If I am looking at it right it looks like the FD steering shaft is a 5/8 36 spline shaft. If anyone else happens to know off the top of their head or doesn't mind doing a gut check for me it would be appreciated. I am in the process of ordering a sweet mfg steering shaft for my LS1 project car.

 

Looking for something else today and remembered this, while digging through steering bits.

Steering column spline appears to be 15.9 and 15 on the minor diameter...say 16mm. Rack pinion is 17.3 and 16.5 minor. Didn't look at spline count and couldn't find the intermediate with the unis either, which I suspect would be different both ends.

 

Yes the FD's steering shaft is essentially a 5/8" x 36 splined shaft. I have the stock wheel and an after market 5/8 x 36 shaft and they fit together very well.

By the way 5/8" is 0.625" and 15.9mm is ~0.626"; thats pretty damn close

 

If your buying u joints:
Be careful, you need metric stuff. I tried to buy american stuff from flaming river and it would not fit witha couple thousands difference. I had to send that stuff back and then bought my steering u joints from these guys:
http://www.woodwardsteering.com/imag...l%20joints.pdf

they are super low profile and needle bearing. They sell it in metric too. you could convert to their 20 spline shaft and run full splined shaft. thats what i did. The diameter is different where it goes onto the rack. Call up woodward with your measurements and they will hook you up with the right stuff. pretty sure i used the 108 and the 111 on the woodward site. I know the 111 doesnt ook right but it fits on a full splined shaft.

CJG