Spline Surface Area

[ae86trueno]

So i have finally Managed to snap an axle in the rally car,
Yes who would have thought you could do it on dirt

The Diff in Question, Early JDM AE86,

So i find someone with a JDM Axle for sale, get it back to sydney, put it next to the the one from the other side, and its a fraction shorter ...!!!!

The Longer one fully Inserted into the LSD has 25mm of surface area,
The Shorter one only has 16mm of surface area in the LSD, 9mm shorter,

Should i hold out and try to find the correct longer one as it will probably strip the spline
or will this be enough surface area ??

Thanks
Ben.

[RobertoX]

Hey Ben,

Did your axle fail in torsional shear? If it did then chances are if you reduce the spline engagement a bit it will still fail in torsion first.

Just from doing a scribbled stress calc, if you measure diameter of the "base circle" of the spline (bottom of the "v" to the opposite bottom). For the spline to have a weaker surface area you need to have a quarter of the diameter of the shaft of spline engagement length. (at the very least! it will fail across the splines below this). ie shaft radius should = 4*spline engagement.

Then you should allow for shock loads so say if the length of splines engaged = half shaft diameter (say measured across the OD of the splines for a bit of extra 'safety factor')(this is an effective safety factor of 4 plus a bit extra - stresses resulting from shock will be higher the closer you get to the contact surface of the splines).

If you want me to type out the reasoning behind this I can, but can't really be stuffed at the moment

Good luck anyway

[RobertoX]

Just out of curiosity has anyone ever stripped a spline? Especially on a OEM shaft?

ok so I got a little bored: http://www.duivesteyn.net/rob/Splinedshaft.pdf
Just in case you are interested... note this is a very simplified analytical answer and not based on any experience with breaking splines (some experience with broken driveshafts though )


It also always amazes me just how much traction you guys can get on dirt! Not as much as sprint cars though

[merc-blue]

Ive seen quite a few cars "wind off" axels in dirt just load up a axel then grip up again,
same as most big HP car can do them over ripple stripps you could do them over a ditch or even just getting really good grip from a friendly patch of gravel,

inface ive seen a WRX STI spin out a CV join, and turn it into mush

[oldeskewltoy]

Hmmmm Is your car originally a factory LSD? There are two different axles available for both zenki(early) and kouki(later) AE86s. AE86s with open differentials had axles that were longer... about 9mm!!! LSD axles are shorter.

[ae86trueno]

Yep i know there are 2 different axles,I have a new LSD axle coming from toyota,
Hopefully that will explain alot when it arrives.I am almost certain it is a TRD LSD,
If it is a Factory LSD it doesnt explain how the long shafts fit ???

Wow thanks RobertoX,

Ben.

[Mr Revhead]

yeah stock LSD shafts are shorter, wasnt aware it was by that much though, but iv never bothered looking at them side by side.

itll work fine, we only carry the LSD shafts over here, as they fit both LSD and non LSD diffs.
the TRD LSD can use either shaft.

one of my best customers uses the stock LSD shafts in his tarmac rally car, and will be using them in his atlantic engined (yes honestly, a real one) circuit car.

[ae86trueno]

Everyone was right, the shorter Axle stood up to the punishment

2007 BRM Silverstone Safari 9th O/R, 1st P2 (2wd 1300-1600cc)

Go the sprinter ....



Ben.

[RobertoX]

Good stuff! Now go and snap it and tell us which part breaks first

Congrats on the class 1st