I have unearthed the prop. from my old 3.0CSi and wonder if anybody can answer the question?
I have measured it, fully compressed, from the outside of each of the flanges. It is c.1580mm. However, the sliding splines mean that I can pull the two parts of the prop apart by c.110mm before they separate. Would it be correct to add 50% of that dimension to give a usable length of, say, 1635mm
I think 50% should be no problem.
Which car and how big of an engine are you going to use it with?
I think I had as little as 30mm contact area on a stock E23 745i propshaft once.
I swapped the stock 3-speed auto with a 5-speed getrag 265 and it was a few cm shorter than the auto so naturally I had to extend the propshaft to reach the transmission.
That car had 350-400(?) hp and a lot of torque (turbo) and weights more than an E24. It was driven hard and I dumped the clutch several times (upgraded clutch and 245/40-18 rear tires), but it held together. It ripped two or three guibo couplings apart and the rear differential mount was ripped apart once (due to age, I guess) so it lived a hard life. What I discovered when I took the propshaft off the car was that the male part were starting to twist right where the female part didn't overlap anymore, so it was no longer able to compress (float) on the splines. Again, that propshaft had to withstand more power than it was originally meant for, so I'm not sure how much sliding the splines apart had to do with it. But I believe the strength will be reduced some.
Conclusion: If you are going to use it on a stock car with stock engine and so on, I think you'll do just fine. That being said, I'm not an expert, I just wanted to share my personal experience with this.
I have no immediate use for the prop, but just wondered.......
I guess the question really should have been ...."When BMW list a two piece-prop shaft, is the measurement they provide the closed length of it, or with the splines halfway home".
