What was porsche thinking when they built the 915 trans?

[javadog]

You know, I think the only thing that was illustrated here was the fact that those people that complained about a 915 had one that needed some work. I'd like to blame Porsche for a part that wears in normal use but that would be going too far.

As for a single 1-2 shift being responsible for dropping a 0-60 time by almost 2 1/2 seconds? Surely you don't really believe that, do you?

Sorry if I keep defending Porsche on this issue but I think the problems with the 915 are way overblown and mostly have nothing to do with the design. It's kind of like the trailing throttle oversteer "problem" a 911 is supposed to have. That one got a lot more air time than it deserved. Any rear wheel drive car can spin in the same manner, if the driver does the wrong thing at the limit. Not exactly news, but for some reason Porsche gets all the blame.

JR

[robert walsh]

JR, regarding the above, let's not forget the corvair and negative air time on that subject. Thanks for your input and believe it or not, I admire the 915, mostly for it's longevity but also it's inherent performance capabilites, when all the pieces line up.

[masraum]

I've driven SCs that shifted decently and an '84 that shifted better than my miata (which is supposed to have a great tranny).

Depends upon the transmission and the kind of abuse/use it's seen over it's life. Also, has it gotten the maintenance it needed/s?

[masraum]

Originally Posted by javadog

You know, I think the only thing that was illustrated here was the fact that those people that complained about a 915 had one that needed some work. I'd like to blame Porsche for a part that wears in normal use but that would be going too far.

As for a single 1-2 shift being responsible for dropping a 0-60 time by almost 2 1/2 seconds? Surely you don't really believe that, do you?

Sorry if I keep defending Porsche on this issue but I think the problems with the 915 are way overblown and mostly have nothing to do with the design. It's kind of like the trailing throttle oversteer "problem" a 911 is supposed to have. That one got a lot more air time than it deserved. Any rear wheel drive car can spin in the same manner, if the driver does the wrong thing at the limit. Not exactly news, but for some reason Porsche gets all the blame.

JR

I see your point, but the 911 does have a great propensity to TTO due to the engine out back much more than a front engined rear drive 60/40 weight dist car.

[RWebb]

"it was never perfect"

well nothing is -- it was remarkable when introduced:

Accolades for the Transmission
The [newly introduced 911’s] 5 speed gearbox is probably the new car’s best single feature.” – CAR & DRIVER, April 1965, p. 30.

The gear “lever remains delightful to use…” Motor, Jan. 29, 1972

The 901 transmission is a “superb five-speed gearbox… provides a ratio for every occasion…[and] requires so little physical effort that winding up and down through all five ratios… when pressing on in twisty or hilly country, is one of the most rewarding pleasures in motoring.”
-- Motor, Feb. 8, 1969

The 901 transmission “gate [is] well-defined.. and the powerful synchromesh is so utterly smooth and unobtrusive that the lever seems hardly to be attached to any mechanism. Upper changes are made as fast as the lever can be sliced through the gate….”
-- Motor, Feb. 8, 1969

The gear lever “movement is so natural, if you try to change across the gate, you’ll muff the shift.” “When other manufacturers want to [brag] their specifications often list Porsche-type baulk-ring synchromesh. The yardstick is Porsche and Porsche gear syncronisation is perfection.”
-- Wheels, July, 1969

The five speed, all synchromesh gearbox is one of this Porsche [911’s] greatest delights; it is light to operate and I find it almost impossible to change too quickly.”
-- Motor Sport, Jan. 1970

[robert walsh]

These are are great accolades 901 transmission, then came the beefier, stronger 915, very similar in design just made stronger. It's odd how they commended the "porsche type baulk ring synchromesh". The baulk itself translates to "causing trouble in achieving positive results". As far as I am concerned I feel it adds to the total non-conformance that the 911 has achieved for decades, resulting in a performance sports car not built for the masses but for the enthusiast.

[ramonesfreak]

amen to the accolades.

i feel like im driving an old race car when i drive mine

love it

[Laneco]

I've never been able to figure out why people complain so much about the 915. Assuming good bushings and adjustment, they shift just fine. They do have a decidedly mechanical feel and reward a light touch, but honestly, they are pretty darn easy to drive.

angela

[p911dad]

I have had an 84 Carrera for many many years and at times the 915 has been balky. I replaced the ball cup, made a careful adjustment of the linkage and had the clutch adjusted correctly. Then installed Swepco. The car is 24 years old afterall, so you can't expect perfection ala a new 911. However, my car shifts fine, not a problem. If you are a speed shifter, especially from first to second, you simply have the wrong car. The 87's were much improved (but heavier) in the shifting dept. I prefer the totally mechanical feel and personality of the 84 Carrera.

[500_19B]

A couple of you have mentioned the importance of a good break-in for a rebuilt transaxle. I have read many opinions on breaking in engine rebuilds, but what is the best way to break in a transaxle?

[Zeke]

The 901 took some finesse to shift 1-2. The 915 in line shift does nothing for the shift itself. Go to the track and listen to the delay out of the pits for any 901 or 915. For that reason alone, I would prefer a 901 any day. Don't abuse 1st and the thing will handle 250 HP (or so they say).

To drive a G50 one has to learn new shift timing relative to the clutch action. Hydraulic clutches suck IMO. These days I have 2 of them. I can drive a 901 like a ballerina dancing the swan. The 915 2nd, 3rd and 4th, the same. The rest are Corvette trannies (not talking about the famous Muncie here; give me one of those any day!).

[J P Stein]

Originally Posted by milt

The rest are Corvette trannies (not talking about the famous Muncie here; give me one of those any day!).

Actually. Milt, the T-10 was a much nicer shifting trans than the Muncies. The T-10 came out in 1957, IIRC. The Muncies have the same problem as the 915.....the gears got too heavy for the syncro set up.

As for the 901.....I figure I loose a couple-3 tenths to the Miatas on every shift.

[Zeke]

Hah! JP, you got me. It was the T-10 I had in mind. I had 5 Corvettes when I was much younger and they were still fairly cool cars. Up until the demise of the Stingray, anyway. But at least 2 were T-10 cars.

[stormcrow]

One of the things I noticed about the 915 is if the shift shaft going into the tranny is not set properly you will have problems shifting it. I found this out after a engine rebuild and install. It took me awhile to get it right. I thought I had everything right, but when I would shift to 1st while the car was still rolling the gear would grind. After a readjustment the problem went away and I could shift to 1st at 20 mph. After that, only had to be careful shifting from 5th to 4th or I would grind the reverse gear.

That adjustment may be part of the problem with people having problems shifting.

Steve

[Rodsrsr]

I had my 915 rebuilt almost two years ago and it was extremely tight at first. The mechanic told me that it takes several thousand miles for a 915 to properly break in. Tonight while driving the car I finally noticed how beautifully the 915 was working and I can tell that its finally seemed to loosen up and shift just perfectly in all gears. (I only drive the car a few times a week) A fresh 915 with swepco, new bushings and factory short shift kit is indeed a beautiful thing.

[dshepp806]

I like the G50 much better than the 915,..not minding the hydraulics whatsoever. Complete butter,......nice short throws on my '89 (stock).


$$$ to fix (rebuild), however (scary).


Best,

Doyle

[DanielDudley]

If your clutch or pilot bearing drag at all it will make shifting a bear unless you are very precise about speed matching the engine to the gears. Having bad syncros can cause a crunching sound and feel, but should not prevent a rev matched shift in any way. Bad linkage bushings can make hunting for the slot a hit or miss affair, and replacing the bushings is an easy and inexpensive job to do.

Any mechanic who tells you he has rebuilt the box on his car and it still shifts like crap is overlooking something.

However... It is worth noting that to upshift a 915 box you want to move the gear lever to the next gear quickly, and offer the lever to the next gear with light pressure. As the input shaft slows, at a certain point the lever will fall into the next gear with almost no effort. You should be holding the knob with the tips of your fingers. This helps you to feel the resistance of the syncros. When down shifting, double clutching and rev matching are highly reccomended. You don't always have to double clutch, but you should always rev match.

For my money, I would always like to buy a 911 that drives well and needs no sorting, but shift issues in a 911 can be dealt with. Guys like Gary Fairbanks KNOW how to rebuild and troubleshoot these gearboxes, but without a good linkage or with clutch issues, it would be still be hard to shift. Find someone in your area who knows these cars, and have him drive it. Someone who has driven a few should be able to tell you what is up, or at least if you have problems.

A tranny rebuild may cost a few thousand, but if it isn't done by an expert it could be a waste of money, and I know this from experience. Just throwing in new syncros is not always going to cut it. Once sorted, a good tranny could last the life of the car, which is a long time.

Prehaps you could find some local PCA members who could drive your car and offer some suggestions or opinions.

[RWebb]

good description of shift feel - every one should go back and re-read that

don't agree re life of a rebuild

i figure the unit body could last a million miles or more - lifetime set by rust or crash issues, not so much as mileage

motor rebuild every 200k

trans. rebuild every 50k to 80k or so...

torsion bars -- 100k?? seems like they just give up eventually

rubber pieces last less time than anything really

[Wayne 962]

If you start out driving a 914, the 915 transmission seems like a dream!

-Wayne

[craigyirush]

I agree with Dave about the Miata.
A colleague has a 2001 with six speed - amazingly quick shifts.

And for those who say that the 915 was good when new - how do you explain
all the criticisms it got from journalists when the SC and Carrera were new?
Most didn't like it at all and thought it was outdated by the 80s.