1999Porsche911

Double clutching is not necessary with a gear with properly functioning syncro. It is a waste of time. As you said, to minimize the wear on the syncro and improve the ability to get into a lower gear, you need to match the speed of the gear with the shaft. You can choose to stop the car from moving and sit with the clutch disengaged for a few seconds so everything stops moving or you can choose to speed the shaft up to a speed that will match the anticipated gear speed. The longer you keep the clutch disengaged, the more your gears will slow down. Shift to be smooth, deliberate and quick.

Often, accelerating right before shifting will accomplish this or you can blip the throttle as you downshift. You do not have to apply the brakes at the same time. Mastering this technique will keep your passenger from even knowing you shifted to a lower gear. Rev matching is extremely imprortant while tracking or drivng aggressively as it helps prevent unnecessary weight transfer on downshifts.

Remember that gear lube has alot to do with how syncro's operate. The wrong lube or cantaminated lube will have negative effects on your shifting ability. Gear lube must be fully warmed up.

SpeedGeek

Ok, I am not an expert on this stuff but I think I understand it well. So take my explanation below for what it's worth.

Simply put, the drivetrain looks something like this:

engine -> clutch -> tranny input shaft -> gears -> output shaft

The wheels are connected to the tranny output shaft (through diff and drive shafts). So if the car is moving, the output shaft is always spinning (regardless of gear selection, neutral, clutch, etc).

When you rev-match with the clutch in, all you're doing is bringing the engine up to speed to match the speed of the output shaft (and wheels). But the input side of the tranny will not be spinning at the correct speed for the next gear. As you select the next gear with the lever, the synchros will spin the input shaft up to speed. That's the resistance you feel as you change gear.

But if you don't have synchros, you must clutch, select neutral, release the clutch, then blip the engine to rev-match the input shaft. Now that both shafts are speed-matched, you clutch again, quickly select the next gear and release the clutch.

With synchros, none of that fancy double-clutch footwork is technically necessary.

However, even with synchros, selecting 1st gear while moving is stressful on the mechanism. Double-clutching makes it all work smoothly. But yes, the 1st gear synchro will do its job if you just push hard. I personally prefer double clutching into 1st on the rare occasion I find it necessary to select 1st while still rolling. Just makes it easier on the synchros. And it's fun.

Hope that helps. If anyone sees where I have it wrong, please correct me.


BTW, even with synchros, it is good practice to rev-match when downchanging, track or street. The syncros will match the shaft speeds in the tranny, so double-clutching is not necessary. But rev-matching means your tranny and clutch do not need to spin your engine up to speed as you release the clutch. This is good practice for vehicle stability, drivetrain stress reduction, clutch wear and comfort. Heel-toe is not difficult to learn - just takes practice. And once you have it nailed it will transform your driving experience.

enthusiast

Hmmmm, I already said that but I guess it takes a couple of different Rennlisters to get the point across to some.

mooty

oh boy...

confusions b/n double clutching and rev matching blips...

i give up...

SpeedGeek

Mooty, where's the confusion?

Rev-matching blips (heel-toe if braking) brings the engine up to speed required for the gear you're changing down to. Double-clutching matches shaft speeds in the tranny, which is no longer necessary with syncros.

Are we still confused?

Sloth

I don't often down shift to 1st gear, but double clutching makes it easier when I have to.

fve

I am certainly no expert, but as a new gt3 owner i can perhaps share my experience. any car that i have ever driven can be tough to get into first unless it is at rest. this seems to be more pronounced in the gt3. I too noticed that if i was approaching a light (in traffic), and i wanted to select first, it would not be easy. Since i was in traffic, i have learned to leave in second most of the time. I have had not trouble getting into first (if need be) with rev matching. It does need a very forceful blip however to match well.

*** Just push it harder. It will loosen up over time. ***

Prior to purchase, the second-gear synchro was completely shot. the previous owner simply thought that the transmission had become balky going into second and starting forcing it. Well, this came up during test drive (there was a whole post at the end of last year about this car) and PPI. Well, the previous owner split the cost of service with porsche and the transmission is all good now. And the second gear synchro is now the steel one.

Just my 2 cents worth, but i would be reluctant to recommend forcing any shift (gt3 or any other manual) too much. If it feels like it does not want to go, then there is likely a good reason (be it technique or mechanical) for it.

The repair work on my transmission took about 5 weeks. Very painful waiting to test-drive the car with a repaired transmission. But it did buy it.

mooty

i am NOT confused. but the various posts are confusing.

1999Porsche911

I never suggested "forcing" it into gear. Many owners baby the gear lever and think that anything harder than a light push is more than enough. This is not the case. These same people are often the ones that complain that their clutch pedal is hard to depress and tires their leg out.

I'll say it again - if you cannot get into first gear moving less that 25 mph on a fully warmed up GT3 transmission, either the driver or the car has a problem. If it is not the driver, then warranty will cover whatever is necessary to correct the problem.