Now there's a name from back in the day!
Levi

 

^ this


there is no pressure on the diff if the wheels are spinning, its like cruisin down the freeway as far as the diff is concerned!

 

and ill add: i think people are a little over concerned about the s2k diff, ill be clear and say they can easily be destroyed, but must of us are plenty carefull

 

Clutch dumping on a car in motion.

Let me answer your question in a different light:
Hold a pencil in the air. Struck it against the desk hard enough and the pencil will snap.
Hold the pencil at the edge of the desk. What happens if you apply enough force to the pencil against the edge of a desk?

 

So you guys are sayIng as long as it breaks traction its not that bad? Like a 5k+ clutch dump? Also who is this Wisconsin guy?

 

Yea as long as the wheels spin it's fine. BUT this issue comes whenever you dump the clutch the pinion bearing ring or w/e it's called, moves back a little due to a lot of pressure. When that ring moves back enough the diff will destroy itself from inside out. I could be wrong though, so don't flame me!

 

why is he clutch dumping from a roll? He should be in the right gear for the rpm to hit the roll.
1st gear at 20 puts you in a great spot for a start, you need only floor it and shift to 2nd.

Seems like pointless additional stress on the drivetrain.

 

This is surely not a way to save your diff

If you can get a 'clean' spin then your diff doesn’t care how fast the tires are spinning relative to the motion of the car, the problem is getting a clean spin every time, and its more difficult to do wile your already in motion due to the lack of power. The hard thing on these diffs is the half wheel spin, when both tires are fighting to gain traction and you get that violent wheel hopping, THAT is what’s really hard on the diff and half shafts.

 

I come from a different school of thought than most people here, I haven't owned so much as a Honda lawnmower before, and I've only owned my S2000 for 2 months.

That said, with every other car I've owned (Mustang, RX-7, Rx-8, some FWD sporty econoboxes) as long as there's no wheel hop or a hard launch from a dig, there's no problem. I've never seen a car puke its diff from a roll, only from a dig. I'm sure dumping the clutch at 5k rpm from a roll diminishes the overall life expectancy by some unmeasurable fraction of a percent, but I'd be more concerned about the clutch at that point. Holding the clutch and the gas at the same time = no bueno.

 

One could make the argument, based even on people's own logic intended to defend the 'rolling launch', that it is worse than a standard launch. I'm stuck at work for 30 minutes so I'll ponder on this one a bit.

If we take the 'breaking the tire loose means it is ok' argument and run with it (which is wrong "IMO", it's better than failing to break the tires loose, but it's still putting significant stress on the differential components and is far from harmless or contributing to only regular wear and tear), you'd have to believe it is 'easier' to break the tires loose at speed than at a stop and thus less stress on the drive train (again, not necessarily what I believe, i am going along with it for this example). A stock car probably can't break the tires loose for more than split second, if at all, at speeds above 60mph even with a full clutch dump in 3rd gear, for example. An AP1 with low compression in two cylinders can still roast the rears if the driver is sufficiently determined.

From a stop, overcoming the initial traction that wants to propel the car forward instead of the tires immediately losing traction is easy. You won't be your clutch's greatest fan but it's easy to get the rear end loose without much gas or too violent of a clutch dump. From a roll there becomes a point where it cannot be done no matter how hard you try. Your failure to get the rear wheel loose is absorbed by the differential.

Think of the mechanical drive train as just one axle connected to one wheel, which is not far off in the context of this discussion. You, however, are the engine and the differential in this situation because there is a plate weled onto the axle where it usually meets the diff with a stick on it. You rotate the stick and the tire spins.

Fortunately, the tire is bald and on some oil you spilled from your last oil change. Even with only a few "human power" you might be able to overcome the friction and get the wheel to spin by turning it very quickly while the car is still (we'll pretend you are extremely strong). If the tire was sticky and the ground clean, you'd have no chance of manually getting the tire to spin in place. When you struggle in that example, the actual diff struggles in real life. If you are trying hard as you possibly can to break the rear tire loose but cannot, that same struggle is shared by your diff. When your strength (the engine spinning the drive train which meets the diff) over powers your arm's ability to transmit it to the non-moving axle, your bone shatters, tendons rip, and you have to get a 'rebuild' at the hospital! The diff does the same thing - power is trying to get it to spin the tires but it can't do it quickly enough to transmit the power further down the drive train. This is why slicks destroy the weakest link in your drive train and when you reinforce that (say the axles), all you do is blow up something else, usually more expensive (i.e. diff or transmission).

Now that we are moving in the rolling launch example, we've lost a lot of our leverage to break the tire free. We may ultimately be attempting to transfer less gross power through the drive train due to gearing etc., but odds are the diff is absorbing more of the twisting force as a percentage than doing a clean launch that breaks the tires loose. Keep in mind 1st gear clutch drop at 9k is not the same applied torque as a 4th gear drop going 70mph (which is not wise but that is a different subject).

All that being said, my experiences are similar to SLWASFK. I have absolutely berated half a dozen or so cars and never had a diff problem. I did several hundred rolling launches in my 96 civic hatch; it was fun to do a redline clutch drop in 2nd or 3rd going through a wet spot since it could actually break traction easily (not recommended for non FWD vehicles).