915 its own worst enemy?
 

The 915 tranny is legendary for being reliable

My only issue is shifting first to second....it's not that bad but it's difficult to do a speed shift at high RPM's. I wonder if folks have problems in any other gears? If so, I wonder if it's time for a rebuild.

sounds like you need a g-50 conversion..............wait, sounds like i do too :D
learning how to finesse a 915 has become a part of ALL 911 owners with these gearboxes, yea they have their quirks but that just motivates us to make it better in one way or the other :)

I've driven a 915 that shifted like silk. I think many people just suck with manual transmissions (I'm no expert myself). I think a person who understands that this isn't a Muncie or a toploader and doesn't try to shift it like a Mustang or Chevelle running the quarter and knows how to treat a tranny can keep these for a long time with no problems.

It does make you wonder? All I come up with is the 911 was so unique and well made that people were willing to overlook it's faults, and we still are and always will.

I agree Bob...its really the most unique road car ever.

Is there a technical limitation to the rear engine design that may have limited the Porsche tranny development in the 70s and early 80s?

Sorry if thats a dumb question...just wonderin.

More likely, it is an issue of engineering resources.

Porsche is not GM. They are a small manufacturer. They only have a (relatively) few engineers and they need to work on the most pressing problems. The tranny had issues but I suspect other parts of the car demanded more attention.

My $0.02

The engineers where busy designing the 924/44 transmission that shifts like butter.

Mine shifts great. A lot of these boxes are old, and haven't gotten the same loving care (and rebuilds) as the motors.

Mine shift very nicely, although the shifter linkage would block occasionally on the track. New after-market coupler fixed that.

I test-drove the 85/28K mile cream puff that SeaDweller bought. It shifted like silk.

Mine works great!!!

The only issue (if you consider it an issue) is the "notch" for reverse is very tight so you have to align the stick perfect to get it in reverse...not a bad thing.

I've never had an issue w/ 915 shifting or durability in over 30 yrs of ownership.

The 901 and the 915 mechanically are not that different. About a month ago I rebuilt a tranny for one of my buddies. After going through his tranny internally, and replacing a bad bearing and a few synchros, dog teeth and a slider, he now has a transmission which shifts extremely well.

We also replaced all the shift bushings and aligned the shift rod and the shifter. A world of difference.

I think that the real problem is that these cars are showing their age. People seem to have no issue spending $5-8K on a proper engine rebuild. But, balk at spending $2-3k on a tranny rebuild. There is nothing like actually checking the internal components.

James

My 915 has been rebuilt and shifts beautifully. I drove another '76 2.7 (targa) last night and the feel was just as nice, only a lot softer than mine.

The G50, however, in the '89 Cab is a very classy gearbox.

Either way, I think they're easy enough to live with. Try a 5-speed 928!

I dunno, mine shifts pretty good. A bit notchy, but certainly adds to the experience. I think with the proper attention and care the 915 is a fine tranny. Not a Honda by any means, then again, there is a reason we drive these cars :)

IMHO, insofar as synchronizing speeds and longevity, the 915 synchro design is not as good as the one used in the G50 and other gearboxes. In addition, I don't think most owners double-clutch when downshifting. Most downshifting (with greatest differential in gear rotation speed compared with 3-4-5th) is into 2nd gear. Thus, the synchros in 2nd wear out faster.

If you double clutch, the gearbox (or at least the synchros) will last longer. Simple.

Sherwood Lee
http://members.rennlist.org/911pcars

Porsche stubborny used their own synchro design (porsche synchromesh) well past it's expiration date. It's a dated design that was probably cool in 1960's but is just plain bad compared to superior Borg-Warner conical synchros, so they finally succumbed and threw it away... lately making a G50 which is actually quite nice gearbox. (Same happened with engine design, but that's another story :-)

They say nice-shifting 915 boxes exist but i never drove one. I believe it's possible to actually shift smoothly for a while after a rebuild, but saying it's a good gearbox is distorting the truth.

Example: OEM Gertrag boxes in older BMW's get often abused when people turbo-convert those cars with triple power as a result. Do they break? No...I've seen Toyota Supras OEM box survive two years of drag-racing with 800hk on tap. Did it break? No...

915...put in a 3.6 engine and it dies. Drive it for a while and it grinds...

You have to confess that to yourself guys... 915 boxes are crap. You cannot expect people to double-clutch in 21'st century.

930 box has somewhat similar synchro design and is more tollerable and much much stronger.

I agree with beepbeep. I always thought that the 915 was the only real sour note in the 911 song. The long pause between shifting between 1st and 2nd just doesn't seem right.

I've rebuilt a few 915's and they do shift nice when newly rebuilt (for a 915) but they will never be a sweet shifting gearbox. Invaraibly, when you take them apart you find that the bearing races are loose in case. The torque of a 3.6 only makes this sort of thing worse.
-Chris

"You have to confess that to yourself guys... 915 boxes are crap. You cannot expect people to double-clutch in 21'st century. "

Okay. Granted. So what now? I'm trying to think of an alternative gearbox (Supra Getrag in a 911) and nothing comes to mind, but I do try to make the shift experience as smooth as possible. New bushings and upgrades help a bunch too. I double-clutch to save the synchros. Side benefits include smoother application of power when downshifting; doesn't upset the chassis as much when cornering; saves a little wear and tear on the clutch as well. If you choose not to double-clutch - not a big deal; just plan on a rebuild a little sooner. Porsche learned their lesson (in many areas) and moved on to the next generation. Should we criticize leaky "windows" in a 356 Speedster or can we appreciate the entire package?

I don't know of any car that's perfect (for me), but a 911 comes the closest, so far.

Sherwood

I've only driven 2 911's in my life but I have to say that David Clarke's 915 shifts wonderfully. Sure it's got a long throw and sure you can't speed shift it but it's got the greatest feel I've ever had with a manual transmission.

Mine on the hand is a little nochy and tough to shift sometimes but I still thinks it shifts better than any other manual transmission I've ever driven.

Overall for a 30 year old design(or transmission) it's not a bad transmission at all. Yes it does have it's limiations but I really enjoy it and it adds to the porsche experience.

Another thing to note is that the 915 was originally designed for relatively low torque small displacement engines. Also, back then, maybe now Porsche tried to design to a spec to maintain low weight. Didn't one of the fellas once say that if they had known the 911 engine could have been expanded to the size it was he would have told the engineers to go back to the drawing board.

My point is, for another 50 or 100 pounds they could have made the 915 sturdier, but that was not the goal. The 930 is sturdier partly because it is only a 4 speed. I guess the main issue is that it took them too long to redesign, but that may have been due to the issues of the late 70's and 80's.

I like my 915 transmission. Its not as smooth as my BMW's shifter but it gives alot more feedback than the BMW transmission. I have to delay for less than a second between 1st and 2nd but otherwise its fine through the rest of the gears. I cannot race people from stop light to stop light in my 911 but I can have a blast with them on the curvey roads. In my opinion there is nothing easy about a 911. Thats why I like it. It is an art to drive a 911 well, but once youve got it, there is nothing else like it.

Redbeard,

I have been wondering and maybe you know the answer, on a 4 speed 901 tranmission is the first gear cantilivered the same way as in the 5 speed 901 ?

-Don

No. On a 4 speed, 1st gear is where we normally think of second.

5 Speed

R 2 4
1 3 5

4 Speed

R 1 3
() 2 4

James

Thanks for your replies. There are things that I absolutely like about my 915 equipped 911...namely the "feel" that you get from it. Very nice. So, in that sense...it fits the car well and adds to the experience.

The notchiness and bad synchros (at only 65,000) I can do without. So..Im taking the steps to rectify these things as best as possible.

James,

Do you think the 4 speed version of the 901 may be considered a slightly stronger transmission than a 901 5 speed since it doesn't have the cantilever weekness that I read so much about ?

Or does the loss of 1 gear spacing and less flexibility matching to engine speeds make it a moot point ?

-Don

I've had VW bugs which shifted better than my 915 does. People talk about treating it like a lady, being a surgeon, an artist, etc. Fact is you have to do those things or you'll wind up destroying it faster. Who EVER heard of a manual transmission needing a rebuild at 50k miles? At 100k miles? I've driven a stick shift all my life: Fords Mustang, Nissan 200sx, Mercedes 230, BMW 318, VWs, Suzuki Sidekick, etc. And all of these cars shifted like butter and were well over 100k miles. With sooo many wonderful things that came with the 911's, it's PATHETIC that the transmission is what it is.

Beepbeep, I think you're right on.

I doubt that there's a single person on this board who wouldnt like to be able to speed shift their 911 or downshift without double clutching. It's funny to see people defending the 915 like it's their child.

Ok--so what is the fix for the 915? or isnt there one? has anyone rebuilt or customized a 915 to shift better, smoother, easier?

G50

Yeah but you cant put a G50 in the pre 87 cars without a substantial mod...

Good question Jon T.

Ruf.

Well, I wrote to the factory and this is their response:

Herr Harry:

Thank you fer your inquirvey. We haft has dis question before und vee all know zat de Deusche design is zee best der ist. Yo foolshish amerikaners und speed shiftin desire is not vot der Porsche ist about.









:rolleyes:

:D

I've read taking mass out of the gears helps along with some beefier parts like billet bearing retainer plates and forced oil cooling. Jim

I've heard of taking mass out of the relatively heavy G50 gears. Do they do that for 915's also?
-Chris

"Do you think the 4 speed version of the 901 may be considered a slightly stronger transmission than a 901 5 speed since it doesn't have the cantilever weekness that I read so much about ? "

No. The weak points in the 901 are the side cover and the intermediate plate and both are thrust issues. And I think they start from oil starvation.

Lightening gears making it shift better????

I would stick to the basics - Replace shift bushing, align shift rod and shifter, adjust clutch, replace synchro's, dog teeth and sliders.

Oh, and unless someone has spent $3k on a tranny overhaul, there are still (replacable) used parts inside the case. Parts alone are about $2500. Just replacing the synchro's without dogteeth and sliders will only get you so far....

James

Actually i despise 915 so much that we opted for 4-speed 930 tranny in our project car, despite using four-banger engine.

Lightened gears have less inertia so the synchro system has to apply less force (torque) to match speeds and hence works better (and faster) and lasts longer.

Jim

I understand the concept, but I cannot believe that they would much, if any, effect.

James

This is more about economics than anything else. The 911s were selling without Porsche putting money into these improvements (what else explains the faulty door pocket design that lasted what, 20 years). When Porsche wanted to expand into other cars, i.e the 924/944 design, they had to make a superior product as they were not 911s. I had a chance to drive a 1987 924S the other day with close to 300,000 miles on the original engine and tranny and it shifted great - like my old 91 Nissan NX2000. I was shocked and said to the owner ' "You mean Porsche made a smooth sifting transmission like this in 1987?" I have a G50 1987 Coupe with a tranny in very good shape and the 924S shifted way better (oh, and the AC worked as well).

I think the 915 is a great thing - and mine needs more work.

Most people have no idea how to drive a "Sports Car", but they can drive a standard stick. This is a car that can damage itself. Speed shifts aren't a good idea, so learn how to drive it so you don't need to speed shift. This is a car that needs you to adapt to it - not vice versa. If you want a car to drive around you, I have a Civic commuter car that is great - with a little nitro will even compete with anything. I personally would rather not have a g50 - why bother with hydraulics, just not worth it for me.

Oh well - thats my .02$
Anthony