Should I get a locking dif???

[faunjoustino]

Hey all!
 

---1999 Subaru Legacy Outback 2.5---

Just curious about getting a center or rear differential that I can lock and unlock.

I know its a good move to improve off-road capabilities however I am concerned about additional damage I might be doing to the vehicle.

Should I be worried about potentially breaking or wearing down parts faster due to the diff lock? If so which parts should I keep an eye on, keep a back up of, or upgrade ahead of time? to avoid being towed home after breaking something I could have upograded or prepared better for.

[idosubaru]

Used properly it's a nonissue in snow, mud, grass, offroad.  There aren't really many options though. 

The rear VLSD differentials wear out and function like the open rear differential you already have so they're kind of pointless to buy used. 

If you have a manual trans you can't get a locking center diff. 

If you have an automatic you can install a switch to manually control the Duty C solenoid output for the rear transfer cluthes (a.k.a. "center diff") - which is what I, and others here, have done before. 

[faunjoustino]

  On 12/29/2021 at 8:12 PM, idosubaru said:

Used properly it's a nonissue in snow, mud, grass, offroad.  There aren't really many options though. 

The rear VLSD differentials wear out and function like the open rear differential you already have so they're kind of pointless to buy used. 

If you have a manual trans you can't get a locking center diff. 

If you have an automatic you can install a switch to manually control the Duty C solenoid output for the rear transfer cluthes (a.k.a. "center diff") - which is what I, and others here, have done before. 

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Hell yea i didnt know i already had a diff i can use, thats awesome! any threads or videos on how to hook that switch up?

 

[Numbchux]

Depends on what you want.

 

Nobody makes a true selectable locker for a Subaru. The duty C solenoid mod for automatic transmissions is decent, but IMO if you're pushing hard enough to need it, it's not strong enough.

I can't find the information now, but there's a company in Europe that can rebuild the viscous center diff for a manual transmission to be significantly stronger.

Lock-rite offers automatic rear lockers for Subarus. These can be a little odd, as when you go around a corner, they only power the inside wheel, and the outside wheel ratchets. But offroad performance is 1000% better.

There are a couple companies that make selectable lockers for Nissan r180 front diffs. Subaru STis use r180s in the rear. I have seen a couple examples where people have found the right combination of pieces to use those lockers in the rear of a Subaru.

If you're a real baller, pontoontodd makes a unit that replaces the center diff on a 2006+ STi 6MT which gives simple FT4WD function (open or locked, no LSD) and a real low range. But you'll probably be in it $10k by the time you get it all set up with the 6 speed swap, and it would be kind of pointless without at least a lock-right in the rear. 

 

[GeneralDisorder]

I wouldn't worry about it. You are not likely to need a rear locker. You can use the parking brake to help with power transfer on the rear or just modulate the service brakes to keep wheels without traction from absorbing all the power. The rear locker isn't cheap, takes quite a bit of knowledge to install properly, and make on-road driving a bit annoying since it will ratchet, pop, and bind around sharp turns. I would leave this mod to people that are doing 4"+ lifts and don't care about on road driving. 

You can do the modification for the duty-c to lockup the transfer clutch - it's easy and inexpensive so worth your time if you are interested. 

GD

Edited December 29, 2021 by GeneralDisorder

[faunjoustino]

  On 12/29/2021 at 10:40 PM, GeneralDisorder said:

I wouldn't worry about it. You are not likely to need a rear locker. You can use the parking brake to help with power transfer on the rear or just modulate the service brakes to keep wheels without traction from absorbing all the power. The rear locker isn't cheap, takes quite a bit of knowledge to install properly, and make on-road driving a bit annoying since it will ratchet, pop, and bind around sharp turns. I would leave this mod to people that are doing 4"+ lifts and don't care about on road driving. 

You can do the modification for the duty-c to lockup the transfer clutch - it's easy and inexpensive so worth your time if you are interested. 

GD

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Thanks for the advice!

I want to lift her only 1"-1.5" with 215/75/R15's all terrains as the smallest upgrade I could find for tires, I don't want to lose too much power by lifting it more than that and putting bigger tires that are require more torque to turn 

what are the downsides of the Duty-C lockup? and will I even need it? 

At the end of the day I just want to drive to some off the beaten path camping spots, I don't want to go rock crawling or aggressive off-roading. I want to baby her while being capable of going on tougher trails. I will drive cautiously and will have proper recovery gear just in case, but I want this thing to be a tank for medium off-roading obstacles.

[laegion]

  On 12/29/2021 at 8:12 PM, idosubaru said:

Used properly it's a nonissue in snow, mud, grass, offroad.  There aren't really many options though. 

The rear VLSD differentials wear out and function like the open rear differential you already have so they're kind of pointless to buy used. 

If you have a manual trans you can't get a locking center diff. 

If you have an automatic you can install a switch to manually control the Duty C solenoid output for the rear transfer cluthes (a.k.a. "center diff") - which is what I, and others here, have done before. 

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I would assume there is a way to rebuild the VLSD rear diffs so that they function properly again?

[GeneralDisorder]

  On 12/30/2021 at 3:30 AM, laegion said:

I would assume there is a way to rebuild the VLSD rear diffs so that they function properly again?

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Then you would assume wrong. 

GD

[laegion]

  On 12/30/2021 at 3:39 AM, GeneralDisorder said:

Then you would assume wrong. 

GD

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Well damn...that's really unfortunate. I was hoping I'd be able to rebuild the one in my '03 if it was bad.

[idosubaru]

 

 

 

  On 12/30/2021 at 2:36 AM, faunjoustino said:

Thanks for the advice!

I want to lift her only 1"-1.5" with 215/75/R15's all terrains as the smallest upgrade I could find for tires, I don't want to lose too much power by lifting it more than that and putting bigger tires that are require more torque to turn 

what are the downsides of the Duty-C lockup? and will I even need it? 

At the end of the day I just want to drive to some off the beaten path camping spots, I don't want to go rock crawling or aggressive off-roading. I want to baby her while being capable of going on tougher trails. I will drive cautiously and will have proper recovery gear just in case, but I want this thing to be a tank for medium off-

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Duty C isn’t designed for continuous use via a switch so that non standard use could wear it out. I’ve never seen it happen and I’ve used it probably more than just about anyone on here in a few vehicles and 10s of thousands of miles. I’ve even used it continuously for 10s of thousands of miles to work around other mechanical issues.  

I like it in snow and mud. It gives definitive immediate traction and no chance of the wheel momentarily slipping and starting a rut.

I also like it on a steep unmaintained (not plowed or treated) snow covered mountain road I drive every day to work. Without the switch the car wants to walk some back and forth and has less control. With it on it goes straight up. When it’s just above freezing during the day, a few people drive over it, and it freezes at night - it’s slick as an ice rink and even making it up with snow tires can be tricky.  At its worst, it’s impossible to go down without studs because it’s so steep and solid smooth ice. I won’t go down jt and go a different way home when that happens.  It’s a pretty good test because I drive it every day to work and have done it hundreds of times with and without the switch. Mostly, but not entirely, in an XT6. Which has the same transmission but a bit of a weight difference from your car. 

Edited December 30, 2021 by idosubaru

[faunjoustino]

  On 12/30/2021 at 11:18 AM, idosubaru said:

 

 

 

 

Duty C isn’t designed for continuous use via a switch so that non standard use could wear it out. I’ve never seen it happen and I’ve used it probably more than just about anyone on here in a few vehicles and 10s of thousands of miles. I’ve even used it continuously for 10s of thousands of miles to work around other mechanical issues.  

I like it in snow and mud. It gives definitive immediate traction and no chance of the wheel momentarily slipping and starting a rut.

 

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Thank you for the advice!

 

Will doing this Duty-C mod cause any "ratcheting, popping or binding" around corners and stuff during regular road driving when its not turned on?

[idosubaru]

  On 12/30/2021 at 5:51 PM, faunjoustino said:

Thank you for the advice!

 

Will doing this Duty-C mod cause any "ratcheting, popping or binding" around corners and stuff during regular road driving when its not turned on?

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No, with it “off” it’s like the switch isn’t even there and was never installed. It just would then drive like every other Subaru on the road without a switch. 
 

this assume it’s installed correctly of course 

[faunjoustino]

  On 12/30/2021 at 8:28 PM, idosubaru said:

No, with it “off” it’s like the switch isn’t even there and was never installed. It just would then drive like every other Subaru on the road without a switch. 
 

this assume it’s installed correctly of course 

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Gotcha, thanks again!

 

how does this work compared to a "normal" diff locker? what are the key differences?

 

[laegion]

  On 12/30/2021 at 8:52 PM, faunjoustino said:

Gotcha, thanks again!

 

how does this work compared to a "normal" diff locker? what are the key differences?

 

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When it's locked it's no different than any other locker. The mechanism is different but the effect is the same.

 

Edited December 31, 2021 by laegion

[idosubaru]

  On 12/30/2021 at 8:52 PM, faunjoustino said:

Gotcha, thanks again!

 

how does this work compared to a "normal" diff locker? what are the key differences?

 

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You should specify what you mean by "normal" diff locker, in Subaru world there isn't a "normal".   

Broadly speaking a "diff locker" usually refers to a rear, or front, differential.  The Duty C switch controls the rear transfer functionality of the transmission, and not the front or rear differential like a truck with a "locker". 

A 4WD truck with a "locker" will have the transfer case and a locking rear diff. 

A subaru with this switch will just have control of the transfer function, it has nothing to do with front and rear diffs. 

[faunjoustino]

  On 12/31/2021 at 4:08 PM, idosubaru said:

You should specify what you mean by "normal" diff locker, in Subaru world there isn't a "normal".   

Broadly speaking a "diff locker" usually refers to a rear, or front, differential.  The Duty C switch controls the rear transfer functionality of the transmission, and not the front or rear differential like a truck with a "locker". 

A 4WD truck with a "locker" will have the transfer case and a locking rear diff. 

A subaru with this switch will just have control of the transfer function, it has nothing to do with front and rear diffs. 

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  On 12/31/2021 at 7:51 AM, laegion said:

When it's locked it's no different than any other locker. The mechanism is different but the effect is the same.

 

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So what am I "locking" with this solenoid if its not the diff? im a little confused. haha sorry yall 

 

[heartless]

  On 12/31/2021 at 5:53 PM, faunjoustino said:

 

 

So what am I "locking" with this solenoid if its not the diff? im a little confused. haha sorry yall 

 

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you were told in the post just above yours..

  Quote

A subaru with this switch will just have control of the transfer function, it has nothing to do with front and rear diffs.  

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[laegion]

  On 12/31/2021 at 5:53 PM, faunjoustino said:

 

 

So what am I "locking" with this solenoid if its not the diff? im a little confused. haha sorry yall 

 

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You're locking the center "diff" (which in most automatic subarus is a computer controlled multi-plate wet clutch in the tail of the transaxle [similar to a clutch in a motorcycle]) that distributes torque to the rear differential. When it's "locked" meaning the duty solenoid that locks the clutches is 100% locked with a switch (or automatically) then it essentially becomes a solid link between front and rear differentials like a traditional 4x4's transfer case (however with no gear reduction).

When it's not locked the ECU controls the percentage of power transfer to the rear diff by changing the duty cycle of the clutch control solenoid, up to and including a full lock but will disengage so drive train components aren't damaged from tire scrubbing on dry surfaces.

Most subaru's have open front and rear diffs. I've been looking into options for rear limited slip and I'm leaning toward looking for an STI rear diff with a torsen posi; although I haven't looked into it much yet and it's possible there is some reason that wouldn't work. Maybe someone else knows more about that aspect of things. It seems it would be easiest to swap in another intact subaru rear diff than swapping in a different carrier as that requires adjusting the diff gear's tolerances from what I understand. I've never done that part before.

Edited December 31, 2021 by laegion

[GeneralDisorder]

It's possible to install an R180 but you really don't want a Torsen for off road. They don't lockup unless both tires have some traction. If you lift a wheel or it's just in really sloppy mud, etc the Torsen won't do anything at all. A clutch style LSD would be better but the STi R180 is designed for street and rally not slow off-road so it's far from ideal. 

GD