Differential Help (Loud clicking/popping)

[Eureka]

I think I killed my LSD, but I'm not sure what happened and how to approach it from here.

So, long story, about 2 months ago I changed the differential oil on my 1999 miata (probably long overdue). Came out black and thick. I only got out around 2/3 quart, and I put back in about .6 quart (Mobil 1 75w90). Most people on the miata forums say it takes nearly a full quart. However, I was pumping until it was overflowing out the fill and then some, so I don't think I underfilled it.

Fast forward 2 months, I get a slight grinding noise from the rear end. Thinking it's something dragging on the brakes, I figure I could let it slide for a few weeks while I get time to look at it. Then suddenly, I get very loud clicking from my differential. In a matter of about 10 miles, it goes from driving fine to extremely loud clicking (you can hear it down the street) and you can feel the feedback in the shifter. The only thing I can think of is that same day I was driving on cobblestone.

I drained the fluid again and I found one small metal shard and a lot of fine shavings on the plug. I tried to fill again and I still can only get 2/3 quart of fluid in. Why is my diff taking less oil and is that the cause or a symptom?

I've been a bit busy lately and the car right now is in the city so I haven't had a chance to pull the diff yet but what should I look for?

 

[LTC8K6]

A new one.

 

[mvbighead]

A new one.

Lol... but this, most likely. In many cases, you can find a new axle fairly easy compared to the whole diff, but that may different with a Miata. The old Jeep I had that had a diff problem was repaired, and then eventually sold because the repair fixed most of the issues, but there was still noticeable gear whine.

Only trouble with replacing the axle is you may end up with a diff that is just as bad or worse than your existing one. Though being worse is not likely given that yours sounds like it is shot.

 

[iamwiz82]

I would bet it's not the LSD itself but rather you lost a tooth on the ring or pinion (or both). Have you pulled the cover or only checked it via the drain plug? Pull the diff cover and take a photo.

 

[Eureka]

I haven't opened the diff yet, only checked the plug. I won't get around to pulling the diff until this weekend.

I'm actually more curious as to how I killed the diff.. The only work I've done on the diff was the fluid change and I made sure it was streaming out the fill hole before I closed it up.

 

[Zenmervolt]

I haven't opened the diff yet, only checked the plug. I won't get around to pulling the diff until this weekend.

I'm actually more curious as to how I killed the diff.. The only work I've done on the diff was the fluid change and I made sure it was streaming out the fill hole before I closed it up.

There are stories in the 944 world of people having the R&P shatter while gently pulling out of a parking spot. Usually this is on cars that have been driven aggressively in the past, however.

It's possible that the R&P was weakened by previous incidents and simply failed at a relatively random time.

IIRC the '99 Miata used a TORSEN LSD, so it's possible that the helical gears in the TORSEN unit are what failed and not the R&P, though that's rather a rare thing in my experience.

ZV

 

[leper84]

I'm actually more curious as to how I killed the diff.. The only work I've done on the diff was the fluid change and I made sure it was streaming out the fill hole before I closed it up.

Your car felt the love when you gave it new fluid, so it returned the favor and gave you a perfect chance for an upgrade.

 

[zaydq]

My 99 mustang was popping and clicking for 2 days until I heard a big bang and grinding/dragging. Needless to say I had to replace the diff and axle. Get it taken care of!