AT Viscous LSD Question
 

Hey there everybody, so sorry if this has been answered but I’m having a hard time finding a definitive answer here..

So I have a 2014 AT Sports model with the viscous LSD, and I’m wondering, am I able to change my gearing to 4.08 or does that require a whole LSD swap?? Unfortunately I know essentially nothing about the differential or LSD’s in general, the more I read, the more confused I get.

Basically I’m just wondering if this is going to require a whole swap to a manual LSD or if I can work on mine somehow.

Thanks guys, sorry for what is most likely a stupid question.

It will require a whole swap to a MT diff. The stock VLSD is garbage anyways. Plan to upgrade that to a Wavetrac or an OS Giken.

Damn that really sucks, but thank you.

So to be clear so I fully understand, would I need to buy the MT LSD and then modify it? That’s the idea right? So I need to acquire the base LSD first.

You can acquire any MT diff. You can get an VLSD if that is what you want. You will have a problem with your cruise control working properly with 4.08 gears. Do some searching on here.

Are you asking if you need to change the carrier unit if going to lower gears. What's your gear ratio now?

Yea I’m wondering if I need to change the carrier unit. I’m uncertain how all this works and the forum postings here have only further confused me, especially since some listings of LSD’s, for instance, the Tomei lsd, says it won’t work with the AT. I’m wondering why and how. Since I have the stock VLSD that comes on the sports package, I’m wondering if there’s some kind of way I can change the gearing or what the best method would be to get myself to 4.08.

I appreciate you guys, I’m a novice in this department for sure.

I've been interested in trying the 3.69 gears from the manuals

You will need a MT diff if you have an AT. MT and AT diffs are different. You can't just change the ring and pinion from one to the other.

AT diff= 3.33 gear ratio

MT diff= 3.69, 3.92, or 4.08 gear ratios available

I bought a 3.69 VLSD from a low mile wreck 2016 manual car off ebay.

Cleaned it up, installed new seals, VLSD coupler shims, ring gear bolts (bearings looked new) and a new Nismo rear cover and dropped it in my 2010 sport touring 7AT. Had to buy one stub shaft to bolt to my axles.

Got hundreds of 12 and 11 sec 1/4 mile drag runs on it with 325 drag radials. I keep the grease really clean and do not let the diff overheat, which it prolly would if hot lapped or road raced.

Cheap solution that has worked well so far.

Thanks so much guys, I have a very clear idea of what I need to do now. Really appreciate all the feedback!

You will need to do a swap to a manual diff to change the gearing sadly, but I've done a manual diff swap, it's easy and fits just fine on the AT. Relatively cheap too. As SG4247 said, you will need to buy a different stub shaft for your left axle. (EDIT: You also want to get the matching right stub axle, as the AT one isn't long enough to actually make use of the VLSD inside the diff and won't be held in fully by a retention ring.)

Personally for the auto I wouldn't recommend 4.08's, I'd go 3.9 at most. The gear ratio for 1st and 2nd gears is very, very high in the AT, and I'm confident that 4.08 would be overkill and result in major traction issues when flooring from a standstill even with the VLSD.