Axles Breaking 99 Boxster

[3RotorRx7]

I have had 3 axles shear right at the splines on the right axle in the last 2 events run. Basically 3 broken in 30 or so launches. Twice at the outer CV and once at the inner CV. This happens during a hard launch in Pro Solo autocross. Car is 2100 lbs plus driver. 315/30/18 on 18x11" rear tires. 2.7 liter motor, but also broke one with 2.5 liter motor. Running 2.5 liter 5 speed and axles.

Trying to figure out a bigger axle swap. Noticed the Tiptronic axles are larger at the spline by 80/1000" of inch, but would have to cut them to make them correct length. Does anyone have a measurement of the axle diameter of the Boxster S axle at the splines of the CV.

2.5 manual axle: 1.142"
2.7 tiptronic axle: 1.222"
996 Boxster S' axle: ?

Thanks,
Erik

[stephen wilson]

Are you getting wheel-hop that contributes to the broken axles? If so, working on a cure for that may be another option.

[Jittsl]

That seems very odd to me. I know of at least one person auto crossing a 3.6 liter without braking axles. I Would be looking for another cause. Is it always the same axle? If so, maybe (and I stress I am no expert on the subject) an issue with differential.

[grubinski]

Originally Posted by 3RotorRx7

Does anyone have a measurement of the axle diameter of the Boxster S axle at the splines of the CV.

As luck would have it, my S axle is currently hanging in space waiting for a CV joint, with the splines exposed. I will measure it tonight.

Mike

[The Radium King]

are you using aftermarket axles and/or cv's? i had a bad experience with jobber axles - softer steel than oem, improper cv articulation, improper fit in transmission flanges due to wrong dust caps. bad steel might be what is causing the splines to shear. or, if after market cv's (or undersized aftermarket axles) any play between cv and axle due to improper tolerances might be causing your shear.

i got good results by buying a used oem axle/cv combo from a wrecker for about the same price as new from a jobber.

[BYprodriver]

Originally Posted by Jittsl

That seems very odd to me. I know of at least one person auto crossing a 3.6 liter without braking axles. I Would be looking for another cause. Is it always the same axle? If so, maybe (and I stress I am no expert on the subject) an issue with differential.

Yes very odd, I autoX my 3.6 Box S with 2850 lbs. & no issues with original CV joints & axles. The weakest link will usually be the 1st to break, in my case it has always been the tires. (265-35-18 DOT)

[grubinski]

Originally Posted by grubinski

I will measure it tonight.

Looks like it's right on 1.2 inches ... so the same as you got on the 2.7

[milliemax]

In my 500 years of experence, any time a spline fails you must replace both the male and female. Both have been stressed to the point of..... DISTRUCTION. So..one gives /fails and the other is ....STRESSED. Replace both...... and you can take this advice to the BANK !!! Max

[3RotorRx7]

Thanks for all the replies and to grubinksi for the measurement. FYI, I have been using OE replacement axles from junkyards, and the last axle came out of a car with 45,000 miles. Certainly, the car is launching on sticky Hoosier A6, which puts the car in the 1.8-1.9 60ft range. Going to try the Boxster S axles and swapping the transmission flange and hub to accommodate, rather than cutting the Tiptronic axles.

Erik

[3RotorRx7]

FYI, Pro Solo Autocross has drag race starts, and no wheel hop. Very uneventful, just breaks as the clutch is released.