915 gearbox stuck in reverse

[IJD]

Hope someone can help, my 915 gearbox has stuck in reverse on its first spring run out.
Car was fully rebuilt last year, and has covered 700 faultless miles since, gearbox however was not touched internally. Box was professionally rebuilt about 5k miles since and has run perfectly until now.

Fortunately only got 400m before problem occurred so after reversing back home (!!) I released it after removing reverse light switch and pin, but then whilst resetting the gear selector alignment it happened again. I'm not sure the pin is actually triggering the switch as lights don't come on, but think that's a side issue.

The gear selector mechanism bushes all feel tight and was setting up the alignment as before (as per Pelican/Haynes etc) when same thing happened again.

I'll replace the bushes in the connector, gearstick and intermediate support as precaution and try again, but is there anything else I should be checking whilst waiting parts?

[911hillclimber]

Possibly a quick call to Mike Bainbridge at MB Engineering in the Lake District?

[hot66]

where in North Yorkshire are you ?

As hillclimber says .. Mike Bainbridge is the gearbox expert so a call to him would certainly help

[911hillclimber]

might help:

http://www.google.co.uk/url?sa=t&rct=j& ... 1Sf7KERwZA

[IJD]

Thanks for the tips, I'll give MB a ring and see what suggestions he may have. I'm near to Settle so Kendal's only 30mins away. Like to get the MFI fuelling set up on a rolling road also, he may be able to help there too.

Released again using the reverse switch pin trick and ordered a set of bushes and a new coupling to eliminate the most likely cause. As it happens the reverse switch isn't working so I'll swap that out too.

Did notice the two cone screws had a slight lip on them, and the coupler bushes allowed a couple of mm fore-aft. All could have allowed a bit too much slack in both planes, waiting parts now.

Had car almost 30 years, raced it, rebuilt it twice, still learning about it.

[911hillclimber]

Snap, 32 years with mine, raced, crashed, rebuilt twice and still have a few head-scratching moments with it!

Your issue is well documented on Google! You are not alone.

[IJD]

Bit of an update on this. Spoke to the ever helpful Mike at MB and the box is now out of the car and on its way to him to check the internal reverse selection is set up correctly.
However whilst inspecting the rest of the mechanism and replacing bushes and coupling, I noticed the actuating rod from gearstick to coupling had a break in it. The fracture appeared to propagate from where the solid spigot joined the tubular cranked rod by a plug weld, the spigot joins to the base of the gearstick. The crack was only visible when clean and under load, very hard to see otherwise. Under load however the movement was very significant.
I've never heard of this before so may be worth checking whilst you're changing bushes in the pursuit of a clean gearshift on 915boxes.
It could be welded up, but suspect it'll recur and new seems to be available from Porsche so I'll go that way.
Tried to post a pic, but afraid so far its failed.

[IJD]

Pic of failed gear selector rod, was not visible unless load applied to it to open up.