Mazdaspeed Miata Differential differences

[iKhanh]

I got my replacement seals in the mail the other day. I read over the few threads that mentioned doing the seal, and the most helpful excerpt was this: "Pry out the old seal with a screwdriver. Be very careful not to scratch the seal bore. The seal is really in there so take your time. Once you have the old seal out, cut away all the soft parts so you can use it to install the new seal. Also, make sure you get the little round spring out. Sometimes, it stays behind in the differential. Clean the seal bore thoroughly with a rag. Lube up the new seal with lithium grease inside and out. To install it, press it in evenly with your fingers as far as you can. Keep it nice and straight. Then, using the old seal and a block of wood, tap the new seal all the way into the bore. The seal will go below the surface of the differential housing, that’s why you need the old seal. Make sure it’s completely seated and even when you’re done." -from http://www.miata.net/garage/diffseal.html

Anyway, I couldn't find any pictures so I figured I'll try to take some while I do this. The main thing I found was that I thought the seal was just just rigid rubber, but no, there's a flat metal ring that goes around it making it so rigid. If I had known this, I would have been more rough with the removal of the old seal. Note that I had done this while the differential was off the car, and also the case has been opened, making this SO MUCH easier.

So this is the replacement part you wanna get. I think they fit all Miata differentials (don't quote me on that), but I may be wrong. But this is the piece I ordered and it worked for me.
IMAG1203.jpg

This is what I'll be replacing, on both sides. The rubber has been torn on the outside. The other side looked similar, if not worse.
IMAG1204.jpg

And here it is on the other side, the side that you don't see, that goes into the differential carrier. That inner raised lip portion has a circular spring in it. Be careful of it falling out when prying on the seal, it's very easy to do so. I forgot to take a picture of said spring. Also, if you look closely, there's these slightly recessed squares in the seal; that's where a rigid metal ring is sandwiched in the seal itself. It's pretty stiff so don't worry about bending/breaking it when prying it out.
IMAG1205.jpg

You'll wanna try to pry it out like this if the differential is still in the car. Don't be scared to put some muscle into it.
IMAG1215.jpg

But since my differential is out of the car, I figured it would be easier to pop out the seal from the inside out, which was quick and easy. Just stick your flat head screwdriver in there, behind the metal ring in the seal, and tap on the end of the screwdriver like a chisel several times all around until the seal pops out.
IMAG1217.jpg

So where the seal goes into, the bore, have some solvent and clean it with a rag. Be careful you don't let any debris into the casing. I used some off the shelf generic Autozone brake cleaner and a shop towel. Mine turned out like this.
IMAG1201.jpg
And from the inside..
IMAG1202.jpg

Open up the new seal from the plastic it came in. Here's what a new one looks like. Notice that itty bitty round silver spring in the seal in that second picture. And in the third picture, you can see that metal ring in those squares I mentioned, without gear oil on them. Also, the seal came with that white ribbed gel already applied.
IMAG1218.jpgIMAG1219.jpgIMAG1220.jpg

Part 2 in the next post, since each post is limited to 10 pics.

[iKhanh]

Part 2 (cont.)

So apply some white lithium grease on the seal. Try not to drop the seal while you carefully position it for installation. Press it in as evenly and far as you can into the bore you cleaned a minute ago. Remember, metal spring side goes INTO the differential, and the cone shape faces outwards.
IMAG1224.jpg

Place the old seal on top of the new one, and with a hammer, pound lightly (but with enough force to progressively press the seal into the bore) around the old seal, to press in the new seal. You can get a block of wood and tap on that too I suppose.
IMAG1225.jpg

After you think the seal won't go in anymore, I suggest tapping with a little more force to make sure it is definitely seated in the bore. It should look like this after you're done.
IMAG1226.jpg

I think that's it. Any ideas, thoughts, comments, something, let me know.

[iKhanh]

By the way, these aren't the OEM MSM differential mount bushing things are they? They're rubber. They don't have the those raised circular sections, or is that the "competition" upgraded bushing? Should I go ahead and just buy aftermarket bushings? And what's better: Polyurethane ones or Delrin?
IMAG1230.jpgIMAG1231.jpg

[mini_fd]

Poly is more comfortble and the in betweem of stock and delrin. Delrin is the most stiff out of the three

[iKhanh]

So I'll be attempting at swapping out my open diff for this during the holiday break. Any good ideas or advice I should know? I decided not to upgrade the differential bushings at this time; maybe in the future.

Since it would be kinda difficult to get gear oil into the carrier once it's installed, is the possibility of filling it up prior to lifting it into place in the car okay? And should I just lube up the end of the axle shaft that goes into the diff with the same fluid as lube?

[iKhanh]

bought some larger sized sockets (diff drain & fill plugs and axle lock nut) and i just wanted to share with you guys some of my findings: the 29mm socket fits the OEM axle lock nut on my 90 with an open diff, but apparently doesn't fit the old one that's on the '04 MSM; i'll be bringing it with me to the store and finding the appropriate size and update this when i can. AND while the fill plug on the original open diff on my car is a 23mm, on the MSM housing, it's a 24mm, which is the same as the drain plugs on both units.

update: according to this http://www.autopartswarehouse.com/se...universal:0%29 website, the rear nut, is a 32mm size. i'll verify when i get a chance. probably won't be for a while though since i noticed that the cv boot ripped.

[iKhanh]

also, while perusing things, i found something interesting. all my previous research has pretty much concluded that the final drive ratio for the MSM is the 4.1:1... but on Miata Roadster http://miataroadster.com/mazda/mazda...s/g-63127.aspx, when you look at the Mazdaspeed model, it says it's a 3.636. now, Bill at Miata Roadster, great reputable guy, i'd value his expertise, so i'm a bit confused. is it a 4.1 or 3.636??

[MixedBreed]

I believe that list is for replacement gear sets that you can buy for that model, not the factory final drive ratio. So say you have an 04-05 Mazdaspeed, you can buy that 3.636 gear set from MiataRoadster to replace the factory 4.1 gear set in your car.

[iKhanh]

just thought i'd put this here. so in addition to axles that's unique to the MSM diff, the driveshaft is as well. seems that every other Miata driveshaft from 90-05 (non-MSM) has non-replaceable u-joints, but the MSM does! good to know.
http://www.mazda-speed.com/forum2/in...?topic=27041.0