I have a 73 240Z with a 4 speed and a stock rear differential.

I am going to change the differential to a Subaru r 180 with 3.9 ratio limited slip.

Do I need to change the speedo gear in the transmission and if yes to which one.

In the future I will be changing to a 5 speed but not at this time.

Thanks for your help with this.

Manny

What rear end gears are you running now? From that ratio to the new ratio, it is purely that % difference, old speedo gear to new speedo gear. That's also assuming you aren't changing tire sizes also. With the sppedo gears that are available, you will more than likely only get close.

I don't really know what the gearing is now. It is the orginal stock diff.

19 tooth white gear is for 3.9

Here's a link in case you need more info:

http://www.geocities.com/inlinestroker/ratio.html

19 tooth white gear is for 3.9

Now that is a sterling piece of info. If you are running near stock tire height you should be good to go with the white gear.

Does the white gear need any reorientation in the tranny case to mesh the teeth with the drive gear?

Thanks guys. very helpful info. I'll find a white one somewhere.

Now that is a sterling piece of info. If you are running near stock tire height you should be good to go with the white gear.

Does the white gear need any reorientation in the tranny case to mesh the teeth with the drive gear?

It depends on the cog carrier. If manny gets a 5 spd from a late 280zx then he just needs to keep the carrier with it's white gear. It "should" already have the white cog. If he just gets the cog from courtesy nissan, he can replace the cog that is in the stock 4 spd with the white one. If he get s 5 spd without a spdo carrier then he can use his stock 4 spd carrier with the white cog and cut a slot on the opposite side and turn the carrier 180 deg.

ok I just confused myself, hopefully you can make sense what i wrote.

Darrel, When the time comes to do this I'll call you.

ok Manny.

I'm just making it sound harder than it really is.

Manny, good luck getting a white speedo cog from Courtesy. Try Zmanofwashington: www.zspecialties.com. 1-800-518-5480. He is a great guy to deal with and usually has these in stock. I got a red cog from him a while back for my 4:11 w/ late model 5 spd. I had to do as Darrel said and rotate the cog holder 180 degrees and cut a new slot in it with my Dremel because it came out of my 4 spd. Piece of cake. Works great...speedo is accurate. If you are going to use your 4 spd you won't have to do anything except swap out the cogs. Be advised, however that you will be turning some high rpms on the highway with a 4 spd and a 3:90.

Cheers, Mike