holy shit man! Thats friekin amazing! Yeah I think that you had too many braces holding it stiff and the only areas where strain was going was the diff itself no flex so it finally said f*ck you and split. Amazing job though none-the-less. Plus you have high horsepower and nitto 555r's so with that and braces you should of seen this one coming. all the stress went straight for the diff housing.

There is a spreading force generated between the pinion and ring gears. With lots of horsepower, a diff that is tough enough not to frag and good traction this spreading force can be enough to rupture the case.

The teeth of the pinion and ring gears act like ramps and try to force eachother apart as power is applied. The snout of the diff case holds the pinion in alignment but if the spreading forces get high enough the pinion will try and move away from the ring gear. The only thing resisting this force is the diff case. If the force becomes stronger than the case you get what you see in the pic.

I don't think the diff brace contributed to the failure. The fracture happens there because that is where the load is greatest; right at the front of the ring gear. That just so happens to be the place where the ppf and diff brace bolt up.

Why read, when you can just post inane responses?

In other words, this is the natural state of things at this point in modification with his HP and traction?

It sounds like you should change your launch technique, or avoid that altogether, since you want to daily drive it, unless you go with the JimLab/Cobra update.

Does anyone know how many diffs Vosko has munched?

That's my opinion. There's also a fine line between launching hard and being abusive. In most cases it only takes a tiny amount of clutch slip to make life much easier for the drivetrain. I have never been able to explain to others the "feel" of how to manage the clutch and wheelspin at launch though. Just like when shifting some people have the touch and some don't. That by no means insists this diff case ruptured due to driver issues though. With the Kaaz I think the next failure mode was the case.

If the tires ain't slippin' something else will ;)


*edit* The smell of diff lube on a hot tailpipe. That must have been positively awful :tear:

What Damon said. :)

With enough traction, if the pinion gear can't turn the ring gear, it tries to "climb" it (upward) instead, which is why cars with enough horsepower and traction lift their front tires on the launch. As Damon said, the pinion gear also tries to climb "out" (sideways) of the ring gear, and the only thing keeping it in place is the rigidity of the front of differential housing. Abuse it or stress it hard or often enough and this is the result.

When I talked to Ari Yallon about his differential/axle failures while figuring out what I was going to do about my car, he said that once the differential was replaced and the axles stopped breaking, the differential housing was next in line. Bracing was added to the housing (cast iron is difficult to weld, BTW, and needs to be heated prior to welding and cooled gradually afterward) to hold it together, but it's not an ideal solution. Most racers not bound by class rules simply get a bigger (and usually stronger) differential instead. I chose the Ford 8.8" for weight and size considerations, as well as adaptability to the stock rear suspension and outer CV joints.

Bottom line, if you drag race, you're eventually going to break parts. The strain of the launch will eventually reveal the weakest link in your drivetrain. It may not happen on the first launch, or the 10th, or even the 100th, but eventually something is going to say "enough". :)

You blew up a diff to right Kevin? Covered under warranty I heard;).

No doubt, with that amount of HP and drag launches something was going to break.

You said you just had the diff apart to replace clutch packs, maybe the tooth contact was off a little when you put it back together.

well, the launch was feeling pretty good, it actually snapped after i totally let out and started to squat the ass end down. maybe age was getting to it? dunno. i'm taking the diff brace off to experiment. i'm getting all the parts to fix it for $235, plus whatever bearings i might beed, so it's not too bad. i guess it should be expected by now! lol i just hope it doesn't happen again, as tearing the diff out is about as much fun as replacing a tranny or a motor