# What happens when a rear differential fails?



## bmw325 (Dec 19, 2001)

I know it will make whining and whooshing noises for quite some time (possibly years) before it fully fails-- but what actually happens when it completely fails? My guess is that it locks up, causing the driveshaft to snap, the car to spin, and extensive damage to the rear wheel bearings, axles, etc.


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## Kaz (Dec 21, 2001)

Are you talking about an open one or a LSD? There isn't much in an open diff that could fail without it being pretty catastrophic.


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## bmw325 (Dec 19, 2001)

Kaz said:


> *Are you talking about an open one or a LSD? There isn't much in an open diff that could fail without it being pretty catastrophic. *


Open diff.


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## Kaz (Dec 21, 2001)

Doug's pretty much right. A standard diff has the incoming pinion, the ring gear, 4 spider gears and not much else. if one of the gears strips, it just won't go anywhere or just drive one wheel, depending on what stripped. If a spider gear came loose and jammed itself somewhere, it would depend on where it jammed.


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## bren (Jul 1, 2002)

I've never had a diff go completely bad but I have had to replace the carrier and pinion bearings in both the front and rear axles on my Grand Cherokee. And yes they howl like mad when they are going bad, especially at highway speeds.

I did loose a u-bolt on my rear driveshaft on a Wrangler while driving on the highway. No spinout or damage other than a loud bang and a big hole in the floorboard before it went flying off into the median.


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## AF (Dec 21, 2001)

I had a rear differential go in my 85 RX-7 and all I remember was the differential was making some really loud whine like an airplane engine and on my way to the dealer I was one block away and the car went 'boom' and stopped moving.
This was back in late 85 and I remember the mechanics came out of the dealer and helped me push it the rest of the way.

The rear went because I used to rev it up to 4000 or 5000 rpms and pop the clutch over & over & over again. At 17 yrs old I had no idea I was doing damage to my car . . . 

I've had differential's replaced on my other cars but they never actually blew like this one did. They just whined louder then usual.


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## teamdfl (Sep 24, 2002)

There are two ultimate modes of failure for a diff. Either it locks up or something breaks and the driveshaft no longer does anything.

I blew a diff at a driver school. Actually, the driver school just accelerated a bad bearing issue but I was able to drive 300 miles home on it. One/some/alll of the bearings were going and heated up the gear oil. The oil got so hot that the speedo sender in the rear cover melted. With no speedo sender in the cover, gear oil easily escaped out the open hole onto the resulting in lots of smoke and an awful burning gear oil smell. At this popint my day was over so after letting the diff cool, I borrowed some Red Line gear oil and limped home at grandmother speeds. I bought a used diff a few days later. At least I experienced some symptoms before it locked up completely because the 300 mile tow would have been expensive. I still have the congealed lump of plastic from the bottom of the diff housing that used to be a speedo sender.


Ed


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