Limited slip diffs

Beachworm

Forum Member
Joined
Oct 16, 2017
Messages
502
Location
Brisbane Australia
Car Year
2010
Car Model
Forester X Luxury, sump guard, bigger AT tyres and 50mm Subieliftoz lift, breather extensions
Transmission
Auto
Is there a separate thread somewhere about LSDs?
 
Plated diffs are a step up from the vlsd, but in the end they will let you down when you need them most. I went from plated lsd to locker for this reason, and the difference is night and day. The plated diff made the car very twitchy in the wet, and even with excellent road tyres it would catch a lot of people out, so sudden and violent was the oversteer. To try it with off road tyres would be a special kind of stupid. Perhaps with a non turbo it would not be so bad. Off road, the plated diff does help, but for those that do more hard core off roading you will find the limitations. That’s when you move up to locker diffs and a new world of off road capability. An all terrain tyre will never, as my video has proved, make up for inferior diffs or inadequate traction control systems.
 
As far as diffs go, I'm happy with what I've got which is an open diff helped by VDC. I don't know if there is even an LSD available for my car that wouldn't also require changing the front diff due to different ratios. I have adopted a very conservative on-road driving style so I don't think an LSD would give me any advantage over VDC in that context.

I wouldn't go down the track of laying out mega dollars to fit an R180 and a locker. A locker is only as reliable as the compressor and I would be worried that if I had the capability I might get so far down a track that I couldn't get back without a locker and a compressor, seal or air line failure would leave me in a pickle.

The reality is that for off-road use, my SH with sump guard, lift and other small mods does everything I want it to do. I might have to have 3 goes at a section of track that others can do in one but that's part of the fun. I can live with that.
 
I think for your needs your traction system is suitable.
 
FYI: For anyone reading this, don't worry about a clutch LSD in the rear causing snap oversteer. If it is doing that something has been done wrong. Assembled wrong, wrong oil, wrong driving technique....something. Even set at 100% lockup (the harshest setting) it still shouldn't be that bad.

The front is a different propostion. Power understeer with a front clutch LSD is a real problem, very disconcerting. Spoken from experience with multiple setups
 
The clutch type diff I used to have in the rear of the Forrie was brand new and set up by the same bloke who pioneered the diff locker. He’d done this before many times and the fact that you have experienced exactly the same characteristics when that same type of diff is used in the front would indicate that this is how such diffs work. It may though depend on the brand of diff, as my wrx isn’t as bad and it runs the sti diff. Maybe the torque of the turbo 2.5 makes it worse, maybe the ride height, maybe a combination of these. I can’t say. It wasn’t like this with the open diff, the vlsd, the torsen diff or the locker (which on road is an open diff). What I am certain of is that it happens and it will catch many drivers out. I’m glad my car isn’t like that anymore.
 
Rally said:
the fact that you have experienced exactly the same characteristics when that same type of diff is used in the front would indicate that this is how such diffs work.
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Totally different. Firstly, you can't compare front & rear LSDs as they produce completely different effects on the car's handling. With your motorsports background you should know this. I agree, snap oversteer is very dangerous esp in the wet & should be avoided, but this doesn't happen with the front.
The front produces power understeer. It's very disconcerting, but all you have to do is come off the throttle & you get the steering back

Second the front clutch LSD is a Cusco whereas your rear was a KAAZ. I have your LSD, it still has the stub axle jammed in it & I can't get it out, so something has definitely gone wrong with it.
 
Sorry, I may not have made it clear. When you put something like a plated lsd in the rear, you increase the likelihood of power oversteer. Apart from cost it’s why most cars don’t have them. When you put that same sort of diff in the opposite end of the car, you get the opposite of oversteer which is understeer. The power understeer which you mentioned. I agree different brands plated diffs will ramp up differently, and this can also be adjusted. Hence my comment it wasn’t as bad in the wrx. For off road use, you want the diffs to be pretty strong in order to be effective. Yet, despite this my diff still opened up when needed most.

The reason the axle was stuck in the diff was apparently due to the retaining clip. Or at least the groove into which the clip goes into in the diff gears. We suspect it wasn’t chamfered, preventing the axle from coming out. The diff is still usable, the cv shaft itself was working fine, as was the diff.
 
I've got a KAAZ rear clutch type diff, a 20 KG sti viscous coupling, and a torsen front diff. I run all terrain (BF Goodrich) tyres. Engine is a H6 which is tuned and has a very even torque curve.

I do a lot of offroading: high country and southern highlands mainly these days, although a recent outback trip to Broken Hill, Menindee, White Cliffs, Bourke was a cracker.

I've found the combination to be nicely balanced, and while I get the occasional bit of wheel spin in steep and rocky terrain, I have enough power getting to the ground that momentum is maintained.

I don't go looking for trouble, but those who know me know that I am not the most conservative driver either! The diff combination I have is a very good compromise overall. Haven't experienced any of the understeer, oversteer or binding that some have reported with some of these components. (in fact i'd say that there is a lot of rubbish spoken and written about 20 kg centre viscous couplings!).

I would say that if you really put the foot down, you are conscious of a weight shift overall when the rear diff "kicks in", but its very mild. It's really a matter of being reminded it's there., but no more than that.

That being said, my suspension is a custom set up from TruTrack in Melbourne, so the spring and damper combination is very balanced.
 
Interesting. I note you said your engine has a fairly even torque curve. Perhaps that is where a good part of the explanation lies. I’m trying to remember if I had the same problem with the na engine, but too much time has elapsed. Too many spec changes to be sure, but there is a fair chance I never experienced the sudden oversteer with the na engine.
 
Is there anyone reading this who has put an LSD into an SH Forester?
 
I was told here that installing an aftermarket LSD on automatic Subarus can result to premature wear of the Transfer Control Duty solenoid as it gets confused on how much torque it will send to the rear with a much more aggressive LSD system. This may be why they opted with vLSD instead of multi-plate. It works with autos and manuals. On a manual gearbox, this is not the case as the whole torque transfer is mechanical, whereas with automatics, torque transfer is electronic.

I think that VDC and X-mode are a good compromise of off-road tracton/performance, cost and maintenance. They really help a lot in diagonal situations. On loose surfaces, though, which we have a lot here, I see the benefits of having the vLSD even with the 4EAT as I can control the wheel spin accordingly. Cheers.
 
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Did you fit the LSD or did the car come with it from new?
 
[MENTION=15642]Beachworm[/MENTION], as [MENTION=114]Kevin[/MENTION] said, mine has the factory vLSD. We also have the option to put in the slightly more aggressive 4.444 R160 with SureTrac which came with some WRXs. I am not sure if there is such an option with SHs. Cheers.
 
Knowing there’s actually a locker solution out there I’m hanging for one in my L - I’ve gone all these years with an open rear. Even just the front LSD makes a huge difference offroad and is well worth the effort. Mine needs some maintenance worth I think, so there’s a box split to do there, which is ok as I want to mess with some other bits while in there too.

Also the type of LSD selected should be made with its intended use. Some can “lock up” quickly almost like a snap - especially if enough berries are given at the time. Or they can be more user friendly and do their thing without the driver really noticing...

Either way, anything is better than open!

Cheers

Bennie
 
El Freddo, isn't your front LSD helical ? If so, it shouldn't need any maintenance.
 
jf1sf5 said:
El Freddo, isn't your front LSD helical ? If so, it shouldn't need any maintenance.
Click to expand...

Yes it is a helical and yes you’re correct. But... this is a quaife rip off by OBX as far as I know.

After installing it a new forum member asked me if I put some rebuild kit through it. No, it’s new!! So after some research I found the dude's website and read about how poorly the OBX pressure cones/washers were constructed and how some were cracked even before use.

After the outing earlier this week with [MENTION=15735]1WD Foz[/MENTION] I didn’t notice the front LSD doing its thing like I used to, so it’s on the list of things to do with the gearbox when it comes out next time. So maybe in three years time something might happen in that department ;(

But typically a helical doesn’t need to be touched, and this is why I chose a helical diff in the first place.

Link to the rebuild kits for anyone thinking of going the OBX LSD route. https://rbryant.freeshell.org/obx_washers.htm

Cheers

Bennie
 
This one is a decently priced aftermarket:
https://www.ebay.com/itm/SUBARU-REA...h=item1cc0ac896e:g:g9AAAOSwrFZb1iqC:rk:1:pf:0

I haven't heard of anyone who has installed it yet. I am assuming though that since they love their Subarus up there, they get some sort of a following. They cover all Subaru models up to 2018.

I usually just buy Japanese aftermarkets and with the previous non-Subarus, I just went with Cusco and plated LSDs. The one on the link might be worth a try considering that the price is a quarter of that of most branded ones. Cheers.
 
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