3.90 Gear and Driveshaft Installed

Hi everybody and thanks for checking out my website,

Today’s project was to install a new 3.90 Ring and Pinion Gear along with installing a one-piece driveshaft. The factory gear is a 3.46, and also came with a 2-piece driveshaft. I am hoping to gain a little more on the bottom end as far as speed goes with the new 3.90 gear, as well as putting in a lighter and stronger one-piece driveshaft instead of running the horrible 2-piece one that the car comes with.

Special thanks to Kevin at Straightline Performance in Joliet Illinois for the install. Great work as always!

PARTS LIST:

Motive Gear 3.90 Ring and Pinion

 

Drive Shaft Shop 3.5″ Driveshaft 1000HP 1-Piece Aluminum Shaft with Direct-Fit Rear Flange

 

THE INSTALL

Drop the pumpkin, install the new driveshaft:

 

Remove the gears, install the new ones:

Use an excessive amount of heat on the side adjusters to remove them. Do not be afraid to use a torch. This is probably the hardest part of the job and is the only way to remove the ring and pinion gear. Do not re-use the stock adjusters. Once they are removed, throw them away and install new side adjusters which can be purchased at GForce1320 Engineering.

Parts used from GForce1320 for the install (minus the gears). Click on the links under the pictures to visit the page where they can be purchased:

Gutted the differential and all new parts installed:

 

RE-INSTALL THE DIFFERENTIAL:

Unfortunately, I have no pictures of the rear end re-installed. We ran out of time trying to get the car back together.

FINAL RESULTS:

The new gears and drive shaft definitely made a difference. The car pulls great and feels faster. And having a lighter, stronger driveshaft makes the rear end virtually bulletproof!

The only real concern I do have is the gears are noisy. Which is a repeated complaint about Motive Gear 3.90 set up. Have yet to read or hear about a 3.90 gear install without any gear noise, so all is well.

 

5 Comments

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  1. Brendon

    How did you recalibrate your speedometer? I would be interested in doing a similar upgrade to my car, thanks!

    1. HP Tuners is what was used to re-calibrate the speedometer. I had my tuner do it for me. Good question, thank you.

  2. Jay jarman

    How do you like the 3.90s? My diff is shot and I recently picked up a trutrac for a steal so the money saved is going to gears. I was thinking 3.70s but after seeing your setup with the auto and all its made me rethink the 3.70s and go 3.90.

    1. I would go with the 3:90 gears to be honest, especially if you have an automatic. Roll on pull is fantastic. Factory gear ratio I believe is a 3:46, so putting a 3:70 ring and pinion in the rear is not going to be a huge noticeable difference over factory. The 3:90 will give you some great pull and you can finish a quarter mile in third gear on an automatic without going into overdrive. The 4:11 gear is great for quarter mile drag racing, but some will find it to be a bit much for daily driving around town and not recommended for the highway. The 4:11 gear will raise your RPM’s quite a bit while just driving around town and on the highway will be very high RPM’s and may be a bit much. You can’t go wrong with the 3:90 gear set up, just be prepared for some gear noise, but you will get used to it. Also be sure to purchase the Gforce1320 gear installation kit found here, and also the billet side adjusters found here.

  3. Jay jarman

    Awesome. Thanks man. Chris from gforce also recommended 3.90s. I definitely planned to get the gears and install kit from gforce im gunna attempt to reuse the side adjusters. If they don’t work out then ill order the gforce ones. Thanks again man. Love the page by the way. Lots of good info on here.

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