Sticks in 5th gear - 915 transmission

Old Goat · 07-31-2002, 05:53 AM

I have a 86 Carrera with the dreaded 915 transmission. Really the thing shifts pretty good with the exception of a tendency to stick in 5th. Does not happen all the time, but when it does I have to give it a pretty good pull to disengage. Could this be a linkage ajustment problem, or more serious? Thanks in advance.

jwetering · jwetering's Garage

Quote:

Could this be a linkage ajustment problem, or more serious

yes and yes....

First: fiddle with the coupler until you are sure that it all lines up ok. I found it extremely useful to remove the rubber boot covering the shift tower so that I could see what was going on at the lever's base.

If that doesn't fix it, spend the $30 or whatever and replace the nylon cups and bushes in the shift tower, then, if it's still no good, spend the $100 to replace the shift coupler itself (don't forget to re-adjust)

If none of that fixes the problem, then something's probably hanging up in the box and you have to make the decision to either fix the problem right now, or to wait until the transmission is apart for another reason.

Wrecked944 · 07-31-2002, 06:42 AM

Interesting, I have a 915 and I was experiencing the same problem. I noticed it only happened when I left the shifter in fifth gear and coasted to a stop (with the clutch disengaged, of course). Frequently happened at toll booths where I'd be cruising down the highway in fifth and leave the shifter in place as I stopped to pay the toll. Then it would be a b*tch to get the shifter out of fifth so I could put it into first. I found if I pulled the shifter out of gear before slowing down, the problem didn't occur. Strongly suggested a synchro problem to me. Anyway, I recently opened up the tranny for other reasons and have found no anomolies in the fifth gear sliders, synchros, etc.

Are your "sticking" symptoms similar? Perhaps we can compare notes.

Thanks,

jabb · 07-31-2002, 07:13 AM

Hi janus:

Hi have the same problem you describe..... does not happen all the time but enough so I try to make sure I do not stop in 5th gear....... Not sure what is causing it but for now I just do not stop in 5th as my fix.

Old Goat · 07-31-2002, 07:51 AM

Just got back from a test drive after adjusting the coupler between the seats. I noticed an improvement in all the gears, but also noticed slop (left to right movement) in the rear coupler. I will try a new rear coupler and see if it helps. My transmission seems to stick when downshifting from 5th to 4th.

Early_S_Man · 07-31-2002, 08:27 AM

Goat,

How many miles on the transaxle? Any problems with 1st or 2nd gear synchros?

Check your oil level! Change the gear oil ... if you don't know how old it is, or if it is more than onr year since last change!

Sticking in gear doesn't have anything to do with bushings! It is a wear problem with 'notches' worn in the 'slider' (operating sleeve) or the 'spider' it moves on -- it is most frequently a 5th gear problem because that gear is driven in for many hours compared to the number of shifts into or out of. Low gear oil level accelerates the wear pattern, too.

The 5th gear sticking is also easy to fix because only the front cover has to come off, and none of the rest of the transaxle has to be disturbed. That assumes there are no synchro issues with other gears that need to be taken care of at the time of the 'sticking' issue.

Sean Hamilton · Sean Hamilton's Garage

It's a common issue (I'm told). Mine's the same.

This is how I deal with it :-
5th back to 4th is selected earlier than for any other gear selection, i.e. it seems to be more engine/trans speed sensitive than the other gear selections. So when I see up ahead that a 5th back to 4th will be needed - I do it sooner than later and it usually behaves. Sometimes if I duff it - I don't bother any further, I'll then double-de-clutch and it will free up immediately to move smoothly into neutral. By that time 3rd gear would be the choice.
Well, this works for me anyway. Besides, the challenge in "how to help it help me" keeps me alert.

Mark McClure · 08-01-2002, 04:58 AM

Similar issue. The 915 in my car is obviously due for a rebuild. In an attempt to get 1st to 2nd smoother I adjusted the linkage obviously this effects the throw on 5th. The result is that the stick in 5th is sometimes solid and will not move. This is only occassionally after driving for a time. A small movement forward before pulling back to 4th solves the problem. I have to look at it but it may be the worn gate guard on reverse moving due to the vibration and jamming against the stick.

It amazes me how many issue people have until you realise this is 20 year old technology.

Hope this helps someone!!!!!!!

sammyg2 · 07:16 AM

Mine did it too, once.
The car shifted fine but sloppy when I first got it, so I replaced all the shift bushings. Afterwards I noticed the sticking in 5th. I re-adjusted the linkage and the problem went away and has not returned. That to me indicates an adjustment problem.

I think it was hanging up on the reverse lock out mechanism, so when I changed the front/rear adjustment the shifter stopped hanging up. In other words I adjusted it so that it disengaged from 5th gear before the shifter hit the reverse lock. If my memory serves, I had to shorten the linkage just a tad.

Wrecked944 · 08-01-2002, 09:45 AM

Okay, this is a very intersting thread. So since I happen to have a disassembled tranny on my workbench which was displaying the 5th gear sticking problem, I followed Warren's lead, pulled out the 5th gear slider and photographed it. I believe I may have found the culprit !! Check the tooth indicated by the arrow. All of the teeth have the same groove, but I think the one indicated is the clearest example. Soooo...do we have a DNA match on this suspect?

Early_S_Man · 08-01-2002, 10:24 AM

Yes, Janus, I believe you have found the reason for 5th gear being sticky! replace that operating sleeve, and the 'dog teeth' on the 5th gear ... and it won't stick any more! How is the 1st-2nd operating sleeve, and their matching dog teeth?

Jim Sims · 08-01-2002, 01:27 PM

All the operating sleeves (sliders) have such a groove; the 1st/2nd and 3rd/4th operating sleeves have two grooves. The synchro ring snaps outward into that groove to keep the gear engaged. Usually it is the opposite problem; the groove wears and the synchro ring won't stay down in the groove and the transmission pops out of gear. Now there could be a wear problem related to the slider causing 5th gear to stick, However, I would first suspect the brake bands with their anchor and energizing blocks (on the inside of the synchro ring). If these parts are worn and hanging up and won't move inward and allow the synchro ring to collapse inward and move out of the groove in the slider then the gear will stick. Cheers, Jim

wcballance · wcballance's Garage

I had a problem with my fifth gear sticking. It would happen when I shifted up into fifth while hard cornering, typically on an onramp. It was very disturbing to have to muscle the stick to pull it out of fifth. The problem was resolved by replacing the transmission and motor mounts. I opted for the sport mounts for replacements.

---
Will Ballance
'82 911SC coupe

Wrecked944 · 04:53 PM

"All the operating sleeves (sliders) have such a groove;"

Aaaah...my little head is spinning...I have nowhere near enough knowledge of these things to form an intelligent opinion...Time for some raw data collection...I am off to the basement to inspect the other sliders...

Post Script: Okay, I just got up from the basement...I looked at the new and old 1st gear sliders and they both have a subtle groove down the very middle of the teeth...so now I am utterly without a semblance of a clue (i.e. my natural state)...a new fifth gear slider should arrive tomorrow afternoon (cost: $250 !! OUCH !!). So then I will be able to compare old apples to new apples.

Early_S_Man · 08-01-2002, 05:24 PM

Janus,

I should have been a bit more specific ... it wasn't the groove that concerned me, but, rather the uneven wear on the individual teeth that engage the 'dog teeth' ... and it looks like some of the slider teeth may be rounded. Can you post a pic of the other side of the slider with the teeth up to see how much wear there is on the leading edge of those engagement teeth? To still be serviceable, the teeth need to still have a discernible 'chisel point' appeaeance.

Post a pic of your new and old 1-2 sliders, as well, both sides (assymetric side is 1st gear, symmetric side is 2nd gear side) ... for comparison.

Wrecked944 · 08:22 AM

Sorry about the delay in posting these pics...I've really been trying to get the best quality images I can with my cheap-a$$ed digicam. I am highly motivated to help find the underlying cause of this problem since it seems to be a pretty common issue and the Pelican-heads have been INSANELY helpful to me so far. So I have a lot of good karma to pay back. And I am uniquely positioned to help since I have a tranny that sticks in fifth gear currently disassembled and available for inspection. So tell me anything I can do to help out. If these pics are not good enough, I know a pro who will gladly take better pics for free. I can also bring the parts in question to any local (New England) experts for diagnosis. I can also email the original pics (unreduced) to anyone who wants to see them with all of the original resolution.

Old 5th Gear "Sticky" Slider

New 5th Gear Slider for Comparison

Old 5th Gear "Sticky" Dog Teeth

Old 5th Gear "Sticky" Slider Hub

How can I help?

Wrecked944 · 07:08 AM

Reviving this thread to provide more data...

After rebuilding my tranny, I can report that I no longer have any problems in fifth gear. It doesn't stick at all. It used to stick pretty often. So obviously something dramatic has occurred. Basically, I replaced the fifth gear dog teeth, synchro rings, and slider. This stuff was shockingly expensive (especially the slider >$250) but it seems to have solved the problem. Of course, the question is: Which part was the culprit? Sadly, I suspect it may have been the most expensive part (i.e. the slider). I took all the old parts up to NH for Chris Bennet to examine and he found tiny little burrs on the teeth of the slider. I don't have pics because they were too small to see without a magnifying glass. But once Chris pointed them out they were unmistakable.

Okay, that is everything I know to date. I hope it helps solve the mystery.

BTW - I still have all of the old parts in case anyone else in New England wants to see them in person.