Quick Shifting Problems?

[calereeves]

I've heard that the older 901-915 transaxles don't like to shift fast, is this true, and if so, why?
Thanks,
Cale Reeves

[old_skul]

True, they don't shift like today's Borg-Warner units or Japanese boxes. Simple fact: it's old technology. Synchronizer technology wasn't as effective back then.

You get used to it, and plan for it.

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Mark Szabo
1986 911 Targa 3.2
1987 Escort 5-speed 1.9 RIP
The Porsche Owners Gallery

[calereeves]

The reason I'm concerned abouit it is I'm trying to develop a "paddleshift" for it, which would provide lightning quick shifts. Will very quick shifting damage the tranny, or is it just hard to shove the gearshift lever into gear?

[Ted Stringer]

Both. Not only will the gears refuse to go in (my 2nd), they will grind if forced. Look around the board and see how many time we have shifted fast with a 901/915 and "crunched the syncro".

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Ted Stringer
nuke3@juno.com
'84 911 Targa aka pocketrocket

[calereeves]

Is there any way to make the synchros better?

[TimB]

I believe I saw some posts on a G50 swap. That might be the way for you to go.

[calereeves]

Call me Porsche illiterate, but whats a G50?
Cale

[pbs911]

A G-50 is the trans that replaced the 915. This change took place in 1987, I think. The G-50 supports more HP and torque. It is also operated by a hydrolic clutch whereas the 901 and 915 were cable operated. The cost to fit a G-50 into a pre-87 car is high and requires extensive work of the torsion bar tubes and mounting areas. The G-50 weighs about 100 lbs. more than the 915.

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Paul
78SC Targa
Pelican Parts Members Gallery

[Superman]

My shifting is balky too, and I think this is one of the bigger problems with these cars, from a speed and performance perspective. I'll deal with the tranny issue as soon as I have the resources ($). Unfortunately, shift time is the major contributor to any acceleration slowness I have. The car is pretty light and the engine is stronb, but I spend between 10 and 20% of my hard acceleration time with my foot on the clutch. That slows acceleration CONSIDERABLY.

I suspect that with fresh synchro parts and Swepco, shifting would be MUCH quicker and a G50 is really not necessary. Comments?

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'83 SC

[Early_S_Man]

The G-50 is not manufactured in-house at Porsche, it is made by Getrag. As are current transaxles for the C-5 Corvette. The decision to go to the G-50 and later versions in current use was an economic one not an engineering one ... contrary to the MYTH that 'there were problems with the synchronizers!'

All of the sports racing cars from the 550 Spyder thru the 1500 hp 917-30 Can-Am car used the Porsche synchromesh system as did a number of Ferrari production models, and that does not represent a frivolous decison!

The Porsche synchromesh is an elegant one, as it depends on friction to slow the parts involving the shifting until speeds are matched before engagement can occur. Grinding cannot occur until the synchronizers are worn, and represent severe wear and breakage of operating sleeve teeth or the dog-teeth pressed onto each major gear that are engaged by the operating sleeve.

The simple fact that the original 917 transaxle was tough enough to handle hp loads from 560 hp to more than 1500 hp is testament to the fact that Porsche engineers were perfectly able to design transaxles for high power levels! The accountants made the decision to go to the G-50 family of out-sourced gearboxes. While not a completely irreversible decision, engineers lost to attrition, retirement and moves to other organizations ... did represent a loss in the Porsche enginerring experience level and 'culture' not immediately replaceable!
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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[This message has been edited by Early_S_Man (edited 10-23-2001).]

[Mully]

I rebuilt my 915 box and when I measured the new out of box
syncro and dog tooth assemblies as per the shop manual specs I found them to be out of tolerance.I lightly sanded the syncro's on a lathe and then carefully sand blasted to the original finish back into the spec. My transmission shifts very smooth and fast with
no problem chirping 2nd gear without power shifting..Just my 2 cents!

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Mully 911

[Natchamp]

Calereeves, what are you considering for paddle shifting? Are you talking about designing/building a system or buying one?



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Mark
The Beast
mark@hargett.com

[calereeves]

Nat,
I am trying to design my own paddle shifter. The whole thing won't be in a porsche though,....please don't hit me.....its going in a 68 VW Beetle I know, *gasp*... This would be the coolest frickin' bug in the world though!!!
Cale

[Early_S_Man]

... until you run into Paul Newman's old 60's VW Beetle convertible with the mid-engined Ford 351 with four Webers and Indy-car rear suspension and Hewland transaxle!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[calereeves]

damn.