Will my axles live??

[thebigsy]

Hi All,

Just about to get my Torana to the strip and try to pull some times but I am not sure whether I should upgrade my axles before I put some slicks on.

I have a shortened 9" with 28 spline axles and Detroit Locker. The car makes 480 lb/ft @ 3500 and I plan to launch hard. Should I upgrade to billet axles first?

Any suggestions would be appreciated.

Thanks

[RJ & CJ]

Well, is there a rating that you coul dpossibly find with some resaerch for your current axles? And even if there is, you still have the possibility of surviving for a couple of launches. I know Honda Civics' need to have axles replaced after ~225ft/lb, but there have been many to survive for quite some time with 300ft/lb on them, if that helps at all

[Bob Parmenter]

Stock 9" axle material twists relatively easily, have taken two apart over the years that weren't in shock use as you've described, and they had a twist in them. With the loads you're anticipating it wouldn't be much further to snapping the splined end off. Makes for a fun ride.

Along with stronger axle stock also go up in spline count, say 32-36.

[pat mccarthy]

the truck axles are much thicker then the car axles and the 28 axles for car are the same as the 28 in the 8 inch . i have had good luck with the truck axles re splined .but i would buy some new axles there not that much play it safe.

[kitz]

Expanding on what Bob said above .............

The torsional stress on the axle is Tr/J where T is torque, r is the outer radius of the shaft and J is area polar moment of inertia. For a solid round bar J=3.14159*d^4/32. d is the shaft diameter (raised to the forth power). The splines introduce a stress concentration as well as reducing the effective radius of the shaft. To be safe one could use the root diameter of the splines in the equation above. Finer splines will increase the effective radius and reduce stress concentrations some.

Since torsion is a shear load, when it gets to about 1/2 of the tensile yield stress for the material in question the axle will begin to twist permanently. So material selection becomes a critcal factor. I am not sure manufacturers publish the materials they use very accurately. For example it is typical to see "chrome moly". There are many chrome moly steels, some water hardening grades and others oil hardening grades. Yield strengths can vary from 80 ksi to 200 ksi! The relative ductility and impact resistence of these alloys varies with hardness as well. The temper of these alloys determines their operational strength characteristics.

My favorite is 4340 heat treated to 38-42 Rc. Other chrome moly grades include 4140 and 4130. Inconel 718 blows away chrome moly but I doubt it is readily available. In any case it would cost you >$1000 per axle.

Look for a 'chrome moly' that has a tensile yield around 150 ksi minimum. IMO I doubt you will ever have trouble with this ..........

Regards, Kitz

[thebigsy]

Thanks guys.. Don't want to get stuck with a tow truck bill from the strip and have to replace them anyway. I didn't think that they would survive.. The car came with them and I thought I would leave them in for the street. I have had no trouble with them on street tyres.

Just one other thing, as I also got the Detroit locker with the car, I have left that in too. Would this become a weak point in a drag car if stronger axels were used? Are they a good street/strip locker or should I just get a spool?

Thanks again!

[pat mccarthy]

the locker will work fine on the street or track but the spool will not work to good .on the street and will be very hard on any axles when you turn some thing as to give tire slipping or axle shaft or spline of the axle shaft . in time . in a turn the inside wheel turns less and the out side needs to turn more this can not happen with a spool so for the street the spool is out

[thebigsy]

Kool. Thanks Pat!

[falcon8r]

I rember the rule of- the axle should handle twice the torque of your application. An aftermarket replacement inexpensive axle like yukon or better -mark williams masterline (street)are rated for 9.90 cars. Your first launch in a "9.90" car would scare the pee out you. The 28s with the locker are fine for 500hp with a 10inch tire and yukons. Race axles are not for daily driving nor is the spool. I use a 460 roller motor with a 175 shot on 31sline/locker/masterline with a huge safety margin- ie upgrades on engine! Have fun! I would not use old oem axles on slicks. At least not too many times -lol..

[thebigsy]

Thanks FALCON8r,

I think I just needed some 'back me up' on the fact that I have to spend more bloody money on my car! lol!

Thanks guys, appreciate the input. I will get some 31 spline billets made up before I race.