot source new "Tulip" receivers for these shafts, so his guarantee does not hold. However, he had some used spares that had the parts I needed in good condition, and the units were cleaned, and assembled with Amsoil CV grease. So I ended up spending more than replacing my U-joints with Datsun parts ($160), but I have a more bulletproof and smoother driveline in the rear.
(One note for those contemplating this swap. Even though you cannot get new tulip receivers for these joints, take comfort in the fact that you will be running the joint in a more compressed configuration than in the 280ZX, and the area where the tripod bearings run in the tulip is unworn.)
The following information on converting the 280ZX Turbo companion flanges for use on the 240Z was provided by Jim Biondo and from Terry Oxandale's write-up on the IZCC web site.
By popular request, here's a picture of the 240Z stub axle (with bearings, grease, and spacer) a 240Z companion flange(bottom right) and a 280ZX Turbo companion flange (top right):
Here are some better views of the 280ZX Turbo companion flange, with the 240Z dust shield installed:
On to the procedure for converting the 280ZX Turbo companion flange for use with 240Z/early 260Z stub axles:
1 left (shorter) and 1 right (longer) 280ZX Turbo CV halfshaft, in rebuilt or good condition
2 280ZX Turbo stub axle companion flanges (The part that the CV shaft bolts to at the stub axle.)
2 dust shields removed from the stock 240/early 260Z companion flanges
2 stub axle washers and lock nuts (use the 280ZX version nut, PN 43262-W1202 - it is a better design than the 240/260/280Z nut)
12 each of new companion flange to halfshaft bolts (PN 39606-W1202), nuts (PN 01223-00041), and washers (PN 08915-13810)
The custom 280ZX Turbo CV halfshaft -to- 240Z companion flange begins with a stock 280ZX Turbo companion flange, with the dust shield removed (press off the dust shield). The dust shield from a 240/early-260 companion flange is removed by carefully grinding the tack welds that attach it. The 240/early-260 dust shield is then tacked to the 280ZX Turbo companion flange. The 240Z dust shield is a slight bit larger on the inner diameter than the outer diameter of the 280ZX Turbo companion flange. Handle this by wrapping some masking tape around the companion flange, removing a small bit of it in 3 equally spaced points around the circumference, and tack weld the flange at these points. Remove the tape and add a few more good tack welds. The 240Z dust shield installs at the same lateral location along the 280ZX Turbo companion flange as it does on the 240Z companion flange, relative to the outboard end of the flange.
The custom inner grease seal is an R200 pinion flange grease seal that has the outer thin layer of rubber ground off, to be able to tap it into the strut housing. I used a 280ZX companion flange retaining nut (a clinch type lock nut) instead of the 240/260/280Z type staked nut.
When these shafts are installed in the R200, the
hub carrier must be moved outward by:
1) Tilting the strut assembly out by removing the strut top isolator nuts from the car, lowering the control arm and strut and swinging the strut out;
2) Removing the front differential cross member and the retainers for the inner control arm bushings at the rear of the arms, and swinging the strut away from the car;
3) Removing the entire strut/control arm assembly; or
4) Removing the spindle pin and swinging the bottom of the strut out;
so that the shaft outer end cap can be inserted into the companion flange. The outer plunge joint (tripod type) ends up nearly bottomed out, due to the narrower track, etc. of the 240Z relative to the 280ZXT. This is not a problem, as the joints move freely over the entire suspension travel. I know some people say that the CV shafts did bind or bottom out on their 240Z, but that is not the case on my 240Z, or on Jim Biondo's early 260Z with this setup.
I bought 12 sets of new companion flange to halfshaft bolts (PN 39606-W1202), nuts (PN 01223-00041), and washers (PN 08915-13810) to assemble these. I used blue, medium strength Loctite also. Below is a pic of the shafts installed, looking over the 280ZX rear disc brakes.