Axle replacement isn't a horrible task if you have the right tools. Figure 2-3 hours per side of you have never done it before. Once you get the process down its an hour or less per side.

You need a ball joint separation tool as well as a torque wrench that goes up to the 340 ft / Lb requirement for the center axle nut.

If you are replacing the wheel bearing it adds additional complexity, time and the need for more specialized tools.

Alignment after should be highly considered but if everything is marked with paint prior to assembly ( which honestly you should be doing anyhow) then you *might* be able to get away without one.

If you have any doubt on anything above you should likely outsource this work

 

Axles come out without the removal of any suspension components. You just need to raise the uprights to get the outer axle out of upright. Simple easy and no issue with alignment.

 

Thank you much. Just ordered the axles and the shop has the tools mentioned above. Appreciate the kind help.

 

Wait, so are you saying get yellows?

 

are they a 997 cup Motorsport part? What else needs to change if going with that axle-just the stub/axle bolt? I'm all in for the extra cost for the peace of mind and less frequent change outs.

 

[QUOTE=chrcook;12561269]
As an unintended experiment, I put on new axles (including front flange axels) and new stubs, bolts and washer with very light grease. One of my front wheels would not torque, but kept turning. Despite never reaching 350 ft-lbs, the clamping load ramped up and I stretched my new axle flange about 1/8", creating a paper weight. [QUOTE]

This seems odd that you would brake one using light grease. Although I would not recommend the use of grease.

I have always used antisieze with no ill effects and the Cf should be about the same for the antisieze as for the grease unless you are using some really fancy stuff.

What we are really trying to achieve is clamp load, not torque, so we are trying to approximate the clamp load with the torque value. I can tell you that doing trials of new vs used and lubricated vs dry there is a HUGE variable in ultimate clamp load on a skidmore machine.

Here is the calculation:

http://www.engineersedge.com/calcula...orque_calc.htm

Now, we know that the cup center lock axles fail while the street car or cups converted to 5 lug do not, so I agree that it must be due to the loading of the center bolt.

I have a picture of a worn centerbolt on the website showing how much the external threads stretch. I did not section one to see the internal threads, but I bet that they are just as bad. This loss of torque either due to the stretched threads or because the thread form of the worn center bolt is poor has a direct impact on the failure of the axle shaft.

I always recommend changing out the stub axles bolts with the axles (at least). I change out my stub axle bolts and nuts once a year as part of my program.

Here is the picture of the stretched threads I was telling you about. (it is the last two pictures on the click to enlarge photos). The threads measured about 45 degrees and 75 degrees on the two flanks instead of the standard 15 degrees.

http://www.demonspeedmotorsports.com...olt-DL-CLB.htm

btw, I am a fastener engineer by trade.

Thanks

Ed

 

Ed: Excellent Insight - Thank you !

 

 

 

So, thanks to ViperBob for the help. Raising uprights made it easy. However,...tightening the stub axle bolt caused the axle to snap in the usual place at about 150ft/lbs. At least the part is warrantied. This is crazy...

 

Yes the Yellows are awesome and we have had on for 2 FULL seasons with approx 18 event weekends. NO ISSUES!!! We just went to the Greens as they were the last axles Porsche delivered at the end of the Gen 2 997 Cups. Same price. They are a direct bolt in (however you MUST use the new transmission flange to accommodate the larger CV joint as well as the new 2 bolt washer rings under bolts due to larger diameter and longer 55 mm axle bolts).

 

Standing starts and attacking curbs aggressively are the differences between one that goes in 10 hrs or 30 hrs. You also can't check them properly to be warned. Just change them ahead of time.

 

So, wanted to ask a silly question. We got the black axles for the 996 cup and we now have snapped two (same side) new axles, one at about 150ft/lbs., the other at 300 ft./lbs. When we took them back to the parts dept. at the dealership, he said the torque values are lower than 350-he said 185. Now is that just because it is a number from the "street" porsche division, or did I get something wrong here. Is everyone using 350 for the blacks and the blue motorsports axles?
BTW, the driver side axle torqued just fine. Also, the old axle went on just fine and also torqued to 350. Maybe just a bad batch of axles?

 

340 from memory here. Just checked on my SPC build a few days ago and that's where they were with stock axles.

 

When you tension fasteners, you want to have a clamp load equal to about 75% of yeild strength of the material.

Now, I am running from memory here, but the axle shaft has a hardness of right around 38Rc (as does the stub axle). That hardness would equate to approximately 176KSI. That converts to about 81,000 lbs of force. Yield is a bit lower than tensile, but it is an unknown at this point, so we can say yield would be about 70,000 lbs force just for talking sake. 75% of this number is 52,500. So we are looking for around 52,500 lbs of clamp load.

A 350 ft-lb torque using a Cf of .1 for a lubricated assembly would give a clamp load of 48,500 lbs of clamp force. Not that far off of the estimated 52k from above.

I believe (again from memory) that the street cars are about the same as the race cars. They use the same basic axles.

Assembling the joint at 185 could actually be dangerous and may cause a cyclic failure earlier than expected.

As far as the premature breakage, when we test externally threaded fasteners we typically do with a wedge. This would promote breakage under the head if there is any issues with the forging that would cause this kind of failure.

I would look for any reason that your axle is not seating in the rear of the hub and may be promoting the break, but in general, I would say that you are seeing an issue with the axles.

Thanks

Ed