Poll: Gearbox life vs shifting technique

[911pcars]

Current and past discussions on why the 915 gearbox doesn't shift as well as other more mundane cars prompts me to inquire, in a limited manner, how owners drive their cars and the experience with how long the synchros hold up.

Do you downshift the same way you upshift; that is, no special technique (save for perhaps blipping the throttle when the clutch pedal is down)?

Do you downshift by double clutching; that is, during the downshift you rev the engine while in neutral with clutch pedal up (entire technique not included for brevity)?

Many hold to the idea that modern transmissions have synchros and thus no special downshifting technique is needed.

Some, including myself, say that synchromesh assemblies are wear items and that double-clutching makes shifting easier and extends their life.

I realize there are more variables here, but it might help if we knew how long you've been driving this particular pcar.

This might be interesting (or not)

Thanks,
Sherwood

[ChrisBennet]

I don't double clutch but I always "blip" on downshift to match revs.
-Chris

[ZOA NOM]

I always double-clutch on the downshifts. It has become second nature, and feels smoother to me. I'm at 170k and counting without opening the tranny, and no symptoms of gear problems.

[450knotOffice]

I tend to blip the throttle once or twice to assist the downshift but it downshifts fairly easily. As far as I know the transmission has never been opened and the car has 135,000 miles on it.

[Paulporsche]

I blip to match revs. I've never found double clutching to be necessary.

[ianc]

I blip also, but do not double clutch. Trans has 190K on it.

ianc

[svandamme]

normal downshift , no doublenothing or blippingnothing
no problems whatsoever as long as no downshifting to 1st at anything higher than 5mph, but 5 speed tranny's weren't designed to do that anyway, even modern cars like my 1997 Golf or my '02 Renault Megane wouldn't shift to first when not slower than 5mph

[dandrews64]

I'm a blipper. Tranny was fully redone 10K ago. And going from 5 to 4 is still sometimes tricky. No grinding, just feels like binding linkage or adjustment issue.

Since it would be tacky to publicly beat up those who did the work (Tillmans in Santa Rosa, CA) for pretending not to notice after they drove it for a week, I will refrain from doing so. ("we can't replicate the problem", what bull*****)

More recently I replaced shift shaft bushing and WOW I feel everything (140K on car), so hard to tell if what I'm feeling is normal or not (my first 911/915)

It is something I will either live with or tear into. Mobile Werks, you may be hearing from me !

[Rex Walter]

I'm with ZOANAS. I always double clutch downshift, and it has become 2nd nature. Saves the syncros and the clutch - and it sounds good. I have people that want to ride to me just to hear the car go through the gears up and down. I have 160K and no trans trouble, and my clutch lasted 150K.

Rex

[ZOA NOM]

Blipping the throttle with the clutch pushed in does nothing to match the moving parts. It gives the illusion of synchronizing, but the only way blipping the throttle helps is with the clutch engaged and the gearshift in neutral. It is the input and output shafts in the tranny that require synchronization, not the clutch plate and flywheel. Blipping the throttle without double clutching simply wears the clutch plate faster.


edit: I meant engaged, not disengaged

[Craig 930 RS]

1) Give it a blip to nearly match revs
2) Ease into gear on initial shift engagement - you are performing some serious gear slowage via the synchros

This will add years to your transmission.

[Craig 930 RS]

Zoanas make a great point - thanks!

[dandrews64]

Originally posted by ZOANAS
Blipping the throttle with the clutch pushed in does nothing to match the moving parts. It gives the illusion of synchronizing, but the only way blipping the throttle helps is with the clutch disengaged and the gearshift in neutral. It is the input and output shafts in the tranny that require synchronization, not the clutch plate and flywheel. Blipping the throttle without double clutching simply wears the clutch plate faster.

Come to think of it, I honestly can't say for sure which way I do it. It is instinctive. Guess I 'll just have to drive the car tonight...

[ChrisBennet]

Originally posted by ZOANAS
Blipping the throttle with the clutch pushed in does nothing to match the moving parts. It gives the illusion of synchronizing, but the only way blipping the throttle helps is with the clutch disengaged and the gearshift in neutral. It is the input and output shafts in the tranny that require synchronization, not the clutch plate and flywheel. Blipping the throttle without double clutching simply wears the clutch plate faster.

Blipping the throttle with the clutch pushed in may not match the transmission's internal gear speeds but it does match the speed of the engine to the rest of the drivetrain. This does save the clutch and most importantly keeps the chassis from getting upset.
-Chris

[JackT]

Downshifting works great on my 915 transmission. Mine only binds from 1 to 2nd if I shift fast.

[ZOA NOM]

Originally posted by ChrisBennet
Blipping the throttle with the clutch pushed in may not match the transmission's internal gear speeds but it does match the speed of the engine to the rest of the drivetrain. This does save the clutch and most importantly keeps the chassis from getting upset.
-Chris

Not so - the rpm's of the motor MAY match the drivetrain, but it is irrelevant since the input and output shafts of the tranny will take the full force of the load once the clutch is reingaged. By revving with the tranny in neutral, the input shaft is spun up (it is free spinning with clutch disengaged) to match the rpm of the output shaft before pushing the gear shift into the lower gear, resulting in a much smoother transition for the synchros, and less wear on the clutch plate and flywheel.

[pwd72s]

I learned to drive in a surplus WWII jeep and a flathead powered Ford F-1 pickemup. Both with crash boxes. Oh, to the younger members here, a "crash box" is a manual transmission without synchromesh. Those vehicles teach you to learn how to doubleclutch...

[Todd Simpson]

I double clutch with a blip in neutral.

You can feel the difference at the shift lever, it almost puts itself in gear.

[ZOA NOM]

Originally posted by Todsimpson
I double clutch with a blip in neutral.

You can feel the difference at the shift lever, it almost puts itself in gear.

That's the tranny's input and output shafts coming into synch. If you're practiced enough, you don't even have to push the clutch the second time. The shifter will just "fall" into gear.

[ted]

Double clutch takes too long.
Imho spirited driving a 911 does not include time consuming double clutch down shifts. I do blip and I do skip gears on downshifts.

Imagine slowing from 130 to 35 mph rowing through the gears double clutching and (heal and toe) blipping the throttle to match revs for every downshift....
5th disengage,
4th double clutch blip re-engage,
4th disengage,
3rd double clutch blip re-engage,
3rd disengage,
2nd double clutch blip re- engage.

My brakes (and most others) would slow the car before I could complete the above process.

Imho it's quicker and less chance of a mis-shift to just...
5th gear disengage,
slow to the correct speed for a second gear engagement...
2nd blip and engage.

Blipping/matching revs on a downshift is a good thing.

My bias when driving the 911 is ultimate performance not ultimate parts life. Still I have never hurt a trans or engine,,,knock on wood product.