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Install Guide: Q45 Differential swap into 240SX subframe

45K views 31 replies 27 participants last post by  Aithanmier  
#1 · (Edited)
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!
 
#9 ·
i know i am off the subject a lil but just for others to know. i have a 95 base s14 and i changed the on wheel wonder diff to a 92 300zx diff but they would not bolt to my axels so i just too out my one wheel wonder ales and put them in the 300zx tranny. been ther eofr a year and no problems. i race at ht estrip almost every other wed. hope this helps someone. now i dont have to swap for the 5 lug conversion and keep my 4 lug wheels
 
#10 ·
i snapped my stock 6 bolt axles with my 95 j30 diff, so i swapped to a 90 z32 n/a diff with 5 bolt axles from a 92-94 j30 5 bolt axles and they look like they can take alot more then the 6 bolt axles, but to let you know on the s14 you dont have to swap out the rear cover on the q45 diff cause it should bolt up to the subframe no problem.
 
#20 ·
or should i just keep tha welded diff till it gives out? ive been dd this car without pawer steering AND diff weldge. most people say dd a diff welded 240 sucks, but i love it. almost a year now and not one complaint
I've been DD'n my welded diff for a few days and I'm already ready to swap in an open diff.
 
#25 ·
Whats the downside to a welded diff, anyone ?

As you know VLSD and LSD diff's will allow the wheels to turn at different speeds, a welded diff does not, so when you make a turn the inside tire of the turn skids, which causes the tires to wear out faster, when your paying $250 - $300 per tire it definatly becomes a concern for me.