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Rx7 diff swap

 
Old 11-05-2017, 07:04 PM
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Default Rx7 diff swap

So, im beginning to build a 2000 for the 2018 grm challenge. Currently the roller has an open diff, as i stole the torsen for my good miata.

Ive found conflicting information about the rx7 diff swap. Im looking at this purely for the clutch type differential. Engine will NOT be stock, and id actually prefer a lower (numerically) ratii for the planned engine. 3.5 or 3.7 would be perfect.

Lsd clutch will be rebuilt and custom shimmed.

What it seems to be is that the 85-88 non turbo rx7, 99-05 aluminium housing, 99-05 driveshaft, 99-05 axles, and it theoretically all bolts together. Or, all thise parts plus the miata hogshead (what mopar calls the complete drop out centersection containing the piniin, diff, and ring) and miata gears with just the lsd from the rx7.

Ive been searching, but haven't seen any still functional pictures, or found the thread that makes it all not confusing.

So what is the real story here?

Thanks y'all
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Old 11-05-2017, 07:13 PM
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99 driveshaft, RX7 LSD diff, 99-05 aluminum housing, 99-05 axles, 99-05 miata axle seals, and you're good to go. I ran this combo myself for years with the diff shimmed. I also have 99 axles, and a RX7 LSD diff laying around if you haven't already got them.
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Old 11-05-2017, 07:29 PM
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So, i should treat this the same as a 9 inch ford, or 8.75 mopar? Pull the axles and driveshaft, remove a dozen nuts, drop whole gear/diff assembly, replace?

i already have all the 99-05 stuff, as its a 2000.

where are you at? Ill need to find the clutch type differential, and then figure out what to shim it to.

expecting 300ft-lbs, 300hp at the wheels.....
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Old 11-05-2017, 08:37 PM
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I'm just north of Houston, TX.

Since you have all the 99-05 stuff, you just need the RX7 LSD and perhaps new bearings if you want to replace them. I reused mine when I installed it and they were fine. I shimmed mine to 200 ft*lbs of breakaway torque, and it worked well. The one I have available is likely worn and needs a rebuild/reshim, but it's easy to do.
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Old 11-05-2017, 09:21 PM
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Little far to drive. How much does it weigh?

and, just for me to be completely honest, im reading this as pull the whole thing out of the 2 foot wide aluminium housing as a self contained unit, replace with self contained unit from rx7. No monkeying with gears, or backlash settings, etc. Just a simple r&r
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Old 11-05-2017, 09:47 PM
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No you have to setup the gears/bearings as the RX7 iron chunk that bolts to the aluminum housing is different than the miata part, so it won't attach to the PPF. But the actual LSD will install into the miata iron/miata aluminum housing no problem. If you want to buy it, PM me. I don't know what it weighs, it's kind heavy it's an LSD made of steel.
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Old 11-06-2017, 01:37 PM
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Only thing I will throw in (because I did it) is you may need the RX-7 axle cir-clips. Granted I performed this swap on my '97, but at the time the instructions I followed made note that those specific cir-clips were needed.
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Old 11-06-2017, 01:42 PM
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I ran stock 99 axles with mine no problem, didn't change cir-clips. I know the '97 axles are different though so perhaps that's why you needed to run those clips.
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Old 11-06-2017, 05:07 PM
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I built mine about 2 years ago in my NA. There are a few resources on the swap and I may mention them in the video or the description. It sounds like you need to do a bit more research before you jump into it. I wouldn't say it is difficult but it isn't something I would jump into without knowing exactly what parts I needed and tolerances. I didn't shim my diff.


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