subi dude Posted August 12, 2012 Share Posted August 12, 2012 Quick question...or two.. What is the difference between a LSD and a VLSD, whats the V ?? Also, my GL-10 Has a 3.90 diff, and my question is, ARE all 3.90 LSD's?? Cause my diff doesnt feel like it is locking up when its slipping when im wheeling... therefore im assuming that not all 3.90's are LSD's. PLEASE let me know. i want an LSD, and need to know if i already have one or not before i go buy another diff.. Thanks, subi_dude Quote Link to comment Share on other sites More sharing options...
natext6 Posted August 12, 2012 Share Posted August 12, 2012 (edited) Not all 3.9's are LSDs The number has to do with the gear ratio. Not all differentials are LSDs either. an easy way to check is to get the rear wheels off the ground, if you spin one wheel, and the other moves in the same direction, it's an LSD (IIRC) if it moves in the opposite direction, it's an open differential. The gear ratio has to match up with the transmission gear ratio. I know that the LSDs available on xt6s had the 3.9 ratio. but that isn't to say that all xt6 diffs are LSD. Hope that helps a bit. V stands for viscous. Edited August 12, 2012 by natext6 Quote Link to comment Share on other sites More sharing options...
natext6 Posted August 12, 2012 Share Posted August 12, 2012 "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.[7] 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...
edrach Posted August 12, 2012 Share Posted August 12, 2012 Viscous LSD well described by previous poster. Clutch type or mechanical LSD is more definite in its action and doesn't need to be warmed up to limit slippage. Most of the mechanical clutch type LSDs came as an option on '85 to '89 GL turbo cars and were all 3.700 ratio. If you find a 3.900 with a clutch pack in it, it was likely modified and didn't come that way from the factory. Quote Link to comment Share on other sites More sharing options...
natext6 Posted August 12, 2012 Share Posted August 12, 2012 I'd take the credit, but I just c/p'd it off of Wikipedia Quote Link to comment Share on other sites More sharing options...
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