1 or 2 Piece Drive Shaft

[3jcelica]

e30-323ti,

Yeah this is why the falcons are where speed limited to around 170 Kph

Roger

[e30-323ti]

Bit of background behind my issue:

The dynamic balancer only spun upto ~3000rpm, and was perfectly balanced.

However, when in the car, top or 4th (being 1:1) had the shaft spinning at ~6500rpm on the track.
Also run up on axle stands (safely of course) you could see the shaft go into 'skipping rope' mode.

Back at the balancers, even with weights (considerable) added to the middle of the shaft it could not replicate the issue.

The tube diameter, wall thickness & length all 'seemed' to be within the acceptable range to not have the issue, but was clearly not the case on 3 different shafts.
2.5" thick wall, 3.0" thin & thick wall tubes, the last being the best (or the least worse, good england there). Thus, back to a 2pc shaft.

[Indelible]

when i got my tail shaft made for manual conversion on a jzx100 i asked about 1 piece and they laughed
and said 2piece is better and can do much higher speeds as it will be better balanced coz the short distance between mounting points instead of one long shaft
. just make sure you get replaceable ( hilux or similar) uni's

[jondee86]

The issue with one-piece drive shafts is the problem of "whirling". This is determined
by the shaft dimensions (diameters and length), the material, and the forces applied to
the shaft. If the critical frequency occurs within the operating speed (rpm} range of the
shaft... Houston, we have a problem !!!!

For any driveshaft, the machine designer must calculate the critical frequency, and
make sure it is outside the operating speed range of the shaft. Adjustments to dimensions
and/or material may be needed to ensure this requirement is met. Reducing the length
of the drive shaft has the effect of making the shaft/tube more rigid without having to
use a heavier wall/stronger material for the tube.

Some information here... http://www.roymech.co.uk/Useful_Tabl...cal_Speed.html

Cheers... jondee86

[beerhead]

JZX100 is IRS right? So there isn't any variable in the pinion angle when the back end is squatting, so 2 piece isn't going to do anything special. If the car has harmonics with a 1 piece, then the machinist who made the shaft doesn't know what they're doing.

In drag and track conditions I've been taught that if the car has a 4 link back end and you have adjustable top arms that you can change the way the car squats by playing with the pinion angle. The longer the shaft the less variance in pinion angle and less power is lost. If its a drag car you watch the angle on the dyno at peak HP and adjust the top arms to make the pinion sit true at max HP.

[50RTD]

With a single piece shaft, there must be merit in eliminating a potential point of failure (middle uni) particularly in factory componentry that is subjected to significant loads above the designed torque output...

Ive read about factory BMW driveshafts twisting splines at the centre bearing with power outputs exceeding 350-400whp, no doubt this is the case for many factory offerings...

Mind you with a strong and readily available uni joint/centre bearing on a custom tailshaft, this is likely to be less of a concern...

EDIT: Beerhead's comment about the difference in IRS and live axle rear ends makes a lot of sense, big variance between the two conditions....