915 gearbox rant

[ClickClickBoom]

Side note, the mechanic setting up the box may have everything in spec but at opposite ends of the tolerances. I was a factory trained Robinson R-22 mechanic in the 90's. I did all my own blade tracking and balancing. Our customers would learn to fly our machines and buy a new Robbie after they got their certificate. They would bring their ships to our shop to have me balance and track their rotors. My secret to a smooth rotor was with a tilting head rotor system, I ran the head at the upper tolerance for tightness and the individual blades at the lower end of the tolerance.
My customers complained to the factory that their setup was really rough and mine was smooth. The factory actually sent their lead tech and design engineer to our shop to have me adjust their factory ship using my procedure and show them the process. They could have just used my procedure on their own, but they wanted see me do it. As advertized it worked and they adopted the procedure as far as I know.

[Jrboulder]

915s can be made to shift well but they're not a modern gearbox and never will be. I just consider it one of the fun quirks of the older porsches. I had a 996 that shifted like a modern car and it was unbearably boring.

[nb6179505]

Mines fine, part of the analog experience, wevo definitely helps to stay away from guessing and psj does wonders

Pause between shifts, this isn't a g50

Sent from my Pixel 2 using Tapatalk

[3rd_gear_Ted]

On the track, a long ratio 915 will cost you at least 3 seconds per lap.
That's my excuse.

[ramonesfreak]

When I first got mine I didn’t love it. Had a short shift kit but sloppy. I replaced the bushings and spent some time getting it perfectly adjusted at the coupler. Was impressed with results. Then a month ago I installed rennshift and I love it. Fell in love with the car all over again. It feels vintage but it’s acurate and satisfying now

My transmission was mostly rebuilt before I bought it which might contribute to my good results

[Dodge Man]

I am old school and heel & toe. Wevo coupler & factory short shift kit adjusted well. Rebel motor & trans mounts to keep things in place. Upgrades made a significant shifting improvement. I run an '86 915/72 these days. A 915 is not a G50 by any means but that is the skill building attraction.

IMHO. If you want it to shift like "butter" then the 100,000 mile wear parts may need matching replacement. Read some of Zimmermann's articles.

UPDATE: Just got my 915/72 (73F) really rebuilt. All dog teeth, all synchro rings, 1/2 slider, 3/4 slider, nuts & snap rings, and Rebel bearing plate. It was not cheap. As a biker once told me "good food ain't cheap and cheap food ain't good".

Some Bozo had "flipped the synchro rings" and ruined the 1/2 & 3/4 sliders. 915 wear parts "break in" to mate with each other. Replacing 1 or 2 parts will work but it will not make you happy with your 915.

[786]

Originally Posted by ClickClickBoom

These transmissions are never going to be a japanese slush box, and for that I am glad.

You must have never driven an S2000, NSX or ITR. Probably the best feeling manuals on the planet.

915 isn't that bad but definitely has a learning curve and can't be rushed.

[OsoMoore]

Originally Posted by 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.

Originally Posted by 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.

I think you need to hit up a cars-and-coffee and have another 915-owner drive yours, and you check out theirs. It sounds like something is wrong, and it might be hard or easy to fix.

With my 915, I can't hammer from 1st into 2nd without a 0.4 second pause. But I still prefer it to my stick shift Focus, where you can't always be sure you're in 1st because everything is so damn smooth.

[GH85Carrera]

My first two cars were VW bugs, a 1960 replaced with a brand new 1973 Bug. That was replaced with a brand new 1974 914 2.0. I drove the 914 as my only car for over 20 years. When I replaced the 914 with the 85 911 it felt like a super precision transmission after a 914.

I have rebuilt my 915 and replaced a few bearings in the differential that had some issues. It shifts great, as long as I take my time, and drive it like a 915 is supposed to be.

[Matt Monson]

Originally Posted by GH85Carrera

My first two cars were VW bugs, a 1960 replaced with a brand new 1973 Bug. That was replaced with a brand new 1974 914 2.0. I drove the 914 as my only car for over 20 years. When I replaced the 914 with the 85 911 it felt like a super precision transmission after a 914.

I have rebuilt my 915 and replaced a few bearings in the differential that had some issues. It shifts great, as long as I take my time, and drive it like a 915 is supposed to be.

That’s more the 914 shift linkage than the gearbox itself. The 901/911 gearboxes, mostly because of their thinner lighter gears, are arguably nicer to drive than a 915. I’ve owned both 914s and 911, and that 1-2 shift across the gate is so much more sloppy on a teener. I pick 4th more than I care to admit.

That 75 911S in my sig has a 911 in it and I freaking love it.

[Jon B]

Originally Posted by Trackrash

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

The synchromesh used in 901 and 915 transmissions was Porsche's own patented design.
OE synchro rings were always manufactured by Goetze for Porsche.

[SCadaddle]

An SC getting from 0-60 in 6.2 seconds is still pretty darn fast considering 4.8 of those seconds are trying to find 2nd gear....

[786]

lol true

[jac1976]

Originally Posted by SCadaddle

An SC getting from 0-60 in 6.2 seconds is still pretty darn fast considering 4.8 of those seconds are trying to find 2nd gear....

That’s pretty damn funny right there

[Arne2]

Best thing I did for the 915 in my '84 was to ditch the factory short shift and go back to original. Massive improvement.

[sc_rufctr]

I'd describe the 915 as an old German uncle who won't suffer fools.

Get everything right and it will do the job it was intended to do.
One problem, there are so many that have been passed around that things are not as they should be.

It may be worth taking the car to another mechanic for a proper assessment but I would bet the shift rod hasn't been adjusted properly.

[pmax]

Originally Posted by sc_rufctr

I'd describe the 915 as an old German uncle who won't suffer fools.

Yes, the uncle who has lost a few front teeth ...

My latest--and perhaps last--911 is an '85 with a 915. I first considered it as something I had "settled" for because the G50s were getting so expensive. But I've really gotten to like it. It is definitely an acquired skill to drive well, but then so is the whole 911 experience. Getting it right is a challenge, and a reward. An added plus is that the clutch and flywheel assembly are a lot lighter than in the G50 cars, so the engine revs up a lot quicker. Plus the trans itself is lighter, so the car feels more responsive than my G50 cars did.

[Synchromesh]

Talked to my friend/mechanic. He said he didn't see anything aside from synchros worth replacing when we took it apart. Considering he rebuilt quite a few including his own 915 in his '72, I'd say he has a good idea of what's up. Also, got to sit in the '72. It had excellent shifts. I may have to borrow his shifter which I believe maybe an original Porsche short shifter he bought in the 80s from a dealership.

Then I today I drove my dual carb'd Bug. That 4-speed with a Hurst short shifter worked just fine. No rev-matching, no fuss, just quick smooth shifts, pop into second any time.

I guess I need to drive someone's 915 pronto. And a G50 as well. Just for comparison.

[Matt Monson]

If he just did the synchros and left the sliders that could be your problem. Even when the tips of the teeth look fine, if the contact surface where the synchro clicks in is worn it wouldn’t be making enough friction to properly speed up or slow down the gear for engagement. It’s a $200+ part that unfortunately gets skipped all too often on a quickie refresh. And the 915’s reputation suffers as a result.