Differences between single and two piece drive shaft

[ramrat]

I am in the market to puchase a new drive shaft for my 240sx vert and wondering what was the reason Nissan went with 2 two piece design instead of a 1 piece - vibration dampening?

I am trying to decide if I should go with the aftermarket one piece aluminum design or the stock one from nissan both roughly the same price.

I am leaning towards the 1 piece aluminum driveshaft but don't want any vibration issues...

[elwesso]

I think its mainly for the ease of installation ...

Doing the driveshaft once on the Q i dont see how you could do it without dropping the exhaust, whereas with a 2 pieces you can sort of bend it... plus i think itd have less vibrations...

It all depends on quality, im sure you can find really good 1 piece and really crappy 2 piece.. But generally speaking the 2 piece one will have less vibrations....

The reason youd go to an aluminum one is for weight savings. Its something like for every 10 lbs of rotatating mass you remove its like removing 40lbs of static mass. Something big like that, thats why people upgrade to lighter wheels!!! Rotational mass is a biznitch!!

However going from OEM to a one piece aluminum probably isnt worth the HP vs vibrations

[89 240 SOHC]

When I swapped engines I went to a one peice steel driveshaft and I've found it's as good as anything

[DAEDALUS]

One likely reason for 2-piece designs is factory cost. The factory doesn't have to worry about the exhaust during installation, except for warranty work. 2 short pieces need less expensive machinery and carry less overhead than 1 long piece. Weigh this against the extra cost of joining the 2 pieces. Unless the joint between them is damped, the design is not for harmonic damping.A straight comparison of rotational mass to static mass cannot be made without considering the diameter of the rotating mass. Wheels have a relatively large diameter, so reducing weight can have a noticeable impact on performance. A driveshaft has a small diameter--decreasing weight there will have less benefit.Driveshafts are particularly challenging to design. Tubes are more weight-efficient the larger they get, meaning the larger the outer diameter, the thinner you can make the wall of the tube, and the lighter the tube get--up to a point. But the larger it gets, the greater the moment of inertia of the tube--increases by r^2.The structural benefits of aluminum over steel are greatly exagerated. Steel is roughly 3x as heavy as aluminum. But it's also roughly 3x as stiff and over 3x as strong as aluminum. Fatigue is as much a concern for driveshafts as weight is. Steel is much more resistant to fatigue than aluminum is. A lot of factors push design...weight, cost, manufacturability (try welding aluminum), schedule, loads, environment/survivability, application, etc.

[ricebike]

from what i can recall, isn't the manual trans driveshaft different from the automatic trans driveshaft?

the rear sections of the shafts are the same length, while the front portions are slightly different.