TheLoyale Posted March 28, 2012 Share Posted March 28, 2012 (edited) I just picked up a 3.900 Viscous Diff from my buddy who has an SS, The case matches mine from the EA81, the only difference is this diff has axle stubs that press into the diff Vs Diff stubs that stick out of it with a roll pin. SO my question is: How hard is it to find these DOJs with the stub build onto them, and can I make a hybrid axle with the EJ DOJ onto my EA81 Axle shafts? Are the shafts the same diameter? Cause I want to drop the whole rear diff assy under my car and bolt it up without changing internals. The only thing I do need to add to the EJ diff is the Bushing plate on top, other then that all looks good. Also where do I get the correct oil for the Viscous diff? I tried to turn the tail shaft, and could not, so then I checked the fluid level and there is no oil in it. Shouldn't the diff still turn somewhat easy with no oil in it? I couldn't really even budge it with a 1-1/8" Socket. -TJD Edited March 28, 2012 by TheLoyale Quote Link to comment Share on other sites More sharing options...
ShawnW Posted March 28, 2012 Share Posted March 28, 2012 Dare I say, the axle held onto the stubs during disassembly? They are supposed to have the male stub with roll pin like older GL's do. Take a photo of the side so I can see. Quote Link to comment Share on other sites More sharing options...
T'subaru Posted March 28, 2012 Share Posted March 28, 2012 Youll need hybrid axles. Suberdave has them dialed in. Quote Link to comment Share on other sites More sharing options...
Numbchux Posted March 28, 2012 Share Posted March 28, 2012 Youll need hybrid axles. Suberdave has them dialed in. Negative. The T-leg LSDs actually have male stubs. Get a set, done. Talk to whoever you got the diff from, and separate them from the axles. If he doesn't have them, you'll have to get them from a T-leg with an LSD, as the splines in the diff are different than an open diff. Quote Link to comment Share on other sites More sharing options...
TheLoyale Posted March 28, 2012 Author Share Posted March 28, 2012 So this is indeed supposed to have Male stubs. Hmm... So I'll need the axle stubs from a Turbo car, guess I better start my search. Thank you guys Quote Link to comment Share on other sites More sharing options...
TheLoyale Posted March 28, 2012 Author Share Posted March 28, 2012 So now I have a better understanding of a VLSD in general. Only thing I am not sure on about this one I have is, Do I need to add an additive to the gear oil? Or is there a sealed unit which is not serviceable like the quote from Wiki states? I do know the Clutch style LSDs are more popular among everyone on the USMB, but the VLSD is still decent, yeah? Viscous The viscous type is generally simpler because it relies on hydrodynamic friction from fluids with high viscosity. Silicone-based oils are often used. Here, a cylindrical chamber of fluid filled with a stack of perforated discs rotates with the normal motion of the output shafts. The inside surface of the chamber is coupled to one of the driveshafts, and the outside coupled to the differential carrier. Half of the discs are connected to the inner, the other half to the outer, alternating inner/outer in the stack. Differential motion forces the interleaved discs to move through the fluid against each other. In some viscous couplings when speed is maintained the fluid will accumulate heat due to friction. This heat will cause the fluid to expand, and expand the coupler causing the discs to be pulled together resulting in a non-viscous plate to plate friction and a dramatic drop in speed difference. This is known as the hump phenomenon and it allows the side of the coupler to gently lock. In contrast to the mechanical type, the limiting action is much softer and more proportional to the slip, and so is easier to cope with for the average driver. New Process Gear used a viscous coupling of the Ferguson style in several of their transfer cases including those used in the AMC Eagle. 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.[6] They do have the virtue of failing gracefully, reverting to semi-open differential behavior. Typically a visco-differential that has covered 60,000 miles (97,000 km) or more will be functioning largely as an open differential;[citation needed] this is a known weakness of the original Mazda MX-5 (a.k.a. Miata) sports car. The silicone oil is factory sealed in a separate chamber from the gear oil surrounding the rest of the differential. This is not serviceable and when the differential's behavior deteriorates, the VLSD center is replaced. Quote Link to comment Share on other sites More sharing options...
92_rugby_subie Posted March 28, 2012 Share Posted March 28, 2012 So now I have a better understanding of a VLSD in general. Only thing I am not sure on about this one I have is, Do I need to add an additive to the gear oil? Or is there a sealed unit which is not serviceable like the quote from Wiki states? I do know the Clutch style LSDs are more popular among everyone on the USMB, but the VLSD is still decent, yeah? From what Ive heard... The clutch type is the best because the Viscous isnt serviceable, so when it goes bad after (I think like 70K typically) they are just useless... I could be wrong, and Im sure Ill be if I am, but from what I recall, VLSDs just arent that great Quote Link to comment Share on other sites More sharing options...
ShawnW Posted March 28, 2012 Share Posted March 28, 2012 Placing a number of miles on failure is rediculous. How its used and maintained is key and thats all. The diff is a sealed unit that takes regular 75W90. I use Extra S fluid from Subaru in all of them here. The clutch type is better for initial launching only IMO. Otherwise they are fairly similar. Quote Link to comment Share on other sites More sharing options...
TheLoyale Posted March 28, 2012 Author Share Posted March 28, 2012 Placing a number of miles on failure is rediculous. How its used and maintained is key and thats all. This is 100% true. Why does a 1947 Dodge pickup still have the original clutch disc in it? When a 2007 Honda needs one replace in 50,000? Depends how it was treated. Shawn, good to know about the Extra S from Subaru. I am debating if I should keep this diff, or give it back (As I only took it home to compare the two) and then I have the option to buy it if it'd work for me. Everything will work, except the axle stubs, I don't think there is any way to use the EJ DOJ on an EA axle, the splines look to different. Has anyone done this? or does somebody offer custom versions? Suppose I could save my self $50 and forget the LSD idea for now? Quote Link to comment Share on other sites More sharing options...
bratman18 Posted March 28, 2012 Share Posted March 28, 2012 Those male axle stubs are specific to the Legacy SS rear diff and specific to each side as well. Just FYI Quote Link to comment Share on other sites More sharing options...
WoodsWagon Posted March 28, 2012 Share Posted March 28, 2012 If he's parting a legacy SS, wouldn't he have the stubs to go with the diff? Quote Link to comment Share on other sites More sharing options...
TheLoyale Posted March 28, 2012 Author Share Posted March 28, 2012 If he's parting a legacy SS, wouldn't he have the stubs to go with the diff? No one is parting anything, the Diff was a spare from his old SS which is long gone, and the stubs disappeared. Quote Link to comment Share on other sites More sharing options...
mcbrat Posted March 30, 2012 Share Posted March 30, 2012 Those male axle stubs are specific to the Legacy SS rear diff and specific to each side as well. Just FYI yes, and the stubs are available from the dealer for about $250.... at least several years ago they were. I bought a set for a 3.9 VLSD that I bought with them missing... were there ever any other 3.9 VLSD rears available? Quote Link to comment Share on other sites More sharing options...
987687 Posted March 30, 2012 Share Posted March 30, 2012 Why can't you just swap the LSD chunk into a different EJ diff? Quote Link to comment Share on other sites More sharing options...
mcbrat Posted March 30, 2012 Share Posted March 30, 2012 Why can't you just swap the LSD chunk into a different EJ diff? you still need the stubs, as they are specific for the "chunk". Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted March 30, 2012 Share Posted March 30, 2012 (edited) Why can't you just swap the LSD chunk into a different EJ diff? It wouldn't help. The LSD chunk requires the SS specific stub axles to work properly. Non-LSD stubs will not work. The SS stubs are side specific and are NOT the same as any later model VLSD. You MUST use stubs from another 91 SS. VLSD's are a joke - mostly a marketing gimick - and are generally considered dead weight after 50k. Sure they may still work to some degree - but it's not even close to worth doing if you have to spend a bunch of money on stubs to even get it installed. Buying one of these - even with stubs - is basically a waste of money unless it's very low miles or new. The gamble is just too great. IMO they are worth no more than an open diff. They cannot be rebuilt or serviced which makes them an unacceptable used purchase. Further - they are only useful for spirited street driving. They are (in the Subaru incarnation) completely useless off-road. The clutch types are almost useless and the VLSD's might as well not even be there. Waste of time and effort. GD Edited March 30, 2012 by GeneralDisorder Quote Link to comment Share on other sites More sharing options...
TheLoyale Posted March 30, 2012 Author Share Posted March 30, 2012 This is why I gave the diff back, I didn't want to get that much into a unit that may not work correctly. Quote Link to comment Share on other sites More sharing options...
WoodsWagon Posted March 31, 2012 Share Posted March 31, 2012 The clutch types are almost useless and the VLSD's might as well not even be there. Waste of time and effort. The clutch type LSD's actually make a big difference if they are still tight. The more abusive you get with them offroad, the harder the LSD grabs. Mine was great for mud, snow, sand, and wet leaf litter that would stop it before. You also don't get the total loss of power and forward momentum when lift a wheel. Plus it was great when I'd have a broken front axle and run RWD for a week before replacing it. Easiest car to do consistent tight donuts in short of an old RX-7. Quote Link to comment Share on other sites More sharing options...
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