Broke a half shaft

[Bicyclops]

Shouldn't have done it, but the Cobra was a half length ahead coming off the stop light and I dropped the hammer in second gear.

Ed


219530

[Hobby Racer]

Sorry to hear that.

I'm always telling myself to practice mechanical sympathy on the drive-train for that very reason!

Let us know your replacement choice as I'm sure it's going to happen to others sooner or later.

[Bicyclops]

I always figured the half shafts were the weakest link so I try to never launch and to be gentle. Got exited and forgot all that. I sent a info request to the driveshaft shop. We'll see what they come back with. I've got an LSD so I was able to limp home. I would have had to call for a tow truck with an open diff.

Ed

[Hobby Racer]

Other's have had good luck with the driveshaft shop. They are pricey but you won't ever break another shaft. But you will find your next weakest link.

[driveslikejehu]

Is your car WRX based? Just wondering if I can expect the same from STi shafts

[Bicyclops]

That's a question I'm asking myself. Would the STI hub assemblies bolt in in place of the WRX? And yes, mine is '02 WRX based. I think the STI splined shafts are a bit beefier. I kinda overspeced my engine. I'm getting 386 WHP and 367 lb/ft of torque. A lot of fun, but I really shouldn't have put my foot all the way down after shifting into second. Previously, I've only done that in third and above.

So, does anybody know if the STI hub is a bolt in replacement for the WRX? Now would be the time for me to do that before I spend bucks on shafts.

Ed

[Hobby Racer]

So, does anybody know if the STI hub is a bolt in replacement for the WRX? Now would be the time for me to do that before I spend bucks on shafts.

No, the STI hubs are not a swap, but they are quite easy to do. There are many older threads that show what mods are needed to make it happen. Another expensive obstacle is the fact that they are a different bolt pattern so your wheels will not work!

[Bicyclops]

Yikes! Hadn't thought about bolt pattern. I'll see what the driveshaft shop has to say before I get too carried away.

Ed

[Bicyclops]

The next weakest link would be the 5sp tranny I suspect. I really never spin the tires so I can't count on that to relieve the stresses. My buddy's Cobra will just spin 'em if he gets a little too throttle happy.

Ed

[Mark Eaton]

After the misery I went through trying to find a CV axle replacement from wrecking yards when my kid slid into a curb I will next time go straight to any specialty shop and pay extra for a quality CV axle that will fit!

[Rob T]

I used the DSS for axles. They were able to put whatever ends you need on the axles. Mine were a bit funky. Also, I have a spare 5sp sitting in my shop if anyone ever needs one. I have a 6spd now. You also may remember that I broke a left rear hub. I had warning signs that I ignored until the catastrophic failure at VIR (Hobby was there). The warning signs sounded a bit like a run out issue from a warped rotor. It was actually a small crack in the hub that became a big crack.....

[Hobby Racer]

You also may remember that I broke a left rear hub. I had warning signs that I ignored until the catastrophic failure at VIR (Hobby was there). The warning signs sounded a bit like a run out issue from a warped rotor. It was actually a small crack in the hub that became a big crack.....

I remember that! I was right behind you when the wheel hub let go going into the climbing esses.

[Bicyclops]

Oh wow! Don't like the sound of that. Browsing the DSS site, I see some axle and spindle kits. Do you know if those spindles go into the WRX hubs and increase the spline shaft size to STI spec. Probably overkill for what I need tho.

Ed

[Bob_n_Cincy]

I have broken axles/hubs 3 or 4 times, and one 5-speed. All auto crossing with stock FXT power. Have not broken any axles on track days. You need to realize that the two drive conversion doubles the torque in the 818.
219640 219641

[Bicyclops]

And I've got limited slip differential. All the power could be going to the one wheel that has traction. With luck, that one would spin.

DSS is quoting $1800 for a pair of 700hp shafts.

Ed

[Hobby Racer]

And I've got limited slip differential. All the power could be going to the one wheel that has traction. With luck, that one would spin.

DSS is quoting $1800 for a pair of 700hp shafts.

Ed

WOW, that seems steep.

[Bicyclops]

Yeah, it does seem pricey.

Ed

[Bicyclops]

When you tighten the axle nut, does the face of the CV shaft seat against the bearing? The way DSS is calling to measure seems about 3/8 shorter than the FFR shaft I broke.

Ed

[Bicyclops]

I don't think I understand all I know. Measuring the way DSS wants from outside of tranny stub to the wheel bearing gets 22 1/4". Measuring the same thing by estimating tranny stub end from roll pin location to the outer edge of the CV gets about 3/8" more. If the CV seats on the bearing how does the shaft account for changes in distance to the tranny while it moves up and down? And how is a slightly shorter shaft going to work where the longer one did?

Ed

[J R Jones]

The CV joint adsorbs enough lateral displacement for suspension travel.
Your fracture looks like torque shear, not fatigue; a photo of the break cross section would provide more evidence.
We ran a Mitsubishi EVO set up for SCCA T2 Nationals and were the fastest Mitsu at the Run Offs, two years running. Second to Factory BMW year two.
We failed a rear axle similar to yours at Elkhart. In our case the axle nut torque was not applied correctly by rolling the bearings while torquing. Joint motion fatigue and the wheel came off coming out of Canada corner.
We were pushing 360hp from the 2.0 @ 21PSI. The EVO is in Greenland now running rallies with success.
jim
219674

[Bicyclops]

It is definitely a shear failure. There are twisted cracks in the shaft that came off. I don't have much experience in this and just want to make sure that I don't screw up ordering high $ shafts.

Ed

[driveslikejehu]

As noted the CV joint at the trans allows axial motion; the tri-lobe thingy slides in and out.
219679

Your failure does look like a torsional failure, though its tough to exclude other combined stresses.
I'm sure folks think about it but its key to ensure the half-shaft doesn't run out of axial play thru full range of suspension travel. I had to cut a shoulder back just a bit to ensure plenty of clearance with my STi setup.

[Bicyclops]

It's ordered. Hoping for the best. DSS should know what they're doing. Not their first rodeo.

Ed

[mikey likes it!]

I also used the Driveshaft Shop. With pin drive and IRS, CUSTOM axles were in order... 44,000 miles later, many track days and a 392 w/Tremac 600 . they have worked great the last 15 years. You get what you pay for.

[gbranham]

I'm still stuck on an 818 trying to race a Cobra.

[Hobby Racer]

It's ordered. Hoping for the best. DSS should know what they're doing. Not their first rodeo.

Ed

Now that I just broke one of my axles, I am very interested to see how yours come out. Please post detailed pics when you get them.

[J R Jones]

As a point of reference, my Subie/818 axle diameter at the failure point is 1.018in diameter. My (300hp) OEM Acura axles are 1.150in diameter at that point (with much larger bearings).
As you would assume, most of the axle strength is in the outer diameter, alternative material can only provide so much.
jim

[RPGs818SNA]

So 44% stronger according to the diameter cubed rule for solid rods. A little extra goes a long way.
RPG

[Bicyclops]

I'm still stuck on an 818 trying to race a Cobra.

Wasn't so much a race as just a little competitiveness on our way to SuperCar Sunday at a local college parking lot. That said, I stay with him pretty well as long as I'm above about 3500 RPM and on the turbo. He's got a small block 400 and no dyno ticket. He's estimating 500hp and he is torquey for sure. I think his car is heavier than mine and I'm dynoed at 386 WHP and 367 lb/ft on E-85, ~28 psi boost. Where I really leave him in the dust is on the canyon roads. He can't stay with me. He just got new tires so we'll have to see. That is once I'm operational again.

Ed

[Bicyclops]

Now that I just broke one of my axles, I am very interested to see how yours come out. Please post detailed pics when you get them.

Ouch. Wilco.

Ed

[Bicyclops]

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My DSS shafts arrived today. They look great. There is a lot of lateral movement in the CVs so I think my apprehension about lengths will prove unfounded. I've got one of them in though nothing is tightened yet.

Ed

[Bicyclops]

I'm operational again. We'll see what I can break next.

Ed