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LSD vs VLSD


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13 replies to this topic

#1 ezapar

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Posted 05 April 2011 - 10:27 AM

Let's hear your pros and cons and what you believe to be true about their differences.

What do you know from experience? Not, what have you read?

After you guys post up, I'll shed some light on the subject. ;)

#2 GeneralDisorder

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Posted 05 April 2011 - 11:26 AM

I have a VLSD on my '91 SS. It seems to react more to higher-speed manuevering on pavement. The rear will step out a bit when I'm taking "spirited" corners. I don't notice it much though.

Jacob's Brat had a VLSD before we did the AWD transmission swap and even in 4WD I had a hard time noticing it was there. When we went to the 4.111 transmission I also built a 4.111 clutch-type LSD and it's much more "tail happy" now.

From my experience and from everything I've read from the rally community - the VLSD's seem pretty worthless. Add in the fact that the clutch-type's can be rebuilt and also "tuned" with preload adjustments and the clutch-type seems the all-around winner for the rear diff. Front and center are different stories since those are less accesible.... the OBX Helical we put in the Brat is not a thing I would reccomend to most people - it changes the driveing characteristics of the car in a big way.

GD

#3 renob123

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Posted 05 April 2011 - 11:29 AM

Let's hear your pros and cons and what you believe to be true about their differences.

What do you know from experience? Not, what have you read?

After you guys post up, I'll shed some light on the subject. ;)


I'm posting mainly for the subscription, but since I've had both in my Brat, I'd say that the VLSD is good for stock power, but it doesn't help with 180HP or whatever I have now. The clutch-type does help with that type of power, and you can rebuild it/reramp it to get the characteristics you want.

Jacob

#4 bratsrus1

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Posted 05 April 2011 - 12:11 PM

Hi This is Jerry, i have bolth of them. The lsd in my hatchbrat well put it this way on black ice the back end will catch up to the front end, not enough weight on the back end. The vlsd i have in my hatch and black ice it dose fine thats why i chose it over the lsd. I do alot of driving on black ice every winter. Thanks Jerry

#5 Turbone

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Posted 05 April 2011 - 05:46 PM

With my RX's LSD, it depends on whether I have the diff lock on.
Theres not enough torque (normally) to really make it break loose.
It could be that the RX has enough weight in the rear to keep it planted.
Click on the diff lock and you better be ready to get sideways.

#6 grossgary

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Posted 05 April 2011 - 06:25 PM

the clutch type seems better for the steep unmainted snow i drive in but it's hard to say given i've only had clutch type in XT6/EA and VLSD in EJ's, not interchanged.

seems like the clutch type is easier to tell if it's "working" and in good condition.

interested what you got coming.

#7 monstaru

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Posted 06 April 2011 - 12:19 AM

they should technically have the same rating, just different actuation.torque rating wise they activate a little differently.but very little difference.same roads, same winter, same vehicle.they were both used, but cleaned and resealed .no reason to think there was undue stress on either...
but i can break anything lose on ice:grin:and do....
however, spring mud that year was fun with the clutch type....not so much with the VLsd. even though rpms were high through the same honey holes ..it just wasn't the same feel...but totally possible it was not up to snuff.
cheers, b

#8 GeneralDisorder

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Posted 06 April 2011 - 01:03 AM

There's quite a bit of difference in how they work - the Viscous units have a fluid that when heated due to shearing forces becomes nearly a solid (very high viscosity) thus "gluing" the stack of plates contained in the fluid. This action takes *time* to occur. Now how much time is determined by the design but it would seem that it's considerably longer (and possibly when they do lock it's weaker) than the clutch types.

Additionally they are sealed and unserviceable and untuneable. You get what you get and there's nothing you can ever do to change it. That's not acceptable for a lot of users.

Personally I feel that Subaru went to the viscous style LSD because they wanted something that would never fail and improve traction to some degree - but "functionality" took a backseat to cost and marketing considerations. Being able to say you have a limited slip is nice and most people aren't going to know the difference. If you look at the 6 speed STi's you'll notice they don't use the viscous coupling devices at all. Nor do most other high-end race inspired setups.... most are using Torsen or Helical (Torsen type 1) diffs or clutch types.

Interesting qoute from Wikipedia:

"Viscous LSDs are less efficient than mechanical types, that is, they "lose" some power. In particular, any sustained load which overheats the silicone results in sudden permanent loss of the differential effect. They do have the virtue of failing gracefully, reverting to semi-open differential behaviour. Typically a visco-differential that has covered 60,000 miles (97,000 km) or more will be functioning largely as an open differential"

GD

Edited by GeneralDisorder, 06 April 2011 - 01:21 AM.


#9 monstaru

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Posted 06 April 2011 - 11:24 AM

yeah well, there was very little difference in how MINE acted.....so, that is why i stated it that way.......you can throw out all the technical mumbo jumbo you want,he asked for personal experience.:)cheers, b

#10 renob123

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Posted 06 April 2011 - 11:33 AM

yeah well, there was very little difference in how MINE acted.....so, that is why i stated it that way.......you can throw out all the technical mumbo jumbo you want,he asked for personal experience.:)cheers, b


You bring up a good point, Brian. To further cloud the comparison, the clutch-type in my Brat is way grabbier than the clutch-type in my other car.

You did mention a noticeable difference in the mud, though.

Jacob

#11 GeneralDisorder

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Posted 06 April 2011 - 11:47 AM

yeah well, there was very little difference in how MINE acted.....so, that is why i stated it that way.......you can throw out all the technical mumbo jumbo you want,he asked for personal experience.:)cheers, b


Certainly - he did at that. And don't take my "technical mumbo jumbo" to mean that your experience is not valid and useful to the discussion. Just that it might be biased due to used differentials of unknown mileage and history..... both the clutch type and viscous type wear out and from what I have read it's not very many miles either. Race teams typically rebuild their clutch types every season - as mentioned in that wikipedia quote there is evidence that the viscous units are all but worn out after 60k or so.

GD

#12 ezapar

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Posted 06 April 2011 - 01:24 PM

My $.02.

Way back when, I procured a vlsd for my first hatch back. Came out of a early t-leg. It didn't work for crap, totally useless, a waste of lots of time and money.

I've had several clutch type lsds, which worked much better than that one, but never compared to a welded diff. If you're stopped in your ea81 off roader, a little off camber, that lsd is useless too. They only seem to work with momentum.

But. I've got one in my imp from an 00 imp RS. It's way smaller, totally looked like an open diff. It has performed amazingly well. As in, to get out of my garage, I always had to get a little run at it, cuz one tire comes mostly off of the ground causing them to spin. Now, I can totally creep out and over that spot without losing any kind of traction at all.

In the mornings, there's a really off camber right turn that would always get the right rear tire spinning. Now they either both spin or both grip.
It's made the car way more predictable and easier to tell when the rump roast end is gonna come out.

This one has 84kish on it.

Like I said, totally DON'T care what anybody read somewhere.

I just have to kinda believe that the VLSD had to be improved over the older huge ones.

Below are images of the two, both sitting next to open diffs.
Posted Image

Posted Image



Mine.
Posted Image

Edited by Zap, 06 April 2011 - 01:27 PM.


#13 monstaru

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Posted 06 April 2011 - 08:46 PM

Certainly - he did at that. And don't take my "technical mumbo jumbo" to mean that your experience is not valid and useful to the discussion. Just that it might be biased due to used differentials of unknown mileage and history..... both the clutch type and viscous type wear out and from what I have read it's not very many miles either. Race teams typically rebuild their clutch types every season - as mentioned in that wikipedia quote there is evidence that the viscous units are all but worn out after 60k or so.

GD


it's ok, i don't need a tampon.that was kinda my point.DEF. a difference in time used, period.if we all had reference of brand new units we could actually call it a comparison.

it is good to know that the design has changed a skosh..i am debating whether or not i should weld this next one coming up here real soon.i am a total fan , but i have been really thinking about stresses lately...

i don't work in the middle of nowhere currently.and do not really need that kind of trsaction.so i'd almost rather get a clutch unit, and rebuild it or run it till it pukes....
cheers, b

#14 edrach

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Posted 06 April 2011 - 11:16 PM

I'll add my 2 cents of "personal" experience with three clutch type LSDs. I've never used a VLSD in any of my vehicles and don't plan to (probably time to sell the ones I have:)).

Anyway, I added an LSD to two of my brats; one of which I used to rallycross. The difference (on the rallycross course) was striking. The brat went from an over steering car to one that understeered drastically. I ultimately had to change my driving technique quite a bit; i.e. no real throttle application unless I was in a straight line. Any turning at all with throttle caused the brat to plow; more throttle more plow.

Due to my dis-like for understeer, I held off on adding an LSD rear to my Impreza until late last year. The Impreza is pretty tail happy (or my driving technique has matured to better control) so I installed an LSD diff to the Impreza. Best thing I've ever done. Car is much more stable in straight line with maximum throttle. As tail happy as the Imp is, I can avoid the understeer almost entirely.

Granted this is not a comparison between VLSD and LSD; just a personal comment on how a rear LSD can improve rallycross performance. Last month I did get into the deep mud and thanks to the mud tires and LSD I was able to power out of it instead of getting stuck (that would have been embarassing:eek:).




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