Is my rear end failing?

[frapjap]

I recently had a post about an aggravating noise in the drive train of my Miata. I got a few responses, read the suggestions and had some time today to really dig into a diagnose my issue. The jist of it is a metallic vibrating sound that is rpm dependent, but only when the car is in gear. Push the clutch in, the sound doesn't go completely away, but its not nearly as bad. http://forum.miata.net/vb/showthread...hlight=frapjap

I R&R'd the drive shaft in the case that U-joints were the problem (start cheap, right?). Pretty quick job, not to hard at all- this car was really well designed. Took the car for a spin- same old noise. Brought it home and put it up on jack stands. Found a loose heat shield around my cat, banged it off and started the car, noise persists.

Then I decided to "drive" the car while it was up on stands. You can hear the noise emitted from the rear wheel wells and then follow it from the axle to the differential, then to the transmission tail shaft area. However, while revving the engine, the sound is more pronounced from the rear of the car. At 150k its completely possible that the diff is ready to implode on itself.

But, just for clarification, I've attached two videos.
http://www.facebook.com/video/video.php?v=877926182155
http://www.facebook.com/video/video.php?v=877922065405

A bunch of you folks here are far better mechanics and more experienced than I am, so if you have a moment, check 'em out, let me know if you think the rear is failing, too. (I'm fairly certain it is)

Thanks!

[ADDirishboy]

Is my rear end failing?

[frapjap]

Sound about right.

[darens13]

wow that halfshaft has got a lot of runout. i would bet that bearing is shot.

[alms24sebring]

They have meds for anal leakage.

Ok seriously it sounds like a bearing inside the diff. Judging by your description thats the only thing it could be. I bet if you were to take a look inside you would see pits in the metal where the bearing rolls on, or on the rollers themselves.

[Oatmealman]

sounds like the gears might have chunked.If i where you i'd pull the diff cover and inspect the gears for damage(i.e chipped,cracks,chunked) and do a pattern check if everything come out ok.I'd pull the half shafts,and the carrier and look at the bearings.If the bearings check out ok,i'd pull the pinion and inspect those bearings.While you've got the halfshafts out id replace them.

[sbird1]

Change your diff oil and check for metal shavings. That'd be the cheapest and easiest way to determine if your diff is toast.

[alms24sebring]

Its easy to check the carrier (? I forget whats its called). It will be obvious when you see it especially if its a very noticable noise

[frapjap]

sounds like the gears might have chunked.If i where you i'd pull the diff cover and inspect the gears for damage(i.e chipped,cracks,chunked) and do a pattern check if everything come out ok.I'd pull the half shafts,and the carrier and look at the bearings.If the bearings check out ok,i'd pull the pinion and inspect those bearings.While you've got the halfshafts out id replace them.

Change your diff oil and check for metal shavings. That'd be the cheapest and easiest way to determine if your diff is toast.

I'll be draining fluid and pulling the cover this week. Didn't have any fluids to replace what gets expelled this afternoon. Really not sure what I'll find, but I'm leaning towards bearing considering it doesn't howl, but it is a super annoying and loud noise. I really don't want said bearing to be in the tail shaft of the transmission. What really gets me about this is that performance isn't affected what-so-ever, in any way (which makes me feel that the gears aren't shot). However, if the fluid is clean and it IS just a bearing, I might as well R&R the damn thing with a newer (read upgrade) diff since I'm going through all of that effort to remove it in the first place.

[Razi]

Just in case, I'd also check the axles, but it does sounds like bad news for your diff.

[nissangirl74]

Major letdown from thread title. But yes, I'm guessing the diff.

[frapjap]

Major letdown from thread title. But yes, I'm guessing the diff.

Thats for you, Becky.

[flohtingPoint]

You can get a new pumpkin for stupid cheap. A buddy I crewed for who runs SSM blew up his diff on track, for next to nothing he had a new one in my hands and I had it in his car in 30 minutes. Moral of the story? Dont sweat the small stuff, a used diff is a race track away. Just look for the folks running spec bumper-car, they're probably in the stewards office arguing about something small.

[skydragoness]

^
What he said.

Aren't you glad you joined the Miata crew Ray? A plethora of parts available!

[Ozzie]

Push the clutch in, the sound doesn't go completely away, but its not nearly as bad.

Have you checked the clutch throw-out bearing, and clutch plate diaphram for wear?
If it were a diff, it wouldn't matter if you pressed the clutch in or not, the noise should stay at the same level.

[Jesda]

Have you checked the clutch throw-out bearing

Yes, this! That was a problem I had on my Mustang. Same symptom.

[sbird1]

That is a good point. Throughout bearing are cheaper, but a whole lot harder to replace than diff innards.

Have you figured anything out yet? I'm interested now...