Thread: Looking at my Bang for Buck options

You have a 3.538 fdgr. You're looking for rear diff out of a 2.0T which is 3.909. Perfect OEM fitment thats as high as you can go as far as I know. Do you have an LSD? The change out it pretty straight forward but if you've got both cars in the same shop it'd be easier to just swap pumpkins.

Thank You

So you are saying this is a simple swap?

I have been looking for a hard confirmation of that!

That this is a simple straightforward swap of pumpkins without any serious complications as to the computer calibrations on engine or transmission, etc.

I have not yet started the search for source of a 3.909 from a 2.0t. Does it matter if the donor is from a manual or automatic 2.0t? Are they both 3.909?

If this is true … then I will start searching for a wreck.

Therefore the simplest would be to go to a junkyard and have them do a nation-wide computer search for pumpkin?

Alternative – Does Hyundai sell new OEM 2.0t pumpkins?

At present I am a stock/ basic 3.8 coupe … unless it came with LSD then I do not have LSD. Should I look into LSD as a good $$$ per acceleration investment trade-off?

In the 70’s I use to change out rear end on my 67’ Vette between street & strip every couple of weeks … is this as simple as that? Is this a DIY job?

Thoughts & Suggestions?

Thanks You
Ron

Swapping theses are like swapping any non-live axel differential. Check with your dealership if there are any specific gaskets or anything that should be replaced instead of reused.

As far as I know, you don't need to change any ECU settings. As long as your wheels are not spinning at different speeds (such as unmatched rims) from eachother then the ECU doesn't care.

I'd have them search for rear differential rather than pumpkin ;)

Hyundai will sell you a new diff, you'll have to check with your dealer for pricing, but from what I understand.. they're not cheap.

Since you have a US 3.8 Base, I'd assume you don't have the LSD. Easiest way to know though is, do you have 19" rims and Brembo brakes?

If you've changed rear diffs before you know your way around a wrench, then you should be able to do this. I'd try and find a buddy to help though and lift just to make it easier.

A LSD will help you get the power to the ground since it basically forces both wheels to power unlike an open-diff. If that translates into quicker acceleration.. well from what I've seen that depends more on the driver than on the diff.

I found this on Hyundai's site while looking for a spec:
2.0T 3.8
Final drive ratio (MT) 3.9:1 3.5:1
Final drive ratio (AT) 4.2:1 3.7:1


now.. my shop manual doesn't issue a different spec for the AT's... but this is from Hyundai's US website.

Thank You Again

Great - I now have a much higher comfort level about starting this project.

Did I understand you correctly … that the fdgr ratio on the 2.0t (AT) is 4.2:1?

So I should specifically narrow my search to that rear end … looking strictly for a 2.0t rear-end from an automatic?

Ok -so the Hyundai LSD is essentially modern version of the old Chevy positraction rear-ends from the 50's & 60's.

So are all 2.0t (AT) rear-ends LSD? … Or is that a sub-group of that differential, which I would also narrow my search around?

I’m glad you mentioned your shop manual. I guess I need to invest in a service/ repair/ shop manual now.

I have looked on-line for one but so far have found only a “2010 HYUNDAI GENESIS COUPE Service Repair Manual” on CD at e-bay. I guess I should check with a dealership parts department for a hard copy.

According to hyundaiusa.com the 2.0T (AT) is 4.2:1, the shop manual however says 3.909:1. If you look specifically for an AT rear diff, you can't lose I guess. I don't think any US-spec 2.0T with an Auto gets an LSD though... you'll have to check into that.

The Hyundai LSD is a Torque Sensing (Torsen) Limited Slip differential, it's a gear type differential designed to make oversteer easier to control and maximize traction. If you're after straight line performance, I wouldn't worry too much about if it's LSD or not, if you want to corner I'd say upgrade to a Cusco or Kaaz clutch-type.. needs more servicing but it's better performing.

I downloaded my shop-manual in PDF format but I can't find the link and I like to keep a copy on my smartphone. But you can access the service manual for free by signing up at Hyundai Service Website, it's a legit Hyundai website that you have to sign up for to get access, might need your VIN for confirmation that you're a Hyundai owner.

Thanks very much for your help.

Below is a link to download Zip Files for both the 2010 2.0t and the 3.8 shop manuals.

Index of /gencoupe

I downloaded both, ran them through the anti-virus software (clean) and opened both zip files. Looks like both are good clear shop manuals.

Today I bought a fdgr 4.2:1 differential to go in my 3.8