I used Redline synthetic in my 915 for about 15 years without issue. My application is track driving and racing.

I used their NS version for many of those years.

No need for debate on tranny lube.

From what I have read, the fact that it seemed to shift find on a street run is perhaps most telling. Before opening up the 915 I'd want to check all four mounts carefully, as well as all of the bushings, et cetera. Really everything external, very very carefully.

Longshot... I'd also check the pedal box area very carefully to ensure junk is not under the clutch pedal. Back in 2002 I had such an issue at Laguna Seca. Wife and I had driven the 911 about 6 times by then, coming from a 951. I thought she was having trouble with the on/off RSR clutch. Wrong. It was crap under the clutch pedal.

She ended up #2 in the TT that weekend. The next time out she got TTOD overall.

After that experience I cleaned out that area after every event. Lots of crap under there, especially rubber. And that crap can move about.

I also bought my buddy a small shop vac as a bachelor party gift after I had my experience. He kept it in his trailer and we could all use it at events to get all the rap out from under the pedals.

Again, this is a longshot. Will think more on this situation.

Meanwhile I suggest more street driving to see if it can be reproduced.

Nice to see we have a Pelican in my home town, MKE.

Hey Frank sorry to hear about this. Gordo here on the forum did a nice video that shows how the main shift shaft inside the transmission transfers movement to the shift fork units. It's a really nice complement to the descriptions Walt provided

https://www.youtube.com/watch?v=LLEWjNRjJTI

I would take a look at the bottom cover of the trans and see if the guide fork is at all a potential culprit. That guide fork acts as a fulcrum to transfer the fore-aft movement of the main shift shaft to the shift fork shafts. It would seem that the "dongle" is able to move side-to-side within the "windows" of the shift fork shaft lugs, as you wiggle the shifter in neutral plane. But when you go to move the shifter fore-aft, it seems that you cannot make the shift forks move. Could be the dongle fulcrum, could be the shift fork shafts.

The shift fork shafts simply move through bores in the transmission case. As long as the forks are properly secured on the shafts, they should move the selector sleeves. Of course the shift fork movement is dictated by the allowance of movement between selector sleeves and tripod hubs for 1-2 and 3-4 gear selection. Those pretty much are what they are and there's no adjustment to them. The 1st-2nd and 3rd-4th sleeves and hubs are not interchangeable (noticeably different in size) so they must be paired together properly.

The above info from me is somewhat meaningless because you were able to shift it fine for a long time on the open public road.

So I have to jump on board with the other guys and say it's external. I would go over the mounting points:

• mounts in the trans crossmember- two main M12 bolts that secure the trans to the torsion bar tube
  
• the four M8 bolts and nuts that secure the mounts to the crossmember
  
• two M12 engine mount bolts in engine bay
  
• the four M8 bolts and nuts that secure the mounts to the engine bay
  
• four studs in the tail case to mount the crossmember to the trans
  
• check four nuts that secure the trans to the engine
  
• check the torsion bar tube to make sure it's not come free from the chassis. I've seen it crack at the outboard mounting points in the wheel wells. This was on one car that had coilovers and the spring plates were replaced with hard-connected 935 spring plates

Don't want to get too far off in the weeds...

Here are some things I do (my application is racing):

I use a WEVO bearing retainer plate. Although one of my expert friends believes that the best benefit of such a plate is with alu boxes-- he believes that the steel inset with mag boxes like mine render aftermarket plates a little redundant.

I used metric j nuts and threadlocker for the bearing plate or alternatively socket head bolts and safety wire to hold the retainer in place.

I use socket head bolts and safety wire for the transmission mount to chassis locations. And I paint dot them.

I use a WEVO shift rod clamp.

After seeing a friend's race ruined by a loose coupler set screw a few years ago, I started to use thread locker on my coupler set screw. I never had mine come loose in about 15 years, but figured why not take a precaution.

Again, the biggest clue I think I see so far is that the thing shifted just fine driving up and down the street.

Chassis cracks... look carefully. The nutserts in the t-bar bearing cover area may need close inspection including a wire brush to see the bare metal.

I think the chassis cracks would have to be substantial to be a cause here... but again, everything probably oughtta be checked carefully

Surgeons leave sponges in patients. They count them and use products with RFID tags. I have stories about that...

I have to thank Matt Monson, Jerry Woods, Hayden Burvill (WEVO) and Mat Lowrance for helping me through the years... plus a few others. And yes I have had at least one tranny mystery in that time-- none of those guys had ever seen it before. That one cost a lot before I located the culprit. But it did not have the symptoms you describe.

Gordo's video is great - much easier to understand than writing about it. What he doesn't show is 5/R: there the dongle tip moves past the 3/4 slot and is out in open space, kept from flopping around by the fulcrum fork, but able to move fore or aft without hitting anything in that part of the transmission.

I still don't know exactly what the "feel" of this not being able to get into 1-4, though. Obviously it isn't just grinding of engagement teeth, or he'd have been able to get into 3d to get back to the paddock. It isn't popping out of gear (he'd have been able to hold it in a gear with one hand on the shift lever to get back off the track). I suppose it was more like the trouble, especially on the older 915s, of shifting into 1st when still moving along? You get the lever in the right position (and it is easy to get 1st into the right position - just hold all the way over) and push hard. The lever moves forward a bit, but that's it - no grinding, but doesn't engage either.

We know nothing obstructs rotation of the lengthwise parts - the dongle moves freely through its three positions, and 5/R work. 5/R working on the bumpy track sort of suggests nothing odd is loose inside the center tunnel of the chassis blocking fore and aft motion somehow.

If you position the shift lever between where 1/2 should be, and 3/4 should be, you can't move the lever fore or aft more than the clearance of the dongle head and its slots, plus the detents, because the detents prevent moving both internal shift rods simultaneously. However, since (without a Seine or other spring loading aftermarket shifter) you are free to move the shift lever right and left while trying to move it fore or aft, and I bet he tried that, this doesn't quite fit the symptoms. Even if the transmission was rotated you'd think he would have been able to get 3d and 4th if it rotated the way it did, and for that matter not 5th - if the dongle couldn't rotate beyond its two slots, for instance, or the 5th/R finger couldn't move far enough to engage that rather shallow slot on its associated shift rod.

But I endorse the check a whole lot of stuff before pulling the transmission approach.

This is really weird - Sebring is bumpy, but not all that bumpy everywhere - why would mount/chassis cracks etc move things around exiting the paddock onto the track when building up speed? But then sag back to where the shifting worked? I can't see a fore or aft up or down motion of the transmission causing trouble - that's why the shift coupler has some degrees of freedom to it. Which makes a rotational movement more likely, if not obviously so.

By now enough guys who have had enough problems or otherwise know a lot about how transmissions work have been stumped to make it especially interesting.

A very sincere thank you to everyone for responding so quickly and thoroughly. At this point i do not have any more hard info. to share. Your suggestions are superb. i sent my backup to the backup gearbox, just gone thru by P. Dawe down to Zotx Racing today. Hopefully they wiil swap early next week and do a thorough check of chassis, mounts, torsion tube, pedals etc. Stay tuned. Frank

Interesting thread … leaving us hanging … what was the culprit??

Should start a poll with our guesss...

I'd missed the "shifts fine in the paddock, not on the track" part.
Club Racers with these now quite old cars are seeing increasing cracking of the tub. One place this seems to happen is at the rear firewall where various parts - the floor pan, the firewall, the tube for the shift rod, and the center tunnel - come together. The operational symptom reported is inability to get gears on track.

I haven't actually looked at a car with this issue, and don't know specifically how it would misalign the shift mechanism (maybe it could cause shift linkage parts to rub or hit chassis parts?), but I believe the shop guys who have mentioned this - it is a real chassis issue. So one could check for cracks.

I saw Frank at the track in September and it seemed fine then, he must’ve gotten it sorted.

Frank, Frank … come in Frank …

HI Everyone. Rosco. Thanks for jogging my amyloid addled mind to respond. and anyones interest in this saga. Well. ... JeezusFC.... what a saga. I think 915s and me are cursed. Anyway. I sent the supposedly pristine newly, totally refurbished , never used box ( THAT WOULD NOT SHIFT AFTER 1/2 lap at sebring) back to the guy who rebuilt it . TOTAL PROFESSIONAL. He told me it was fockin armageddon inside the box. everything. dogs, bands, shift rods. etc , SIMPLY MAKES no SENSE at all. The only real issue was that I had used synthetic lube in the very beginning and during that weekend at Sebring.) and not the recommended Swepco 210. Plus, not sure my trans cooler was working well, but temp never got over 160 which I log on my AIM system. even when I was hammering it outside the track. Matt tells me that the wrong lube in a highly stressed racing 915 box can cause quite rapid deterioration. BTW I had the 901 shop at track at sebring exchange the synthetic for their "custom. magic 915" gear oil.. bluish stuff .... that still did not solve the problem) . So. to be clear. I ran synthetic ( stuff you are supposed to use for G50 boxes) for the first warmups and starts at this one event,. in reasonable heat. BUT still I cannot get over the fact that I could take the car outside the track EVEN WITH THE SYNTHETIC GEAR OIL. and it worked fine. I am talking pounding on it for 30-40 minutes up and down Rte 98. in high heat of day. from ": Spray and Pray " gun shop to Lordida and back. IT WORKED FINE!!!. Then I take it to the next start at Sebring in the afternoon and it totally locks up just after that right at tower turn...... riddle me that Batman. thanks again for everyones input. FRank. OH. BTW. Bill Rader did the build initially and then was kind enough to redo it when I sent it back to him ., literally for close to free,. That is truly amazing customer service ....

Bill Rader is the best!! I love that guy....I won't let anyone else work on my 915 (well, except for one guy but he is retired).

Stick with the Swepco 210....you will be happy...but actually filling the 915 with the gear oil helps with longevity!!

Weird 915 Race Gearbox Problem: Need the braintrust..
 

My guess is you have a Wevo gate shift in there … and the engine and trans was able to move enough (lateral G’s) on rough sections on the mounts to upset the selector .. which would then relax again once cooling down back in the pits. Reports from way back of hard driven race cars unable to find gears due to engine / trans movement on the mounts .. Wevo gateshift exacerbates this ..

Good call Roscoe., indeed it is a Wevo.... will check it