What was porsche thinking when they built the 915 trans?

[robert walsh]

I have an '83 sc with a 915 transmission, I have no synco or shift related problems, beyond the norm. But I am wondering why porsche built and installed this type of transmission in so many of it's cars. The mere fact that brand new from the factory these were a bear to shift with any speed, let alone any accuracy, combined with gross amounts of slop and freeplay. The 1st to 2nd gear shift is so uncalled for in cars costing 35k in their day. Don't give me any crap, I love the car and certainly have learned how to shift it to the best of it's abilities, but why did the USA , JAPAN, GERMANY (BMW) an the BRITISH all make transmissions that worked, when the world leader in performance seemingly missed it's mark.

[javadog]

Robert,

A 915 wasn't difficult to shift when new, as you describe. They are not bad at all, if they are in good shape. I'd say you 've never shifted a good one. If you are having problems with the 1st to 2nd shift, yours needs work. Porsche designed their own version of a synchronizer years ago and it works really well.

I have a freshly built gearbox in one of my cars and it shift as quickly as you can move the lever, with little force.

JR

[Grady Clay]

Robert,

Part (most?) of what you may feel as ‘slop’ in current 915s is age. The first producton models were in 1972. The last 915 was delivered in 1986. When every part in the system was new it was relatively ‘tight’. Today it is impracticable (impossible?) to build a new 915.

Porsche developed the 915 out of the need for a stronger transmission to succeed the 901/911 series. Part of the frustrating difficulties arise from moving the cantilever gear to be 5th gear from 1st gear as in the 901. This caused a somewhat “Rube Goldberg” linkage for shifting.

In hindsight Porsche would have done better having the shifting enter the side of the transmission (like the race cars of the day). This would have made for more positive shift linkage design as well as accommodate mid-engine installation (914/916) as was intended.

Another was Porsche continued use of the “Porsche Patent” syncro system. They were still too proud to abandon that in favor of the much better Borg-Warner system eventually used in the 950 transmission (G50).

Today you can still maintain the shifting components close to new. There are a number of often ignored problems that effect shifting performance. To choose one; the clutch disc must be absolutely free to slide on the splines of the input shaft and must completely release from the two steel friction surfaces of the flywheel and pressure plate. Otherwise there is a slight drag and ‘pop’ when coming out of a gear at the expense of syncro and shift component wear.

Best,
Grady

[robert walsh]

I have driven probably a dozen or so, I would put my current one very close to the top. As perviosly mentioned I have no syncro issues whatsoever, and it has a wevo gated shift kit, so most of the freeplay has been eliminated. I have no problem finding gears, either while up or down shifting. The transmission itself does not allow for a 1st to 2nd gear shift with anywhere the speed that the others do. I am certianly not talking about the obviuos inablility, need or desire to truely "speed shift". I test drove a '76 911 brand new, loved it (couldn't afford), so I had to settle on a new TR-6, (OF ALL THINGS). I clearly remember how much nicer the TR-6 shifted, (still have a TR-250), I also clearly remember how much more i loved the 911. Also all my shifting bushing's were replace in an engine out service 4k ago.

[JeremyD]

You realize these are fighting words for Rwebb?

[89911]

I can't believe your knocking Porshe trannys. My 89 shifts great.

[CharlesJones]

My previous wrench prepares 911s for racing, and he says that in his race cars the 915 and linkage is practically new, having been rebuilt with fresh new parts, and he told me that they still shifted like crap. Maybe part of the reason for the 915 being so appalling might be that Porsche limited development on it in the late '70s since they were anticipating the 928 to replace the 911, although it still amazes me how such a slow gearbox should make it's way into such a dynamic car.

[Formerly Steve Wilkinson]

I've always thought the basic reason for the 915 design and its compromises was its light weight and compactness.

[javadog]

Originally Posted by robert walsh

The transmission itself does not allow for a 1st to 2nd gear shift with anywhere the speed that the others do.

This is where I have to disagree. A transmission with fresh internals shifts just fine from 1st to 2nd. As the 2nd gear synchro wears, it slows the shift and the driver compensates by putting more force on the lever. The timing of the shift matters, too. Too fast, or two slow, and the effort goes up.

These gearboxes need to be broken in, so that '76 you drove new didn't shift as well as it would with a few thousand miles on it. Porsche made continual improvements to the 915, with a significant one coming in 1977. If you had bought your '83 new and put a few thousand miles on it, you would be amazed at the difference over what you have now. I know you think your gearbox is in good shape but what you describe says otherwise.

The newer gearboxes "shift better" in some peoples' minds but they are not all things to all people. I have an '85 928 with Borg Warner synchros. Guess what? It's throws are long, and the 2nd gear synchro likes to be warmed up before being shifted "fast." I usually skip 2nd all together until the gearbox is warmed up. It hasn't been abused either. It has all of 31,000 one-owner miles and fresh (correct) fluid.

I just bought a new Boxster S for my wife. It can be a little reluctant to engage a gear from rest (Porsche was working on this same problem in 1977, with the 915...) and sometimes takes a little more force to engage a gear than I would think ideal. I'm not saying it's a bad gearbox but It's not a light switch either. I have a sensitive hand and I don't just cram the lever from gear to gear. I tend to feel what the parts are doing and adjust my hand pressure accordingly.

I used to have a Lamborghini that used Porsche synchromesh. There was no linkage; the shift lever went directly into the gearbox. The throws were short and very tight but a consequence of that was that the shift effort was ungodly high. It was easily double the effort of the shortest-shift linkage available for a 915. Would it have been better with longer throws and a lighter feel? Maybe.

If yours bothers you enough, get it rebuilt by someone that knows what they are doing. If you take care of it, it will last the entire length of time you own your car.

JR

[seafood10]

I have an 84 and my tranny blows. Why upgrade the power plant only to have it compromised by the transmission, and I did have it 'rebuilt' a few years back. It seems to grind going into 2nd more when it's cold than warmer, should I find a 950?

[javadog]

Originally Posted by seafood10

I have an 84 and my tranny blows. Why upgrade the power plant only to have it compromised by the transmission, and I did have it 'rebuilt' a few years back. It seems to grind going into 2nd more when it's cold than warmer, should I find a 950?

No, I'd suggest you find a better shop to work on your car.

JR

[seafood10]

You are probably right. I put rebuilt in quotes because I don't think the shop that did it last time really knew what they were doing and they ended up going out of business.

[crustychief]

I am lucky I guess, my car shifts good, downshifts good ( except to first, have to be under 25 ). My car was always tended to in a timely / preemptive manner. My VW shifted horrible when I got it, negligent maintenance played a huge part in that. You have to remember that the USA , Japan and the rest of the world did not have a four foot stick going to their transmissions, sometimes their gearshift lever ended in your hand and the other side of that lever was on the actual gear you are changing

[84toy]

Although I don't think that the 915 is the best shifting tranny around, I do think it works fine when "properly" rebuilt. I notice a lot of people throw in new syncros and call it rebuilt. That just won't cut it most of the time for first and second. The shfit sleeve needs to be replaced too. Many times the teeth look fine on the sleeve but internally the shape has worn too much to work properly. It's one of those things that you can't look at and tell that it's worn without comparing it to a new one.

I rebuilt mine and spared no expense. I added a performance shifter and I have to say it shifts better than my 08 Subaru. No slop, no balky shifts. Proper break in is critical to a good shifting 915. If you skip it, it takes a LONG time to start shifting smooth and easy. I can downshift into first at any speed I want without issue. It's all about new parts and break in but that's just my opinion.....

[Moses]

I have an '83 with a 915 as well. I used to hate it.

Fresh syncros, ball cup, properly adjusted then added a WEVO shifter. I LOVE my 915.

[N11Porsche]

I had the 915 transmission rebuilt and from that point on, it shifted very smoothly. Downshifts, including the rolling downshift into 1st, were smooth and easy.

I had a 1979 911SC and when you buy a 25+ year old P-Car that has been driven hard for most of it's life, you can't expect it to shift like a newer manual tranmission. Most vehicles have the shfter either bolted onto the side of the tranny or going directly into the top of the tranny. Porsche has long linkage going to the rear of the vehicle. Not the ideal situation for speed-shifts.

[Grady Clay]

89911,

Your ’89 has a G50 (type 950 transmission) with Borg-Warner syncro system.

Stephan,

The 915 was basically a larger and stronger type 911 with the gear locations rearranged to not have 1st gear cantilevered off the ends of the shafts loke the 901. It really was just a ‘natural progression’ from the VW ‘crash box’ to 519, 644, 741 and 901 with a few race transmissions thrown in to test ideas.

All,

Porsche transmissions (901, 911, 914 and 915 particularly) are very easy to ‘rebuild’ – almost to a fault. Any but the most klutz mechanic can take one apart and generally get all the pieces back together. Therein lies the problem.

Many (most?) transmission ‘rebuilds’ need a skilled pair of eyes to recognize what they are looking at. There are the issues as to what to replace and what is reusable. There are all the ‘upgrades’, up-dates and back-dates that need to be considered. Most of the special ‘P-tools’ can be locally fabricated but you need to know what to build. The most difficult part is recognizing that one seemingly perfect part needs to be replaced while another that appears ‘beat up’ will last for another 250K mi. There are issues with the quality of replacement parts. Even putting a 915 back together exactly the way it came apart has its pitfalls. Another Pelican here has his virgin ’82 915 apart. It had the 1-2 sliding sleeve in backwards from the Factory (it must have been assembled after ‘beer-thirty’).

There is no substitute for experience, knowledge, skill and patience when ‘rebuilding’ a 915. That is where this Forum is so useful.

Best,
Grady

BTW, The G50 is for Getrag (9)50 and the back then engine M64 was for Motor (9)64. Just Porsche’s ‘nomenclature committee’ at work.
G.

[jtkkz]

Install WEVO and your 915 will shift very precise and smooth

[silverc4s]

Originally Posted by Moses

I have an '83 with a 915 as well. I used to hate it.

Fresh syncros, ball cup, properly adjusted then added a WEVO shifter. I LOVE my 915.

Same here, I used to cuss mine on every drive. Then I replaced the front bushing, ball cup, added a WEVO coupler and a J West Engineering shifter. NOW I like to get in and drive just for the joy of shifting. This is a 73 vintage 915 rebuilt once in about 1995, and being constantly torqued by me & a 3.2 engine...

[MOMO3.2]

I LOVE this thread!

Mike
87 G50 Carrera