I couldn't get along with the 915 in my AutoX car at first, luckily I usually only shift once a run!

I would try to shift from 1st to 2nd and the transmission would simply not let me into 2nd gear. No grinding, it would simply not shift.

It really helped me to understand how the split ring synchro works (as opposed to a cone type). There is a difference in how they work, and the resulting feedback to the gear lever. Someone mentioned they shift better if you try less and that's a good way of putting it. I think in a worn transmission the blocker ring binds up and playing a little nicer with it helps things drop into place.

You need to apply pressure to the lever to allow the blocker ring to bring the next gear up to speed (synchronized with the shaft) but more isn't better, too much and it will bind and lock you out of gear.

It's pretty satisfying when you get it right.

Seine gate shift mod will help it spring to centre

When upshifting, engine revs normally drop. Thus, all that remains is for the speed of the next gear (e.g. 2nd gear) to naturally drop to the speed of it’s output gear to complete the upshift. No sweat and minimal effort by the synchro - that is unless one attempts to speed up the process in which case the synchro is there to help match rotational speeds. However, during downshifts, synchros are tasked to “mesh” gears with often vastly different rotational speeds. Repeat this for thousands of typical downshifts and the synchro ends up saying, “No mas”.

Actually there's no shared genetics. By the 70s VW had moved on to Borg-Warner synchros and is a totally different beast than a 915. A Beetle shifts better than a 915. I learned to drive on a 78 Bus Camper and that thing was easy as pie.

Matt, thanks for straightening me out on that...I wouldn't want to perpetuate any un-truths. May I ask a couple of questions?
In terms of Porsche gearbox history, do we know why Porsche went to Getrag for the 915 replacement instead of doing it themselves? And is the Borg Warner synchro system bigger than the Porsche system...meaning, does it take up more space and require a bigger transmission/transaxle? Thanks in advance, John

Alfa Romeo Spyders use the same synchros style as the 915

The reason that Porsche stuck with the 915 system as long as they did is because they had it patented and it was proprietary. Getrag manufactured the 915 gearboxes for them. That wasn't any sort of change and the relationship between the two companies goes back to the 50s.

The change was being willing to pay the licensing fees required to use BW's designs in their gearboxes. It started with the 924 and 928, and then when the 911 was removed from the chopping block and left in production at the end of the 80s Porsche sucked it up and accepted the better technology.

and lighter too... how much did you shead? 25-30lbs?

Thank you Matt.

I will say that for shifting without a clutch, like when the clutch cable breaks on you while out on the road, the VW beats the 915 hands down. I've driven some fairly long distances with each, and wondered if somehow I'd lost the touch when it happened on the 911. It told me it was the VW system, and not my skills, which mainly allowed me to get along so well with the VW. Didn't help that the 911 wouldn't start with the key in 1st, so having to stop other than on a hill was cause for panic - but that was an engine tune thing.

But I've raced with both, and with the improvements I've made to the shifter for the 915 (like the Seine) I can't say there was a difference in terms of how far off the track records for the different cars I was.

I second the notion that since you have a mag box, if you decide to rebuild it you should keep that box, because the girdle holding the two shafts back by the differential is much stronger, and hose key bearings aren't apt to spin where they weren't meant to.

But you'll be amazed in the improvement if all you do is replace two bushings under the shifter, and those in the coupler at the rear.

Thanks all for the great info!