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Old 09-07-2016, 06:14 AM   #1
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Seeking gearbox expert advise, lost 5th & 6th gears

Yesterday after shifting into 5th, the gear did not engage... you can feel the lever "falling into the gate" but the when you release the clutch it acts like is in neutral (reminds you of a half shaft failure), and if you shift into 6th you get the same results but with a faint gear grinding.

Got the car on the ramps to ensure that both of the cables at the gearbox end were fully into their brackets and saw that the heavy duty nylon ties that I used as an extra protection (to keep the shift cables secured) are still in position.

Then proceeded to remove the console and everything on the gear lever side seems to be fine (cables wise).

Questions:

1) Is there a possibility that the end of the cable where you have the nylon round thingi (that clicks into the gearbox) has somehow worn out? Even if reverse and 1-4 gears are operating properly?

2) Or (a more sinister possibility) could be that the selector fork inside the gearbox worked itself loose and is no longer able to slide the gear on it's shaft? Are 5th and 6th gears on the same shaft?

A few years ago I saw a picture posted by Erick533 (Hergesheimer Motorsports), showing a gearbox (still installed on the car) with the rear gearbox housing removed, if the possibility of # 2 above is the cause, perhaps I may be able to secure the fork into the shaft without removing the gearbox.

Some background: This gearbox was sent to GBox in 2014 to replace the pinion and mainshaft bearings that had failed and they also replaced the 3rd and 2nd gear synchros (along with a OS Giken LSD).

The gearbox worked very smooth and never had an issue until now (20k miles later)..

Any comments will be greatly appreciated, as I had to drive the car today on 4th gear because my other car, an Alfa Romeo, is also down for repairs (when it rains..)

Thank you in advance for your suggestions
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Old 09-07-2016, 08:59 AM   #2
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Hello,

differential and gearbox are 2 independent parts. Gearbox can be completely separated from the differential.

Problem i see is the input and output shaft, which have to be connected precisely to the differential and clutch. I would not remove the gearbox with the differential in the car.

Regards, Markus
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Old 09-07-2016, 10:44 AM   #3
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Quote:
Originally Posted by Smallblock454 View Post
Hello,

differential and gearbox are 2 independent parts. Gearbox can be completely separated from the differential.

Problem i see is the input and output shaft, which have to be connected precisely to the differential and clutch. I would not remove the gearbox with the differential in the car.

Regards, Markus
Hello Markus,

Yes, I know about the differences between the differential and gearbox.

On the picture I am talking about, it shows the complete transaxle (installed on the car, were you can see the complete gear cluster) but without the external rear housing (removed to drill and install the AN fittings for an external oil cooler).

For this reason I was inquiring about the possibility of my car having a loose bolt (the bolt that secures the selector fork to the shaft) allowing you to move the selector shaft back and forth without actually moving the gears to engage.

I am not sure if what I am trying to my explain makes sense or not (English is my second language)..

Last edited by Gilles; 09-07-2016 at 10:49 AM.
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Old 09-07-2016, 02:53 PM   #4
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ASk GBox for advice since they did the repair/upgrade.
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Old 09-07-2016, 05:08 PM   #5
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I found the picture..!

Thanks Eric..!

http://i118.photobucket.com/albums/o93/addictiveCompound/IMG_0094.jpg
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Old 09-07-2016, 09:43 PM   #6
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Hello Giller,

thanks for the photo.

Problem i see is that you have to manage to bring everything together exactly and without tenseness. Means to fit the shafts into the bearings of the housing and torque the housing to the differential. In general this is why you mount the gearbox housing to the differential while the differential shows shafts up.

5th and 6th gear: Don't think it can be caused by the cable. If one gear works and it is the right cable, shifter and gear lever all gears should work. More probable that a claw can cause this problem.

Have you tested to put in 5th and 6th gear manually at the transmission?
Do you have a short shifter mechanism?

Regards, Markus

Last edited by Smallblock454; 09-07-2016 at 09:52 PM.
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Old 09-09-2016, 06:07 AM   #7
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Update...

After disconnecting the shifter cables from the transmission, I tried to engage 5th and 6th gears manually (car on jack stands) and after several attempts only once managed to engage 6th... this shows that it is an internal issue and not cable related.

Yesterday I called two specialty shops, both of them specialize in Porsche transmissions: GBox mentioned that it could be a broken shift fork and the other shop California Motorsports, mentioned that it could also be a broken retaining clip, and either way the transmission has to come out..

For reference are the numbers 6 and 7 on the attached picture.

Last edited by Gilles; 09-09-2016 at 06:10 AM.
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Old 09-09-2016, 07:48 AM   #8
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Hello,

shift fork that is what i've meant with "claw".

Number 7 on your picture is the shift fork 1st/2nd gear.

---

Number 32 is the shift fork for 5/6th gear. As you can see it is fixed with a hexagon bolt (13). Maybe this came loose. This would explain why you could push in 6th gear one time.



Number 6 on the photo is the push rod for 5/6th gear. It has some locking elements (7/8) in it. If they get loose i think you won't be able to shift these gears anymore.



Hope this is helpful.

Regards, Markus

Last edited by Smallblock454; 09-09-2016 at 07:53 AM.
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Old 09-09-2016, 10:23 AM   #9
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You can remove the rear cover from the rest of the transmission without removing the whole transmission. It takes a little manipulation to get the shift forks re-engaged, but it is doable.
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Old 09-09-2016, 02:21 PM   #10
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Markus,
Your explanation is quite plausible. How did the bolt loosen? No thread-lock?
Those are very useful and detailed parts drawings.Invaluable for these discussions. Are they from the PET ? If they are ,can you offer us a link ?
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Old 09-09-2016, 11:22 PM   #11
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Hello Gelbster,

in general this screw won't come loose, but as Gilles mentioned the gearbox had an overhaul and got replaced pinion and mainshaft bearings and 3rd and 2nd gear synchros (along with a OS Giken LSD).

Number 34 on the lower photo is fixed gear wheel of 3rd gear. Number 20 is shift rod for 1st/2nd gear.

To replace the synchros of 2nd and 3rd gear they needed to disassemble the complete gearbox. So maybe this was the time when the fault was built in. But that is only a guess – everything can fail sometimes.

Sorry, can't offer a link.

Regards, Markus
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