speed shifting

[g sturgill]

Well, after almost 2 years of nursing, cursing, and fussing with a 73 911t that had been sitting for years, and, by the way, lots of advice and encouragement from fellow pelicaners, my car is now running and I'm learning how to drive it.

A question on the gearbox, however. It shifts smoothly enough, no noise or vibes, but shifting from 1st to second, at any rpm, requires a little patience. Try a quick shift and crunching occurs. It also requires 2 or 3 tries to get it into 1st gear when stopped. Is my learning curve a little slow, or is it a quirk I'll get used to? Would converting to a short throw shift help?

Thanks, g

[schumicat]

it is normal to need to shift slowly with this gearbox to prevent grinding. the difficulty getting into 1st isn't normal. look at host site tech articles for how to adjust the shift coupler.

[Oh Haha]

Speed shifting(accelerator floored with no let off during shifting) is a huuuuuge no-no with this gearbox. You have to pause between 1-2 shift.

Adjusting the coupler will help with selecting the gears but a short shifter CAN sometimes make things worse.

I learned the hard way($$$$$$$) about not speed shifting my 911.

[Quicksilver]

Synchronization in a 915 box has a "time based" component. In other words: The friction of the syncro is somewhat fixed so you must give it time to synchronize the gears. When the syncros are worn you must give them even more time to match the gear speeds so you need to slow up your hand right before the point where the gear engages.

Adding a short shift kit will make this worse.
Learning to doubleclutch 1st to 2nd will make this better by giving the syncros less work to do.
Repairing the syncros will make this go away.

[911pcars]

Originally Posted by Quicksilver

Synchronization in a 915 box has a "time based" component. In other words: The friction of the syncro is somewhat fixed so you must give it time to synchronize the gears. When the syncros are worn you must give them even more time to match the gear speeds so you need to slow up your hand right before the point where the gear engages.

Adding a short shift kit will make this worse.
Learning to doubleclutch 1st to 2nd will make this better by giving the syncros less work to do.
Repairing the syncros will make this go away.

Double clutching while upshifting is normally not necessary as engine speed normally drops to match gear speeds.

However, downshifting is another matter. Engine rpm/input shaft speed must increase to reduce speed difference the synchros must generate. See archives for the proper way to double-clutch (not just a blip). 1st and 2nd gears receive the most synchro wear.

A new/rebuilt gearbox shifts fine. A pre-owned gearbox most likely wasn't shifted properly and that's what most of us are working with. The 901/915 gearboxes don't have the most long-lived synchro mechanisms to begin with.

Sherwood

[hesaputz]

Shifting a 915 --- Tick-Tock. Tick is pulling the shifter out of gear and up aginst the next gears synchro lightly but firmly. Tock is completing the shift.
Try touching second before inserting into first - works for a lot of guys.

[RSTarga]

It's all about touch. What oil is in the gearbox? I don't want tostart another oil thread here but if you do a search on Gearbox oil here you'll see that on a 915 gear oil is very important for proper syncro operation.

[DanielDudley]

If it is hard to get into first from a stop, you may have a dragging clutch or a binding pilot bearing. In general, don't rush the shift.

[Joe Bob]

It's not a B&M rock crusher nor a 1/4 mile rocket. Shift slowly and play in the twisties.....wtach the headlights fade in the rear view mirror.

[dienstuhr]

Speed shifting = great way to destroy a 915 ;-)

[j911brick]

Don't kid yourself - you need to rebuild the trans before you do any real damage.

[twin plugged targa]

I have found double clutching form 2-3rd gear and 3rd-2nd helps with my 930 as 3rd synchro is on it 's way out.
With the 2-3rd it helps when changing gear at anything above 4K revs otherwise it is not necc.
rgds Ben

[g sturgill]

I put a few more miles on the p car yesterday after my initial post on "speed shifting". Following the sage advice from feedback I received, I found patience was the virtue needed to complete the upshift pattern from 1st to 5th. I also discovered the same is true for downshifting. Fourth to second is a no-no.

In response to the question as to what oil is in the gearbox, I have no idea. I'm still in the process of mopping up years of neglect. it's on my list of to-dos. Any recommendations?

Thanks, g

[sancho]

although 915 is not the fastest shifting gearbox, I think you can still do it reasonably fast.
as long as your shifting linkages and bushes are properly adjusted etc.....

But Iam still concerned with the fact you cannot shift from 4th to 2nd, I do not have any problem with mine, as far as the oils everyone will recommend Swepco oil and they swear by it, but I could not see any difference from swepco to castrol and mobil....

[euro911sc]

The amount of time you save between speed shifting and shifting at a sane speed is not worth the risks you take of blowing up the box. I speak from experience here... I shifted so fast I jammed the decel block of 3rd gear in-between the synchro and the hub of the dog gear... Think about that for a second... Nothing 'blew' up, but it required a complete dis-assy. of the box and some new parts.

After reading Speed Secrets I totally agree with the author that shifting is the absolute last place to try and pick up some time...

*shrug*

That said, it sounds like your box needs some professional attention.

-Michael