Are all 5-speed 915’s created the same?

[fueledbymetal]

I’m looking to pick up an air-cooled targa and test drove the first candidate this weekend. It was a 77 with a 915 and I was surprised at how awkward and sluggish it was. I realize they’re not known for smoothness, but my ’79 Jeep CJ-7 felt better. The car has 19x,xxx miles and the owner said he just replaced one of the bushings, so is it possible with wear it had degraded to a state that would cause this poor feel? I know there were small changes made throughout the years & models, but I wouldn’t think that would be the reason.

[pampadori]

i suspect that car was in need of the shift coupler bushings being replaced. Its extremely common. by that many miles, every 911 will need to have them replaced at least once.

It makes the gear changes feel very sloppy like an old school bus.

[E Sully]

There are a few linkage parts and bushings that probably need replacement, and the shift coupler also. It has never been known as a great shifting box, and with 19x,xxx miles, if the transmission has never been gone through, it should be checked and refreshed internally. There are aftermarket shift couplers that can help improve shifting.

[911pcars]

Awkward and sluggish? Can you be more specific? Those terms aren't usually attached to gearbox issues.

Worn shift bushings only affect shifting gear to gear. Once in gear, the vehicle responds to whatever power the engine can deliver to the rear wheels.

Sherwood

[spuggy]

The '77 has a mag 915; later ones are alu and got progressively stronger/heavier - but basically the same.

Original box in my car, with 230,000 miles, looked to have been gone through at least 3 times before once taken apart. And it was done. Spun bearings, blued gearsets, non-existent synchros/dog teeth etc.

A rebuilt 915 is a beautiful thing. Lovely to drive. They have an old-school charm but shift nicely. Including into 1st while moving above 10MPH. Although, once you know how much synchos cost to replace, you'll work hard to rev match to avoid wear on those...

A tired 915 does things like won't select 1st when stationary (unless you rock the box through 2nd first, which often helps - as can briefly lifting the clutch slightly and trying again with a different orientation), much less when moving (yeh, that's what dog teeth are for), may baulk at shifting into 2nd from 1st (holding more RPM helped mine here), a 15 count with the clutch down isn't long enough to stop the grinding when selecting reverse, and the shifter feels like a stick in a bucket of rocks...

You can learn to drive around these things and they become second-nature. Then, when the box actually works like it should, it's kind of an eye-opener...

The service life of a 915 between overhauls is generally reckoned to be about 100K - and bill for overhauls has been steadily rising for years, so there's probably a lot out there with some "deferred maintenance".

If you're lucky, it could be just the shift coupler and a few bushings. But with 190K, my money would be on it being time for more than that.

[911pcars]

.....you'll work hard to rev match to avoid wear on those...

Rev matching won't save wear and tear on synchros. All that does is reduce wear on the clutch disk facing and allow smoother torque transition from gearbox to road.

This is rev-matching, not double clutching. This also demonstrates why second gear synchros are usually the first to go:
http://www.youtube.com/watch?v=-cjvsI9i3vU


Not bad, but there's more to learn. In order to synch gear rotation to reduce synchro wear, the following demonstrates proper double-clutching - the ONLY way to extend synchro life.
Note: Those of you who have issues with a woman teaching you how to downshift, go find a better looking video dude.
https://www.youtube.com/watch?v=NSup4MLX2GU

Sherwood

[Geronimo]

The 915 might be one of the worst transmissions ever put into production... I took my Porsche out for its first little drive tonight, that darn 915 just ruins the car sadly.

I would guess mine is due for a rebuild, though the last rebuild was in 2012, and the car has 110K but i'm sure it saw some DE's and autocross. Even though you would have a hard time changing my mind on the slug of garbage called a 915

[Oneredspyder]

I have an 86 with a 915 box with 86,000 mi. I have nothing to complain about. I do not know why they get so much grief. Think about how many races were won with that box in the years of production. It was Porsche's heyday, and the 915 was there. Mine can not quick shift from first to second but It really doesn't bother me much. In fact the gentler I am, the easier it shifts. Putting red line trans oil in the box made a difference. Do you know who makes the smoothest transmission? Alfa Romeo's from the early 70s, shift like silk, a pleasure to drive. A friend of mine adapted one into a vintage Ferrari, it was a better box!

[clutch-monkey]

Originally Posted by Oneredspyder

I have an 86 with a 915 box with 86,000 mi. I have nothing to complain about. I do not know why they get so much grief. Think about how many races were won with that box in the years of production. It was Porsche's heyday, and the 915 was there. Mine can not quick shift from first to second but It really doesn't bother me much. In fact the gentler I am, the easier it shifts. Putting red line trans oil in the box made a difference. Do you know who makes the smoothest transmission? Alfa Romeo's from the early 70s, shift like silk, a pleasure to drive. A friend of mine adapted one into a vintage Ferrari, it was a better box!

They get grief because it is simply outdated tech even at the time and often the slow agricultural shift is at odds with the sports car nature.
As for smoothness mine is ok and is an extremely good example of a 915, so I’m not keen to change it for anything.
But there are better options

[Coastr]

Compared to something like an NA Miata box they do shift like a tractor.

Most people just convince themselves it’s part of the charm and when you do learn to drive it, it’s second nature and doesn’t spoil it. You just can’t abuse the box by slamming shifts.

The biggest issue is the lack of torque rating which makes forced induction a tricky exercise.

[911pcars]

901 and 915 gearboxes in good condition are fine as long as you operate them properly. If yours shifts badly and/or makes noise, thank the previous owner for not adhering to the first sentence.

[proporsche]

i tried to tell clients all you need is 3 fingers to shift with 915 if not good, there is a problem with alignment or with synchros.
The op has asked if all transs. are the same, not they are no. Some have different ratio and some have limited slip and Euro models have oil cooler on the side.
like this one.............

[Bill Douglas]

Even a toyota will shift badly after 40 years of enthusiastic drives, racing wannabees, and few oil changes.

With fresh oil and syncros, they are OK. One corner I do I drop from third to first, even my Corolla wouldn't like that.

[gomezoneill]

I rebuilt the 915 in my 83sc and it shifts beautifully.

[ADDvanced]

I like my 915 though I think it's weird that it doesn't spring into the middle area, if that makes sense. I also get a grind when I downshfit to 2nd. I read that changing the fluid to swepco would help, it made it 2x worse.

[panzerfaust]

i would like to have a mag case 915 with electronic speedo for a rebuild.

[G450X]

A 42 year old sports car with 200k miles has a worn gearbox?

Rebuild the poor thing, treat it with respect, and it will give you another 42 years and 200k miles (I have heard of carefully used 915’s lasting a long time) of service.

How many 1977 vehicles of any type are still “above ground?” I’d be more worried about the mag engine case myself...

[jjeffries]

I had a 74 Beetle as a kid and my mum had a 79 Super Beetle Cab. My 82 SC's 915 feels similar to both...shared DNA. The car has 188k miles and someone had been in there before, replaced 1-2 synchros but not the slider...and 1-2, 2/1 and N/1 shifts were nasty. I've since had it refreshed, very reasonably, by Auto Associates in Canton CT, and added a Seine kit. I love how lightly it can be operated now.

[mnez]

Originally Posted by fueledbymetal

I’m looking to pick up an air-cooled targa and test drove the first candidate this weekend. It was a 77 with a 915 and I was surprised at how awkward and sluggish it was. I realize they’re not known for smoothness, but my ’79 Jeep CJ-7 felt better. The car has 19x,xxx miles and the owner said he just replaced one of the bushings, so is it possible with wear it had degraded to a state that would cause this poor feel? I know there were small changes made throughout the years & models, but I wouldn’t think that would be the reason.

Basically, yes. If that was the first 915 you have driven, then they definitely feel awkward, and you could say sluggish (as in they don't shift so quickly) compared to almost any other car you have driven. My '77 Fiat shifts nicer. But as others have said, refreshing the linkage makes it as good as it can be, and after a while you get used to it.

[rkeele]

Originally Posted by panzerfaust

i would like to have a mag case 915 with electronic speedo for a rebuild.

that's what I run in my 3.8 race car they have a cast iron intermediate plate much stronger than the latter alum. ones, that and a billet side cover, shifting is fine