05 outback diff ratio help

I picked up an 05 Outback, (2.5, non-turbo, AT) a couple of months ago. The previous owner had the torque converter replaced to solve the shudder and supposedly replaced the rear diff with a junkyard unit to solve a bearing whine. I took a chance on it. I've never owned a Subaru before.

 

45 miles later on my way to work, I snapped a rear CV axle and called for a tow. I was suspicious when I replaced the CV as it wasn't a knuckle failure, the shaft snapped in half and there was no rust, showing a clean/sudden break. I checked the rear diff as well as I could through the fill/drain holes and found no chunks, no shavings, etc. Put it back together and before I get 3 feet the rear diff is clunking. OK, so the diff is toast. For the record, it broke at 60mph on dry pavement and the transmission 'sport' light came on.

 

Knowing that the diff was replaced, I need to verify whether or not it's the right ratio so I know what I need to buy before I break this thing open. Do these have something similar to a GM RPO code or anything that might be able to help me ID the gear ratio in the front? I ran across this post >>

https://legacygt.com/forums/showthread.php/transmission-gear-ratios-and-final-drives-229267.html <<

that makes it look like the previous owner could have easily grabbed the wrong ratio. They're also very close together (ratio-wise) which makes it more plausible that I could have driven and not noticed any binding.

If You can turn it , rotate the tire 1 turn and count how many rotations the driveshaft yoke does.

2005 Outback NA should be a 4.111 according to the tranny chart:

https://www.rallispec.com/downloads/Transmission%20ID%20Chart_Public.pdf

 

You should have transmission TY757VCABA I believe.

 

What do you mean by "break this thing open"?

I would just source the correct ratio rear diff, install, and be done.

Edited September 25, 2020 by Infosecdad

If You can turn it , rotate the tire 1 turn and count how many rotations the driveshaft yoke does.

 

does that work with the front end though? My concern is that the rear is not original and may not be correct.

 

Again, this is my first Subaru. I'm used to building Toyota differentials.

Edited September 26, 2020 by short_arms

2005 Outback NA should be a 4.111 according to the tranny chart:

https://www.rallispec.com/downloads/Transmission%20ID%20Chart_Public.pdf

 

You should have transmission TY757VCABA I believe.

 

What do you mean by "break this thing open"?

I would just source the correct ratio rear diff, install, and be done.

 

that chart only lists 5/6 speed MT. I have an auto trans. My problem is that I can't figure out the correct ratio because I don't trust that the previous owner put the right diff in it. My basic plan was to either

 

A-replace the whole diff and housing with a junkyard unit because it has the wrong ratio and I'd rather not deal with a full build

B-replace the bearings in the existing diff and bolt it back together.

 

I'm still stuck on that part of sourcing the correct unit, or at least finding out how to ID what is in the front end so I know what I need.

Ah, I missed that, sorry.

This should do it. I don't really know how to tell what you have, but I wouldn't trust it at this point. You should be able to find a 4.44 rear diff without too much trouble.

 

http://www.cars101.com/subaru/outback/outback2005.html

 

Automatic 4spd

1- 2.785

2- 1.545

3-1.000

4-0.694

final 4.444

Ah, I missed that, sorry.

This should do it. I don't really know how to tell what you have, but I wouldn't trust it at this point. You should be able to find a 4.44 rear diff without too much trouble.

 

http://www.cars101.com/subaru/outback/outback2005.html

 

Automatic 4spd

1- 2.785

2- 1.545

3-1.000

4-0.694

final 4.444

 

THANK YOU for that page, that's the cleanest breakdown that I've seen. This has been a huge waste of time just trying to figure out what ratio it's supposed to have.

You can open the rear diff cover and count the number of teeth on the ring and the number of teeth on the pinion - that will give you the ratio of the rear diff.

You can open the rear diff cover and count the number of teeth on the ring and the number of teeth on the pinion - that will give you the ratio of the rear diff.

 

It's not the existing rear diff ratio I'm concerned about...It's verifying what is *supposed* to be in there to match the front end.

 

Based on what infosecdad found above, I'm assuming i need 4.44:1 at this point. Haven't had time to get the car up on stands, and now it's covered in snow so...

You can open the rear diff cover and count the number of teeth on the ring and the number of teeth on the pinion - that will give you the ratio of the rear diff.

 

 

It's easier to just count number of rotations on incoming and outgoing to get the ratio. If you lock one wheel then it would double the speed of the other wheel. Use a sharpie to mark positions and then start the rotation exercise.

 

 

Taking off the rear diff cover is excessive.

 

 

The front diff is a bit more complicated though.