What or is there a difference between a G28/03 and a G28/07 gearbox?
03-13-2023, 05:57 PM
#1
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Thread Starter
What or is there a difference between a G28/03 and a G28/07 gearbox?
Working towards restarting my gearbox project and bumped into a potential good deal. I have a G28/03 box and bumped into a cheap G28/07 box. Can anybody confirm the gears etc are interchangeable or what the difference is?
thx again!
thx again!
03-13-2023, 07:38 PM
#2
Archive Gatekeeper
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The gear ratios are slightly different, as is the ring and pinion set. I don't know how much of the boxes are physically interchangeable. Sliders are the same, I think the shift forks and rods are the same.
03-14-2023, 03:05 AM
#4
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Thread Starter
@Rob Edwards @Mark Anderson thanks for the feedback. I will look further I need a replacement for my ring and pinion since I broke it trying to get the massive bolt of the axl 
Last edited by wopfe; 03-14-2023 at 10:53 AM.
03-14-2023, 09:24 AM
#5
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Your numbers seem to imply that a GTS G28.57 input shaft can be installed in a G28.55 box? I am guessing that it would need also a G28.57 bearing, since Erkka years ago suggested the G28.57 shaft is thicker... If that's the case, there is a massive money saving since the GTS pinion and crownwheel are about 40% of the cost of the G28.55 ...
Alex
03-14-2023, 11:21 AM
#6
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Rob,
Your numbers seem to imply that a GTS G28.57 input shaft can be installed in a G28.55 box? I am guessing that it would need also a G28.57 bearing, since Erkka years ago suggested the G28.57 shaft is thicker... If that's the case, there is a massive money saving since the GTS pinion and crownwheel are about 40% of the cost of the G28.55 ...
Alex
Your numbers seem to imply that a GTS G28.57 input shaft can be installed in a G28.55 box? I am guessing that it would need also a G28.57 bearing, since Erkka years ago suggested the G28.57 shaft is thicker... If that's the case, there is a massive money saving since the GTS pinion and crownwheel are about 40% of the cost of the G28.55 ...
Alex
I ask because I have a 91 GT transmission with a broken fifth gear input shaft.
Kevin
03-14-2023, 08:43 PM
#7
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Can somebody point me to the bearing I will need to retrofit the GTS input shaft?
Last edited by Kevin in Atlanta; 03-14-2023 at 10:43 PM.
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03-14-2023, 10:24 PM
#8
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They're #22A on sheet 303-05 in PET, 999 201 402 00. FWIW they are included with a new GTS 5th gear.
03-14-2023, 11:00 PM
#9
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If so, what do I need to modify to swap the GTS gearset into my 91?
I have to modify something, right? Pardon my ignorance.
03-14-2023, 11:19 PM
#10
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Yes, order a 92830290534 and you get the input shaft, the 5th gear that goes on the layshaft, the needle bearings, and a spankin' new synchro. What's in the box is below in the pic.
I have to confess that I have not done this conversion, so I don't know what else needs to be modified. Just looking at the part numbers of the bits in and around the mainshaft and layshaft between a G28-12/13/55 vs. G28.57, the needle bearings are different, but the input bearing, layshaft axle, and the layshaft gear cluster are all the same. I do have a bare GTS pinion shaft here, if you need measurements off any part of its nose.
I have to confess that I have not done this conversion, so I don't know what else needs to be modified. Just looking at the part numbers of the bits in and around the mainshaft and layshaft between a G28-12/13/55 vs. G28.57, the needle bearings are different, but the input bearing, layshaft axle, and the layshaft gear cluster are all the same. I do have a bare GTS pinion shaft here, if you need measurements off any part of its nose.
03-14-2023, 11:27 PM
#11
Rennlist Member
Yes, order a 92830290534 and you get the input shaft, the 5th gear that goes on the layshaft, the needle bearings, and a spankin' new synchro. What's in the box is below in the pic.
I have to confess that I have not done this conversion, so I don't know what else needs to be modified. Just looking at the part numbers of the bits in and around the main shaft and layshaft between a G28-12/13/55 vs. G28.57, the needle bearings are different, but the input bearing, layshaft axle, and the layshaft gear cluster are all the same. I do have a bare GTS pinion shaft here, if you need measurements off any part of its nose.
I have to confess that I have not done this conversion, so I don't know what else needs to be modified. Just looking at the part numbers of the bits in and around the main shaft and layshaft between a G28-12/13/55 vs. G28.57, the needle bearings are different, but the input bearing, layshaft axle, and the layshaft gear cluster are all the same. I do have a bare GTS pinion shaft here, if you need measurements off any part of its nose.
I'll reach out when I get to the point I need that.
Kevin
03-15-2023, 08:47 AM
#12
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I have a 1990 G28.55 with spalling on the Crownwheel teeth. Porsche wants £2500 for a new set, while the GTS equivalent is only £900, hence I am severely tempted. The G28.13 is even cheaper and would swap straight over, but then I lose the 2.72 rear end vs 2.64...
So what would I need to change to swap a GTS pinion and crownwheel into a GT box?
So what would I need to change to swap a GTS pinion and crownwheel into a GT box?