Smyrna388Z Posted February 11, 2017 Share Posted February 11, 2017 By chance has anyone on this site changed the gear ratio of a 1989-1996 Q45 differential? My project is to change the 3.54 gears in a Q45 differential to the 4.08 gears from a NA 300ZX. The Q45 differential is currently installed behind an LT1 and 700r4 transmission in a 1976 280Z. Thank you to anyone who may be able to give me some information. Quote Link to comment Share on other sites More sharing options...
Smyrna388Z Posted February 18, 2017 Author Share Posted February 18, 2017 (edited) OK, no replies or supporting information to my original post. So, I am going to attempt this swap and document it here. The top carrier is from a NA 1996 300ZX. The bottom carrier is from a 1994 Q45. My plan over the next two weeks is to transfer the 300ZX 4.08 gear set into the Q45 carrier; replacing the 3.54 gear set and improving 1/8th mile ETs. Stay tuned. Edited February 18, 2017 by Smyrna388Z Quote Link to comment Share on other sites More sharing options...
Smyrna388Z Posted February 18, 2017 Author Share Posted February 18, 2017 The swap is possible and easy to do. Simply remove the VLSD carrier, axle stubs, and input flange from the Q45 carrier case and install them into the 300ZX carrier case. The Q45 differential I am using is a non-TCS differential. It is longer than the 300ZX differential, but the pinion gears are the same length. With the input flange from the Q45 installed on the 300ZX case, the total length is back to the original non-TCS length that I need. I need this length because I am replacing a non-TCS Q45 differently that is currently in my 280Z. The VLSD carriers of the 300ZX and Q45 are identical with the exception of the axle size they will accept. The Q45 stub axle is larger and this is why I am keeping the Q45 carrier. Because they are identical including the 13mm ring bolts, I should be able to install it back into the case just as the 300ZX carrier was installed. No need to setup the pinion depth and backlash. The pinion was never removed and I will place the carrier left and right shims just as I found them. Quote Link to comment Share on other sites More sharing options...
Smyrna388Z Posted February 27, 2017 Author Share Posted February 27, 2017 (edited) Confirmed. Q45 carrier installed in 300ZX differential housing with 4.08 gears and Q45 input companion flange. The Q45 carrier shifts right (passenger side) due to the 4.08 gear setup. Because of this, the Q45 left side stub axle is too short! To overcome this, a ~.312 spacer would be needed between the ring gear and carrier. This isn't the difficult part. The difficult part is finding 10 M13-1.25/30 bolts to reach through the spacer. Because of this, I'm taking another approach. I am going to use a right side stub axle on the left side. This is going to require the shaft to be cut shorter. Note; you will need a right side axle stub from a Q45 that has 'full length' splines cut in it. You can see the different types in the attached picture. I will be cutting the center stub axle. The left axlet is the one that is too short after the carrier shifted right. The sealing surface length needs to be longer so that the shaft will fully engage the VLSD coupling and the support bearing. You can see that this surface on the center stub axle is longer. The surface is the same on the right axle, but there will not be enough splines once the shaft is shortened. Edited February 27, 2017 by Smyrna388Z Quote Link to comment Share on other sites More sharing options...
Smyrna388Z Posted March 2, 2017 Author Share Posted March 2, 2017 (edited) Problem resolved! Cutting a right stub axle to be used on the left side worked great. I built a wooden jig to spin the axle under a chop saw. I used this setup to cut a cir-clip groove and to shorten the axle. Awesome results. I used two clamp collars to help guide the chop saw blade, this made for precise cuts. All I have to do now is replace the seals and install it in the car. 4.08 rear gears will be pushing my 280Z down the road. trim.11990050-DDBD-4E19-B3FF-4B71435BBC12.MOV trim.79395761-6E43-4FB2-8151-FC67A0514FF8.MOV Edited March 2, 2017 by Smyrna388Z Quote Link to comment Share on other sites More sharing options...
mutantZ Posted March 2, 2017 Share Posted March 2, 2017 That is an ingenious use of a chop saw. How did you chamfer the end of the stub axle? Quote Link to comment Share on other sites More sharing options...
Smyrna388Z Posted March 2, 2017 Author Share Posted March 2, 2017 (edited) A sanding belt took care of it. Here is finished product ready to go in the car. It is in the 280Z now and everything works great. The 700r4 finds the right gear around town and on the highway to keep RPMs right around 2k. Probably 2700 or 2800 on the interstate in OD. Edited March 2, 2017 by Smyrna388Z Quote Link to comment Share on other sites More sharing options...
sectumsempra Posted July 10, 2017 Share Posted July 10, 2017 This is great! Quote Link to comment Share on other sites More sharing options...
MaxSorin Posted November 5, 2021 Share Posted November 5, 2021 @Smyrna388Z I know I'm bringing this thread up from the dead, but do you still have the 3.54 ring and pinion lying around? I am trying to do the EXACT opposite for my NA diff and get the 3.54 gearing instead of the 4.09. Quote Link to comment Share on other sites More sharing options...
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