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Old 03-16-2011, 12:37 PM   #1
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Default Diff swap, what do I need to buy?

I have a new diff, but it's just the diff without the cover or shafts or anything. It looks like it was stored open in a woodshop for a while before it was sent to me.

What do I need to replace mine? I know I need fluid, I can handle that. Do I need a new gasket anywhere or anything like that? Also, how do you guys recommend cleaning the sawdust off the gears? There isn't too much of it but it seems a little caked on so I don't think compressed air is going to cut it.
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Old 03-16-2011, 12:41 PM   #2
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I would flush it with mineral spirits a couple times, put a cheap oil in and drain after a slow trip up/down the street. You need the axles and driveshaft if doing a 1.6 to 1.8 swap. If just doing a 1.8 open to 1.8 torsen, then all you need is the diff.
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Old 03-16-2011, 01:04 PM   #3
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It is a 1.8 4.3 open to 1.8 3.9 torsen swap. So there is either no gasket or a reusable gasket between the two big pieces of the diff? Sorry I don't know the terms, but all I bought is the steel part, I'll be reusing the aluminum piece with the fins, and the arms that attach to the car, and my shafts.

On a side note, how hard is it to fix the speedometer so it will read correctly with the new gearing?
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Old 03-16-2011, 01:05 PM   #4
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When I swapped mine I sprayed it with engine degreaser, then pressure washed it til it was spotless.
Also replaced the seals on the half shaft openings, and put a thin bead of silicone/sealant on the surface where the carrier bolts up to the diff. There is no gasket there.

For the speedo you'll need a new speedo gear.
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Old 03-16-2011, 01:55 PM   #5
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I have heard of this speedo gear, but where do I find them and how hard is it to replace?
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Old 03-16-2011, 02:20 PM   #6
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There is no gasket, just use a gasket maker for it.

Definately buy a case of brake cleaner and spray it out as much as possible.

Also change the the axle seals.

Buy cheap diff fluid and change it a couple times in the first week...then put in good stuff and forget about it.
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Old 03-16-2011, 03:09 PM   #7
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Clean it with degreaser / brake cleaner until spotless, replace axle seals, use a thin line of rtv to seal it to the rear case, speedo gear can be found at the dealer although I am not sure weather you change the one on the sensor or the one in the trans. Change the fluid after about 15 miles it will be fine.
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Old 03-16-2011, 03:11 PM   #8
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You change the one on the sensor IIRC
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Old 03-16-2011, 03:15 PM   #9
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Good to know. If anyone else wanted to know if you have a 92 miata with a 2j and a w58 trans with a speedo drive out of a r154 trans and a rx-7 diff it will be within 2 mph.lol
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Old 03-16-2011, 05:04 PM   #10
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Quote:
Originally Posted by 18psi View Post
You change the one on the sensor IIRC
That sounds easier than changing the one in the trans.

Is there anything I should know when I start swapping the diff? What's the easiest way to get it out? And the axles?
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Old 03-16-2011, 05:10 PM   #11
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Use a big prybar to pop the axles out and be ready to catch it when you take the top bolts out.lol
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Old 03-16-2011, 05:18 PM   #12
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Quote:
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Use a big prybar to pop the axles out and be ready to catch it when you take the top bolts out.lol
Pry bar? You lost me there... do I even have to remove them at the hubs? And since it's an '02, don't I have two-piece axles? I'm new to working on the back end of a car if you couldn't tell.
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Old 03-16-2011, 05:27 PM   #13
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The 02 has one piece axles like a honda would have. You should be able to remove the rear wheel remove the upper control arm mount to the spindle and the sway bar link. This will give you enough movement to get the axles out. Now take a pry bar and pry between the end of the axle and the diff housing they should make a pop and slide out. Push the out and let them hang then remove your diff. You can take the axles all the way out by removing the axles nuts at the hubs and pulling them out if you want.
I would recommend lubing the PPF Frame bolts for a few days if possible to make things easy.
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Old 03-16-2011, 05:28 PM   #14
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I did the swap twice without touching the rear wheels/hubs/or control arms.
Its a little more finicky coming out, but I still got it done both times.

If you drop the diff it gives you some room to pull each shaft out 1 at a time. Just gotta get a little creative with it.

Its not hard at all IMO. Just takes time

And yes pry-bar will help you big time
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Old 03-16-2011, 05:31 PM   #15
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Thanks for the tip 18psi I will have to try that next time I have always popped off the upper control arm. Never really thought to drop the rear first. Either way will work.
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Old 03-16-2011, 05:38 PM   #16
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Sweet, sounds a lot easier than swapping a clutch. I'm going to attempt it Friday morning by myself. Good news is I have a lift to use.
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Old 03-16-2011, 05:45 PM   #17
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For the speed sensor gear you just remove a 10mm bolt on the top rear of the tranny and it comes right out. Jack the back end of the car higher than the front or fluid will run out of the transmission. As for where to get the sensor, I've had great luck with partsgroup.com.
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Old 03-16-2011, 08:03 PM   #18
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<rant> Well, I'm quite frustrated. I went all over creation after work trying to find axle seals, but of couse nobody carries them for a miata. I'm going to do the swap on Friday morning so I don't have time to order them and have them shipped. If I had one complaint about the miata, it would be the lack of local parts. Sure, you can get anything you want but you have to know you need it a week in advance. My other car is a '93 Cherokee, and I can get any part I want for it at any store, usually for less than $20. The fact that I can't do that for the miata pisses me off. </Rant>

So anyway, I'm going to just swap the diff without changing the axle seals. It looks like the axle seals are on the part I'm re-using anyway, so I already know they don't leak.
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Old 03-16-2011, 08:49 PM   #19
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Someone please jump in and correct me if i'm wrong, but isn't there a much more substantial process than "bolt it in and go" involved?
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Old 03-16-2011, 11:03 PM   #20
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I think if the differential was new, and not an already used and broken in diff there would be more to it.

I would also recommend having a pickle fork around, for this job and many others down the line.
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