3.90 LSD installation

[Will]

Goodday Legacy Lovers,

I have obtained my 3.90 rear limited slip differencial and I hope to soon install it. Before I do so, I need some help from you guys.

Here is what I am thinking at this point:

From the information I have read this is a vicsious coupling LDS that is supposed to have a breakaway pressure of 45 pounds. The fist thing I need to do is determine if it is still working at this pressure.
There is information on how to do this in another post (...). If it's still at 45 lbs then it should be as easy as taking my open diff off and bolting this one on. If not, I will have to open it up and add shims/washers to increase pressure.

Is that correct? I see gears inside but no washers, so I am wondering.

What kind of fluid should I use when I put the new one on?

Does anyone still have the web addresses for the LSD info that out there on a couple sites? I found them from this forumn but I can no longer. I did have one bookmarked but it is no longer good.

Thanks,

Will.

p.s. I have some photos of the unit that I will post.[/img]

[ciper]

If the LSD is out of spec shimming is not the correct fix.

You are right that its a removal and reverse installation. Ive dont it once so I dont mind to help with any questions. My first suggestion is to have someone help you and to remove the exhaust piping. Also have the correct size punches for the axle pins.

I suggest mobil 1 75w-90 synthetic. Its cheap and easily available at all the major auto parts stores. Get two bottles and you can do the front and rear differential.

[Qman4x4]

LSD's and VLSD's need the friction additive. Subaru uses GM additive along with 75w/90wt oil. I have always used Kendall limited slip oil for all mine.

If the pressure is not right on your diff you can rebuild it. It basically is a set of clutches similar to a transmission. clutch plates and steel plates placed inside the housing. As long as you don't change the ring and pinion you shouldn't have to adjust the lash at all. Just keep your shims and side bearing cup together and install them back on the side they came off of.

Ken

[ciper]

Qman4x4: None of that is right.

All of the subaru LSD are either strictly mechanical or a fluid based. No clutch based.

All the Viscous units are SEALED, meaning you use normal fluid in them.

A rebuild would consist of replacing the special fluid inside the lsd unit, not only is it not available but a procedure to open and reseal the unit doesnt exist.


If you use the friction additive in your differential all you will do is reduce gas mileage.

[Qman4x4]

Ciper, I'm not sure where you got your info but i know for a fact(read, I have taken them apart) that ALL r160 LSD's are clutch type limited slips. The Viscous are sealed and may take standard fluid but if you run a standard fluid in a LSD you will indeed burn it up. The following images have been taken from the 1988 FSM







Qman

[Qman4x4]

Oh, and regarding the rebuild. There is a procedure for it. It is a complete LSD kit. Granted the kit from Subaru is not "servicable". However, I have disassembled the units and you can flip the outer domed washer for higher pressure on the clutches. This is not recommended for street use. Which I should have stated in the first post. We use these reset units in offroad applications.

I'm not trying to get in a battle or flame war with you, Ciper. But, if you call me out you better be right.

Don't let my post count deceive you. Just as I won't let yours.

Ken

[ciper]

Qman4x4: I have also takena few differentials apart. You are not correct.

I should edit my post to say all current generation subaru are viscous or mechanical, this is after all a LEGACY web site. I didnt think any loyale/justy/xt/leone/brat information was applicable. That looks like the service manual for my XT6, which has a 3.7:1 LSD just like the image.

The Legacy turbo and all legacy platform vehicles use VISCOUS based units. (including impreza and forester)

Will someone host an image for me? Im pretty sure I still have a picture of the viscous sticker right on the differential cover.

edit Here is mine

Here is another

Its small, but you can easily read the VISCOUS on the sticker

[Will]

thanks for the info so far.

As I said in my first post, I took some photos of the LSD that I want to install. I hope to have a minute to upload them to my site tonight. Ciper, I can host an image for you if you like - email to will@higgerty.com

My case is the same as the one in the photos you uploaded - i.e. "Fuji Major Industries 3.90 Viscious LSD".

Assuming that this is a sealed unit and not "shim-able",

a) should I even bother to test break-point or break-out pressure before installing?

b) is it OK to just put it on, fill it up with fluid and go?

Thank you,

WILL>

[ciper]

Will: That first image is actually the one I wanted to post. I found a free image host at villagephotos.com

I dont think there is much you could do to the diff even if it was bad, except buy another unit to replace it. I think you should get the wheels off the ground after the LSD is installed and while the car idles in fist gear stop one rear wheel. With a helper you could put a needle type torque wrench on the axle nut and slowly start the wheels spinning and measure the amount of torque, that would give you something that the rest of us could try so we could compare numbers.

5 speed or automatic?

Qman4x4: Come back and post, dont misunderstand the tone of my post. I enjoy going back and forth with you. No hard feelings.

[Will]

OK, I like the sounds of this - I can just do it!

One more thing I wasted to ask about as seals and gaskets. Should I order new ones before I start this job? If so, what is the part number? If not I will just get that diff oil and go for it.

I have 4EAT.

Thanks again. I will let u know how it goes.

WILL>

[ciper]

Seals and gaskets for what? The differential? I didnt do it but it might not be a bad idea for the seals. My original open 4.11 differential was leaking on the drivers side sligtly. The gear oil is so thick it never was a problem but the spot was always wet.

If anything do it like I did. All by myself I got the car on 4 stands and let it idle in gear. I was able to stop one wheel by hand and it was quite a bit of power even while idling.

A good test would be to find a dirt area and try a few donuts. If you have ever played in the dirt before the difference will be noticed right away.

[Qman4x4]

If there are signs of leakage fix 'em while it's out of the car.

Side seals and diff cover gasket are a piece of cake. Most use silicone on the cover but I recommend the factory gasket. The pinion seal is practically impossible without air tools.

Ciper, no grief, But I am right I am, I am, I am!!! and no it probably wasn't relavent to post the info about the LSD. But, I read his original post as LSD and viscous fluid rather than viscousLSD. Interpretation is an awfully grey area.

As far as break away pressure. My experience with VLSD's are that they don't really come on until higher RPM's. We have tried them in offroad applications and they don't always lock. They seem to be like a centrifical(?) type posi IMO.

[ciper]

"My experience with VLSD's are that they don't really come on until higher RPM's"

You are right that the amount of torque doesnt really matter until the speed difference is high, but you can see the effect of the LSD at low speed

"Most use silicone on the cover but I recommend the factory gasket"
I actually reused the gasket from my old one. One of them ripped in half but the other came off just right. Ive never seen a differential leak from the cover though. From all the junk yard legacys I have seen the leak is usually on the drivers side seal around the axle stub. Since he isnt going to open the cover anymore I dont think he needs that gasket.

I think we are both right, I know I could have made my post more clear.

[Will]

Here are the pics of the 3.90 LSD I mentioned.

BTW, so I order those seals from the dealer? Part number anyone?

[Will]

oh, about the confusion with what kind of LSD I am talking about - that would be due to the fact I had no clue Gives me a whole different idea of LSD. Now I know - viscous

The big test will be in the snow. It was very easy to get one front and opposite back spinning on snow. In Drive, w/ a bit of gas and side bumper nudged into a snowbank, the tires (NRH2) would just turn - and the car would sit.

I will check for tires posts later. Now I think Hakkapalita (sp?) for snow.

[LegacyT]

Not really related, but I just saw pics of your car Will, Wow that car is clean! Guess you wash it often. Don't Let her rust

Mark,

[Will]

Mark, actually if you saw my car right now you would not be using the word clean at all. I do not wash it often - that was the last time. I just made sure to get some pics right after. In the winter I will wash it weekly to keep the salt off. Plan to get it oil sprayed soon as well. We have a Subaru owners club in Ottawa and they get a group buy for oil spray also winter tires. WILL>

[georryan]

What is oil spray and what does it do for your car?

-Ryan

[ciper]

Will: Looks just like the one I swapped.

The two wheel spinning problem you mentioned is exactly what I had happen in the dirt, preventing the car from sliding sideways.

Trust me that you will have to relearn how to drive the car after you install it, and its a good thing

Be careful when removing the stubs. I suggest NOT removing them unless absolutly necessary. Otherwise you will break the "spring wire circlip" that holds it inside. Not an easy part to source. I HAD TO MAKE MY OWN!

[LegacyT]

Oil spray is an anti-corrosion fluid, sorta like oil, but not, with an adhesive. Every year its srayed into the chassis of a car where it sits and displaces any moisture. It gets into seams and crevaces and also coats surfaces so that water doesnt really come in contact with the structure. If done every year it does wonders in saving a car from rust.

Mark,

[ciper]

So you get a big can of WD40 and do it at your house. You know what WD-40 stands for right?

[LegacyT]

Ya, but WD-40 Lacks the adhesive qualities of an oil spray. And WD-40 tends to dry out very quickly. Usually oil spray around here costs about $100, and its worth every penny of it in my opinion.

Mark,