My differential frys when I use spare tire
 

Everytime I use a different size tire on my svx rear my differential starts making noise, please tell me what this is. ANYBODY

You cannot use odd/different tire sizes on ANY AWD vehicle. All tires must be matching in size.

The only way to work around this is to insert the FWD fuse. It will put the center differential into "FWD mode", effectively turning off the rear end and transferring all the power to the front end. It is in the engine bay fuse box, 10 amp.

even with the fwd fuse in, it will still burn up the rear diff as it is limited slip.

Tom

...which means you have to use a spare with the same outer diameter as the other tires. Like, the one that came with the car.

dcb

That's the one I use
 

I only have the one spare that came with the car but once I put it on it fried the differential. It was the only time I used it. But I do have 18's on the car but with low profile tires it's almost the same in diameter.

The thing is, all four corners have to be pretty much exactly the same, under all circumstances. And you should never use a "space-saver" spare for any longer than absolutely necessary.

dcb

You have to be within 1/4" difference in the circumference. So unless you have 195/45-18's, 175/50-18's, or 145/60-18's you're always going to do damage to your entire drivetrain whenever you use the stock spare. Either get a spare in the right size, or get regular tires in the right size.

I have the four stock size tires and the bologna spare tire. I have driven 160 miles at 50 mph with the spare and had no problem from the rear diff. This has happene twice now

Any time you use a spare, even if you have a blown rear tire, the spare ALWAYS goes on the front of the car. Read the Handbook

That's surprising. I figured the opposite. Seems you'd want your best rubber up front, especially with only the front wheels doing the work.

dcb

Front diff= open
read diff= limited slip

Still should only drive what is absolutely needed on a spare

Tom

I agree :D

I will add that I wouldn't drive any more than 30mph and no more than 30 miles on a spare. (Same as towing instructions)

Any difference in circumference on ANY of the tires will cause unnecessary wear on the AWD. For our cars though I would think the smaller tire on the back would be safer on the AWD but harder on the rear diff since the TCU would think the rear tires are spinning faster than the fronts and not send any power to them.

i've been riding on the spare 'donut' since April 30...500+ miles thus far...

luckily my new wheels will be here tomorrow.

(This is just an observation, not intended as fuel for debate.)

My owner's manual ('92) makes no mention of limiting the use of a space-saver spare to one axle or another, nor of inserting the FWD fuse while the spare is in use. Curiously, though, it does read:

"This tire has a smaller diameter, so road clearance is less. When driving across rough terrain, always be sure there is sufficient clearance."

Smaller diameter? That's a surprise. It continues with cautionary copy about keeping speed below 50 mph and limiting the spare to temporary use.

Was this changed in later models?

dcb

I am not sure what the handbook says to do. It only makes logical sense that you would keep the spare on non-powered wheels. For FWD keep it on the rear axle and for RWD keep it on the front axle. For an AWD car like ours it can only make sense to keep it on the axle with and open differentials as to not wear out the limited slip clutches in the rear differential. Although the front diff is an open differential it will cause damage if high speeds are obtained or long distances driven. It would be like driving with 1 wheel and it would fuse the spider gears in the front diff to the cross pin. So it makes perfect sense for an AWD SVX to keep the spare on the front. Only drive it the needed distance to get a new tire. All other options should be obsolete as they would be detrimental to the vehicle's driveline.

Tom