I Just Pulled A 4.38 Diff

[71Nissan240Z]

Hey guys I just pulled the front diff of a nissan 720 4x4. I wanted the 4.11 but ended up with the 4.38 which is fine.

I'm a little confused because when I pulled the speedo gear it was yellow. From my understanding it should be purple. Any ideas??

[Zed Head]

Don't forget tire size.  With a bigger tire the diff will spin slower.  A big tire and a 4.38 might spin the propeller shaft at the same speed as a small tire and a 3.36.  Yellow is way down at the other end though.  Count the teeth to be sure what you have. Maybe it's old white.

[71Nissan240Z]

It's a 19 tooth speedo gear. I pulled it off the transfer case. Maybe because it's 4x4 and anticipated big tires is why nissan put that there. Looks like I need to find a 21 tooth somewhere.

I'm a little worried with how low the diff is geared. I wanted the 4.11 but when I finally got it out and saw it was a 4.38 I decided to keep it since it was so clean inside. What are your thoughtz?

[Zed Head]

I can't find the man reference usually used but the one I found says that 19 tooth is the white gear for a 3.9.  A lot closer to a 4.38 than a yellow, for a Z.  510's and Z's both use the same size tire, I believe

 

http://community.ratsun.net/topic/26704-matching-speedo-gears-after-rear-end-swap/  Post #7

 

A similar question came up on another forum and someone posted the link below.  It will give you an idea of the difference you'll see between the two.  It really depends on how you intend to use the car.  Nissan designed the systems to allow starting from a stop easily, including hills, and cruise at freeway speeds.  Race cars need to accelerate from corners and go fast on the straights.  Drag cars need to accelerate and top out in a gear as they hit the lights.  Auto-cross: in the powerband with throttle control.  Stuff like that.

 

http://webspace.webring.com/people/cz/z_design_studio/

[71Nissan240Z]

This setup looks badass. How accurate is this system? With the wheels and tire combo it's setting me up to have a nice drive train with a decent cruising gear 65 mph at 2819 rpms. Still better than the factory 3.36 diff and 4 speed. The red line I have set at 7000 rpms on my ignition controller but usually shift at 6500rpms. It has second gear reaching 60 mpg (mph, shitty android auto correct ( at 6500 rpms.

What's cool is where the rpms stay.

Shifting from first at 6500 into second drops to 400 0 rims

Second to third is 6500 to 4500 rpms

Third to fourth is 6500 to 5000 rpms

And forth to fifth is 6500 to 4800 rpms.

Since my torque is most noticable between 4-5000rpms. It should be a monster. I do notice a power drop after 6500 rpms. But I'm still running a stock manifold embarrassing enough. So that might net a few more ponies up high.

What are your guys thought?

Oh yah. Background info

82 zx 5 speed

4.375 truck 4x4 diff combo

235 45 17 wheels and tires

L28 modified but stock manifold

[madkaw]

I will just say that the ZX trans was meant for a 3.90 diff factory with the gearing. You have increased tire size considerably from stock so that offsets your gearing. You probably are closer to 4.11 gearing in the back with those tires. It should make for fun and quick Z. 

[gnosez]

I have a similar ratio diff (R180 for me) which will get a Quaife installed next month. Your tires are 1.5 inches taller than the 225/50/15 we are required to run in Vintage.

What's next is figuring out the right tranny gears to match the track.

[71Nissan240Z]

I have the same wheel and tire combo for vintage as well. How do u like the diff ratio? Are u using a zx transmission?