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NY65912's Avatar
 
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Question Root cause of 915 1-2 slow shifting ?

After a search I still do not believe I understand the actual reason a 915 transmission needs to be shifted slowly from 1st to 2nd.

Please shed some light on this age old problem.

Regards

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Old 10-09-2005, 01:54 PM
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The engagement teeth on the 915 gear and shift sleeve are quite tiny and have very little space between them. This requires that the idler gear be in nearly complete synchronization with the shift sleeve for the two parts to engage smoothly. However, the early Porsche patented synchronizer doesn't do the job of synchronizing as well as the Borg Warner cone-style synchronizers found in other types of transmissions. With today's slippery oils, the problem is even more pronounced.
Old 10-09-2005, 02:51 PM
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Mikes,

What gear oil are you using? Swepco 201 works wonders at improving all the shifts. The PO of my '66 said the II synchro was shot, he was using some Valvoline something-or-other. I put Swepco 201 in the box and amazingly, no more bad synchro!

201 was actually developed in collaboration with Porsche, so I read somewhere.
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Old 10-12-2005, 07:34 AM
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durn for'ner
 
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Changed to Swepco 201 recently. No dramatic improvement. A little less eager to grind perhaps, but first and second gear still a bit bulky.

From what I have read here - major gain with Swepco is longevity of the box.

It does have a very sexy color though...
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Old 10-12-2005, 07:42 AM
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The reason they shift poorly is because it's a Poor(sha) design. The new 911's shift like Japanese cars. Of course that could be because the gearboxes are from Japan...
-Chris
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Old 10-12-2005, 09:46 AM
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On the worn units the conditon is aggravated by a 'groove" being worn on a part called a slider which hangs it up somewhat.( My mechanioc showed me this during the rebuild of mine).

My 1`-2 is still "stiff", but a lot better after the rebuild.
Old 10-12-2005, 10:07 AM
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From what I understand the 915 box was a "home made" Porsche patented design.

Hanging a flat six out behind the rear wheels was another thing Ferdinand seems to have been obstinate with. Air / oil cooling with that nice smell of gasoline and burnt oil in the coupé.

The passenger compartment in it self an ergonomic mess.

Its only a vehicle for the consecrated fanatic. But for us (the few - the brave ?) there is no substitute.

Makes me wonder though. With such talent and championship winning recipe - why did they patent such a crappy gear box ??

Or does it have redeeming features that I am not aware of ? Low weight ? Slim figure ? Cheap to manufacture ?

Anyway, I love my 915. When I am on top of it (not literary) I feel like a real competent driver.
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Old 10-12-2005, 10:25 AM
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I am not experiencing any bad issues with my gearbox. The lube is Sweepco.
The reason for the question was to be educated as to the root cause of these problems. Hypothetically, if someone were to try to re-engineer the 915 for better shifting.....would this be mechanically possible?
Obviously tha answer is probably no as no one has done it yet.

I'm not talking about shif gates but re making those parts in question to work better. I'm sure it would take plenty of engineering but the question remains.....can it be done?

Best regards, Mike

Hey John when am I gonna see that SWB car of yours?
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Old 10-12-2005, 10:42 AM
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Quote:
Originally posted by NY65912
I am not experiencing any bad issues with my gearbox. The lube is Sweepco.
The reason for the question was to be educated as to the root cause of these problems. Hypothetically, if someone were to try to re-engineer the 915 for better shifting.....would this be mechanically possible?
Obviously tha answer is probably no as no one has done it yet.

I'm not talking about shif gates but re making those parts in question to work better. I'm sure it would take plenty of engineering but the question remains.....can it be done?

Best regards, Mike

Hey John when am I gonna see that SWB car of yours?
Wevo will convert your 915 to a "dog ring" racing style box. It wouldn't be really suitable for the street but you might consider it an "improvement". http://wevo.com/PORSCHE.htm
-Chris
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Old 10-12-2005, 10:51 AM
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Mike,

So, re-engineering the 915 for faster shifts and more reliable operation? Such as by eliminating the synchronizers, going to straight-cut gears and dog-ring engagement?

Our man Hayden strikes again.

http://www.wevo.com/xtpics1.htm
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Old 10-12-2005, 10:53 AM
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Achtung! Chris beat me to the punch! But I included a photo.

Mike, next time we have a get-together with cars AND beer instead of just beer, I'll bring her out. Until then, here's a picture of her, with her younger sister. . .

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Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Ex-'89 944 Turbo S (Sold 8/21/20)
Old 10-12-2005, 10:55 AM
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I should probably add/change my gear oil soon. Is there a tech article on this or is it fairly straight forward? Probably seems like a simple thing to most but it's something I just haven't tackled yet!

Thanks

nix
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Old 10-12-2005, 11:26 AM
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so how much fo rthe wevo.. why would it only be good for experienced street drivers?
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Old 10-12-2005, 11:41 AM
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nix,

Check out my thread "Giving up on gear lube change".

At the end of my own misery it turned out a rather comprehensive discussion.
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Old 10-12-2005, 11:44 AM
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Quote:
Originally posted by hkspwrsche
so how much fo rthe wevo.. why would it only be good for experienced street drivers?
ha, straight cut gears are not something you want on the street (noise).

otherwise, yes, nonsynchronized gearboxes require additional techniques.
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Old 10-12-2005, 12:04 PM
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I've looked at adapting VW Type I parts (Borg Warner style synchros), but they just won't fit.
Old 10-12-2005, 12:23 PM
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very clever! do you think another bw style synchro might fit? Hard to say unless you have a big box of synchros from other makes and models, I guess.
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Old 10-12-2005, 12:47 PM
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Quote:
Originally posted by NY65912
the question remains.....can it be done?

anything can be done. 930 synchros will improve or you can rebuild the entire box around your driving style. straight cut gears might help if you can match revs as quick as most people can shift but my personal oppinion would be to beef up the synchros when next you need to disassemble the trans. - at that point you could also improve the 4th and 5th gears for the track. just remember that everything is a trade off for something else though. what do you need more quick shifts or trans longevity? (money is also a factor)
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Old 10-12-2005, 01:31 PM
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jack olsen has documented well his transmission improvements for the 915 box when used mainly for racing. might be worth taking a look...
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Old 10-12-2005, 01:32 PM
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I found that the best cure for the ever so lovely shifting 915 is to be patiant. The car will teach you how to shif the way IT wants you to do it.
Getting out of my BMW and trying to shift my 915 was a comedy for my wife, she got alot of laughs at my expense.( She drives the car very well to make matters worse)
I re-built the shifter and coupling and added the sexy-smurf-blue Swepco 201(thanks nostatic) and it all helped but I found that the only way to shift quickly is not to pull the stick until the left foot hits the floor. If it comes out of 1st easy it goes into second like a dream. If you shift out harsh you can kiss 2nd good bye!
After some practise I have gotten fairly quick and smooth.

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Old 10-12-2005, 03:26 PM
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