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Install Guide: Q45 Differential swap into 240SX subframe

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Install Guide: Q45 Differential swap into 240SX subframe

Old 07-28-2007, 06:59 AM
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Install Guide: Q45 Differential swap into 240SX subframe

First off, I'd like to start out by thanking the staff at Matchless Performance in Carrollton, TX (Dallas) for providing the install photos and labor.

While there is information about this swap on the web, I wanted to provide a concise photo step-by-step install guide for the members.

After installing the Mazworx Drag Axles, and blowing both of the Mazworx modified factory 240sx 29-spline output shafts on the first pass, I found myself looking for upgraded output shaft options.

After talking to SMRacing on FA, he told me about the Q45 differential and the stoutness of this piece.

The 90-96 Q45 (R200) features the same beefy 6-bolt 30-spline axles, hubs, and output shafts used in the 90-96 Nissan 300ZX TT (R230).

All Infiniti Q45's came with VSLD differentials, making this a great upgrade for those looking to upgrade to R230 durability without having to modify the S13/S14 subframe.

The 90-96 Q45 had a 3.54 final gear, and the 97-01 had a 3.69.

The swap is VERY easy to do, and is a rather bolt-in affair using the S13 or S14 differential cover from your current differential.

Parts list needed:

A.) (Your Model S13 or S14) differential cover
B.) Q45 VLSD differential
C.) Q45 or 300ZX TT Wheel Hubs (great upgrade for the 4-lug guys who have been looking for a reason to go 5-lug)
D.) 300ZX TT Driver Side Axle (installed on driver side of 240SX) and Infiniti Q45 Driver Side Axle (installed on passenger side of 240SX).

Here are two comparison photos of the stock Non-VSLD 240SX Output Shaft (left), Q45 (middle) and Mazworx Modified 240SX Output Shaft (right).

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OEM Q45 Output Shafts (driver and passenger)

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1.) Start out by swapping the Q45 differential cover with your factory S13 or S14 diff cover.

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Before we move to the next step, let's take a look at the size difference of the input flange on the Q45 vs 240sx differential. You will need to remove this piece from the Q45 differential, and prepare for modification.

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2.) You will need to take a marker of same kind, and draw out the 240sx driveshaft yoke bolt pattern onto the Q45 input shaft, and prepare for drilling (4) holes.

You could also order a Q45 yoke and have it swapped onto the 240SX driveshaft. However, I dont see the need for the added expense, as the Q45 input shaft flange is large enough that I dont feel tapping four more holes will hurt the structural rigidity.

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All done, now to install back onto the Q45 differential.

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Richie painted this piece black for aesthetic purposes, but here is the drilled input flange installed onto the differential.

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After this step is finished, simply bolt the differential into the 240sx subframe, and re-install.

Note: Your factory driveshaft will not need to be modified in any way.

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I put together this spreadsheet that shows the effects of the Q45 gears on the RB25DET Transmission. It is simple to manipulate, as your choice of transmission may differ.

http://www.undergroundmotorsports.com/rb25q45.xls

Happy Driving!

Last edited by underground; 07-28-2007 at 07:42 AM.
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Old 07-28-2007, 01:25 PM
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great write up!
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Old 07-28-2007, 02:02 PM
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great write up.
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Old 08-02-2007, 02:25 PM
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nice write up but why go through all the work for a Q45 diff. why not just get the J30 diff. with axles, i hear its much easier and you dont need the hubs off a 300zx or Q45 they bolt right up to the 240 hubs and you dont need to remove the diff. cover or anything. Correct me if im wrong thats what i heard
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Old 08-02-2007, 03:04 PM
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Excellent write-up with some great pictures, especially the underbelly shots! That's something that you don't get to see everyday.
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Old 04-20-2011, 05:16 AM
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I LOVE this writeup. thankyou!

one question tho. waht do you do for the speed sensor to keep the speedo accurate? I know for this swap on the z32 na, you use the 97-01 diff with the 3.69 and you can just grab a speed sensor from the twin turbo model and it all works out perfectly. I'm new to the 240sx scene and I dont know what speed sensor from what model would make this all work because the wheel diameter on the 240 is different from the 300 and the 240 doesnt have a stock sensor for the 3.69 gear from my knowlege...
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Old 03-01-2013, 09:11 PM
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It's fairly easy to hook up your speedo for total accuracy. The Q45 diff comes with a ABS sensor on the nose just behind the driveshaft flange. It's a two wire sensor that you hook up to a $80 Dakota Digital speedo box. Their instructions are fairly clear for the initial hook up. After you have it wired as they call for then call their tech line and they will help you dial it in. It will work with any tire diameter you can fit on the car.
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