The transmission wiring harness connector(s) is usually found at the back of the engine/on top of the bell housing under the firewall. (Follow the harness from the Inhibitor Switch on the right side of the transmission up and forward. There's another harness that I believe goes up the left side. The two come together at the top of the transmission.)

If I understand the procedure, the desired "failsafe" is actually disconnecting the wiring to the AWD duty solenoid (amongst other circuits), which on the 98, should cause the AWD transfer clutch hydraulic pressure to be at maximum when the engine is running. With the clutch fully engaged, and the transmission in neutral, turning one raised wheel should cause the other raised wheel to turn the same number of turns (if the ratios are the same).

I'm not sure if, when the harness or TCU is disconnected, the transmission will develop the normal line pressure in the absence of signals to the line pressure duty solenoid, in which case, the clutch might not be engaged.

Another possibility is that the clutch will be sufficiently engaged in neutral without having to disconnect anything, because even in neutral there is some pressure applied. Perhaps check for this first -- raise the car etc, and turn one wheel while someone else tries to hold the other wheel. If it's difficult, then there's probably enough pressure to ensure no slippage in the clutch, and therefore no need to disconnect to do the ratio test.

Take the appropriate safety measures, do the test, and do let us know how it works out.

 

cool worked, had to disconnect the one closer to the drivers side to make it work. just putting it in neutral doesn't work.

 

I know this is an old post, but I am trying to perform this same test with my 2004 Subaru Outback, 4EAT 2.5L.

I just replaced my rear differential with one from a junk yard. I know the rear differential is a 4.44 axle ratio, but the car is making a knocking noise when driving now. I got the car cheap and noticed the rear end was not hooked up, with the drive shaft chopped and the rear CV axles missing. I figured this was because the rear diff. was bad, so I replaced it.

I tried doing the axle ratio check as described above, (because I suspect that the transmission has been changed), but when I manually turned either of the lifted wheels, nothing happened with the other. I am guessing that the AWD transfer clutch is not engaged as it should be. Is there a way to make sure that this is engaged and that the transmission is in failsafe mode?

Also to note: I checked the tire sizes and the rear tires are smaller, 225/60 R16 in front and 215/55 R16 in the rear. (1.32 inches smaller diameter in the rear) Could this be the root cause of the issue with AWD? In my mind it could very well be, and I am going to replace the rear tires to match the front and hope that that resolves my issue. I was hoping to do this test just to verify that the front and the rear axle ratios are the same.

Thanks in advanced if anyone has any input, expertise, or personal experience.

 

Subaru wants tires within 1/4" CIRCUMFERENCE so, yeah, your tires violate the spec by a lot.

you could try driving with the FWD fuse in place. There's a slot for a spare fuse in the fuse block underhood, near the left/drvr's side strut tower. check the manual about using the spare tire.

 

The test method described in post #1 might not work with a 2004+ because the AWD transfer clutch control system was changed. Whereas in the earlier years, if the control signal from the TCM is lost, as it would be when the connectors are removed, the default (failsafe) condition of the control valve in the transmission itself is full pressure on the transfer clutch when the engine is running. It's this engagement that the procedure uses to link the front and rear drives (wheels).

But in 2004+ the system is reversed. If the control signal is lost, the default valve condition is to turn off the hydraulic pressure to the AWD clutch; no pressure, no linking of front and rear drives and the test doesn't work. I don't recall a similarly simple method, as above, to cause the AWD transfer clutch to remain engaged for this type of test.

The suggested use of the FWD fuse, which disables the AWD by turning off the pressure to the clutch, can be used to determine if the knocking is being caused by torque buildup in the drive train, as would be the case if the front and rear differential ratios are different. But that presumes that all four tires have the same rolling circumference, which usually means the same brand, model, size, and remaining tread depth. With different circumference tires, even with the differential ratios the same, there could be torque buildup. This could cause damage to the drive train, and possibly wear out the friction surfaces of the AWD transfer clutch plates.

 

On an '04 and up you'd need to cut and splice into the wire going to the duty cycle solenoid.

You might be able to put all 4 in the air, put it in 1 (but more lockup than D), and try using the brake pedal to allow the tires to slip slowly. The front brakes should grab a little bit more than the rears, just applying the brakes to the front is ideal but not easy to arrange for a quick test (unless you have drum rears, then just de-adjust the rears).

 

1. Drive it in FWD
2. Drive it in AWD
if it drives great in FWD and binding/bucking/noises in AWD - you know there's a mismatch.

Google the TZ number of the transmission to see if you can figure out a model and gear ratio, AT's are usually convoluted and this doesn't work but easy to try.

Pull the front diff plug, mark the teeth with a grease pen and count the number of teeth or count rotations to figure out gear ratio.

 

1. Drive it in FWD
2. Drive it in AWD
if it drives great in FWD and binding/bucking/noises in AWD - you know there's a mismatch.

Google the TZ number of the transmission to see if you can figure out a model and gear ratio, AT's are usually convoluted and this doesn't work but easy to try.

Pull the front diff plug, mark the teeth with a grease pen and count the number of teeth or count rotations to figure out gear ratio.