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New-ish 911SC Targa Owner
 
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5th gear - closed for business

My 915 has always had a weird shift into 5th gear since I've owned it. I would usually have to shake the shifter as I was going forward on the 5/R plane for it to sync into gear well.

Its gotten worse lately and sometimes I just couldn't get 5th to engage and would have to finish my route in 4th gear instead. It felt like there was something blocking the shift fork or slider. If i shut off the motor sometimes I could then get 5th to engage but then later it would refuse again. It was about a 50/50 chance that I would have 5th gear most days. Now its 100% no 5th.

**I have a solid coupler and a rennspeed shifter so I really doubt that there are any bushings that could be contributing to this. I fear its....internal.

So what exactly would be common for this issue and how big of a pita is it to repair? Would it be worth it to send the trans out for a full rebuild or buy one that has already been rebuilt? I've seen them from $3500 or so with a claimed rebuilt status.

No clue how many miles are on the trans as the chassis probably has 300k and the motor was a mix of different years and parts.
What would you do if you weren't exactly independently wealthy and had little experience tearing into transmissions?

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Old 01-02-2019, 05:39 AM
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KTL KTL is offline
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5th gear is the easiest to service and requires a minimal amount of work to disassemble because it's in the tail case of the trans. But you still have to take the transmission out of the car to service it.

Here's a crude video to show you how reverse operates on the trans and fifth is right there on the same fork, opposite of reverse.

https://www.youtube.com/watch?v=lTLh75Uldoo

Peter Zimmerman's wiki tutorial will tell you all you need to know tackling the disassembly and assembly of the 5th & reverse parts in the tail case section of the trans

Porsche Wiki
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Old 01-02-2019, 09:59 AM
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I had the same problem in one of my previous 915 cars. It was caused by the coupler being slightly out of adjustment. I suggest you look into that first. Wayne's book has the procedure to adjust it.
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Old 01-02-2019, 11:10 AM
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Shaun, I know you said you have a solid coupler and a rennspeed shifter, but yeah it does sound like something isn't set up properly.

A few years ago, I bought a 911 from a guy who said it had a 4 speed box.. well, after I bought the car and adjusted it, I had a 5 speed box! He had the car 20 years and never knew it was meant to be a 5 speed.

Anyhow, as long winded as it sounds, I'd try removing your coupler from the shifter, and reinstall everything again. This would be a lot easier than pulling the box and rebuilding.
Old 01-02-2019, 11:35 AM
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Ok, that sounds easy enough. i'll spend some time adjusting the coupler a few different ways and see if I can find a "free" fix for it! That would be ideal after all.
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Old 01-02-2019, 12:13 PM
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Make sure after you adjust the coupler that you're still engaging the reverse lockout feature. It doesn't take but a minor adjustment in the coupler position to throw off what's happening up front at the shifter itself.

Even though you have a solid coupler and a rennspeed (Rennshift?) shifter, I suggest you may want to look at the ball cup bushing under the shifter lever. If this bushing has come apart at all, that also can mess up your shifting. Seems plausible to me since you described how your ability to select 5th gear changed from difficult to forceful to now being a no go.
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Old 01-02-2019, 12:35 PM
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Recently had a local friend with 5th/reverse issues. Turned out to be a bent shift selector shaft inside the transmission. The bend was in such a way that when you would rotate the shaft going into the 5/R plane it would push past the fork and not want to move the fork.

Sounds to me like the box needs to come apart for investigation. Could be dog teeth/slider mesh problems, shift fork alignment, or some other part along the path from shift selector to shift fork and slider.

Can you manually put it in 5th grabbing the coupler by hand?
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Old 01-02-2019, 01:29 PM
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I adjusted the coupler a few different ways and still could not get 5th gear engaged. It "feels" like its something internal. I suspect a bent shaft like what you found in your friend's car Jamie.
I guess I'll remove the trans and poke around some.
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Old 01-04-2019, 08:37 AM
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You can also open the inspection port and check the guide fork. the nuts tend to loosen up
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Old 01-04-2019, 12:43 PM
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Something tells me this doesn't look as it should. This part is called the slider, correct? Or is this the shift sleeve?

Anyhow, those little teeth shouldn't be worn like that, should they? And the cogs or whatever on the ID look very worn too, right?
Could this cause 5th gear not to engage?



Here are some other pics but I'll be honest, I don't really know what I'm looking at here. Anything jumping off the screen at you?


Old 02-11-2019, 02:52 AM
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Not sure about the Rennshift, but there are several bushings in the stock shifter. All are prone to wear and can make for vague shifting, in addition to the coupler. Pelican sells a kit that includes the ones you need to rebuild a 915 shifter.

Oops - didn't read the whole thread before posting. Looks like the ID of your slider is worn. It may not have been engaging properly with the 5th gear synchro ring and wore out to the point it no longer engages. See pic of a new one at the link below and you'll see what it should look like.

https://www.pelicanparts.com/More_Info/91530222709.htm?pn=915-302-227-09-M260

Last edited by stownsen914; 02-11-2019 at 04:57 AM..
Old 02-11-2019, 04:48 AM
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The best thing to do, is find the new part picture on google. The shift sleeve should be replaced. The teeth on the other side, are similarly worn, look to be missing the top taper and are smaller than normal.
Old 02-11-2019, 04:54 AM
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The points on the shift sleeve look like they're missing in several locations. Those points mate up with the points on the gear to smoothly mesh together and engage the gear. The points on the gear and the friction band actually look pretty good. The points should be rather, well, pointy looking. Badly worn points don't get pointier. They get blunted and rounded off.

Unfortunately that 5th-Reverse shift sleeve is really expensive when bought new, as you can see from the Pelican link. Put up a WTB listing on the classifieds and I suspect you'll find someone with a decent used one that has all the teeth. This sleeve is usually the least abused in the whole gearbox because most of the time 5th gear is not shifted very hard/fast and the friction band has to do the least amount of work to do, to spin up the input shaft and match speeds with the pinion shaft.
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Old 02-11-2019, 05:15 AM
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Quote:
Originally Posted by KTL View Post
The points on the shift sleeve look like they're missing in several locations. Those points mate up with the points on the gear to smoothly mesh together and engage the gear. The points on the gear and the friction band actually look pretty good. The points should be rather, well, pointy looking. Badly worn points don't get pointier. They get blunted and rounded off.

Unfortunately that 5th-Reverse shift sleeve is really expensive when bought new, as you can see from the Pelican link. Put up a WTB listing on the classifieds and I suspect you'll find someone with a decent used one that has all the teeth. This sleeve is usually the least abused in the whole gearbox because most of the time 5th gear is not shifted very hard/fast and the friction band has to do the least amount of work to do, to spin up the input shaft and match speeds with the pinion shaft.
Would it be your opinion that the points being how they are would cause the engagement of 5th gear to be difficult or impossible? I just don't know what I'm looking at here and don't want to have to go through removing it again to throw another part at it if the issue isn't this slider.
Can I take any other pictures to help with diagnosis?
Old 02-11-2019, 06:41 AM
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When the material has built up sufficiently at the point indicated below, the gear is most certainly "closed for business". Your sleeve is worn WAY beyond what I've pictured.

Old 02-11-2019, 07:12 AM
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Quote:
Originally Posted by mikedsilva View Post
Shaun, I know you said you have a solid coupler and a rennspeed shifter, but yeah it does sound like something isn't set up properly.

A few years ago, I bought a 911 from a guy who said it had a 4 speed box.. well, after I bought the car and adjusted it, I had a 5 speed box! He had the car 20 years and never knew it was meant to be a 5 speed.

Anyhow, as long winded as it sounds, I'd try removing your coupler from the shifter, and reinstall everything again. This would be a lot easier than pulling the box and rebuilding.
+1, unless you have unlimited funds, always attempt the cheapest/easiest route first. I’ve adjusted various types of gearboxes and the linkage set up is critical. I have a S PSJ and Rennshift on my ‘82, and after adjustment (and bushing replacements) it made a big difference in shift quality.

I wish the 915 had a tool for installation set up like some cars. I recently installed a transmission in a VW MK3 and thought it shifted OK after I replaced all of the shifter bushings. I spent $12 on a factory tool set up tool and now it shifts incredibly smooth in all gears.

Love the story about the “4 speed” 911!
Old 02-11-2019, 07:17 AM
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That's the most toasted 5th/rverse shift sleeve I've probably ever seen. Carry on.
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Old 02-11-2019, 07:40 AM
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Paul's super closeup picture of the sleeve tooth points (this is actually a 1st-2nd sleeve) shows you the edges/sides of the teeth. Over time those edges get knocked back which raises the edges. Those raised edges "narrow the gap" as Paul has previously told us and that makes it harder for the gear points to find their way home into the sleeve valley. When the points get past the edge, the flanks are angled in such a way that the two parts are pulled together and slide into each other. Without the points in place on the shift sleeve, the gear points and the sleeve aren't trying to slide together "automatically." I think the only way you could get the gear to engage is by the teeth lining up with each other by luck/chance, along with you being excessively forceful with the shifter?

I found a picture of the 5th-Reverse sleeve I posted back in 2015 (ignore the camera time stamp- it resets to 1/1/06 when the battery dies) and you can see how prominent the points should be on a functional sleeve. Yours are wasted compared to this picture.

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Old 02-11-2019, 07:46 AM
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I wonder if there was a loose shift fork or a poor adjustment to cause that much wear on the teeth. Especially considering the fifth gear synchro doesn't usually get abused.
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Old 02-11-2019, 07:55 AM
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I suspect this car has over 300k miles on it and the transmission might be original. I can't tell if it has been rebuilt before but I suspect it has. It shifts lovely into all other gears and isn't noisy. 5th has just always been odd and hard to engage since I've owned it. Now it looks like I might know why.

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'05 E500 wagon in minty cond
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Old 02-11-2019, 08:22 AM
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