915 its own worst enemy?

Sonic dB · Sonic dB's Garage

The 915 tranny is legendary for being reliable

brawlins · 05-14-2003, 06:17 PM

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.

bell · bell's Garage

sounds like you need a g-50 conversion..............wait, sounds like i do too

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

masraum · 05-14-2003, 06:35 PM

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.

Bob's Flat-Six · Bob's Flat-Six's Garage

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.

Sonic dB · Sonic dB's Garage

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.

HarryD · 05-14-2003, 06:54 PM

Quote:

Originally posted by Sonic dB
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

Bob's Flat-Six · Bob's Flat-Six's Garage

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

Jack Olsen · 05-14-2003, 07:38 PM

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

APKhaos · 05-14-2003, 07:54 PM

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.

k9handler · 05-14-2003, 08:01 PM

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.

Bill Verburg · Bill Verburg's Garage

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

red-beard · red-beard's Garage

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

Adam · Adam's Garage

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!

Vipergrün · 05-14-2003, 10:23 PM

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

911pcars · 05-15-2003, 12:25 AM

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

beepbeep · 07:25 AM

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.

ChrisBennet · ChrisBennet's Garage

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

911pcars · 05-15-2003, 11:08 AM

"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

Tim Walsh · Tim Walsh's Garage

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.