KAG
08-02-2008, 12:53 AM
The past 2-3 months I have been researching on how to put a rear limited-slip differential in my 2000 'L', which GT models came standard with. The past few days, I accomplished just that.
Yes, there is this way (http://wac.addr.com/auto/obs/lsd/lsd.html) to do it, (and no disrespect to the author, Wayne Chin) but for the money, it's not the very best idea. Here's why: the 3.90 r160 diff from a 91/92 Legacy SS 5mt is a viscous unit, which means it uses a silicone fluid to become slip-limiting. A diff from that specific car would be 17-18 years old, meaning it has been heated up and cooled down for almost two decades and possibly over tens of thousands of miles, depending on the vehicle. Over time, the fluid breaks down and the unit becomes less and less slip-limiting. Therefore, it's not as 'limited-slip' as it should be. Also, as Chin states, the Legacy SS r160 has axle stubs. I'm not entirely sure which year Subaru started using male axles, but my car definitely did. The axles from the 91 SS were female. There were also some issues with the input flange.
Now for the way I did it.
My car: 2000 Legacy L Sedan 5mt
I had: 3.900 open diff
I wanted: 3.900 limited-slip diff
If you don't have access to power tools, a good amount of experience, or the will to do this, I do not recommend you attempt this swap. Have a good local shop do this for you. I did it because I wanted to do it myself and learn how these things operate. I searched everywhere for a way to do this, and I found next to nothing. One more thing...DO THIS SWAP AT YOUR OWN RISK!
First things first. Check your rear diff's gear ratio. There may be an easier way to do this if you can match your gear ratio.
I used a 5mt WRX carrier with extremely low mileage. My diff is 3.900, so 39 teeth on the ring gear, 10 on the pinion. The WRX diff also has 39 teeth, but 11 on the pinion. Hence, 39/10=3.900 and 39/11=3.545. If it weren't for the pinion, they'd be exactly the same. I used this because it was available to me at an unbelievable price locally. As long as you find a good working LSD, you should be fine.
Now, let's get started.
What you will need:
Jack stands (or lift if you're cool like that)
Power tools
12mm, 14mm, 17mm, 19mm wrenches and sockets & 1 1/4 socket for axle nut
Hammer and bit (dead blow hammer worked well)
Pry bar
Flathead screwdriver
75W-90 gear oil
Shop rags
An entire day, if not two
1. Jack up the rear end, put stands on both sides. Drain your diff.
2. Remove wheels. Loosen axle nuts with 1 1/4 socket.
3. Put car in neutral and take off parking brake.
4. Using your 19mm, remove the three (3) lateral link bolts. Shown in the picture is the two bolts that hold up one end of the arm. There is one more you can't miss that holds up the other end. If you can't get to those two bolts, remove the cover shown at the bottom of the pic. There are three small 12mm bolts and a 12mm nut that hold it on.
http://img171.imageshack.us/img171/2674/subaru019kb8.jpg
5. With those three bolts removed, you should have enough room to pull back the hub and get the axle out. I ended up having an axle frozen in the hub, so I had much more work to do. If this happens to you, ask me and I'll tell what you how to do it. Now, use your pry bar to gently pry the axle out of the diff. DO NOT PRY AGAINST THE COVER, IT WILL CRACK. Use one of the five bolts as a point to pry against.
6. Once you have the axles out on both sides, you are ready to begin removing the diff. For safety, I put a small jack under the diff in the event it slips out of it's place. There are two 17mm nuts holding it up from the rear cover, two 17mm bolts held on with a nut from the crossmember, and four bolts connecting the diff to the drive shaft. The drive shaft bolts are held on by a 12mm nut. Do these first and use two wrenches to take these out. Be careful and find the best way you feel comfortable getting them out. Then, remove the nuts from the cover so you still have support on one end. Before removing the other bolts, make sure your drive shaft is out of the way when the diff comes out. It is possible to drop the diff down by yourself if you have a tranny jack or something similar, but I'd recommend someone help you.
http://img523.imageshack.us/img523/6175/subaru020wc8.jpg
http://img393.imageshack.us/img393/9899/subaru021xg9.jpg
7. Place your carrier some place where you will have much room to work. With a 14mm socket, remove all the bolts holding the cover on. There will be a cap, or breather, that you will need to take out in order to get the top right bolt out. It should pull right out. Gently take the cover off, and try not to spill any leftover fluid that didn't get drained out. You will see a gasket that says UP on the upper right corner on it. Take it off, and put it somewhere safe. Next, take bolts out of the side caps off with a 12mm socket. DO NOT START PULLING THE CAPS OFF. Get your dead blow hammer or hammer and small bit and start making small taps around the cap. Try to ensure that they come off perfectly straight and that you do not lose the two shims that come off with the caps. This should allow you to take your open diff out of the carrier. Play around with the diff. Watch how the gears allow the axles to turn either way.
If you bought an entire carrier for this swap, repeat for that carrier, but make sure you keep all parts with their original carriers. If you have just the LSD unit, move on to the next step.
8. Compare the two units. Notice how the open diff lets you turn the gears both ways. The LSD unit will not let you turn the gears at all.
9. What you are going to do now is take the ring gear from your open diff and put it on the LSD. This takes precision and if the gear is not on the diff properly, well, all hell can break loose. Use a 17mm socket to remove all the bolts holding the ring gear to the unit. Try using a hammer and bit to get the ring gear off. If it doesn't come straight off, use your flathead screwdriver to pry around it and get it off. Do the same with the ring on the LSD unit. Make sure you know which one is which! Now you will put your ring gear onto the LSD unit. Pretty much a reverse process. Place the ring gear onto the diff as equally as you can, working it on very slowly. Once on the unit, you will need to use the bolts from the LSD carrier as they are longer. Some units you may be able to use the original bolts. If you have some Loc-Tite, I'd recommend adding a dab to the bolts for safe measure. Start the bolts by hand, them move to the power tools. In a star pattern, tighten all the bolts. Shown below is a quick pic of the bolts attaching the ring gear to the unit.
http://img139.imageshack.us/img139/9836/subaru013by5.jpg
10. Take a breather. You are almost done. No need to get in a hurry and risk doing something wrong.
11. Work the LSD unit into your carrier. You are staying with the same ring gear, therefore, you need to stay with the same pinion. It may be tricky working it in, so take your time. Make sure your ring gear is on the left side of the diff and you didn't put it in backwards. Use a shop rag or similar cloth to clean the side caps and shims, they must be as clean as you can get them. Put a tad of your diff fluid on the bearings, caps, and shims. Slip the side caps and shims on the same way you took them off - equally and slowly. Put the bolts in and start them by hand, then use the power tool. It should now look like this: (top)
http://img291.imageshack.us/img291/526/subaru014li3.jpg
Spin the ring gear a few times to make sure it is intact with your pinion and everything feels right. You should have a little 'play' between the r&p. The play should be within thousandths of an inch.
12. Put a little bit of fluid over the gears. You can now put the cover back on the diff. Make sure you go get your gasket that should have been in a safe place. Clean it off as best as you can. It can never hurt to put silicone around the cover to prevent any fluid from finding a place to leak out. Bolt the cover to the carrier the same star pattern you re-attached everything else. It is now ready to go back into your car.
13. Raise the diff into the car. It should be able to rest on the side where you pulled the two nuts off the cover. Put the two 17mm bolts through the holes so the diff can rest completely. Tighten all nuts and bolts, then reconnect the driveshaft with the 12mm bolts. The washer goes on the nut side, I made that mistake while wondering why I couldn't get it to tighten.
IMPORTANT: You may need LSD specific axles depending on your car and the car you took the carrier out of. LSD axles tend to be 10mm shorter than non-LSD axles. I had bought the diff with axles still attached, so if I needed axles I had them. My axles actually turned out to be shorter than the wrx axles and they did not have certain features my axles had, so I stuck with my axles. Sometimes it works out that way.
14. Reconnect axles to the diff first, then slide them through the hubs.
15. Re-attach the lateral link with the 19mm bolts. If you took off the covers, re-attach those also.
16. Tighten axle nuts. Put the wheels on and tighten them.
17. You are not done yet. While the car is still on jacks, use a breaker bar to check all the bolts you removed during this swap...for safety!
18. Fill the diff with your fluid of choice. I used Mobil 1 synthetic 75W-90.
19. Test drive the car and make sure there is no binding or strange noises. My car ran perfectly fine for three test drives, so I was good.
20. Take a sharp corner a little faster than you normally would. Watch what happens, you will be shocked. Then, take it to the snow and haul ass. You are good to go.
I highly advise you have an alignment done after you do this. Mine was done the day after, the toe was off by a whole 1/16 of an inch - I got lucky.
If I had the money, I could have gone with an entire transaxle from a Subaru with rear LSD. I don't have that kind of time and money, and my tranny is in too good of shape to replace. Sans the 91 Legacy SS, Subaru never made an r160 geared 3.900 with LSD from the factory. Several 3.90 diffs, none LSD. If I were to change my transaxle, I would have had to change my gear ratio to something higher like the GT's 4.11 or the Outback's 4.44. Or I could have also done an entire transaxle swap with a wrx, but again, money is always a factor. I wanted to keep my 3.90 gearing for slightly better gas mileage due to a lower rpm at highway speeds, and I simply like the longer gears.
My total cost for this project was unbelievably low since I found a good diff locally, had access to a good shop for free, and I was able to get a couple weekdays off work. Total cost was $200. Yeah, I got lucky.
I have to give a HUGE amount of credit to Matt (gator gt) for all the information and help he gave me on this swap. Thanks Matt!
Take care and enjoy. Feel free to PM me for any questions.
Kyle
Yes, there is this way (http://wac.addr.com/auto/obs/lsd/lsd.html) to do it, (and no disrespect to the author, Wayne Chin) but for the money, it's not the very best idea. Here's why: the 3.90 r160 diff from a 91/92 Legacy SS 5mt is a viscous unit, which means it uses a silicone fluid to become slip-limiting. A diff from that specific car would be 17-18 years old, meaning it has been heated up and cooled down for almost two decades and possibly over tens of thousands of miles, depending on the vehicle. Over time, the fluid breaks down and the unit becomes less and less slip-limiting. Therefore, it's not as 'limited-slip' as it should be. Also, as Chin states, the Legacy SS r160 has axle stubs. I'm not entirely sure which year Subaru started using male axles, but my car definitely did. The axles from the 91 SS were female. There were also some issues with the input flange.
Now for the way I did it.
My car: 2000 Legacy L Sedan 5mt
I had: 3.900 open diff
I wanted: 3.900 limited-slip diff
If you don't have access to power tools, a good amount of experience, or the will to do this, I do not recommend you attempt this swap. Have a good local shop do this for you. I did it because I wanted to do it myself and learn how these things operate. I searched everywhere for a way to do this, and I found next to nothing. One more thing...DO THIS SWAP AT YOUR OWN RISK!
First things first. Check your rear diff's gear ratio. There may be an easier way to do this if you can match your gear ratio.
I used a 5mt WRX carrier with extremely low mileage. My diff is 3.900, so 39 teeth on the ring gear, 10 on the pinion. The WRX diff also has 39 teeth, but 11 on the pinion. Hence, 39/10=3.900 and 39/11=3.545. If it weren't for the pinion, they'd be exactly the same. I used this because it was available to me at an unbelievable price locally. As long as you find a good working LSD, you should be fine.
Now, let's get started.
What you will need:
Jack stands (or lift if you're cool like that)
Power tools
12mm, 14mm, 17mm, 19mm wrenches and sockets & 1 1/4 socket for axle nut
Hammer and bit (dead blow hammer worked well)
Pry bar
Flathead screwdriver
75W-90 gear oil
Shop rags
An entire day, if not two
1. Jack up the rear end, put stands on both sides. Drain your diff.
2. Remove wheels. Loosen axle nuts with 1 1/4 socket.
3. Put car in neutral and take off parking brake.
4. Using your 19mm, remove the three (3) lateral link bolts. Shown in the picture is the two bolts that hold up one end of the arm. There is one more you can't miss that holds up the other end. If you can't get to those two bolts, remove the cover shown at the bottom of the pic. There are three small 12mm bolts and a 12mm nut that hold it on.
http://img171.imageshack.us/img171/2674/subaru019kb8.jpg
5. With those three bolts removed, you should have enough room to pull back the hub and get the axle out. I ended up having an axle frozen in the hub, so I had much more work to do. If this happens to you, ask me and I'll tell what you how to do it. Now, use your pry bar to gently pry the axle out of the diff. DO NOT PRY AGAINST THE COVER, IT WILL CRACK. Use one of the five bolts as a point to pry against.
6. Once you have the axles out on both sides, you are ready to begin removing the diff. For safety, I put a small jack under the diff in the event it slips out of it's place. There are two 17mm nuts holding it up from the rear cover, two 17mm bolts held on with a nut from the crossmember, and four bolts connecting the diff to the drive shaft. The drive shaft bolts are held on by a 12mm nut. Do these first and use two wrenches to take these out. Be careful and find the best way you feel comfortable getting them out. Then, remove the nuts from the cover so you still have support on one end. Before removing the other bolts, make sure your drive shaft is out of the way when the diff comes out. It is possible to drop the diff down by yourself if you have a tranny jack or something similar, but I'd recommend someone help you.
http://img523.imageshack.us/img523/6175/subaru020wc8.jpg
http://img393.imageshack.us/img393/9899/subaru021xg9.jpg
7. Place your carrier some place where you will have much room to work. With a 14mm socket, remove all the bolts holding the cover on. There will be a cap, or breather, that you will need to take out in order to get the top right bolt out. It should pull right out. Gently take the cover off, and try not to spill any leftover fluid that didn't get drained out. You will see a gasket that says UP on the upper right corner on it. Take it off, and put it somewhere safe. Next, take bolts out of the side caps off with a 12mm socket. DO NOT START PULLING THE CAPS OFF. Get your dead blow hammer or hammer and small bit and start making small taps around the cap. Try to ensure that they come off perfectly straight and that you do not lose the two shims that come off with the caps. This should allow you to take your open diff out of the carrier. Play around with the diff. Watch how the gears allow the axles to turn either way.
If you bought an entire carrier for this swap, repeat for that carrier, but make sure you keep all parts with their original carriers. If you have just the LSD unit, move on to the next step.
8. Compare the two units. Notice how the open diff lets you turn the gears both ways. The LSD unit will not let you turn the gears at all.
9. What you are going to do now is take the ring gear from your open diff and put it on the LSD. This takes precision and if the gear is not on the diff properly, well, all hell can break loose. Use a 17mm socket to remove all the bolts holding the ring gear to the unit. Try using a hammer and bit to get the ring gear off. If it doesn't come straight off, use your flathead screwdriver to pry around it and get it off. Do the same with the ring on the LSD unit. Make sure you know which one is which! Now you will put your ring gear onto the LSD unit. Pretty much a reverse process. Place the ring gear onto the diff as equally as you can, working it on very slowly. Once on the unit, you will need to use the bolts from the LSD carrier as they are longer. Some units you may be able to use the original bolts. If you have some Loc-Tite, I'd recommend adding a dab to the bolts for safe measure. Start the bolts by hand, them move to the power tools. In a star pattern, tighten all the bolts. Shown below is a quick pic of the bolts attaching the ring gear to the unit.
http://img139.imageshack.us/img139/9836/subaru013by5.jpg
10. Take a breather. You are almost done. No need to get in a hurry and risk doing something wrong.
11. Work the LSD unit into your carrier. You are staying with the same ring gear, therefore, you need to stay with the same pinion. It may be tricky working it in, so take your time. Make sure your ring gear is on the left side of the diff and you didn't put it in backwards. Use a shop rag or similar cloth to clean the side caps and shims, they must be as clean as you can get them. Put a tad of your diff fluid on the bearings, caps, and shims. Slip the side caps and shims on the same way you took them off - equally and slowly. Put the bolts in and start them by hand, then use the power tool. It should now look like this: (top)
http://img291.imageshack.us/img291/526/subaru014li3.jpg
Spin the ring gear a few times to make sure it is intact with your pinion and everything feels right. You should have a little 'play' between the r&p. The play should be within thousandths of an inch.
12. Put a little bit of fluid over the gears. You can now put the cover back on the diff. Make sure you go get your gasket that should have been in a safe place. Clean it off as best as you can. It can never hurt to put silicone around the cover to prevent any fluid from finding a place to leak out. Bolt the cover to the carrier the same star pattern you re-attached everything else. It is now ready to go back into your car.
13. Raise the diff into the car. It should be able to rest on the side where you pulled the two nuts off the cover. Put the two 17mm bolts through the holes so the diff can rest completely. Tighten all nuts and bolts, then reconnect the driveshaft with the 12mm bolts. The washer goes on the nut side, I made that mistake while wondering why I couldn't get it to tighten.
IMPORTANT: You may need LSD specific axles depending on your car and the car you took the carrier out of. LSD axles tend to be 10mm shorter than non-LSD axles. I had bought the diff with axles still attached, so if I needed axles I had them. My axles actually turned out to be shorter than the wrx axles and they did not have certain features my axles had, so I stuck with my axles. Sometimes it works out that way.
14. Reconnect axles to the diff first, then slide them through the hubs.
15. Re-attach the lateral link with the 19mm bolts. If you took off the covers, re-attach those also.
16. Tighten axle nuts. Put the wheels on and tighten them.
17. You are not done yet. While the car is still on jacks, use a breaker bar to check all the bolts you removed during this swap...for safety!
18. Fill the diff with your fluid of choice. I used Mobil 1 synthetic 75W-90.
19. Test drive the car and make sure there is no binding or strange noises. My car ran perfectly fine for three test drives, so I was good.
20. Take a sharp corner a little faster than you normally would. Watch what happens, you will be shocked. Then, take it to the snow and haul ass. You are good to go.
I highly advise you have an alignment done after you do this. Mine was done the day after, the toe was off by a whole 1/16 of an inch - I got lucky.
If I had the money, I could have gone with an entire transaxle from a Subaru with rear LSD. I don't have that kind of time and money, and my tranny is in too good of shape to replace. Sans the 91 Legacy SS, Subaru never made an r160 geared 3.900 with LSD from the factory. Several 3.90 diffs, none LSD. If I were to change my transaxle, I would have had to change my gear ratio to something higher like the GT's 4.11 or the Outback's 4.44. Or I could have also done an entire transaxle swap with a wrx, but again, money is always a factor. I wanted to keep my 3.90 gearing for slightly better gas mileage due to a lower rpm at highway speeds, and I simply like the longer gears.
My total cost for this project was unbelievably low since I found a good diff locally, had access to a good shop for free, and I was able to get a couple weekdays off work. Total cost was $200. Yeah, I got lucky.
I have to give a HUGE amount of credit to Matt (gator gt) for all the information and help he gave me on this swap. Thanks Matt!
Take care and enjoy. Feel free to PM me for any questions.
Kyle