ProCoach

Not a P-car, but a very good explanation of how synchros (and the individual components) work.


I doubt this is a synchro failure, because there is no grinding. Instead, there is NO ENGAGEMENT (cannot move the external lever, or internally within the transmission, the slide) into the lower gear under lots of decel force.

mark kibort

you got it! yes, let them diagnose and fix on their dime. dont settle for its good enough or to spec, because if its doing what you say, and under warranty, they need to fix it! it might be a new synchronize! if so, thats their fault. if they made them like the T56 gear boxes, they wouldnt go bad!

mark kibort

thats the grinding mode of failure as you say (depicted in the video), i think its an indexing issue. i think the cone fuction is fine, it just cant get into gear due to the teeth being worn flat on tops, or too much gap radially so that they "over index" and cant line up.

nwGTS

^^^ in that case the synchro is doing its job matching speeds. The toothed rings are not 'indexing' as you say so they are not overlapping. They are basically fingertip to fingertip instead of interlocking fingers. That could be worn teeth or bad trans oil. I think the trans oil flush is really going to help because just yesterday Reverse had a slight grind. I always leave it in 2nd when parked. Turned it on with clutch in. Moved to Neutral with e brake on. Ran until idle drop. Clutch in and put it into Reverse with slight grind which has never happened before and hasn't happened since. So I'm guessing the trans oil is really dirty and may have some debris. I'll have them save a sample of it and send to Blackstone. Again, we'll see if the issue persists after all this. Bonus, I called PCNA and they are giving me a $300 voucher (from unrelated issue w/ battery) to use toward the trans oil change. So Part 1 will cost me basically just time.

mark kibort

yep... you got it. the lock out issue, isnt likely the oil. like you said, you tried 3 times while slowing and got locked-out, you couldnt engage. but, you never know. the porsche synchros when there is too much speed differential, will lock out from engaging a gear. (and sometimes not grind) this also is a synchro issue, but the oil could help here to speed up the driveline with increased "bite or friction" when the clutch is in and you are selecting a gear.

keep us posted! Hope the oil does the trick!

Mark

ProCoach

Not going to continue contributions to this thread, but the synchro is NOT working if what Mark is saying is correct ("indexing").

I have never heard of "indexing" in thirty-five years of diagnosing, validating and repairing Porsche-style baulk-ring synchronized transmissions specifically addressing shifting problems... I think I understand what Mark is trying to say, but that's not how it works.

The very engagement of the baulk ring onto the "cone" of the gear rotates the baulk ring to line up the interlock BEFORE compression. This compression, as the engagement completes, is what spools up (or down) the gear speed.

The chance that the ring (synchro) is frozen to the cone (gear), which is the ONLY way this "indexing" would not occur, is non existent if the synchro works sometimes.

The grinding into reverse bugs me a little because unlike everything I ever worked on, reverse IS synchronized in the 997.2 manual transaxle. The oil change is the first step...

Gofishracing

long thread- I didn't read it all. I'd start with transmission mount and function first insert

mark kibort

I thought indexing issues can arrive if the teeth are ground flat or there is to much radial gap due to wear. if that is not a possibility, sorry for suggesting it... im no expert here. however, i am an expert in hearing the shop telling customers there is nothing wrong. the fact that it works well in normal driving, but not in race conditions due to the lockout points to synchros or possibly the oil. Seems like a major issue for just an oil type solution.
Also , the fact that it is happening in 2nd, but not 3rd, could be a clue to a shift fork adjustment issue, given the fact they are on two different selector shafts and maybe the transition or handoff is not happening when under stress.
Im guessing and going off a few situations ive had to reflect on for this.

I hope he gets the correct answers to what is going on.

SuperPenguin

You didn't miss much. I think that would solve my issue, not sure if its same as OP's

nwGTS

Quick update. Got the car back late last week. The gear selector is MUCH more precise with less play. I can tell the system uses plastic bushings mated to a plastic frame with a long throw but it's still fantastic. (make me seriously consider a GT3 or numeric shifter upgrade). The gear oil change seemed to eliminate the problem and I was unable to reproduce the lockout on the street with a hard brake in 3rd gear shifting into 2nd. I'm still not thoroughly convinced until I'm on the track and while braking can consistently shift into 2nd from 3rd without lockout. That may be a few weeks but I'll update this thread once I have the chance to do that. Fingers crossed.

ProCoach

Great news. I'm optimistic!

mark kibort

very good news...... I had similar luck with swepco put in to mine way back when. (non borg warner synchros) it really made a huge diff, but my problem was not a lock out....... glad to hear its much better.
Hope its that way on the track....

Mark

nwGTS

1 year update after 8 track days this season. Had the issue reoccur during a couple sessions early in the season but not nearly as bad. I changed to semi solid engine mounts after my second track day and under the same conditions I have absolutely no issue going 3-2 now. I've not had the problem since. I'm chalking it up to refreshing the shift cables and locking down a large moving mass of an engine/trans as the solve.
Cheers.