Subaru little spare causes problems

Help! I put the little spare on my sub and the rear differential started whining and became extremely hot. Itook the car to a dealer, he said I blew the rear diff and damaged the trans. Car has 200000 mi. I took the car to another guy who put on a full sized tire and changed the oil in the diff and trans. He says the car runs ok with a little noise. Hmmmm? Am I risking my neck to drive the thing? Is there an easy diagnosis for major differencial problems?

How Far Did You Drive On That Donut?

Those spares are included to get you to a safe location. They are not meant as a replacement for a real tire. There should be warnings on the car, in the Owner’s Manual and even on the tire itself.

Please tell how far you drove. This will help us assess the damage and could be a service to other drivers.


Thanks for your reply, I drove it about 8 miles, never over 40 mph.

Few questions

  1. how far did you drive with the donut spare?
  2. Manual or automatic transmission?
  3. Can you recall changing rear diff fluid?
  4. Have you run different tires in size, wear/tread depth, make/model in your ownership?

Drove it about 8 mi
I have used the spare early in the cars life for about 20 miles
I had fairly regular full service until the last two years

The unfortunate thing is most if not all older Subaru’s with automatics have a spare tire fuse that disables the AWD while you use the spare. You may have thrown the AWD mechanicals over the edge.

Lastly did you put a new full size tire or repair the old? If a new and the tread depth is different by a decent amount or a different make/model it will likely lead you to problem like yours. Do you have matched tires on the car? Lastly what year is this car.

Don’t Subarus usually have a fuse that you have to pull when putting on the compact spare? Did you do that?

I believe the owner’s manual instructs you to insert a fuse in the FWD receptacle under the hood to disable the AWD system when you mount the temporary spare. This is to prevent exactly what you’re talking about.

8 miles at <40 mph should not be enough to damage either the rear differential or the AWD transfer valve (if it’s an automatic) or the viscous coupling (if it’s a manual).

At 200K miles I wouldn’t worry too much. If there was any damage it’s done and there’s not much you can do about it now. I recommend you keep an eye on the transmission fluid (or oil) and the differential oil and drive it as long as you can.

If you currently have tires that don’t match each other you may be in for bigger trouble in the future. Subarus are very sensitive to differences in tire circumference.

I think you are asking the wrong question. What you should be asking is what will happen if the rear differential fails? If you will just end up with coasting to a stop with oil all over the road, then the answer is probably to invest in an AAA membership and a Tracfone and keep on driving it. If it is likely to seize up, lock both rear wheels and pitch the vehicle into oncoming traffic then you probably should fix or scrap it (that’s 200K miles, right? Not 20K). I don’t know the answer unfortunately, but I suspect that some folks here do.

Second, you have quite unknowingly, injected yourself into an ongoing argument between those who feel that Subarus are fine vehicles that sometimes fall into the hands of idiots, and those who feel that (older, automatic transmission) Subarus seem to have an quite fragile drivetrain and are not packaged with adequate warnings about the limitations of the drivetrain. Was there a big sign on that spare warning you to pull the AWD fuse? There probably should have been. Come to that, the vehicle should probably have been sold with a full size spare and a warning not to drive over X mph until a tire shop has been able to evaluate the wear on your spare vs the wear on the other tires.

Or maybe, it just shouldn’t have been sold. OTOH, it lasted 200K miles so far – which is pretty good when you get right down to it.

I concur, on 8 miles or 20 miles not enough time.

The thing that is not clear is, are the tires matched on the rear axle where the clicking comes from?

The poster stated automatic so maybe the clutch pack is done too, I believe it is more a less a wear item. 200k is not bad but I just wonder again if tires are mismatched.

There is definitely a warning in the Owner’s Manual regarding the insertion of a fuse to disable the AWD mechanism when using a “donut” spare. Of course, since most car owners (or at least the ones who wind up damaging their cars from misuse) do not bother to read the Owner’s Manual, there is a strong possibility that the OP did not do what is required when using that “temporal” spare tire.

Just one more example of the price that one pays for failure to read the Owner’s Manual, I guess.