How do you double clutch down into 1st on a 915?

[oly]

Does anybody have any techniques for doing this? Or is the 915 just not meant to do this?

I've only driven about three different cars with 915 transmissions but it seems like double clutching down into 1st with a 915 is impossible. Attempting it grinds the gears. My car has just under 30k miles. Its appearance and maintenance receipts indicate that it was treated VERY well. And I can double clutch down into any other gear okay.

[emcon5]

I don't. Only use first gear from a dead stop.

Tom

[barney911rs]

+1

[VFR750]

I can catch 1st at about between 2-5 mph. Any faster and it is a real crunch. All other gears are OK w/o double clutch even at 110K miles.

It is possible, I believe the fast autocrossers do. But I gave up trying.

[oly]

So does that mean that people don't autocross with a 915?

[VFR750]

I've autocrossed with my 915, but I don't use 1st except to start out. There are times where being able to get into 1st would be a good thing. I'm just not going to try. I just leave it in 2nd, plant my left foot on the dead pedal until the end.

[oly]

So does that mean that people don't autocross 915? I was looking forward to that. But I'm not willing to spend THAT much for the experience.

[VFR750]

People AX 915 equipped 911SCs all the time. I do.

I just don't downshift into 1st during a run. Not a huge deal.

[oly]

Thanks VFR750, I'll give AX a try.

[HarryD]

Oly,

Your 3.2 L should have plenty of torque to take adavantge of not wasting your time shifting. I AX my '73 (with a 915 box) and almost always short shift into second as soon as I can.

If you are seeking quicker gearing in second, go to lower profile tires to reduce your tire radius.

[oly]

Harry,

Thanks for the post. What does "short shift into second" mean?

I never though about using lower profile tires to get quicker gearing; that is an interesting idea.

[HarryD]

Originally posted by oly
Harry,

Thanks for the post. What does "short shift into second" mean?

I never though about using lower profile tires to get quicker gearing; that is an interesting idea.

Short shift ---> Shift into the next higher gear before you reach peak torque.

For my car, I will short shift to second when I hit about 4000 rpm. I a competitive situation, normally I would shift at 5500-6000 rpm where my power is peaking.

[LARRY SHARP]

About the only one I know who shifts into 1st gear is Terry Zaccone and he is in a 901 gearbox 1968 911,, since he only has a 2 liter he doesnt have the torque to pull out of corners in second gear. I would think any car that uses a 915 box has enough low rpm torque to stay in second gear during an autocross run .

[oly]

Harry,

I'm missing something; why would you short shift in AX? Isn't that a competitive situation where you'd want to maximize your acceleration? Or do you short shift so that you can use both hands for steering ASAP?

[oly]

Larry,

Thanks for the information.

[HarryD]

Originally posted by oly
Harry,

I'm missing something; why would you short shift in AX? Isn't that a competitive situation where you'd want to maximize your acceleration? Or do you short shift so that you can use both hands for steering ASAP?

I find the slight gain in power is more than offset by my wasting time shifting at places where either I would rather not shift, cannot shift to maintain balance, or I end up being at the rev limiter until I get to a place where I can shift effectively.

[VFR750]

Harry is right,

It is kind of hard to shift at redline in the middle of a slalom.

Some course allow enough room to wring the car out before the first corner, others throw cones at you so quick, that getting into 2nd early avoids the unsetling effects of power off/on while shifting. Just a matter of adapting to the course. Which is part of the fun.

[rfn026]

Last year in Topeka (the Nationals) I was really surprised how many people ran right into the rev limiter rather than shift. And these were the fast people. It seems like they felt they were losing less time hitting the rev limiter than shifting.

Shifting just takes so damn much time.

Richard

[dfink]

Scince rebuilding my tranny I can downshift to first even from fairly fast fast speeds 20+. I don't double clutch but it is not a very fast shift. I ususally do it while slowing down for a very tight corners. We have small courses here.
I just push in the clutch.
Take out of second
Leaving clutch engaged gently start to push until pressure is felt
While keeping pressure on the shifter let the syncro do it's job
After maybe a second then slide into first
If you can blip the throttle just a bit to keep car from jerking and let out the clutch slowy as first gear is short and can unbalance the car very quickly.
The only time I have have problems getting into first are when not moving.
Oh I will be one at the rev limiter on short course. On a larger course like topeka I will probably go to second. It however depends on the situation. Data logger says it takes .5 second to shift on a good shift. A blown shift to second and add another second to that.

[stealthn]

I took the advice of a Porsche Mechanic and race car driver not to ever downshift into 1st unless stopped or close to it.

I would love to be able to have first in a couple of turns on our track, but just don't do it. Your 915 will last longer.