I would assume even with proper shimming this would be a help? Tim usually knows his shet.

 

my guess would be because of tim's comment about not being able to see whether the set is shimmed properly unless a window is cut in the housing. this piece eliminates that need. just a guess

 

i'm sure you're right, and it isn't lost on me that as near as i can tell, of ALL the stopgap fixes, the best one and one most likely to last indefinitely? is in fact tim's, so credit where it is due.

 

to the o/p make sure you get new lock nuts. this was randy's transmission after a fresh build less than 6 months in. tech reused the old nuts and didn't torque them correctly. result was another 6000$ in repairs that the pcar shop the tech worked at had to pay for
https://www.youtube.com/watch?v=Yn5I...ature=youtu.be

 

rep for you for makin them pay. i'd say dont mess with texas, but the TN valley authority is no joke either.

 

would love to take the credit but a small shop i use in atl had randys car there while mine was. they found the problem and randy had a field day with them. he was ready to sue for the entire build since the tech did all the work on the side at the dealership and used dealership paperwork for ordering parts receipts etc. they settled quickly!

 

I already ordered the new parts, including the new nuts. I should have all the parts late this week or early next week.

 

Let me start by giving my basic understanding of what's causing 2nd gear pop out. It's not an issue with the larger teeth on the gears themselves. Hopefully the picture below will help illustrate the parts I'm going to reference.

Basically there are teeth on the inside of the shift collar that mesh with the "small" teeth on 2nd gear and the teeth on the guide sleeve. The guide sleeve is fixed on the output shaft and the shift collar rides on the guide sleeve between the free-wheeling (loose gear) 1st and 2nd gears. When you select 2nd gear, the shift collar slides towards the loose gear 2nd gear and engages the small teeth on the gear. At this point the shift collar has engaged the loose gear 2nd gear and the fixed guide sleeve, causing the guide sleeve to drive the output shaft.

If you miss a shift, or have a bad shift, the teeth in the shift collar grind against the small teeth on the loose gear 2nd gear. At this point, the teeth of the loose gear 2nd gear and the teeth of the shift collar are damaged and no longer engage at full strength. This causes the shift collar to slip off the loose gear 2nd gear small teeth, disengaging 2nd gear. Basically, this is what we call 2nd gear pop out.

Actually the Shift Arrester makes a lot of sense. Keep in mind that the fixed second gear is machined on the input shaft. Given this, you don't really want to move the loose gear wheel 2nd gear on the output shaft. If you re-shim (move) the loose gear 2nd gear on the output shaft, then the large teeth on the gears will not mesh correctly.

What you want, is for the shift collar to move as far as possible onto the small teeth on the loose gear 2nd gear, to reduce the reliance on the leading edge of the small teeth (which are what wear or get damaged). This way as the teeth wear, you will not immediately get 2nd gear pop out.

The shift arrester (which replaces an almost identical factory part) appears to have a slightly different profile, which will change the travel of the shift rod slightly causing the shift fork and collar to more fully engage 2nd gear.

It appears to be a little insurance for very little money.

Tim,

Thanks for reminding me of this piece. It will give me a little peace of mind as I'm spending a lot of money on a new loose gear 2nd gear, shift collar and guide sleeve.

Later, Steve

 

Great info thanks.

 

while that all might well be so, i'm not sure that is the "cause" of the original issue itself. that had more to do with improper tolerances of the shims used, not the gears themselves.

the dogring of the 2nd gears triple cone designed synchromesh gets 'rounded" owing to a missed shift and once "rounded' will never engage as its was designed to. in addition, porsche discovered that their gear stack placement ( and where 4th gear sat in the stack (iirc?) was not within the proper spec so as to allow the 2nd gear to fully engage, further exacerbated by a rounded dogring, per above.

whether any of this has been addressed in your detailed post isn't clear to me nor does it make any difference. if you don't address the fact that porsche's original tolerances were not optimal, for the engagement of the gear with a perfectly fine synchro and accompanying dogring, then the significance of a slightly rounded dogring takes on an added significance and also creates a propensity for improper gear engagement, that does not exist once the gear stack placement is changed with PROPER shim placement so that 4th gear is placed a bit differently in the gear stack placement. yes, it's millimeters at most.

but, that's why once porsche changed the shim tolerances and placement, the problem occurred less and less, ( or not at all ) until it was no no longer a prevalent issue.

conversely, rebuilt gearboxes ( even from porsche themselves ) that were initially replaced with new 1/2 mainshaft gears and all new synchs tended to exhibit the same symptoms as the original CAUSE of the defect had not initially been addressed!

once the shim tolerances were changed by porsche to alter the gear stack placement, the issue of 2nd gear pop out miraculously stopped happening.

whether you have or not addressed that in your play by play w pics, is beyond me. the issue, and the proper fix for the issue itself are not. but that's why a detent, an 8mm ball bearing, or a shift arrester work, as they mechanically limit the movement in the box. when the properly shimmed gearbox would also eliminate predisposition and/or the cause or propensity for a rounded synchro dogring to improperly engage 2nd gear, resulting in it "popping" out of second gear.

whatever works!..i had mine rebuilt properly ( twice ) after much back and forth with both porsche and pcna. good luck.

 

The issue, is we can't correct the tolerances by changing the shims, if we don't know what the new spec should be.

My only option is to install the shift arrester and hope it helps.

Later, Steve

 

i'm sure it will help. no doubt. as i mentioned earlier, the "newer" specs may even be "proprietary" to porsche, and as such, not even readily available. it was, after all, THEIR mistake.

for those of us old enough to remember, they didn't even want to admit there was a "problem" and that alone took some doing.. at first.

i had a genuine battle with them initially. but i rather enjoy a good fight, as long as its verbal, and although i emerged successfully, they STILL had to open my g'box... TWICE!

btw the arrester and/or the 8mm ball bearing, i would think you'll be fine. esp with new 1/2 parts. again GL w it.

 

Hi,

Very interesting post so thanks the the detail. My car is back at a specialist to sort as the 2nd popout issue remains, very frustrating. Fortunately they will cover any work needed to put it right.

Can someone give a how to fix summary so I can ensure the issue is resolved. I believe someone mention changing 1st and 2nd gear rings to GT2. Looking for advice please. Appreciate it might be a case by case but a generic 100% fix solution would be useful info.

Many thanks

 

I had put all new gt2rs 1-4 gears with CMS arrester, still 2nd popped out. Sent an email to helpful CMS crew.
their advise was 2nd loose gear needle cage. I replaced it and problem fixed. So start with a new bearing on the 2nd at least.

 

the KEY to the remedy for this issue irrespective of whether or not you go for "upgrade" parts ( gt2 steel etc etc ) is that the shop be fully aware of the porsche factory *AMMENDED* shim tolerances, that were NOT known for the first couple of years of production! this is why you never see or hear of this issue in MY "03 and beyond.

ask me how i know