S4 gearbox in S3

Gearboxes, clutches, diffs, wheels & tyres....
Post Reply
User avatar
gt_james
VIP User
VIP User
Posts: 800
Joined: Sun Apr 06, 2014 4:10 pm
Location: Tewkesbury UK
Has thanked: 30 times
Been thanked: 53 times

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?

User avatar
ian65
Admin
Admin
Posts: 6151
Joined: Wed Mar 30, 2011 12:11 am
Has thanked: 189 times
Been thanked: 204 times

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
New custodian of 'Gus', K plate series 3 viewtopic.php?f=4&t=27
1992 Peugeot 205 1.9 GTI
1975 Honda SL125 Street Scrambler
2003 Mercedes SLK 200 Kompressor

TOOL
VIP User
VIP User
Posts: 2581
Joined: Thu Sep 01, 2011 10:30 am
Location: Switzerland
Has thanked: 0
Been thanked: 18 times

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.
Listening to the cowbells

User avatar
gt_james
VIP User
VIP User
Posts: 800
Joined: Sun Apr 06, 2014 4:10 pm
Location: Tewkesbury UK
Has thanked: 30 times
Been thanked: 53 times

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?

TOOL
VIP User
VIP User
Posts: 2581
Joined: Thu Sep 01, 2011 10:30 am
Location: Switzerland
Has thanked: 0
Been thanked: 18 times

Re: S4 gearbox in S3

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

195/50R15s on it.
Listening to the cowbells

User avatar
gt_james
VIP User
VIP User
Posts: 800
Joined: Sun Apr 06, 2014 4:10 pm
Location: Tewkesbury UK
Has thanked: 30 times
Been thanked: 53 times

Re: S4 gearbox in S3

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

Ah same as me then 8-)

Post Reply

Return to “Drivetrain, Wheels & Tyres”