915 gearbox after refresh, thoughts, etc.
 

I've been driving my '84 Targa almost daily since I got it back a week ago Monday from a refresh job on the gearbox. From the repair order: Replace 1st and 2nd gear teeth and shift sleeve, replace all synchros, replace clutch disc, pressure plate, and throwout bearing. Just some anecdotal thoughts on my car and experience, since it seems this comes up a lot here.

I've had a number of G50 cars, and a 930 (late 90's) with a 915, but it felt much different than the one in my Targa. Without any recent point of reference I thought my car shifted okay, maybe even better than I expected when I got it, relative to the reputation 915's seem to have. It needed slow and deliberate changes, and didn't like to downshift into first gear without being at idle and double-clutched. 2nd gear always felt vague, like the lever never fully pressed it into gear, but it was. I installed a Wevo shift coupler, which made it feel a bit more precise, and figured that's just the way they were. I got the car with an original 43k on it, and what appeared to be the original clutch. After a couple of thousand miles I'd get an occasional grind and decided to have a great air-cooled tech drive it for me. He immediately said it needed synchros, which led to the above list of work.

After nearly two weeks of driving the car, I'm thrilled with the difference it made. I wouldn't say it feels like a "modern" gearbox, and it still has the long throws and moderate effort, but when you shift into a gear it actually feels like it's fully sliding in, and no issues downshifting into low gears or need to double-clutch. It's much more precise and can be shifted about as quickly as a modern gearbox.

I guess the point is that shift couplers, sport shifters, and new bushings aren't a substitute for making the gearbox right and even cars with low mileage, like mine, can have issues. The cost was very reasonable and I'm really happy with the way the car shifts now.

Does anyone have any best-practices for a refreshed 915 to ensure that it shifts well for a long time?

shift gently and precisely. double clutch when possible.
don't let anyone else behind the wheel.

If you wouldn't mind; can you tell me what that rebuild cost you in this day and age?

Thanks.

Yes...even on a rebuilt box I double clutched simply to lengthen its life span.

You could swap out the oil after a while as there may be a few bedding in bits of metal and contaminants floating around.

Great post, very helpful to those of us on the fence. Did you use a local shop, or send it to one of the specialized rebuilders?

I would definitely replace the transmission fluid more often. 30,000 miles is essentially forever in most 911s Fresh fluid seems to improve the ability of the synchros to do their job.

Arguments on what brand to use go here:

i use Motul 75/90 synthetic gear oil. :)
a noticeable difference for me.
YMMV.

I had a lot of other stuff done but I think the gearbox was roughly $5k with clutch. My gears and bearings were fine however

Local-ish air-cooled Porsche specialist an hour from Houston.

IMHO, certainly a worthwhile investment that makes a big difference in driving pleasure. Bought my SC with 38K on the clock and noted during the test drive that it had a bad 2nd synchro and needed a clutch. Replaced the clutch and then, shortly thereafter, 3rd synchro became an issue.
So, after the 2nd driving season it was engine drop and trans rebuild time. Sent it west to JW rather than use local talent and it was not stupid expensive. Synchros, sliders... Still shifts great after several years and was money very well spent. No more grinding, double clutching out of necessity.
And I am pretty much the only one who drives it. Couple of buddies now and then who also have 915's and know what they are doing with the trans and the rear mass snap oversteer. Not that I don't get requests.
Glad that you are happy with the outcome.

I drive my 915 with 59k like grandma Moses....lol

Had no idea she had a 911.....the stuff you learn here is amazing!

I agree, but on the other hand this is against the very nature of what a sports car is supposed to be and do. Difficult to combine swift 0-60 accelerations with waisting seconds in shifting...:(

Just the way it is. Our old cars will never shift like a mustang GT or a Honda Civic SI. Our vintage 911 cars are endurance cars never intended to be quarter mile cars.

I have 250,000 miles on my stock, never been apart transmission. Shifts great. My wife asks why modern cars don't shift this well. Great advice above:

shift gently and precisely - no speed shifting.
double clutch when possible.
don't let anyone else behind the wheel
Change the fluid often.

Yep, similar situation for me. 185k miles on a mag-cased 1976 915 and it has never been apart. And...it has thousands of track miles on it (I tracked the car for 17 years). No shifting issues at all. I can even shift into first while coasting up to a stoplight, etc. But...I do not abuse it at all. Very deliberate and gentle shifts, etc.

This thread may be my undoing. Making plans to start down this path...

Mine has 207k miles and was rebuilt in the late 90s at 180k because it couldn't shift into first. I bought it at 205k, never ground the gears and double clutch when possible, but it still doesn't want to shift into first.

History: the man I bought it from had owned it from '79 to 2019 and was only selling it because he and his wife (in their late 90s) could no longer drive it. It was taken care of, but I get the feeling the clutch may be ready to be replaced.

I'm going to try re-aligning the mechanism and replacing bushings first, but I too fear a transmission rebuild is in my future. 2-3, 3-4, 4-5, 5-4, and 4-3 are always perfect, but 1-2 and 3-2 are unpredictable.

Wow, 250k miles, that’s amazing - take that G50!

I’ve noticed that most of the higher mileage (with no rebuild) 915’s seem to be mag cased with the 8:31 R&P. Could the slightly lower h.p. & torque (versus SC & Carreras) of the mid 70’s models contribute to their longevity?