240z vs 280z Stub axle strength???

[JSM]

I was reading through the sticky at the top:

http://forums.hybridz.org/showthread.php?t=114798

 

Jon said about the stub axles,

"280 stub axles can be installed in 240 struts with no modifications and the wheel bearings and seals are the same in both cases. This upgrades the inner part of the shaft from 25 to 27 spline."

 

If the diameter of the 240 and 280 are the same and only the spline count is different, how does having more splines generate more strength?

[jeffer949]

Another thing to think about is the fact that the 280zxt uses the same 25 spline count. Why would Nissan go with a weaker part for a more powerful car?

[fastzcars]

The Diameter is SLIGHTLY larger for the 280 stub. The width and depth of each spline are the same on both axles, hence the circumference is longer by 2 splines for the 280z.

[JSM]

Going back to the original thread, I just dont see it. I understand the slightly large outside diam on the splines, but how many fail like the picture below? Do most fail in this area or also in the other areas shown in the thread?

[fastzcars]

In my own opinion, I've seen most axles fail at the base of the splines. I one picture from classic is a result of over torquing the axle nut! The pictures I posted are several examples I complied from members here, let alone other's that haven't posted pictures! Most if not all of them caused by drag racing style launches. But then it all depends on the loads people place on there cars. I'm sure if John C were to comment, he would say that weld joint at the base would be the weak link to the axles, since road racing would place a higher load on that part of the axle. So it all depends!

[JSM]

Thanks, I'm just trying to really understand more than anything.

[johnc]

Going back to the original thread, I just dont see it. I understand the slightly large outside diam on the splines,

 

Larger diameter = more material = more strength. I don't see the confusion here.

 

Obviously Nissan engineers saw a potential for failure in the heavier 280Z using the 25 spline 240Z stub axles. They developed a solution that was some percent stronger and it reduced the potential for failure to a level they could accept.

 

IMHO... most stub axles failures are at the fusion weld where the flange meets the stub axle. I've seen 8 over the years in 240Zs that have been road raced (as predicted by fastzcars )

[zcarnut]

Another thing to think about is the fact that the 280zxt uses the same 25 spline count. Why would Nissan go with a weaker part for a more powerful car?

The diameter of the ZX stub axle (where the bearings seat) is actually smaller --30mm vs. 32mm, than the first generation 1970-78 Z cars. The reason for this is that Nissan increased the outside diameter of the outer wheel bearing on the 1977 Datsun 810 from 70mm to 75mm. However, a “standard†sized 75mm OD bearing is only available that will fit on a 30mm diameter shaft. You cannot use 27 splines on a 30mm diameter shaft so Nissan returned to using 25 splines.

 

What does this have to do with the 280ZX? Well remember Nissan copied the 810 suspension for use on the 280ZX.

 

BTW, the Z31 stub axle starts out at 30mm diameter but then it tapers out to a diameter of 35mm where the wheel flange is.