915 gearbox rant

[Synchromesh]

Question here: am I the only one that hates the 915 gearbox with a passion? I have one in my '84 Carrera. Now before you say "oh, you just didn't set it up right", let me list the things done: Jwest shift tower, Wevo short shift kit, Wevo coupling, new OEM synchros on 1st and 2nd, fresh Kendall oil, relatively fresh shifter bushings, recent coupling adjustment. So I went the whole 9 yards. Shifts way better than I got but still far from good.

Now, I maybe spoiled by the modern gearboxes since I've owned nothing but manuals since 1998 including multiple NA Miatas, Integra GS-R, WRX and even a '72 Beetle. The latter is what got me into Porsches. The 4-speed box on the Beetle is a lot easier to live with. It doesn't require rev matching and only minor issue has been a bit of a grind on the first on a standstill but I can live with that. I won't mention others because the Miata and Integra boxes are in a whole different league compared to the 915. They're not even the same sport really. The only one that was just as crappy was the 901 in the '75 914 I owned for a few months a few years back.

Enter 915. That thing just seems to get into 2nd gear whenever it feels like it. Rev matching or not, even with a new synchro I can't get it in some of the time when not upshifting sequentially. 3-4-5 gears are somewhat acceptable providing some rev matching is happening but the first two are absolute horror. Even the first gear won't always engage despite a new synchro prompting my getting the horn from behind more than once.

I haven't driven a G50 car but I imagine it's a lot better. Have driven a 993TT and obviously that gearbox was working fine although the clutch was admittedly rather weird. Still it wasn't too bad and I learned to drive it smoothly quickly enough.

So I'm curious, any other owners who dislike 915 or is it just me?

[petrolblue83911]

Sounds like your transmission is off some how. Have you driven other 915’s for comparison?

I’ve never experienced the 2 nd gear issue you are describing, Ive owned 2 sc’s and 2 Carreras.The most typical nuance is that shifting into 1st or reverse sometimes requires slow and deliberate action, aside from that , the 915 really isn’t that hard to use.

[Sabai]

I think it's going to depend on your usage. I enjoyed my 915 on the weekends but hated it Monday thru Friday. In my opinion, the 915 adds something special when you are at full tilt but is otherwise quirky. That being said I sold my 78' and kept my 87'. I do, however, miss the 915.

[Gordo2]

Originally Posted by Synchromesh

...new OEM synchros on 1st and 2nd...

I have a similar setup for my 915 (all the Wevo stuff, Kendal, DIY rebuilt w/new synchro's...) and mine shifts well through all the gears - as good as a 915 can be.

Granted, it doesn't shift like a modern trans - but I can grab 2nd under hard acceleration without hesitation, and I can drop it down into 1st at 15-20 mph without worry of grinding or hesitation.

Who did your trans / synchro replacement - was the 1-2 shift sleeve replaced along with the synchro hubs & rings (i.e. all 1-2 synchro components or partial)?

Gordo

[DanielDudley]

There is a legend that if the lay shaft isn't absolutely straight, the car won't shift correctly. And then there is clutch drag and pilot bearing drag that can cause havoc. And Swepco oil makes the shift to second a real drag in colder climates. IMO, it makes the shift to second a really deliberate process on any car I have run it in.

I don't know if you have a problem or not, but I'd look at changing the fluid first. You can always tell if there is Swepco in the box.

The sweetest 915s are very sweet, and talk to your fingertips. Some are only going to respond to a rebuild by a real persnickety expert, or so I'm told. Having driven some over the years, for every doggy one there is another that is a gem, and a bunch of average ones. But I never drove even a balky one wouldn't go into gear if you drive them the way they want to be driven.

[fiminod]

Exactly..."talk to your finger tips" Its technology that's 35 years old, regardless of your "upgrades" its not going to feel like anything from 1998.

[john walker's workshop]

A short shift, a partial rebuild and a linkage adjustment that's out of wack. What could go wrong?

[jjeffries]

I'm with Gordo...bet it needs the 1-2 slider. Wish you could drive mine or another nice 915 for reference.....mine was horrible until a proper, competent shop repaired it, which included synchros AND said slider. That said, it'll never be like a Miata, Civic, S2000 etc. and the comparison in kinda meaningless. John

[jac1976]

Originally Posted by john walker's workshop

A short shift, a partial rebuild and a linkage adjustment that's out of wack. What could go wrong?

He he.

[pgeorgeson]

Your 915 is not working properly. The symptoms you describe do not describe how a properly working 915 gearbox works. Try a rebuild by a reputable shop and it will not behave like that.

[Rodsrsr]

If you recently rebuilt your 915 it will be quite tight for some time. It takes a while especially if you only drive it on the weekends but once it loosens up it's a nice gearbox. Shifting into 2nd will be significantly improved but never perfect. Its just one of the characteristics of that gearbox and part of what makes driving an early 911 unique. BTW, the heat and A/C suck too. 8-)

[Matt Monson]

Originally Posted by Rodsrsr

If you recently rebuilt your 915 it will be quite tight for some time. It takes a while especially if you only drive it on the weekends but once it loosens up it's a nice gearbox. Shifting into 2nd will be significantly improved but never perfect. Its just one of the characteristics of that gearbox and part of what makes driving an early 911 unique. BTW, the heat and A/C suck too. 8-)

No, That's some BS that got pushed off on people because for a long time the parts being sold were not to correct spec. It doesn't take very long at all for a fresh 915 to break in. The number one key here is that the replacement dog teeth must have a 9 degree backcut on them. German OEM dog teeth don't have it. R&S replacement teeth didn't have it until about 2 years ago. Literally, for 2 decades, 915 gearboxes have been getting rebuilt with out of spec parts.

[Evan Fullerton]

There may be some issues with your 915 but you are not wrong that it is very old technology and even when "perfect" it isn't a Miata or a BMW 3 series or any "good" shifting trans.

VW bugs and 901s use the same syncro technology and basic architecture but they shift better because the gears are smaller and lighter, use smaller clutch disks and the syncros don't have to work as hard. Close ratio 915s shift much better as well as using a non sprung "puck" clutch disk as this decreased the inertia that the input shaft has. Not something you really want in a pure street car though. I found with my 915 with stock gearing I could downshift faster that then syncro if I double clutched the downshifts but that takes a lot of time to master and is really only for on the limit driving you can't or at least shouldn't do on the street. Learning to work the gearbox is part of the 911 experience........ or you buy a G50 car and put in a light weight clutch and flywheel and it shifts like an '80s BMW......... I am in the process of doing this, it's a big project.

[john walker's workshop]

Bugs don't have 901/915 style syncros.

[Trackrash]

Originally Posted by Evan Fullerton

VW bugs and 901s use the same syncro technology and basic architecture but they shift better because the gears are smaller and lighter,

Not true. The 901s and 915s use the ZF style synchros. The VW Bugs use the Borg warner brass rings.

I have a warmed up '67 Bug, in which I have a built (by me) heavy duty custom trans. I also have a modded, by me, 915 in my 911. The only thing the VW box can do that the 915 can't is to speed shift from first to second gear. In normal driving not a world of difference.

As Matt says, and others have mentioned, there are subtle differences in the parts of these 915s that can make a huge difference in shifting.

You should find a 911 with a good shifting 915 to compare. It may be that your rebuild needs to be rebuilt.

[Synchromesh]

Originally Posted by Gordo2

Who did your trans / synchro replacement - was the 1-2 shift sleeve replaced along with the synchro hubs & rings (i.e. all 1-2 synchro components or partial)?

Gordo

A friend of mine who works on Porsches. He has a '72 with a first year 915. I helped him rebuild it (he blew 3rd gear on it years ago) and we put in some updates and the Wevo kit. It shifted pretty well even with a factory shifter from what I recall.

My car has a rebuilt tranny to begin with, it was replaced about 10-12 years ago by a local shop. Found it in records. I only put in the OEM synchros because it was a sub job of rebuilding the engine. We did check the other parts and they looked good so I didn't put anything else in aside from the Wevo kit.

Originally Posted by Trackrash

I have a warmed up '67 Bug, in which I have a built (by me) heavy duty custom trans. I also have a modded, by me, 915 in my 911. The only thing the VW box can do that the 915 can't is to speed shift from first to second gear. In normal driving not a world of difference.

Yes it can! And yes, there is a world of difference, especially if driving in the city. That speed shifting is pretty important to me as all my other cars can do it with ease but on the 911 it's a major chore. I don't understand what Porsche was thinking when they designed this godawful second gear.

[pmax]

Originally Posted by Synchromesh

Yes it can! And yes, there is a world of difference, especially if driving in the city. That speed shifting is pretty important to me as all my other cars can do it with ease but on the 911 it's a major chore. I don't understand what Porsche was thinking when they designed this godawful second gear.

The 915 does require a short pause between shifts. Mine downshifted fine until 1st sprung one too many teeth and spilt its guts half mile away from home.

But, yeah, I hear you, for "spirited" street driving in stop and go commute traffic, the 915 just doesn't cut it, unless you like holding up traffic at the lights !

[Evan Fullerton]

Originally Posted by Trackrash

Not true. The 901s and 915s use the ZF style synchros. The VW Bugs use the Borg warner brass rings.

You should find a 911 with a good shifting 915 to compare. It may be that your rebuild needs to be rebuilt.

My mistake on the VW box but my 915 shifted as well as any of them do.
https://www.youtube.com/watch?v=Ns6nEPXHrFo

Close ratios and a really light clutch disk gets you to here
https://www.youtube.com/watch?v=xAYVTTIgBto

But you need a G50, close ratios, and a multi disk small diameter clutch if you want truly superb fast shifting. https://www.youtube.com/watch?v=zyM-egecTlw

[RWebb]

the OP may not be a "Porsche Person"

get the box checked out - if it's good then wuss out and buy a G50 car

[ClickClickBoom]

Originally Posted by john walker's workshop

A short shift, a partial rebuild and a linkage adjustment that's out of wack. What could go wrong?

I'm with John on this one. Apply basic logic, Do you really think Porsche would sell a luxury sports car with a transmission like yours seems to be working? There are plenty of shops that profess to be aircooled pros, but from the discussions on this board alone, a good percentage aren't exactly what they profess. These transmissions are never going to be a japanese slush box, and for that I am glad.
That being said, you cant just throw parts at them and think its gonna be more *****en, by some percentage with every part added.
My car is also a 1984 Carerra, and the trans shifts with very Teutonic precision, no grinding in any gear unless I do something stupid like not release the clutch all the way. I have a extended shifter, short shift kit, Stomski shift coupler, new bushings, Rebel Racing trans and engine mounts. I couldn't think of anything I would change, except for a Wevo shifter setup.
I will also say with a rigidized shift linkage, a couple mm in coupler position or one spline left or right equals a huge change in shifting to include grinding and working poorly.