Zajicek

So I'm swapping my diff to a 1.8, along with driveshaft and axles.
While I'm in there what else should I swap out or upgrade while the access is easy?

I'm doing Energy suspension diff bushings, brake upgrade, and motor mounts (maybe) at the same time.
I'm definitely putting better fluid in the diff, probably going to drain the trans and do that too while I'm there, a couple of the posts said you would have to unless you raise the rear high enough, and it could probably use better fluid.
Should I bother replacing my rear trans oil seal when I pull the driveshaft, or only if it is worn and already an issue?
What other wear items could/should be replaced? What performance upgrades would make sense to do at the same time?

Included are pics of the new diff, driveshaft, and axles for no particular reason.

engineered2win

I just did this to my 10AE and I'm OCD as ****, so you may enjoy this.

Things to do:
-Disassembled everything rear of trans.
-Powdercoat control arms and subframe.
-Disassembled diff (so it would be easier to get the bushings out)
-POR15 diff pumpkin and bead blast aluminum case.
-Zinc plate all the rusty bolts (1/3 the cost of new bolts from Mazda) - I'm in the rust belt so just getting everything apart was a challenge
-Remove pinion damper from pinion flange (the cloverleaf dongus in the pic) - it's held to the pinion flange with a rubber bushing that can fail and then the dongus flails around.
-Slather anti-seize all over those axle spines. I've had a hell of a time getting them out of the hubs and they weren't even rusted.
-POR15 spindles and exposed steel on axles

Things to check/replace:
-Noticed some rough spots in the rear u-joint, so replaced DS with 949 Racing part (actually balanced and has replaceable u-joints)
-Check/Replace the pinion seal and axle seals (FYI Timken 2008S pinion seal did not fit my Torsen; I had to buy the correct part from Mazda)
-Installed poly diff bushings
-Installed poly suspension bushings and zerk fittings.
-replace rear hubs (reasons 1 to n: https://www.miataturbo.net/race-prep...ar-hubs-72613/)
-Install ARP wheels studs, since you're replacing your rear hubs
-since you're already replacing the hubs (see above why)- replace wheel bearings & repack with Amsoil Dominator 2000 grease so you don't have to touch them again

I admit some of this stuff isn't necessary, but you asked for it... The seals and hubs are cheap enough that they're worth doing "while you're in there." I bought the Dorman hubs from Rock Auto for like $15 each, and the seals are around $20 total.

I don't have a tow vehicle and racing is supposed to be fun. I don't enjoy driving a few hundred miles only to fix things on the ground, in the paddock, which could have been done in the comfort of my garage beforehand. My goal this year is to not touch anything at the track other than bleed brakes occasionally and swap wheels. One month to Mid Ohio!!

Zajicek

I'm pretty OCD too, but also lazy. Nevertheless, that was quite satisfying.

Went through that thread today.
Didn't want to bump it if I didn't have to, what hubs did you use for the rear? The Dorman 930-550 apparently switched knurling sizes for wheel studs and no longer fits the new or old miata ARP studs, but will fit an unknown Mitsubishi sized stud. According to Bundy the proper studs are ARP 100-7717.
Also figured if I'm doing rear hubs I might as well do front hubs, I think I'm going to go with the FM blueprinted fronts.
Also while following a link in the thread, I found the garage sale section of Planet Miata which has the energy suspension diff bushings for half the price.

Schroedinger

Replace the vent on the 1.8 diff that's going in. I've heard that they can get clogged and cause oil to blow past the seals. I'm not sure if it's true, but the part is like $10 so cheap insurance.