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Old 11-06-2013, 10:10 AM   #1
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Default Possible differential future explosion?

Morning all,

A few threads on here try to address odd clunking or noises coming from the rear of the car as suspension noises. I am curious if the rear diff makes noise before going BOOM.

When I start from a stop, put in the clutch to change gears while in motion, and accelerate after a gear shift, i hear a noise that resembles medium size stones rolling over rocks. The noise if very prevalent at low speeds, but they may happen in higher gears but its too loud to notice.

So, the question is, does the diff have tell tale signs of the internal parts tearing apart, does it just let go one day, or am I way out in left field and need to focus more on suspension issues? Thanks guys.
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Old 11-06-2013, 10:17 AM   #2
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Exhaust secure?
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Old 11-06-2013, 10:23 AM   #3
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The exhaust is a bit...... ghetto may be the right word for it. When I bought the car it wasn't secured in the back and I would get a hollow clanking when the tail pipe connected the frame, normally through corners. I have since re-secured it and haven't had issues from that even while autocrossing. It is possible something else maybe loose, but it seems like the sound is literally from gears engaging to move forward... I can check the exhaust tonight.
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Old 11-06-2013, 02:52 PM   #4
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1990... stock rear end?
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Old 11-06-2013, 03:16 PM   #5
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I believe its the original stock rear end at 140k miles
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Old 11-06-2013, 03:19 PM   #6
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Time for a 1.8 diff. Yours is fucked. They're known to break even at stock power levels.
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Old 11-06-2013, 03:21 PM   #7
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It's been said the 1.6 diffs can explode under stock power, so... maybe?

Check your rear CV joints in the axles and universals in the driveshaft. Also make sure the PPF bolts are still present and tight at both the trans and diff ends. What is your service interval on the trans and diff fluids?

Edit: Lol, thenuge beat me to it. It's probably time to start looking for a 1.8 torsen swap
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Old 11-06-2013, 03:22 PM   #8
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I know that the 1.6 diffs are made with glass parts, I guess I'm just looking for clarification that what im describing is INDEED the diff. I would hate to go and swap out the differential and find out it really is......some bushing causing something to hit or whatever.

I have not been looking forward to this, but if its the diff time to save my pennies.
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Old 11-06-2013, 03:27 PM   #9
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If you aren't convinced its the diff, check that stuff I said and be sure.

If you are worried its the diff housing bushings, put the car on jackstands and blocks and whatnot and crawl under there and shake/kick things like the diff housing and suspension arms and uprights with the rear suspension at full droop. That should show busted bushings pretty quickly.

Don't drop your car on yourself in the process, that would be bad. Don't say I didn't warn you.
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Old 11-06-2013, 03:31 PM   #10
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Sorry about that EO2k. Hit reply at about the same time. Its getting awfully close to winter here so ill test a few things out before it goes into storage and see what I can come up with. I'll do some shopping in the meantime. Thanks for the quick responses and I'll try not to drop a car on my face.
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Old 11-06-2013, 06:28 PM   #11
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Diff of poverty.
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Old 11-06-2013, 07:47 PM   #12
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What exactly is it that fails on the 1.6 diffs? ring gear? Are there treatments or coatings that can be applied to the parts to prevent failure?

I am absolutely stuck with the 1.6 size diff, currently have an open one, and will be installing a vlsd soon. I am also considering a plate style diff but I would like to hear what it is that fails in these so often.
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Old 11-06-2013, 08:04 PM   #13
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Nice pictures over here:

https://www.miataturbo.net/build-thr...f-75100/page3/

Why are you absolutely stuck with the 6" diff?
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Old 11-06-2013, 08:14 PM   #14
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Quote:
Originally Posted by hornetball View Post
Nice pictures over here:

https://www.miataturbo.net/build-thr...f-75100/page3/

Why are you absolutely stuck with the 6" diff?

Mazda 4wd cars only ever came with the 6" diff and the ring gear has to match the ratio on the output of the transmission. 4wd specific ring gear ratio.
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Old 11-06-2013, 09:26 PM   #15
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Well, I ran my VLSD for about 20K miles at around 150-160RWHP levels. Showed mechanical empathy (no shenanigans in 1st gear) and didn't have problems. But I may have just lucked out with a good one. Over the Spring, upgraded to a Torsen for tracking and to start turning up the power.

Mazda 4wd car? What would that be? Was there a 4wd 323GTX?

Last edited by hornetball; 11-07-2013 at 11:47 AM.
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Old 11-06-2013, 09:46 PM   #16
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Quote:
Originally Posted by hornetball View Post
Well, I ran my VLSD for about 20K miles at around 150-160RWHP levels. Showed mechanical empathy (no shenanigans in 1st gear) and didn't have problems. But I may have just lucked out with a good one. Over the Summer, upgraded to a Torsen for tracking and to start turning up the power.

Mazda 4wd car? What would that be? Was there a 4wd 323GTX?
Yeah I have a few of mazdas 4wd variants.

1988 gtx, its a 1.6 boosted motor.


but I also have two 1990 protege 4wd models. Same as the later gtxs they had in japan but the lowest trim level and motor were offered to america. I have 1.8's for all three cars. I found a vlsd cheap so I figured I'd have it put in a spare diff and see what it does. The japanese gtr spec 323 had a vlsd rear from the factory.






anyways, what I was looking for is if cryo treating the ring gear helps or if there are billet bearing caps available?
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Old 11-07-2013, 12:50 AM   #17
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It's not the gears in my experience (I killed 7 of them). In my experience the input shaft bearings always start to fail, and then the alignment is out followed quickly by the gears.

Dann
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Old 11-07-2013, 01:17 AM   #18
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Quote:
Originally Posted by nitrodann View Post
It's not the gears in my experience (I killed 7 of them). In my experience the input shaft bearings always start to fail, and then the alignment is out followed quickly by the gears.

Dann

Cool, I'll be sure to replace all replaceable items.

Also, turns out that certain Nb's had a lsd in the same 3.909 ratio (would that be the torsen?). That solves the issue of useing the specific ratio but I will need to check for clearance as the housing is still unique to the 4wd variants.
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Old 11-07-2013, 11:49 AM   #19
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Cool cars.
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Old 11-07-2013, 12:00 PM   #20
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Yeah I think all NBs with 6-speeds had 3.909 torsens except the MSM.
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