S4 gearbox in S3

Gearboxes, clutches, diffs, wheels & tyres....
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gt_james
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S4 gearbox in S3

Post by gt_james » Mon Mar 27, 2017 7:08 pm

Has anyone got any experience with swapping an S4 gearbox into an S3?
I am fitting an S4 13B 6 port into my S3, I would like to use the S4 gearbox as the original 12A box is noisey/worn and the S4 has much lower mileage. From what I understand changing the tail housing is fairly straight forward, but I am concerned that it will end up over geared as the diff is 4.1 in an S4 but 3.9 in my S3. Also which speedo drives should I use?

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ian65
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Re: S4 gearbox in S3

Post by ian65 » Mon Mar 27, 2017 7:43 pm

use the S3 speedo driven gear and drive gear in the S4 box
1986 Series 3 13B Turbo II
http://rx7fb.com/viewtopic.php?f=2&t=2400
1992 Peugeot 205 1.9 GTI
1975 Honda SL125 Street Scrambler

TOOL
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Re: S4 gearbox in S3

Post by TOOL » Tue Mar 28, 2017 4:37 am

I have a S4 box in my red RX2. It works fine with my 3.9 LSD. The gearing is better in the S4 box.

It's about 10mm longer than a S3 box iirc.
Back in sunny France

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gt_james
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Re: S4 gearbox in S3

Post by gt_james » Tue Mar 28, 2017 1:01 pm

Thanks for the response guys. I will be using smaller tyres than the FC used, so hopefully this will negate the effects of the 3.9 final drive. I will be using the FB tail housing to account for the shifter being further back. What size tyres did you have TOOL?

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Re: S4 gearbox in S3

Post by TOOL » Tue Mar 28, 2017 3:24 pm

195/50R15s on it.
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gt_james
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Re: S4 gearbox in S3

Post by gt_james » Wed Mar 29, 2017 9:57 am

Ah same as me then 8-)

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