I'm thinking about changing my gear ratio and have a couple of questions. I have a 2010 coupe 3.8 Track, manual. To go to a 3.9, what can I swap internally so that I can keep the lsd? And will a 2010 2.0t with the automatic transmission be a suitable donor? It's final drive is 3.9, but it doesn't have a 6th gear. Or do I have to find a 2.0t donor that is manual with lsd, and swap the whole differential?
3.5 to 3.9 swap
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15,550 Posts
Supposedly everything is interchangeable. So just bolt the ring gear to the LSD and then have the proper spacers to get the correct backlash and pinion gear meshing the ring gear correctly.
transmissions don't matter.
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15,550 Posts
ring gear and pinion gear
So it would be easier to just move over the lsd to the 2.0 carrier, and not have to get new seals, if you don't remove the pinion gear.
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998 Posts
I went from 3.73 to 4.181 and it was probably one of the best changes I've made aside from the turbo swap. It was my first time doing any gear work and I was able to figure it out so I bet you will be able to as well.
Easiest way IMO is to:
- Buy the whole 3.9 carrier assembly from a donor car (lots of them on ebay, just verify what you are ordering so you get the correct gearing)
- Then take the LSD out of your current carrier
- Attach the 3.9 ring gear to you LSD
- Check backlash and pinion gear depth - I used the spacers that were in my car paired with the LSD, but this might not work for you.
- Take your LSD with the 3.9 ring gear attached and install it into the donor car carrier assembly
- Turn it by hand to make sure its moving freely before you reinstall it.
For me it was a direct bolt in to put my LSD in a 4.181 carrier, I didn't have to adjust pinion depth or backlash, but you might have to play with the shims and if you do it can get a bit tedious to get it right. After I installed it I filled it with new gear oil and ran it easy for 500 miles, then changed the oil again. I ran it for the summer and changed the oil one last time before putting it away for the season. I only did this to help ensure the gears meshed correctly and then clean out any metal particles that resulted from that process.
Easiest way IMO is to:
- Buy the whole 3.9 carrier assembly from a donor car (lots of them on ebay, just verify what you are ordering so you get the correct gearing)
- Then take the LSD out of your current carrier
- Attach the 3.9 ring gear to you LSD
- Check backlash and pinion gear depth - I used the spacers that were in my car paired with the LSD, but this might not work for you.
- Take your LSD with the 3.9 ring gear attached and install it into the donor car carrier assembly
- Turn it by hand to make sure its moving freely before you reinstall it.
For me it was a direct bolt in to put my LSD in a 4.181 carrier, I didn't have to adjust pinion depth or backlash, but you might have to play with the shims and if you do it can get a bit tedious to get it right. After I installed it I filled it with new gear oil and ran it easy for 500 miles, then changed the oil again. I ran it for the summer and changed the oil one last time before putting it away for the season. I only did this to help ensure the gears meshed correctly and then clean out any metal particles that resulted from that process.
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22 Posts
Swapping soon...
I would agree, all of the research i have done leads to doing this. Otherwise you will have to press pinion out and deal with the seals.
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