Driveshaft question
 

So I'm picking up a 1.8 diff this weekend. It's open and from a 2001 M/T car, coming with axles.

my car is a 1991 1.6 auto.

I'm having trouble finding the right driveshaft from forum discussions. Apparently the 1.6 auto has 10 splines and is a different length from the M/T version, and the 1.8 driveshaft has 11 or 12 splines and may or may not be two different lengths.

I suppose my first question should be do I even need to switch driveshafts when swapping diffs?
If so, which length/model/year/spline driveshaft do I need?
is there any benefit to a new driveshaft if the old one isn't damaged and the power goals don't exceed the limits of it?
and finally, apparently summit has a diy driveshaft kit. I was wondering if anybody had used that and impressions.

Thanks

You need any 1.8 drive shaft. Splines are all the same, since transmissions are compatible from 90-05.

This thread:
https://forum.miata.net/vb/showthread.php?t=556060

and this thread:
https://forum.miata.net/vb/archive/index.php/t-188275.html

seem to disagree, which is why I asked. Am I missing something? Since the 1.8 driveshafts are definitely 2 different sizes, how will any 1.8 driveshaft work?

I'm sorry BustyJugs and Cherry Bomb weren't able to help you.

Maybe try asking your question here, where someone gives a fuck:

https://www.miata.net/

Sorry if I offended you or something, I'm just getting conflicting answers, so I wanted to make sure I'm not going to have to buy things twice.

You say it works, they say it doesn't. How am I supposed to know who's right, that's why I asked questions to clarify, and gave you sources where I was getting the information from instead of making shit up out of my ass.

Since it seems unlikely that yours is an auto since most people's aren't, I was looking for someone that had done the specific swap I was asking about.

If I'm wrong feel free to let me know, but please tell me why because it doesn't make sense to me as presented so far.

I've done a few diff/torsen swaps in my life, never had issues with a drive shaft going in unless I wasn't lining it up properly. I can say without a doubt that if you're taking a US sold 90-05 Miata and using a US sold 90-05 driveshaft, it'll fit. If you have a 94-05 diff, you'll need a 94-05 driveshaft, and vise versa for 90-93 shit.

Oh I just read your last post.

Why the fuck do you have an auto.

It's neither US sold, or a manual.
I got it imported from Japan.

Because my legs are lazy and I'm uncoordinated. And according to Pat's compound turbo build thread it'll be strong enough for my power goals and shift faster with less drivetrain shock.

The guy only wants 75 for the driveshaft, so I'm going to pull the trigger on it and we'll see what happens. Will update with success or failure.

EDIT: it fits.