Does the 915 have ANY advantages over the G50?

[Markus30]

Regarding weight, durability, cost of maintenance, etc.? Just curious.

Markus

[pwd72s]

It's quite a bit lighter than the G-50. And, it handles power & torque a lot better than the 901. I just had my 915 gone through, I DO run a synthetic gear oil (no, don't want to start a beef with the Swepco fan club), and since I don't try to speed shift, I fail to see why some are so down on the 915...it's a good gearbox.

[rstoll]

A car thief might have a harder time getting away with the 915.

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Robert Stoll
83 SC
83 944

[Early_S_Man]

Are you buying a car or a transaxle upgrade?

The 915 has a much wider variety od gear artios, both OEM and aftermarket, more ring & pinion ratios available ... if you have any intention of trying to customize or optimize the ratios for street or competition, there isn't a more flexible transaxle on the planet, short of Hewland competition boxes starting at over 5 figures!

If you have ever heard of Mark Donohue ... he had some 'engineering-oriented' ideas about optimum gearing for the American market and roads that were expressed in a 1969 Car and Driver test of the entire 900 series lineup. The 915 allows one to fully explore those ideas, should you choose to explore them!

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

[Markus30]

Hi S-Man,
I actually currently drive an 80 SC Targa and am fine with the 915. Since I've never driven a G-50 911, and with all the posts praising that gear box, I was just curious if there were any possible advantages to having the older unit. Thanks for the reply.

Regards,
Markus

[APKhaos]

915s get more than their share of bad press. Given that we staunchly defend Porsche engineering [despite the great thread recently on classic design bungles in the 911 line] we have to wonder if Porsche would have persevered with the 915 for so long if it were fundamentally flawed. As Warren says, there is an entire industry built around adapting the 915 for every street and race configuration imaginable!!

OK, so back to reality....while there are certainly many quirky 915s, there are many more that are well over 100K miles and going strong. Mine shifts like butter at 140K, although its true that the shifter design tends to be slow and vague. Not perfect, but better than most. The mechnical clutch provides more feel than anything I've ever driven!
Tony K
85 Carrera

[old_skul]

It's an "old-school" box. If you learn to double-clutch it, and you're really, really kind to it, it works great. Seriously, it's smooth as butter when you get the linkage correctly adjusted and the linkage bushings refreshed.

Since my 915's rebuild I have put in Swepco, installed a new ball cup bushing and a new set of coupler bushings, and the difference is night and day. With good double-clutching, you almost don't need a clutch.

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

[jlex]

I drove my sister's '88 Carrera with the G50 when I was in Atlanta in the Spring... was directly comparing it to my '85 Carrera's 915. Hers felt somewhat remote from the driving experience...shifted nicely, but was more like a Japanese shifter... more dainty and with less feel to the process... maybe I was just used to mine, though. She's a physician, not a gearhead, so I'm sure she appreciates the more delicate feel. Hers did show a little balkiness around second when the RPM's didn't match a second gear shift... so I felt right at home there.
Felt a lot more comfortable when I got back home & rode my '85 around.
The 915's okay... you just have to develop a sense of rhythm while shifting it... and I believe it takes about a year driving it to develop that sense. Mine shifts flawlessly as long as I pay attention to what I should be doing. I believe most people complain because they've been horsing around with it or letting inexperienced drivers take the wheel to grind a few gears.
regards,
jlex.

[Pillow]

Old_skul, do you double clutch on the way up or only on the way down?

I thought there was no advantage in double clutching while moving up the gears? Only when lining up the sychros on downshifts.

I like the 915. Simple and semi-rough mechanical feel to it like you know it is a tough machine working hard. Mine has been very good to me except for the gates for 1st and 2nd which I think will be corrected when I replace the shift couplers which are probably shot.

Thanks,


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Adrian Pillow
1979 911 SC
1966 VW Microbus
PCA - Peachstate Region

[86cpe]

I agree with all of the comments. I had a small leak in the case and decided, as long as engine was out to replace the clutch, to reseal and rebuild the 915. Looked really good inside at 100K miles, no absuse by PO, we replaced fewer parts than we thought. Syncros were good but were replaced on some gears. Swepco added.

Before the rebuild and new clutch the driving feel was unappealing and a bit depressing. No joy ever.

Now I find the transmission to be very much in keeping with the rest of the car -- raw, honest, tough feeling, more like a competition car than street car. Once you develop a rhythem for shifting you never have difficulty finding a gear and the shift action is precise.

There's nothing wrong with the G50, but like the post above mentions it feels more Japanese. A neglected one will never feel as bad as a neglected 915 but when both are properly set up there is very little difference in overall appeal. My opinion is that too many people have formed an opinion of the 915 after evaluating a poorly maintained or worn one.

I heard the 915 weighs significantly less than the G50 (anyone know how much?).

Porsche changed the rear suspension slightly in 1987 concurrent with G50 introduction to once again give a little less oversteer. I understand the change is a minor one but the 87-89s feel a little less responsive than the pre-87s.

For some reason overseas many Porsche fans prefer the 915 over the G50, they say the G50 is "American".

They're both good transmissions it's just that the 915s need more attention to keep them at their peak.

One thing I don't like is not being able to let a valet park my 86 Carrera. Getting the clutch take up just right is tough.

[pwd72s]

I remember driving a friend's (then) new '87 Carrera, the first year with the G50. The shifting felt "funny" to me, probably the hydraulic clutch as much as the gearbox? Overall impression was that 911's were turning into Buicks. Couldn't wait to get back in my '72S!

[old_skul]

Pillow, I double-clutch in both directions, upshifting and downshifting. Of course, I'm still getting the hang of it, so in a high-workload situation - downshifting from 4th to 3rd at the end of a 120 mph straight, with a 90 degree corner at the end - I let the synchros do the work. One day I'll be good enough to do the tap dance fast enough to double-clutch there.

So it's my pet project for the next year - to learn how to double clutch in both directions smoothly and without thinking about it. Also, left foot braking, but that's a different story.

The reason for the double clutching action is because IMHO the synchros in the transmission are of a very early design and you have to be really nice to them to make them work well. So on an upshift, I'll double clutch with no throttle input to slow the input shaft down. On a downshift I'll heel-toe and blip the throttle with a double clutch to "spin up" the input shaft to an easily synchronized speed. If the speeds of the input and output shafts are, say, within 5% of each other, the synchros work great. A 20% difference makes them work a hell of a lot harder, and the shift isn't smooth at all.

I've learned loads about the 915 in the past year and I'm currently watching Ebay for a used one that I can rebuild over the winter as a project. That'd be fun and I'd have a whole new 915 to abuse next summer.

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

[Roland Kunz]

Hello

The pre 950 tranys have the Porsche synchro mesh. This was the fastest synchronisation on the marked and even used in licence by other companys.

Today the Borg Warner is more refined and has nearly the same shift speed. But if you compare period cars you will find out why Porsche used it so long and many racers still swear on it. ( OK most swear on non synchronized straight gears )

The 915 is the last evolution form.

Grüsse

[89Targa]

Sounds like the G50 works and the 915 is a work around.

[Roland Kunz]

Hello

The 915 is superior to the "lousy" G50 but the operators and the heavy cars forced Porsche to cut a other piece race technology away and adopt a lower engeniered technology. Porsche investet very much brain into the Borg Warner synchromesh as they needed it for the 928. All other companys used the technology as Porsche made it with the money and backup from ZF & Getrag who sold it to there costumers ( Aston Martin, Ferrari, Corvette, ) The Ferrari progress in shifting was done by Porsche engenieering.

Porsche could also have enlarged the own synchronisation but this would have enlarged the whole transmission and didn´t feel better.

The advantage from the Porsche synchronisation is that you can shift faster. But most drivers needed a "blocked" shifting action to prolong the lifetime from the synchronisation.

The Porsche system does work while shift. The "Vollkonus" (BW) does brake down the speed and then shift.

The last 3,2 915 and the follow up the 950 have similar wight. The 915 got some 10 kg heavier from the first 1972 version. The 950 had not the oilcooler and was tricked out maximum to keep slim in wight.

The best trany for the race track is still the 915. ( YMHO ). Racers don´t care to much for wear. They rebuild the parts if they start to loose time.

Grüsse

[Jdub]

The 915 synchro operation is a masterpiece of design. Read PaulF's "911 Story" entry and pic/diagram on the 915 alongside PP's exploded view at(http://www.pelicanparts.com/911/911_Parts/1978-83/3-3-3.JPG) and you just have to appreciate how smart these guys are.

And it is so related to how you shift. To know, and picture in your head, exactly what is going on synch-wise as you shift is to never, EVER force a shift again. The genius is in the way the gear to be engaged is run up to speed: it is the rotation of the hub/slider that causes the engagement to "lock" under the dogteeth, freeing ONLY when the now-spinning gear is up to speed, and then mating together. Friction is everything: as there is a differential of speed the 'dogs cause enlargement, but the moment the friction caused by differential speed is gone, the 'dogs go loose and the ring diameter is reduced, permitting engagement.

You can feel this as you shift, the slight pause as the 'dogs force the ring into a larger diameter, catching under the dogteeth, spinning the slow gear up to speed, then permitting full engagement. Just marvelous.

I highly recommend the study of this gearbox design to better understand just how amazing these cars are. BorgWarner is damn good, but I must say the 911 is definitely from Mars! .

Jw

[This message has been edited by Jdub (edited 08-23-2001).]

[Clark Griswald]

Anyone have illustrations of the internals of the 915? Specifically I would like to see some detail on how the synchros work.

Same for the G50.

[Randy W]

Nobody has yet mentioned the advantage of the '72-74 915 tranny's 7:31 ring & pinion over the 8:31 used from mid 75 to 86. This produces a much shorter and tighter final ratio gear set, offsetting the inherent disadvantage of too high an overall tire diameter in 17" wheels. The cases using the 7:31 are also magnesium, so they are lighter than the later aluminum ones, although more fragile. The one thing that is often done to strengthen this case is to substitute a later aluminum side cover for the magnesium one to improve durability with greater loads from larger engines.

Randy Wells

[pwd72s]

Maybe this post should be given a new title:
Does the G-50 have ANY advantages over the 915?

[Early_S_Man]

There are also good explanations of the Porsche syncronizer operation in Elfrink and Clymer 356 books, and the Clymer 912 Handbook!

A couple of notable cars using Porsche-licensed synchronizers ... Datsun 2000 roadster of the '68-'70 era, and all of the Ferrari Dino road cars! More than one journalist has noted the irony of a Ferrari using Porsche-synchronized transmissions!

Cost accountants probably played a factor in the discontinued use of the Porsche synchronizer ... after one of them saw how quickly a Borg-Warner 'cone' brass synchro ring just plops on the stack of parts in two seconds vs. probably a minute to assemble a 915 driven gear and synchronizer assembly! There may have been a cost reduction in outsourcing production of the G-50 transaxle to Getrag. It can't have been a happy moment on the 911 production when the '87 model production started with a 'foreign' transaxle, after more than 40 years of doing their own assembly in-house!

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