1996 Subaru rear differential fire!

subaru
outback
impreza

#1

Hi there- I have a Subaru Impreza Outback (1996) wagon (AWD). Before heading out for a long 450 mile road trip, I took the car in to a mechanic as I smelled a burning/rotten egg type of smell coming from the car. Also, the car felt like it was tugging a bit, like the axle was rubbing against something it shouldn’t.



He told me that the rear output shaft seal was leaking and needed to be replaced. He accounted for the smell because my power steering pump and gaskets were leaking onto the exhaust pipes (?) (he replaced those too).



I drove 60 miles out and suddenly felt like I had a flat tire. I looked underneath the car to see that the rear differential was on fire! (put the fire out…) Now the whole thing needs to be rebuilt.



My mechanic says it was caused by a bad bearing, creating friction and ultimately, a fire. Is this possible? Is this the best explanation for such an event. Before I left, he also refilled the gear oil. Where would the gear oil be leaking from in the first place?


#2

It’s not likely a bearing caused this problem but any bearings are now toasted because of it.
The problem is more than likely the ring and pinion gear trying to seize up, which was causing the tugging you felt. Lack of oil would cause this and is often preceded by whining or howling sounds.

If the oil was missing in the differntial then it either leaked out or was drained and not refilled by someone.


#3

I think your mechanic is correct. In it’s final stages, a bad bearing can get hot enough to set the lube oil on fire…“Checking” this bearing before hand is almost impossible as it is well hidden and if there was no slop in it, finding it would be very difficult.

Consider yourself lucky. The fuel tank rests just above that differential…I would look for a used gearbox in a salvage yard…


#4

I agree that the oil leaking out of the box is the most plausible explanation. I remember getting towed to a jiffy lube (cuz that is as far as they would take us) and they emptied the fluid and were saying there wasn’t much in there (and it was all burned). So where could this have been leaking from? He replaced the seals, but if there was movement of the axle looking thing that goes into the output shaft, the seal would do almost nothing, and fluid would leak out. A movement that could be explained by a bad bearing…? Bad bearing = Movement of axle = ineffective seal = leaking of oil = fire …??

Do you think my mechanic should/could have noticed this? Or am I an unlucky gus with a bad bearing? OR could the leaking (from somewhere else?) have caused the bearing to become ineffective?.. Thanks for the responses.


#5

Have the mechanic look at the transfer coupling from the front transmission to the rear drive shaft. On a manual transmission car this will be a viscous coupling on an automatic car the coupling will be electronic modulation of hydraulic pressure to a cone clutch. The amount of power being transferred to the rear differential should be a lot less than that sent to the front wheels.

If there is something wrong with the transfer coupling that causes it to lock up, there would be a binding condition between the front and back wheels which would overload the ring and pinion gears and rear differential bearings causing the overheat. The overheat would boil the lube out the vent and ignite it if it got hot enough. When the mechanic fixes the present problem, drive the car for 20-30 miles and carefully feel the temperature of the rear differential. If it is blazing hot, the problem is still not fixed.

Just an idea.