Hi guys,
OK, planning on putting a 351 and FMX auto into my XB and I want to temporarily use the original tailshaft. To do this I need to fit the 31 spline slipyoke which suits the FMX to my tailshaft which has a 28 spline slipjoint on it right now - what I need to know is are the actual uni joints the same dimensions? I've had a quick measure and the bearing diameters seem to be the same, also from a very quick look the actual space the unijoint sits in seems to be the same width too. Are these uni joints the same, or same size?

Thanks!

yeah same uni's i just changed fmx > c4 in my xd, same tailshaft and same uni. There is a 20mm difference in geabox length, but the slip yoke should take this up, the c4 i think was longer. Also the speedo will be out by around 10-12% due to the different amount of teeth on the output shaft.

If there isn't surety about this it would be best to check i imagine, otherwise you could do nasty damage.

If you wanted to check in the suspension bump direction with leaf springs, you could either progressively load it up, or remove the rear hanger and let the end sit up under the chassis, which might get you close enough to make a judgement. Or you could take some measurements.

it will be fine, the FMX is physically shorter by approx 20mm, but the slip yokes are about 150mm long, so wont be a problem. I went from FMX to C4, and had around 20mm of clearence before the slip yoke bottomed out, going C4 - FMX will mean you will have 30-40mm clearence

I love this forum ! Thanks heaps guys, as its going to be a big swap in a short time period by myself in the driveway, I want to iron out all the glitches before I discover them right in the middle of it...thanks again for your help.