Possibly it's a transmission/torque converter issue, but it's also possible that the gear ratio of front differential in the Impreza transmission isn't the same as the rear differential on the outback. Both gear ratios have to be the same to avoid "wind up" of the drive train when the AWD transfer clutch is engaged. When the FWD fuse is installed, the clutch is disengaged, so there's no conflict between the front and rear drives that would be turning at different speeds.

Another factor to check is that all four tires are the same brand, model, size and treadwear.

 

The tires all match and the first thought was the gear ratio. I have talked to 2 people now that tell me the trans is the same ratio-1 had the Junk yard cross referance sheet and the other at Cindy's Subaru heaven. The guy at Cindy's seamed pretty knowledgable on what fit what-the guy at the junkyard not so much! I would drive it this way in 2WD myself but I bought it for my son and his fiance and would like to make it right as in the rain it has poor traction. With winter comming soon here I am concerned with snow traction-this is why I thought it would be a good car for them in the first place. I have more into this than planned and don't want to invest more without return, again any insight would be appreciated, Bruce

 

It's still the same torque converter and transmission with and without the fuse, so I don't see why the shuddering would disappear when the FWD fuse is installed, and reappear with the fuse removed.

When consulting the junk yard and Cindy's, are you sure they were looking at the final (differential) gear ratios and not the transmission ratios?

Someone recently posted a method that seemed to work for confirming if the front and rear differential gear ratios are the same:

http://www.subaruoutback.org/forums/66-problems-maintenance/39978-axle-ratio-check-question.html , and

http://www.subaruoutback.org/forums...s-maintenance/39827-missing-rear-section-drive-shaft-my-outback.html#post372741.

This might be worth a try if there's any doubt the differential gear ratios are the same. (Note the safety issues -- use jack stands, block the wheels securely, do not move the gear lever to a drive gear etc . . .)

Another consideration is the rear propeller shaft. A bad U-joint could lead to heavy vibration under acceleration, and would also disappear when the FWD fuse is installed.

The propeller shaft was obviously replaced. Does it fit right and are all the joints and center carrier bearing in good condition?

Let us know . . .

 

All you need to do to fix this is swap in a 4.11 rear differential.

Look no further, it's the wrong gear ratio - 100% positively.

The "new" trans has a 4.11 final drive.
The original trans had a 4.44 final drive.

Installing a 4.11 rear diff will match the 4.11 front diff in the transmission assembly and it's fixed.

Subaru rear differentials almost never fail so they're nearly worthless and don't cost much. I don't even keep them if i part a car out, there's no value and no demand in them. $25-$50.

 

OK so I did the ratio check and the rear wheel only turned 4 5/8 turns compared to 5 on the front. This confirmes that I need a 410 ratio diff for the back correct? Are 410 and 444 the only ratios there were? I found something on line that said 390 in 97 Legacy wagon (mine is an outback but) I want to search for used diff so what cars would I be looking for to get the right ratio? Thanks

 

The 5 turns versus 4-5/8 is a ratio of about 1.08. That corresponds close enough to the ratio between a 4.44 and a 4.11, confirming that that's the two final ratios you have, with the 4.44 being the rear differential. There is/was a 3.9 as well but you would want to stay away from that.

As far as which cars had the 4.11, I can't say with any assurance. But checking the ratio of a rear differential is relatively easy, even on the bench, so any good supplier should be able to verify what it is before offering it to you, or before you take it, especially if they know there's at least three possibilities (which you would, of course tell them).

You could to go through the service manual specs for the differentials for all Subaru models over a range of years, which would be rather onerous. Perhaps someone has put together a table based on this approach, but I haven't seen it. Alternatively, look through various Subaru forums, such as this one, subaruforester.com, legacygt.com, USMB, etc -- the question: what differential ratio does my car have? or variants of it, is seen quite often, and piecing the answers together could give you a range of models and years that you know are 4.11.

 

Last night I got in an ice cold car after work and it was binding (felt like the brakes were locked up!). The Trans light was blinking at start up and I also noticed the FWD light was out. I checked the fuse and it was good, I checked the connector to the trans and it was tight then I ran it in park and checked the fluid level and it was good full and clean. Then for no reason I can tell the FWD light came on and it worked fine. Tried to run codes with th SHS but the light stayed on solid. I can't drive it without the fuse in due to the ratio differance is this the reason I get no test results?

 

When the TCU OBD detects a problem with the AWD solenoid control system, the FWD fuse is disregarded. In other words, if there's a failure with the AWD duty solenoid that causes binding and the AT Oil Temp light to flash, inserting the fuse won't correct the binding. But when the solenoid problem is corrected, the TCU will respond properly to the fuse.

Did the "(felt like the brakes were locked up!)" appear when turning or when going straight? Binding due to the AWD clutch being engaged usually shows up only when turning, not when going straight, unless the tires are not the same.

 

It didn't seem to matter. I was pulling out and turning to start but after straighting it out it still was tight. I turned the car off and it was like someone snapped a rubber band. I restarted it and it was tight in a straight line too. Reverse came easyer than forward but turning in reverse got tough too. If I put it up on jack stands and took out the fuse will this work to get codes? By the way the light quit flashing now at start up and I didn't have any problems today. Do the codes have any memory or do I have to wait for this to happen again and then jack it up?

 

If I put it up on jack stands and took out the fuse will this work to get codes?

Not sure what you mean. There's no procedure requiring the car to be raised to read the trouble codes.

There is a procedure for checking the transmission trouble codes that I believe applies to a 97 and might be worth a try. See this thread: http://www.subaruoutback.org/forums/111-gen-1-1995-1999/35763-atf-light-flashing.html

 

The question is why doesn't the secret handshake give me codes? The other question is will it show past problems if the light is not presently flashing? With 2 differant differetials I can't drive it without the FWD fuse being installed. Will the fuse keep me from being able to pull codes? I would have to get the car off the ground to make the wheels go above 12 miles per hour (per test procedure)without the fuse.

 

Ah, okay, now I understand.

Unfortunately, I can't say whether or not having the fuse is will prevent the handshake from indicating the codes, if there are any.

As far as I know, if there are any codes, they are usually stored even if the AT Temp Light stops flashing. But this might be different with the earlier models. Perhaps someone with the same generation vehicle will know for sure and will respond.

But that said, perhaps you can drive it with the fuse in to complete the "more than 12 mph" driving sequence, then take it out when you stop to read the codes.

That said, I wouldn't be surprised if the problem with the binding is due to the different ratios, and would be resolved when the ratios are the same.