Easily. Jack it up- both rears in the air. Uncouple the driveshaft from the diff (four bolts). With the brake off, spin the rear wheels by hand. If the diff is chunky salsa, you'll know.

No one likes a braggadocio. :fawk:

lifted the drivers side rear, driveshaft is still bolted and looks ok. Do I have to replace the entire diff or just the gears?

It doesnt matter if your in a parking lot or on the street, the 1.6 diff is overly weak. Look at this comparison photo:

http://www.miata.net/garage/diffguide/01.jpg

Thats your diff on the right. You can get it back on the road w/ another 1.6, but I would recommend a 1.8. Hell you can find even a 1.8 open on the cheap.

Im sure it was the diff, I blew mine 3 weeks ago and it was the first time I blew a diff in any car. At first i thought it was the drive shaft beacuse of the vibration in the shifter but it was just the vibration from the diff down the driveshaft. I find it hard to believe that anyone could break a drive shaft on stock power, if installed correctly.

ok so which years 1.8 diff will work with a 1990 1.6?

http://members.aol.com/solomiata/Drivetrain.html

and this will help when shopping

http://www.miata.net/garage/diffguide/index.html

I figured you need to hear one more time to believe everyone else.
IT'S YOUR DIFF.
Complete 1.8 diff swaps are found fairly easily, make sure you get a complete swap, though, otherwise you have to worry about interchangable parts etc.
I highly recomend you get a RX-7 clutchpack as well since you are already at the best time to upgrade to a LSD. Now go utilize the search function and leave me alone to scratch my nuts.

Thank you Newbsause

ok I just checked a few yards around here only 1 has any miatas out of 5, and they dont have any 94s for a 90 dif was told $470

ok to the linkes newbsause posted, is it just a 94 that would work?

http://car-part.com/

Any '94-'05 will do, so long as you get the driveshaft and axles. If you can get the axles with the hubs still attached, all the better- they'll bolt right onto your 1.6 control arms, so you don't have to move heaven and earth to get the axles nuts undone.

If you want a Torsen, use the following chart to determine whether or not your donor car came with one. http://www.miata.net/faq/Miata90-97A3.pdf

ok anything 94 or newer with a 1.8 and I need the driveshaft, halfshafts and a diff, anything else Im gonna need to do the swap?

When I did the swap in my first miata I found a full rear subframe and drive shaft and swapped it all in one shot. It was actually cheaper that way.

I am far from being that lucky, far far far far far. I can barely even find any Miatas in the area. I might just go sit in the car and cry

Yes, you'll need four new nuts & bolts to hold the driveshaft to the diff. The 1.8 uses larger bolts- 10mm I think. Those are a hardware-store item, they don't have to be OEM.

Oh, and a chisel.

Look in the classfieds on all the Miata forums, that will be your best bet if car-part doesn't come up with anything.

yeah I mailed a few people on the m.net classifieds.

Why a chisel?

You'll figure it out when you remove your diff...d'oh, said too much ;)

oh crap, would a diff from an auto work? or does it have to be a manual?

I have the manual 5spd