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Diff is out of a twin turbo RX7, engine is GSXR1000. It's been making the clunking sound since I bought the car few weeks ago and thought it wasn't a big deal. Yesterday it stalled out in second gear as I hit the brakes in a parking lot and made the usual clunking sound but this time it felt like it did some damage. Now when I take off in first gear I can feel the differential grinding hard. The grinding isn't loud enough for the microphone but I can definitely feel it. It feels like I'm running over a bunch of rocks and goes away after I pick up some speed. It happens 50% of the time and only in 1st gear. I'm guessing it has something to do with stalling out in 2nd gear yesterday.
The fluid seems clean and it is filled right up to the fill hole. Should I take out the diff and inspect the gears?

Videos:
https://youtu.be/_LVe4ucF-GE
https://youtu.be/_RKA-hpQLWo

I'd drain it into a clean pan, and maybe shove a magnetic screwdriver in the drain hole and fish around the bottom to see if it comes out all furry.

It may just be the limited slip chattering?

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Honey anyone?

Stop driving it immediately before you do more serious damage.

I believe the differential front mount is loose or broken. You will need to either lift the car up or pull off the top of the tunnel to see and get at it. I can hear it in the video. I also agree with Bent if I had not heard it in the video.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Ok. Going to jack it up now and see if I can figure it out. Didn't drive it much after the grinding started yesterday, just went around the neighborhood today for the video. But I guess you're talking about the clunking sound? Wish I knew it's not supposed to do that sooner because I've tracked it twice in the last month

I took some pictures from under the car. Is that the front mount in the first picture? It's only on one side, other side doesn't have that.

That bearing cup looks mighty suspicious...

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"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

Yes it does. You've definitely got a problem at the front of the diff.

I also noticed the nut on the bottom of the blue threaded bolt through the front diff mount has just about complete removed itself. That would have been ugly! You can tighten it back up but the problem will return without correction.

I'll send you a pm.

Also, it looks like you have a 94 or newer miata diff and not an rx7 diff. The T II designation maybe be referring to the torsen, but otherwise a miata rear suspension, brakes, and manual transmission diff. That means you can get a ring and pinion with a numerically lower ratio installed, such as 3.6:1 which would be a huge drop in highway rpms and a wider gear spread.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12