rebuilt 915 stiff shifting - Help!!!

Gav P · 10-27-2006, 01:05 AM

Hi all....

My 915 box was rebuilt about 1000 miles ago (mainly town driving), and whilst it never graunches or shows the old synchro problems, it has an intermittent stiff shift from 1st to 2nd and 3rd to 2nd.

Sometimes it works like a dream, others it requires excessive force on the lever, occasionally resulting in a completely missed shift during more spirited driving. The problem is much more common at higher revs. Double-declutching doesn't help... suggesting to me that its nothing to do with the synchros.

Very frustrating after a £1500 (ie a lot of $$$$!) rebuild by so-called experts... starting to wish I'd tackled it myself...

Other new parts include all shifting bushes, coupler bushes, clutch and engine mounts...

Is it just a case of needing a much longer running-in period?

Thoughts, experiences greatly appreciated guys!

jester911 · jester911's Garage

Gav, do a search on this. One of our members named John Walker who is a porsche mechanic does these rebuilds all the time.

He has given some recommendations on break in and such.

dickster · 10-27-2006, 02:57 AM

Gav,

Sorry to hear that.

As a matter of interest who did it? I need to get mine done one day...

wcc · 10-27-2006, 02:59 AM

Have you tried adjusting your coupler?

Gav P · 10-27-2006, 03:31 AM

Cheers for the suggestions guys.. quite often perform searches here, and there always seems to be some amazing info on tap if you have a bit of time to sift through the archives! Still working through the John Walker material.... what a fountain of knowledge.

Its looking like rebuilt boxes occasionally need quite a bit of breaking in, which surprises me because presumably they didnt need this when new... or there'd have been lots of frustrated owners of new 911s in 1973 surely?!

Maybe I'm expecting too much... all I want is a nice light(ish) shift into all gears, doesn;t have to be lightning fast. My 912 901 box was much easier to use than this one.

Anyway, re coupler - I'm pretty sure this is good, as the shifting problem into 2nd is only intermittent; sometimes all 5 gears are as light as a feather, and even when stiff they are always to be found where you expect. However, I may yet tinker with the coupler again since I've just replaced my engine/tranny mounts (in a bid to "cure" poor shifting"!!)

Rich - will PM you the shop name.. not posting it here as I have a few words to say about some of their workmanship (not just gearbox related).

Ho hum!

Gordo2 · Gordo2's Garage

Mine shifts as you describe... It has 190,00 miles on it; I hope it breaks in soon

Seriously though, continue the feedback on what you find and if it changes as you get more miles on it. Hate to think when I rebuild mine that it won't shift much better.

Best of Luck,

Gordo

Gav P · 06:23 AM

Quote:

Originally posted by Gordo2
[B]Mine shifts as you describe... It has 190,00 miles on it; I hope it breaks in soon

Maybe I'll give it 'till 250,000 then to be on the safe side...

Half of me wants to tear it to bits not let it go 'till it works as I feel its supposed to.... but thats tricky when I dont have a firm diagnosis. The other half says "ignore it and drive it..."

dickster · 10-27-2006, 06:39 AM

Gav,

Mine shifts better/worse depending on temps, etc.

I know mines had it though because the synchros have most definitely seen better days in 1st and 2nd. 1st is particularly bad.

The fact that yours sometimes shifts perfectly seems to indicate that the rebuild is ok? The 915 is well known for its vagueness!

GRAYBEARD · 10-27-2006, 07:33 AM

Gav,
I had my 915 rebuilt about 6000 miles ago. When I first had it rebuilt, I wasn't sure I liked it at all. I was told that it would get better as time went on. Well now it's 6000 miles later and I will say it has shown a remarkable improvement. Although it is not as light shifting as it was before(it was just worn enough to be almost sloppy, but, very easy to shift) it is now way more positive in engagement and it is smooth enough that I actually like it now. It didn't start showing real improvement until about 3500 miles after rebuild. I had a lot of faith in my wrench before the rebuild, and now I have even more mainly because he predicted everything that I experienced to within 500 miles of actual event. Give it time and hopefully you will have as good an experience as I have had.

hammer down,

Steve 82SC · 10-27-2006, 07:53 AM

I've had the same experiences as Graybeard and have about 5000 miles since the rebuild. It gradually loosened up, but I still occasionally have to finesse it into gear when downshifting. I've also noticed that it upshifts very smoothly if I wind it out a little....can be somewhat balky if I granny-shift it. A friend of mine advised me that since it's now broken in, a shift coupler/bushing adjustment should smooth it out.
Steve

john walker's workshop · 10-27-2006, 08:01 AM

"reluctant" shifting in one or more gears after a rebuild is pretty normal. i'm sure the factory broke them in before shipping the cars out. if you baby the problem, it will take longer to break in. say 2nd was stiff. get the speed up to 15mph, push in the clutch and work the shifter back and forth between 1st and 2nd or 2nd and neutral many many times. then up to 30 mph and do the same between 3rd and 2nd. back and forth, when it resists, keep pulling firmly so it pops in. sometimes it takes 10 minutes, sometimes a couple of days.

Gav P · 10-27-2006, 09:47 AM

Thanks all, I'm building up a pretty good idea of where I stand now...

Quote:

Originally posted by john walker's workshop
say 2nd was stiff. get the speed up to 15mph, push in the clutch and work the shifter back and forth between 1st and 2nd or 2nd and neutral many many times. then up to 30 mph and do the same between 3rd and 2nd. back and forth, when it resists, keep pulling firmly so it pops in. sometimes it takes 10 minutes, sometimes a couple of days.

Now this sounds worth a try... am about to use the car tonight so will give it a go from then, and start making it a habit. Thanks for this

Quote:

[i]get the speed up to 15mph.... [/B]

...plently of opportunity to drive around at this sort of speed in London! (or less). Could be ideal break-in conditions!

911pcars · 10-27-2006, 11:50 AM

Using Swepco? If not, try some before more drastic measures.

Sherwood

Motorhead-45 · 05:39 PM

Quote:

Originally posted by 911pcars
Using Swepco? If not, try some before more drastic measures.

Sherwood

I had a similar experience with the feel of my car after rebuilding the transmission. I wasn't happy after about 500 miles as things still felt really tight and first gear was still somewhat baulky. One of the recommendations to aid with break-in was "get rid of the Swepco for now". It took another 2000 miles or so of break-in for my car to feel right after the gear oil swap to an off-the-shelf auto parts store gear lube. I still haven't gone back to Swepco and it shifts fine (well maybe not fine but pretty good for a 915) now. Anyone care to guess which well known Porsche mechanic made the dump the Swepco recommendation?

FenderGuy · 10-27-2006, 04:36 PM

Funny my tranny was a rebuilt unit and had the same problems as described above then I had Don Jackson swap out the thin gear oil for the SWEPCO....guess who won?????

Gav P · 10-30-2006, 01:00 AM

Quote:

Originally posted by Motorhead-45
One of the recommendations to aid with break-in was "get rid of the Swepco for now".

Mine came from the rebuild shop with Swepco. Since its so commonly recommended I'm reluctuant to swap it out, but maybe its not the best for a tight box fresh from rebuild.... maybe I'll try this if the break-in doesnt show results anytime soon...

bede · 10-30-2006, 01:13 AM

I went through my 915 box for an inspection replacing all the seals & gaskets,the syncros& bearings were good.When i drove it i had the same problem with 3rd gear, finding it hard to get into 3rd either way.We dont have Swepco in Australia or i cant find it,so i replaced the gear oil with Mobil1 full synthetic gear oil & it became a new box 3rd is easy to get now