EJ AWD with locked rear diff..?

Phizinza · Post by **Phizinza** » Tue Jun 02, 2009 3:11 pm

Can anyone give me info on how this performs? How has it gone with the centre VLSD? Has anyone blown a gearbox because of a locked rear diff in an EJ AWD car? Just kinda wanting to know more about how well this works and if it is a good or terrible idea.

vincentvega · Post by **vincentvega** » Tue Jun 02, 2009 4:01 pm

no one has done it yet because its fairly obvious that it will fry your center diff eventually.

how long it will last I don't know. If you can afford to experiment let us know how you go.

Phizinza · Post by **Phizinza** » Tue Jun 02, 2009 4:46 pm

vincentvega wrote:no one has done it yet because its fairly obvious that it will fry your center diff eventually.

I am sure I have read on here about someone taking a rear driveshaft out from a Liberty to drive on the road.

A quick search showed up this showpost.php?p=36930&postcount=13
But that isn't the post or person I was thinking of, so I was hoping some people with experience in the matter would chip in

AlpineRaven · Post by **AlpineRaven** » Tue Jun 02, 2009 7:41 pm

I would be interested too but no one really talks about it..... that link was from me that was like about 3 years ago with my silver Liberty when i had welded the diff in...

Cheers
AP

Phizinza · Post by **Phizinza** » Tue Jun 02, 2009 7:58 pm

Alpine, aside from the fact you didn't have it in there for long (?) how did it go offroad? Did it want to spin the front wheels much?

Subafury · Post by **Subafury** » Tue Jun 02, 2009 8:12 pm

brennyv had it in his liberty for a little bit. worked good offroad as youd expect. but did end up breaking the centre, but was rwd at the time (getting abused at the time) i think.
if you take it easy should last a bit longer.

AlpineRaven · Post by **AlpineRaven** » Tue Jun 02, 2009 8:30 pm

Phizinza wrote:Alpine, aside from the fact you didn't have it in there for long (?) how did it go offroad? Did it want to spin the front wheels much?

yeah I can't remember how long i had it for - i think it was couple of weeks, I was scared about breaking the rear CV joints on the road and it was too hard to remove the rear cv once i get on the road. nah it didn't spin the fronts, and I didn't have the chance to give it a go on slippery surface, off road had better traction but I didn't push it which I was thinking back and I could have to see what happens.. Having locked rear diff would be very handy on off road (been there done that and I know what its like!)

I've been looking around but not hard enough is that I am still looking for VLSD or CLSD (prefer CLSD)

El Freddo has welded diff - I'll let him explain..
Cheers
AP

Edit - why i was scared? because one time I saw a picture of rear axle (at the same time when I had welded diff) going thru the rear floor narrowly missed an kid which was sitting in the rear seat... - didn't one of you guys get an email with that picture? I've lost it..

Phizinza · Post by **Phizinza** » Tue Jun 02, 2009 9:01 pm

Mate, I've run welded diffs in both my Brumby and My current sedan. In the sedan I run it on the road with the shafts in (just pump the rear tyres to 40psi and its fine). So I know what a welded diff is like. I can just see if the rear is locked it will not want to slip thus putting more stress on the centre diff which wants to push power to the easiest wheel possible (front one thats off the ground). I actually often lift wheels so this might be an issue.

I actually ran my Brumby with its 4sp while in 4wd with a welded rear diff on road for a little bit couldnt take it outta 4wd. Held up fine, that gearbox is still going strong in our race wagon. And that box has over 4000km of dry blacktop 4wd driving on it.. Tough little cars subies are.

AndrewT · Post by **AndrewT** » Tue Jun 02, 2009 10:17 pm

Brenny's 5spd AWD box was also damaged prior to that. It was able to run in RWD (just by removing front shafts) because the centre VLSD had actually been burnt out and ended up fused together so kindof acted like an L series box.

Edit in answer to the question, I think it would put extra strain on the EJ centre diff and wear it out prematurely, it just seems to make sense that that would happen. In an L series or MY box, yeah they can put up with the welded rear diff for quite a while especially if you take one shaft out on the road, but when they do finally let go I bet it's gonna be something to do with the centre...

Phizinza · Post by **Phizinza** » Wed Jun 03, 2009 9:59 am

Lets just say instead of a welded rear diff, what about a locker (one of those Detroit auto lockers just say). How do people think the gearbox would hold up then? Because you'd only be putting more stress on it while offroad.
I've got a VLSD centre in my shed and I can understand how they can fuse together. The preload is metal on metal and that would heat up the oil in the box pretty fast if it was pushed hard.

vincentvega · Post by **vincentvega** » Wed Jun 03, 2009 10:47 am

detroit is no good either. any time it is driven it is locked. which is all the time behind an AWD EJ box..

Phizinza · Post by **Phizinza** » Wed Jun 03, 2009 12:35 pm

You don't understand how auto lockers work do you? I've had first hand experience with installing them and using them. They are auto unlockers. They are only locked when there is potential for wheel spin. Under normal onroad driving they ratchet away without locking the rear wheels together.

bluesteel · Post by **bluesteel** » Wed Jun 03, 2009 2:20 pm

not quite...

normal lsd, or open diff will let the inside wheel spin slower

detroit, and other UNlockers will let the outside wheel spin faster (and make the lovely ratchety sound)

so there will still be speed differences between the front and the rear, thus wearing out the centre diff quicker, as to how much of a difference there is... and how much quicker it will wear it out... who knows

on another note, has anyone run a welded rear with awd ON road and kept standard size tyres? in theory it should give you more rear grip, reduce turn in a bit, and make it a horrible car to drive in a parking lot.
but hopefully the tyres would slip b4 breaking axles or diffs?

AlpineRaven · Post by **AlpineRaven** » Wed Jun 03, 2009 2:36 pm

bluesteel wrote:not quite...

normal lsd, or open diff will let the inside wheel spin slower

detroit, and other UNlockers will let the outside wheel spin faster (and make the lovely ratchety sound)

so there will still be speed differences between the front and the rear, thus wearing out the centre diff quicker, as to how much of a difference there is... and how much quicker it will wear it out... who knows

on another note, has anyone run a welded rear with awd ON road and kept standard size tyres? in theory it should give you more rear grip, reduce turn in a bit, and make it a horrible car to drive in a parking lot.
but hopefully the tyres would slip b4 breaking axles or diffs?

Correct abt parking, or cornering, i didn't like the shuddering feel and it wore out tyres faster in the rears due corners. It was a pain in the arse.
Cheers
AP

YouTube · Post by **El_Freddo** » Wed Jun 03, 2009 11:56 pm

bluesteel wrote:not quite...

normal lsd, or open diff will let the inside wheel spin slower

detroit, and other UNlockers will let the outside wheel spin faster (and make the lovely ratchety sound)

so there will still be speed differences between the front and the rear, thus wearing out the centre diff quicker, as to how much of a difference there is... and how much quicker it will wear it out... who knows

I would imagine that it wouldn't wear the centre diff any quicker - If you think about it the centre diff is only there to split the required power between the front and rear axles. If there's an Un-locker or an LSD out the back the centre diff won't care as it is still required to do the same thing - to split the power between the front and rear axles when cornering. A welded diff will be the same.

On the L with the welded diff I find it easier to drop back into 2wd than with the open diff because the binding tension is between the two rear tyres, not the front and rear axles...

If I had a detroit, I'd be glad to hear the ratchety sound - it would mean its still there

So who's going to be the guinea pig to prove my theory wrong?

Cheers

Bennie

Phizinza · Post by **Phizinza** » Thu Jun 04, 2009 9:20 am

Yes, at least a welded diff would not bind the transmission like on 4wd subarus (unless your in 2wd). A locker is obviously the best solution, I know someone with a Detroit, I under if I could borrow it once I get the Liberty haha.

But I am still more worried about if it were offroad and it were to lift a front tyre. That's a lot of stress the center diff has to take care of and my guess is it would be a lot happier spinning that front wheel then trying to drive two rear wheels. Its a two to one traction problem. Think of it like lifting a wheel while in 2wd, that wheel gets all the power. Putting a VLSD in the mix isn't going to help much because they only work off the preload when crawling, and that isn't much tension.

discopotato03 · Post by **discopotato03** » Thu Jun 04, 2009 9:45 am

There was a long thread here a couple of years ago I think about diff centers and the "No Spin"/Detroit Locker" was discussed at length .

Firstly a Detroit Locker is NOT a differential AT ALL , it is a device that can drive one axle or both but it cannot differentiate axle speeds like a planetary or bevel gear diff center can .
I've been there with these critters and there's nothing sweet about them or how they feel to drive .

In a straight line the left and right hand side dog clutches engage to provide drive to the axles/wheels . If for any reason the teeth on one of these clutches is not lined up you get one wheel drive until the other aligns and locks - often with a god almighty bang like a center fire rifle going off .

As far as these things "auto unlocking" goes well that's debatable . If you've got the boot in going around a corner they stay locked and act just like a CIG/BOC locker or spool hemisphere .
To get them to let one side go you really have to feather the throttle which unloads the thing and yes then it unlocks one side and it goes click click click around the bend until you straighten up .

They are an added complication in an AWD vehicle because as I said they don't act like a normal diff ie you don't get the corner apex side wheel turning slower than its opposite side one .
Really with a normal bevel diff its three major components all travel at different speeds going around corners - hence "differential" .
What they do is allow the inner wheel to turn slower than the diffs hemisphere while the outer one turns faster .
With yon Detroit the inner wheel turns at the same speed as the diffs hemisphere because its axle is physically locked to the hemisphere . So you can see why there is no "differential" action occurring , what's happening is the wheels either side of Mr Detroit don't bind because one is effectively disconnected .
When you go around a corner in an AWD vehicle all four wheels need to turn at different speeds otherwise they bind and do silly things , the reason why you need a center diff is to allow the front and rear diffs to rotate at different speeds in relation to one another , basically the front faster and the rear slower than the center diffs carrier housing .
I know people get off on this "torque split" business but if all four wheels have firm grip an equal amount of torque goes both ways .
In Subaru AWD gearboxes the center viscous hub is really just a drag mechanism to try to limit the difference in speed between the front and rear drive outputs , they still have a mechanical bevel center but with effectively an Alvey reel star drag on one side in a sealed unit swimming in VLSD goop .
Viscous center diffs are a compromise mainly leaning towards the not too serious general driver/off roader . The serious version needs a mechanical lock like a dog clutch - or PT L type selectable RWD .

For rear diffs in Subarus I reckon the best compromise is the RX L type Salisbury LSD (preloaded clutch plates and beveled spiders) because they don't suffer VLSD shortcomings and to a degree the more you load them up the greater pressure is applied to their plates .

Your calls .

Phizinza · Post by **Phizinza** » Thu Jun 04, 2009 10:02 am

discopotato03 wrote:Viscous center diffs are a compromise mainly leaning towards the not too serious general driver/off roader .

Yes and this completely makes sense as to why the STi lowered street car comes with a tighter VLSD centre diff.

VLSD works great with high speed cornering where you are taking maximum weight from a single rear wheel. If you had an open centre diff (like I had in my Brumby) you find all there power is lost once that wheel comes close to leaving the ground. And you see blue smoke too.

discopotato03 · Post by **discopotato03** » Thu Jun 04, 2009 10:28 am

Yes Fizz and they are also a lower volume niche market model that I wouldn't expect to see go off road too often - like many here aim to do .

You won't find that center in the electronically controlled WRC transmissions .
The greater resistance VLSDs boarder on being a PITA for normal use so you could say they are a compromise biased towards the performance enthusiast .

If you can get hold of him ask Gareth what his EJ25 powered Brumby felt like
with an even higher rally rated VLSD centre , it used to bang and crash and creak and groan - and wanted to understeer at anything less than higher speeds . Compromise biased towards rally dirt work ...

This is why I said that I reckon the best compromise is an open center diff that can be locked/unlocked . It won't wind up in high traction conditions and won't feed all the drive out to the wheel with the least grip when locked .

A .

Phizinza · Post by **Phizinza** » Thu Jun 04, 2009 12:46 pm

My FT4WD box was hopeless rallyXing unless it was locked, then as you say it caused bad understeer. I think a EJ AWD box would work better rallyXing then the FT4WD box.