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Axle shaft size(spline) versus material(stock, 4340, 300m), biggest bang for the buck

Lil'John

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Title kind of states it.

What is the best way to upgrade axle shafts assuming there is spline count and material changes available?

For my example, I'll use a Tundra 10.5" center section used as a front axle.

Stock spline count is 36 and 1.45" diameter. Upgrade path is 40 spline and 1.7" diameter. What type of strength will I gain going from 36(1.45") to 40(1.7")? If it is easier, use standard Dana 35 spline and 1.5" diameter.

From a material standpoint, I'm starting with stock Spicer inner shafts. I can get to 36 spline from the 35 spline shaft. If we go with same spline count, what type of strength gain is going from stock to 4340 chromo? How about going from stock to 300M?

For bonus question, is it worth going from 1480 to 1550 ujoint? What is the strength upgrade in upgrading?
 
Spline count doesn't mean much.
Diameter is where it's at.

Since I doubt you can find 40sp 1.71" in "stock" material, no matter what if you go to 40p you'll also move to 4340 or 300M (or better for that matter).
 
min. diameter matters in terms of spline count.

the same OD shaft in 40 spline will have a larger ID than a 31 spline shaft and that is where the strength difference is rooted. also in the spline engagement, but i'll say "less so" than the min. diameter.
 
Spline count only causes minor diameter to change if pressure angle is fixed.
 
Size for size back when Bobby was breaking them, I remember d60 35sp stock breaking in the 7-9k ft-lb range. 4340 import chromo went to 12k. 300m stalled his machine around 15k IIRC and he couldn't break it.

I don't remember the whole equation off the top of my head, but the torsion strength size factor is d^4. So all else equal, a 1.7" shaft will be about 1.9x as strong as a 1.45" shaft. Being that spline minor vs spline major will drop a bigger percentage of diameter from the smaller shaft, when you account for spline minor, that factor will get bigger, but not by a lot.
 
I don't see why you would compare shafts by spline major OD since that just adds the spline angle as an additional variable.
 
Thanks ScottRS for providing some real tech/info and not going off on un-useful minutia with no tech added to help answer the question.

The purpose of this thread is to find the best approach for creating a D60 outer to Tundra center hybrid that isn't going to be full width(ie custom length shafts are on the plate). The Tundra is 36 spline(1.45" OD) while the D60 is 35 spline (1.50" OD) so I will be looking at having to do something custom; side gears or axle shafts.

The choices I'm considering:
  • Get axle shafts made that are Tundra 36 spline... benefit is I can use stock open Tundra thirds. ARBs are on the plate but may be delayed in getting. This route, I can just get stock shafts resplined. I could also get the 1550 upgraded u-joint in non-chromo form. Downside is not many places were willing to touch 36 spline.
  • Get Tundra locker and make sure the side gears are Dana 35 spline... I know ARB will provide this option as an extra. Benefit is I can use a stock short side without touching it. Also of benefit is everyone and their grandmother will do 35 spline. I have a local source that will do it. Downside is not possible to broach Tundra 36 spline side gears to Dana 35 spline.
  • Broach side gears for 40 spline and buy new shafts. Benefit is not being forced to get a locker first since the open side gears can be broached. Obvious downside is costs although Branik shows only ~$150ea cost difference when doing 4340 chromo. Another downside is I haven't found a 40 spline lockout yet.
Since I may or may not have stock shafts in hand, I may have overhead of buying stock shafts and then splining them... which is why chromo shaft strength vs stock shaft strength becomes a question.
 
In for tech...I am in a similar boat with my rear axle, go bigger diameter or use better materials with existing diameter.
 
I'd do 35sp side gears from ARB and custom 35sp axles for the simple fact that you can get them from different places and with less waiting time than custom 36sp.

Custom anything already takes forever these days, don't want to wait even more.
 
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