915 3rd gear blues.

[r lane]

I track a 78 911. 9 out of 10 races, the 3rd gear shift will cost me as more than once 3rd gear will balk. The 2 cars that I just passed are now passing me while I thrash the shifter. I have felt it was gearbox related not shifter related, but apon ponder, maybe not. At this particular track, I shift into 3rd 4 times, 2 on the upshift and 2 on the downshift . just occurred to me that it only balks on the upshift. I think my move latterly from 2nd to 3rd is overcoming the 5th/rev spring lockout and hitting both 3rd and 5th simultaniously. A stock short shift with a Sein lockout. I have a Wevo that has been sitting on my shelf. Am going to install and see. Any thoughts and experience in this department would be greatly appreciated. Bob

[yelcab1]

Make sure you adjust the shifter rod at the coupling so that ... the lock out does not rub on 3rd shifts. The 915 is not the greatest fastest quickest gearbox.

[shoooo32]

Does this happen at a specific time in the race (beginning or end) or is it random? What oil (brand/weight) are you running?

[PeteKz]

The 915 is what it is--an olde design. Try the Wevo. Maybe it will prevent those missed 2-3 shifts. If not, then you may have to think about installing a G50, or selling the car and getting a G50 equipped car.

[Alan L]

It could be a linkage problem - you are crossing the H pattern. It doesn't take much to screw things up with these boxes. They ain't the best.
When I am racing the 930 I go "$s and cents" between downshifts. Thats no time lost really - hard under brakes anyway, so I take the extra second. Shifting up , and 2-3 is OK. So it may be a linkage issue - not quite as precise in finding the slot you are looking for. Very recently redid the bushes etc on the 930.
I once went from 2nd to 1st - looking for 3rd. The G forces on that corner are throwing you left. I left the track before I knew it. Dunno how it ever made it in to 1st.
Alan

[dwa917]

are you upshifting under lateral load? I had a similar problem back in the 90s when racing a 915 box... if so, then replace all shift linkage bushings to new, and make sure you have really good alignment of shift linkage/coupler... if it still persists, try more stiff engine and gearbox mounts... the body twists under lateral load... That cured it for mine... I eventually went to race with a 901 for shift pattern, but the 915 was fine after those adjustments.

[Alan L]

How does it shift on the cool down lap - when no stresses in the system? If it can upshift OK then? Then I would put it down to the flex as dwa17 mentions, with linkage imprecision. Re doing my 930 linkages recently improved the shifting outta sight. Very small play translates to big imprecision.
I have hard mounted gbox/engine mounts (no flex).
Alan

[r lane]

Does appear to happen later in the race as in 5th or 6th lap. Swepco 210. I think as discipline allows, push it into neutral with no grip on the knob, it will center itself and then forward into 3rd. Like a running back waiting for the hole to open. I actually have a G50. those boys are heavy. Am putting one in a similar car and am trying to figure out how to rebuttress the torsion bar tube as had to cut a good bit out. And this was on a shortened box. Thanks for all your input. Bob

[Jonny042]

It's possible for the shift dongle inside the transmission to catch the shift rail for 1st and 3rd simultaneously as you move towards 3rd from 2nd. It actually can catch the gap between them, get a little bit stuck, push both forward, and the interlock system inside the transmission prevents either gear fork from moving any further.

On my 915 this was partially due to an excessive gap between the fingers, but no matter how tightly you space them on assembly the possibility exists.

A Wevo gateshift is a sure fire solution to this. It's expensive but worth it IMO, especially if you are racing.

[Jonny042]

I should add - if you sit in the car and feel for it, what I describe above might be easily replicated. If it is, and it feels familiar (like the internals of the shift mechanism hitting a hard stop, which they are) it might be a clue as to what is happening.