What is a Limited Slip, and what are the different types?
What kind of Differential came in my 510?
Where Does Subaru Fit in?
How do I find a Subaru LSD?
Sure Ways to Tell if it's an LSD?
Which Subarus do I look at to find an LSD?
What about Halfshafts and Stub Axles?
Other Datsun 510 LSD Options?
Which Subaru parts do I need to get?
How do I install the Subaru LSD?
Subaru Spotter's Guide

In the quest to improve the Datsun 510's performance, one item often overlooked is the installation of a limited-slip differential (LSD), as you can only get so much traction to the ground through the right rear wheel.  Fortunately there are solutions to this problem.  Unfortunately, most of them are either very expensive or unsuitable for street use.  This FAQ outlines the selection and installation of the Subaru R-160 clutch-type limited-slip rear differential into the 1968-73 Datsun 510 sedan.  It will also briefly discuss other types of LSDs, as well as suggest alternative solutions for the crop of higher horsepower 510s (>250RWHP) now prowling the streets.

What is a Limited-Slip Differential, and what are the different types?

A differential of any type allows two output shafts to spin at different speeds (See http://auto.howstuffworks.com/differential.htm for more information).  This is important when going around corners, as the inside and outside drive wheels are spinning at different speeds.  Most differentials are of  the "open" type, meaning they have no limitation on the difference in speeds between the two output shafts.  Without a limited slip differential, when one drive wheel gets stuck in a ditch, it could spin 100mph while the other drive wheel stands still.  By their very nature, open differentials send power to the wheel with the least grip.  An LSD is a differential that prevents one rear wheel from spinning while the other just sits there, but still allows for a variation in speed between right and left wheels as the car goes through a turn.  In other words, the LSD unit limits the speed difference between the two wheels, allowing torque to be applied to a wheel when the other is spinning without traction.  Why would anyone want an LSD differential?  They allow power to be applied through two tires instead of one, and often means you can apply the power sooner coming out of turns.  It is important to remember that although we steer the front wheels of a car, the car actually rotates around the rear axle.  Limiting the differential's slip limits this rotation somewhat.  Drivers preferring to drive the rear end of the car (oversteer) prefer a locked or severely biased limited slip, whereas drivers that prefer to drive the front end (understeer) of the car prefer a looser differential setup.  Both differential types can be fast but consider that the looser differential is gentler on tires and may be easier to drive.  What are the downsides?  An LSD installed into an already balanced chassis can cause a dramatic increase in understeer on dry pavement, and may even cause oversteer on wet pavement, requiring changes in swaybars, springs, and shock settings to return the car to neutral.  There are several variations of LSD differentials, which are very well discussed on Gordon Glasgow's LSD tech page (http://www.gordon-glasgow.org/lsdtech.html) or at http://auto.howstuffworks.com/differential6.htm , but I will briefly list them below:

Welded Differential:

Actually, this is not an LSD, but the modification is a popular with road racers as a low-cost way to make a locked rear end.  By welding together the side gears and the spider gears within the differential in several places, the rear wheels are both forced to spin at the same speed.  By definition, this is no longer a differential, as the rear wheels cannot spin at different speeds.  This is fine at higher speeds on the race track, but is really unsuitable for street driving, as the rear end of the car skips/hops across the pavement as you go through low-speed turns since one wheel cannot spin at a different speed from the other.  It also can cause severe understeer in a 510, not to mention breaking at the worst possible moment when those welds let go.

Detroit Locker:

A popular option on the Detroit Muscle cars, this is mechanical differential that acts like an open differential until power is applied, at which point it locks up and gives power to both rear wheels simultaneously.  Unfortunately, this differential either gives you complete lock-up or no lock-up at all.  These are available for the Datsun/Nissan pick ups, but will not be discussed here.

Limited Slip Differentials:

These come in several varieties:  Clutch-Pack (or Salisbury), like the Subaru LSD, Kaaz, Cusco, ATS, and Power Brute units, Viscous Fluid units (as used in the early Miata, 240sx, 300zx, and '91-92 Subaru Legacy turbo 4WD sedans, as well as all LSDs found in '00 and up Subaru Imprezas, WRXs, Legacies, and Forester GTs), and the Mechanical Torque-Sensing units like the Quaife and the Gleason-Torsen (the latter came in the '94 and newer Mazda Miatas and 3rd generation RX-7s, Lexus IS300s, HumVees, etc.).  All of these combine the streetability of an open differential with the advantages of a locked differential, but there are differences between the three types of LSDs.  A brief history of LSD technology and applications can be found here.

The Clutch-Pack ( Salisbury) LSD is what we're interested in.  This is the kind of R-160 unit you can buy new from Nissan Motorsports or Subaru for $800, or used from a salvaged Subaru for under $300.  These LSDs have an assortment of friction disks and shims inside, arranged so that the limited slip typically has a factory breakaway setting of 45 ft-pounds (allowing the rear wheels to turn at different speeds if they have to).   See exploded diagrams of this differential from the Subaru Manual here and a close-up diagram here.  The major downside is that as these clutch disk units wear, their breakaway torque setting gradually lessens, so they become more like an open differential until you rebuild them again to get the breakaway back up to 45 ft-lbs. Gordon Glasgow's web page (link URL is at the beginning of this FAQ) tells how to rebuild these units, but it is tricky, as the only way to adjust the breakaway is to use different thickness shims, reassemble the entire LSD, and then see what you've got.  When Bluebirds list member Gary Savage had his LSD rebuilt, adding only one extra shim sent the breakaway up to 180 ft-lbs, which is a bit too much for everyday street use.  For reference, the 2.5 Trans-Am race series BRE 510s had breakaway settings adjusted to 150 ft-lbs.  Too high a breakaway pressure will cause clutch-pack LSDs to function as locked differentials, as well as creating severe understeer at corner entry as well as power-on corner exit.  Anything under 100 ft-lbs should be fine for a dual-purpose street car.  Pro:  Cheap (used Subaru R-160), easily bolts in.  Con:  Hard to find, limited ratio (3.7), unless you swap R&P, clutch discs wear out, hard to adjust breakaway setting.  For serious on-track duty, these setups generate HEAT, so a differential cooler may be in your future.  See the section on Other Datsun 510 LSD Options for more information on the various aftermarket LSD units.

The Quaife and Gleason-Torsen (stands for TORque-SENsing) units are often regarded as the best LSD.  Their locking action is via a complicated worm gear setup (read the technical paper here or go to the Torsen site), so they have no clutch plates to wear out and do not have the delay in locking up that some report with the viscous fluid LSD units.  In a no-slip condition, the differential splits the torque 50:50 between the two drive wheels.  When wheel slip occurs, the unit sends more torque to the axle with more grip (via the torque-multiplying characteristic of the worm gear mechanism), which in an autocross or race track situation is the outside drive wheel.  By design, these LSDs separate the speed differentiation and torque distribution functions of a differential, resulting in a proactive LSD that actually prevents excessive wheelspin under acceleration.  Different applications come with different torque transfer ratios (torque bias ratio, or TBR), capable of transferring torque to the non-slipping wheel at a ratio of up to 9:1.  The locking action of these units occurs only under acceleration, and is instantaneous and progressive in nature. Under braking, the differential behaves like an open unit.  However, there are no OEM applications that easily fit under a 510, and they are very expensive (Miata Torsen units are $1200 used, $3000 new, and I have no idea what a Lexus IS300 Torsen would list for).  There are rumors of both Miata and 3rd generation RX-7 rear suspensions with LSDs being installed under 510s, but I have not seen any of these in person.  Probably the easiest solution (if you can afford it) comes from Quaife.  Quaife now has an LSD unit that fits in a Nissan R-180 or Subaru R-160 case that sells for $1,500 new, though they can be found at times for $900.  Ted Hedman has one of these R-180 units in his 200hp Autech-powered SR20DE 510.  One thing to know about the Torsen or Quaife units:  they require BOTH wheels to have some traction in order to work as an LSD, as the differential "senses" the difference in torque between the two.  If a drive wheel comes off the ground, it will spin just like an open differential, as zero available torque (a spinning wheel) when multiplied, is still zero.  Pro:  Durable unit, smooth, quick action  Con:  Pricey, no traction if wheel comes of the ground, cannot "tune" locking action.

Viscous LSD units are popular OEM  LSD solutions, as they are relatively simple and cheap to produce.  They come in many performance Subarus, Nissans, Mazdas, Toyotas, etc.  The LSD unit consists of stacks of thin plates with holes or slots, all suspended in a special silicone fluid.  They have no clutches to wear out, and locking characteristics can theoretically be changed by varying fluid viscosity.  Generally, however, these units are non-serviceable, and require no special maintenance.  As the differential spins, the plates shear the fluid up to a point, after which the fluid provides some resistance to shear, allowing 15-25% torque transfer to the other wheel.    The downside is that these units don't act like a limited slip until one wheel actually starts slipping (i.e., they don't prevent slippage), which means the VLSD action often kicks in after you've already exited the corner.  Compared to the proactive nature of the Torsen LSDs, the VLSDs are reactive units.  They do not prevent slippage, they merely sense differences in rotation, not torque.  They also don't allow for very much torque transfer, compared to mechanical or clutch-pack LSDs.  They do still work well for starting from a dead stop in slippery conditions.  It is important to note that VLSDs locking characteristics occur both during acceleration AND braking, as it can't tell the difference between the two, but merely reacts to the rotational speed differences between the two drive wheels.  Another problem with VLSDs is the limited availability of applications that easily fit 510s.  Subaru USA lists the '91-'92 Legacy 4WD Turbo 4 dr sport sedans as having an R-160 viscous 3.9 LSD option.  All OEM Subaru LSDs since 1991 are viscous R-160 units (Note:  No U.S. Subarus between 1995 and 1999 came with LSDs).  These LSDs have their half-shaft axle stubs held in with internal C-ring retainer clips, not bolts as described below.  See Adobe Acrobat pdf pages from the Subaru Repair Manual with diagrams of these LSDs here.  The viscous LSD can be fitted under a 510 with major half-shaft modifications, as the 510 rear track is about 50" and the Subaru rear track is about 56" wide.  The modifications would include either a way to use the 510 bolt-in axles stubs with the circlip LSD diff (how?), or shorten the stock Subaru half-shafts and somehow make an adapter so it bolts to the 510 wheel hubs, or choose to make custom half-shafts from scratch -- you choose.  I have never seen one of these conversions in the flesh, but when I do, I'll report on it here.  Pro:  Readily available from newer Subarus (R-160), Nissans (R-200), smooth action, no special maintenance needed.  Con:  Delay in action, axle stub/CV halfshaft mods needed to make it work under a 510.

What kind of Differential came in my 510?

510 Sedans:

Stock 1968-73 Datsun 510 sedans came with a nice semi-trailing arm independent rear suspension setup using half-shafts and u-joints, unlike many cars of their era.  The Hitachi differential installed into the 510 sedans at the factory was an open unit (not a limited-slip) made by Fuji Heavy Industries, which is partially owned by Nissan.  These differentials are known as R-160 units, as the ring gear is 160mm in diameter.  They came in several ratios on the 510.  Early cars (1968s) came with 3.70 ratios, but the rest came with 3.90 ratios (except for the Non-USA IRS L-13/L-14 510s, which came with 4.38 ratios).  Some 510 owners have also replaced their R-160 units with the beefier (and heavier) R-180 or R-200 differentials from Datsun Z-cars either because they wanted a different ratio or needed extra strength.    

510 Wagons:

The 1968-73 Datsun 510 wagons, because of their solid rear axle suspension, do not have the R-160 differentials, and therefore cannot use the Subaru LSD.  Their 3.90 ratio differentials were an H-190 rear end, which is the same unit that came in the Datsun Roadsters and in some Datsun  pick-up trucks.  There are several different versions of this H-190 differential out there (with parts that aren't interchangeable).  Check out the Nissan Motorsports Catalog or  Datsun Roadster web pages for more information.  Limited-slip units are available for these differentials too, but make sure you know what you're buying, as repair and rebuilds of these units can get expensive fast.  Used units from roadsters seem to cost $500 to $800 each depending on ratio and condition.  It may actually be cheaper to have a NEW Ford 8.8" or 9" limited slip rear end with shortened axles installed under a wagon, rather that going with a used roadster H-190 unit.

Where Does Subaru Fit in?

Subaru is also partially owned by Fuji Heavy Industries, and through miraculous good fortune for us 510 owners, decided to use the R-160 differentials as the rear differential in many of their all-wheel-drive cars starting in about 1985.  Cars which use the R-160 include the BRAT, Loyale, GL, RX, XT, Impreza, WRX, Legacy, and Outback.  Most of these R-160 differentials are NOT limited-slip, but as they come in 3.70, 3.90, 4.11, and 4.44 ratios, they are an attractive replacement unit for a tired 510 differential, and can often be purchased for less than $50.  Note that LSDs were NOT available in any 1995-1999 U.S. Subarus.  Installation of an Subaru open differential would be the same as the LSD instructions that follow below.

How do I find a Subaru LSD?

The hard part about finding these LSD units is that almost any Subaru could be ordered with one, yet very few actually were. I'd guess that less than 5% of the cars came with LSD units, judging by what I've seen in yards.  Perhaps those of you in mountainous/snowy climes might see more LSDs than those of us in flat/hot areas.  What this means that there is no "one" Subaru that for sure has an LSD unit of a given ratio. Most likely clutch-pack LSD candidates are the '85-89 EA82 platform 4WD turbo cars, often with the 4AT (4 spd Auto) tranny.  Rumors have it that all Turbo 4WD RX coupes and Turbo 4WD GL-10s came std. with LSDs.  High-buck XT-6s, XT Turbos, and possibly even Brats may also have them.  Anyway, the LSDs you'll find will be 3.70 ratio.  This is fine for a street 510, and will actually make freeway driving less buzzy, as your engine revs will be lower at any given speed (compared to the stock 510 3.90 ratio), but it may hurt your 0-60 acceleration times.  For an auto-x or road-racing car, you'd probably be happier with a 3.90 or 4.11.  I've heard rumors of 3.90 and 4.11 clutch-pack Subaru LSDs, but never actually found one myself, nor seen one.  As an aside, most manual transmission Legacys have 4.11 R-160s that are non-LSD (Auto tranny cars have 4.44 ratios), giving you a 4.11 ring & pinion you can drop the 3.70 LSD clutch unit into (using the special LSD bolt set described below).  I did just this by purchasing a used Subaru 3.70 LSD unit and a used legacy 4.11 open R-160 differential and creating a 4.11 LSD unit from the parts.  I paid a rear-end shop $120 to drill the six 10mm holes out to 11mm so the LSD unit's bolts could be used, and to set up the newly assembled unit with the correct tolerances.   Gary Savage did put a Subaru LSD carrier from a 3.70 ratio differential into his 510 using the 510 differential case, the NISMO LSD bolt set and the Nissan 4.11 ring & pinion to get the 4.11 LSD he wanted.    '00 and newer Subaru Foresters and Legacys are available with 4.44 R-160s (open or viscous LSD), with rumors pointing to the finned rear cover being a clue to the identity of the LSD differentials.  2002-2003 WRXs are available with 3.54 Rear Viscous LSD. 

Used Subaru R-160 LSDs go for between $100-$300 at the yards (when they have them), though I've heard of smart shoppers getting them from U-Pull-It yards for as little as $30.  The good news is that most of these rear differentials are barely broken in, so they shouldn't need rebuilding.  A major problem is that most yard folks don't know much about them, and don't know how to tell an LSD from an non-LSD unit.  Furthermore, I've heard from several yards that there are different universal listing code numbers for an open and a locked Subaru R-160 differential, but that there is just a single code for all 3.90 ratio Subaru differentials, making it impossible for them to search via teletype for 3.90 LSDs.  Many people I know have been sold LSDs that actually weren't, so make sure it's an actual LSD before you pay for it or at least know what the return policy is before you leave the yard.  For these reasons, I prefer to buy from a local salvage yard and let them deal with getting the LSD from a far-away locale.  You could also try calling Troy Ermish at the 510 Parts Outlet in Fremont, CA (510-252-1001) to see if he has any of these R-160 LSDs in stock.  There are also many yards on the web that have searchable inventories.  Don't forget Ebay!

However, Subaru made it easier for us to tell what kind of differential is installed in their cars by just looking under them.  Almost all of the older Subaru differentials (both LSD and Non-LSD) have a gold or silver foil sticker on the outside of the rear case cover stating the Subaru differential part number, the ratio of the differential (i.e. 3.70, 3.90, 4.11) and whether or not it is an LSD (if it is, it will have  "LSD" in 1/2 inch-tall block letters on the left side of  the foil sticker, as you can see in the picture below).  The above ratios are the ones I've seen on Subarus in yards around the country.  Sometimes the gold foil gets really grimy, but you can gently scrape it with a screwdriver to pull off a clear covering from it (like a helmet visor tear-off) to get a better view.  The foil sticker makes it really nice and easy to see the differential ratios from under the car without counting ring and pinion teeth or driveshaft/rear wheel revolutions (see picture below).  Forester differentials, by the way, do not have the gold foil stickers on them.

Foil Sticker off Rear Case of Subaru R-160 LSD Differential (Left),  

Image of same sticker from Subaru Manual (Right)

Subaru LSD (Left), Subaru LSD Innards (Center), Installed LSD under Dan Davis' 510 (Right)

Sure Ways to Tell if it's a Clutch-Pack LSD:   (Tell this to the salvage yard person!)

1. Check the sticker! It should have the letters LSD on it (see pictures above).
2. Rotate one of the half-shafts (both half-shafts rotate the same way if it is LSD.  If one rotates backwards and one forwards it isn't)!
3. Drain the fluid from the differential and peek inside through the fill or drain hole with a flashlight.  The clutch-pack LSD unit looks different from the open unit.  You could also stick a finger inside the fill or drain hole and feel the difference between the two.  The clutch pack is pretty obvious.  The internals of some Subaru viscous LSD units will look the same as an open unit, as the viscous plates are hidden behind the ring gear.

Also, all Subaru ring & pinions (R&P) from 4/86 onwards use 11mm fine thread bolts (instead of the 10mm x 1.25 ones used in the 510) to attach the differential carrier.  This means that if you want to use a Subaru LSD and the R&P it came with, you're fine.  But if you want to use the Subaru LSD with say, the Subaru non-LSD 4.11 R&P, and don't have the LSD bolts, you'll need to get the eight longer 11mm bolts from Subaru.  The standard 11mm R&P bolts are Subaru part # 8002 11130, while the longer ones to use with the LSD are part # 8002 11140.  Cost is $2.40 each.

Which Subarus do I look at to find an LSD?

Look at ALL of the 4WD Subarus mentioned earlier.
If a salvage yard wants specific cars and models, list member Steve Josephs sent me a collection of Subaru parts manual pages which show model years and differential part numbers.  These part numbers can be found on the infamous gold foil stickers:

Clutch-Pack LSD:
1985-1986 (production up to 3/86) XT 4WD is listed with a 3.70 LSD option (Subaru part # 7220 11000).
1986-1987 (production from 4/86-10/86) GL 4WD is listed with a 3.70 LSD option (Subaru part # 7220 11001).
1986-1991+ (production from 11/86) Loyale/GL 4WD is listed with a 3.70 LSD option (Subaru part # 7220 11002).
1988-1991 GL and XT-6 4WDs with single range transmissions are listed with a 3.90 LSD option (Subaru part # 22011 GA022).
July 1986 onwards LSD assembly (just the carrier) is also available new from your Subaru dealer if you wish (Subaru part # 22049 GA010).

Viscous LSD:
1991-92 Legacy 4WD turbo 4dr  sports sedan is listed with a 3.90 viscous LSD option (Subaru part # 27011 AA131 or maybe 27011 AA070 -- the manual is unclear about the AA070 unit).
Any Subaru's since 2000 that came with an LSD came with a viscous unit.    
**Remember that all R-160 viscous LSDs need half-shaft modifications to work under a 510.**

Here is a table of various newer AWD Subarus with their respective drive ratios and VLSD Availabilities:

(from Wayne Chin http://wac.addr.com/auto/obs/lsd/lsd.html )

Other North American Subaru models with VLSDs, either as standard equipment or available as an option:

• 2000-2002 Forester S (All Weather Package)
• 2003 Forester XS
• 2000 Legacy GT, Outback
• 2001-2003 Legacy (all)
• 2003 Baja

NON-LSD  
Most R-160s you see under Subarus will NOT be an LSD.  There were no LSDs of any kind in 1995-1999 Subarus.
Look for the following Subaru part numbers (look at the foil sticker for part number and ratio):
7220 11010:  3.70 ratio
7220 11011:  3.70 ratio
7220 11012:  3.70 ratio
6220 06020:  3.90 ratio
6220 06021:  3.90 ratio
6220 06022:  3.90 ratio
27011 AA151:  3.90 ratio
27011 AA040:  4.11 ratio
27011 AA110:  4.11 ratio
27011 AA111:  4.11 ratio

What about Halfshafts and Stub Axles?

Most of us use the stock Datsun 510 halfshafts and stub axles.  Use a good quality 14mm combination wrench to undo the nuts/bolts (Snap-On really is best) to avoid scraped knuckles. Some PBBlaster or Kroil penetrant always helps too.  Consider thoroughly checking, greasing, or replacing any suspect halfshaft U-joints when you do an LSD swap.  Nissan U-joints are best, but are pricey (you do seem to get what you pay for, however).  Some folks have had good luck with Spicer units for less money.

List member John Arnold reports that his stock 240z R-180 halfshaft stub axles would NOT work with a Subaru LSD because the stub axle dust shields would not engage in the differential case.  The 510 and 240z halfshaft stub axles appear to be the same (same number of splines, taper, & length) except the metal dust shields are different.  The 240z halfshaft dust shields are not as deep as the 510 ones, resulting in a gap between the rubber seal (on the differential case) and the metal dust shield that is tack-welded to the stub axle.  Seems that stock 510 halfshafts & stub axles are the way to go unless you modify the placement of the dust shields. 

For those of you with higher-HP motors, you can get custom CV-jointed halfshafts made, but expect to spend $600-$1600 for a pair.  Expensive?  Yes.  But if a stock halfshaft shatters under 350+hp, how much will it cost you to fix the resulting carnage?  Portland, Oregon Bluebird List member Steven Pepka has made custom CV-jointed halfshaft sets that bolt under 510s.  He makes a 100mm CV-jointed version good for up to 200rwhp starting at $650 for the pair, and a Porsche 930 CV-jointed version good for up to 500+rwhp starting at $1000 for the pair.  Ron Tyler (www.rontyler.com), the fabricator responsible for installing a twin turbo VG30DETT motor into Dave Lum's 510, has made stub axle adaptors.  Modern Motorsports makes adaptors allowing use of an R200 differential with 280z stub axles and flanges, and slightly modified 4 bolt Z31 300ZX Turbo CV-jointed halfshafts for $215 a set (http://www.modern-motorsports.com).   

Salt Lake City, Utah former 510 owner Allan Anderson (now into S13 Silvias) had some custom CV-jointed halfshafts made for his VG-powered 510.  "The outer CV joint was a 280zx joint the flange of which bolts onto the stock control arms.  The inner one was a  Subaru unit, the flange of which bolts into the stock rear end.   All of the CV's were brand new with Zero miles."  Allan made it to Mt. Shasta 2000, at which time he was running an R-180 VLSD under the car.  Australian Peter Liebig's SR20DET car uses custom-made CV-jointed halfshafts with an R-180 VLSD. 

England's Datsun Guru Eddie Rattley (www.ratdat.com) had this to say about the VLSDs:  "The big problem with the V-LSD shafts it that one of them has a double spline on it...one for the side gear and another further into the diff that goes into the stator.  I'm working on this at present, with dismantling the Subie inner CV and machining the CV housing down to allow the fitting of an adaptor to allow the use of 510 shafts.   Be a while yet but I might be able to make a small batch of adaptors or at least supply a drawing of it. The reason for pursuing this is that plate type Subie LSD's are impossible to find here but V-LSDs are common."

Other Datsun 510 LSD Options:
 

• R-160 Subaru LSD (w/o mustache bar or stub axles) = 50lbs
• R-180 open diff from '83 Maxima (w/o mustache bar or stub axles) = 60lbs
• R-200 open diff from '87 200sx V6 (w/o diff mount attached without stub axles) = 75lbs
• He also weighed an open R-160 from a 510 and an R-200 LSD. They are both within 1-2 lbs of the weights listed above.

What's the deal with Phantom Grip LSD units?

Phantom Grip units are advertised as a way to convert an open differential into an LSD unit.  They run $250-$300, and have applications for R-160 and R-180 differentials.  I have heard of these working ok for awhile, then suddenly not working, leaving you with an open differential.  For the price, you might as well buy a genuine LSD.  Bluebirds List member Jeff Cook has this to say about them in a Bluebirds posting:

"They call it a "Phantom Grip", but I call it something else. If I may be permitted to reprise an email I posted sometime back... From the looks of it, all this unit does is spring-load the side gears against their washers, turning them into half-assed clutches, while adding a wedge ramp to increase the pressure as the side gears try to turn relative to the cross shaft. There are several problems with this approach. First, those side gear washers have no clutch material on them, and the Phantom Grip (Phantom Menace?) unit doesn't appear to come with any that do. (Not that it would do much good, there being no provision in the differential case for a proper stack of frictions and steels.) As this unit operates, you're gonna be wearing away the side gears and differential case. With the spring pressure against them, but without the waffle surface of a clutch disc, there's not much opportunity for lubricant to get into the side gear washers. Since the "clutches" are just metal-on-metal, and running virtually without lubricant, the breakaway characteristics are not going to be very progressive, or predictable, as things heat up. The wedge ramp also induces stresses on the differential case that it was never designed to handle. When (not if) this unit chatters, the wedge ramps are gonna be trying to split the differential case in two. Incredible testimonials aside, this seems to be a very poor substitute for a proper LSD, and way overpriced for what is essentially a couple machined plates and a few springs. I would certainly not consider the Phantom Grip in the same league as PowerTrax or Air Locker."

What about other aftermarket Clutch-Pack LSDs?

With the popularity of higher-powered Subarus, as well as increased use of the 240sx in drifting, there are many quality Japanese aftermarket Clutch-Pack LSD units.  Choices include Cusco, ATS, KAAZ, and Tomei Trax, with prices from $900 to $1500.  Not all brands are available in R-160, R-180, and R-200 sizes, so check for actual applications to be sure.  OEM LSD units usually have two pinion gears.  Most of the aftermarket units have four pinion gears, theoretically making them stronger.  The aftermarket units vary in construction and clutch plate material (steel alloys, carbon fiber) as well as mode of action.  They usually have between 12 and 24 clutch plates, which depending on how they are assembled, can vastly vary the locking action of the unit, allowing the owner the ability to "tune" the LSD to their car and driving preferences.  Furthermore, many of these differentials can be purchased in 1-way, 1.5-way, or 2-way configurations.  1-way units act as an LSD upon acceleration only.  1.5-way units act as an LSD on acceleration, as well as to a lesser extent on deceleration, but with less understeer than the 2-way units.  2-way units have full LSD action on both acceleration and deceleration.  Some of the units can be easily changed from 1-way to 2-way, etc.  Because of the tremendous hype surrounding the various brands, it is hard to know which unit to use, so do your research before your buy.  

Which Subaru parts do I need to get?

Ideally, all you need is the pre-1990 Subaru clutch-pack LSD differential unit inside it's case with the half-shaft stub axles still attached. You don't need the half-shafts or the mustache bar or other mounting hardware.

How do I install the Subaru LSD?

1. First you need to remove your 510 differential.  Follow instructions from whatever manual you have handy.  Notice where those little square u-shaped spacers that go between the diff and the rear crossmember go.  You'll need to drop your exhaust system where it goes through the rear crossmember.  You'll also need to undo the e-brake cable yoke.  Unbolt the four bolts that attach the rear of the drive shaft to the differential tail shaft using two 12mm combination wrenches.  Don't pull your drive shaft out of the rear of the transmission unless you want to spill tranny oil everywhere.  Next unbolt the four bolts on each half shaft u-joint.  You may choose to drop the differential and mustache bar together after you drop the driveshaft.  It's much easier if you also drop your rear crossmember down a bit (or all the way).  Now would be a good time to slot your rear crossmember or install one of Bluebirds List member Kelvin Dietz's  DAMB Productions Penultimate adjustable rear crossmember if you haven't done so already.  You could even install Energy Suspension or TMC polyurethane differential and crossmember mount bushings if you wish.  You will need to undo the rubber brake lines and rear shocks if you plan on completely dropping the rear crossmember.  Now you can clean everything up and actually see what you're doing when you bolt in the Subaru unit.  A neat tip prior to re-installation is to pull out the two studs (that bolt into the moustache bar) from the diff's aluminum rear cover and get a pair of metric bolts and lockwashers to replace them when you reinstall the unit.  Note that the threads of the ends of these studs are different from the threads where they go into the aluminum cover.  Make sure you get the right size/pitch bolts. 

 
2. The early Subaru differentials (both LSD and non-LSD) bolt in just like the stock R-160 units we know and love except for having different half-shaft stub axles.  If the Subaru differential is still in a Subaru, removal is just like working on your 510 except for pulling the half-shafts off of the differential stub axles.  There are no bolts, and there is no need to rip open the Subaru CV joint boots!  Clean off the grime on the half shafts next to the differential to find the single 1/4" roll pin hole on each side.  Drive the roll pin out with a long 1/4" punch or 1/4" drill bit (I use a masonry drill bit backwards) and the halfshafts will literally fall off.  EASY!

 
3. Remove the Subaru LSD half-shaft axle stubs. Go buy or find a friend with a deep Torx E-10 socket and an impact wrench or breaker bar (a deep 1/4" 8mm socket also fits over the Torx bolt head in a pinch) to remove the half-shaft stubs from the Subaru unit.  Snap-On sells these sockets for $13.50 (Part # STLE100), but they only come in 1/4" size.   MATCO sells a 1/4" drive impact-rated E10 socket (part # A10XRA, about $8.00) that also works well.  If you have to pay the salvage yard dismantler or a mechanic friend $10 to do this, it'll be $10 well spent, but go easy.   I find these bolts either come out really easily or you snap off their heads.  If you strip these Torx bolt heads, your nightmare has just begun.  Now you must either drill out the bolt, or use an EZ-Out (bolts are hardened), or use a cut-off wheel to cut off the stub axles and grind out the tapered part of the bolt head.  I had to do the latter.  It wasn't that bad, and an electric cut-off grinder is only $50.  Takes less than 20 minutes per side if you go really slowly.  Be careful you don't ruin the rubber dust seals, and wear eye and ear protection!



Here are pictures (compliments Bluebirds List Member Dan Davis) of the stock Datsun 510 and Subaru LSD stub axles side-by-side after removal.  The 510 axle is on the left in each picture: 



4. You can also do this at home by yourself with a breaker bar and socket by using a vise or vise grips to hold the Subaru stub axle and keep it from turning (since you won't be using the Subaru stub axles anyway). Note:  There are some newer model Subaru differentials (incl. the viscous units) that have these stub axles held in with internal retainer C-clips rather than Torx bolts.  I've never used these, so can offer no help as to how to make them work in a 510 other than to surmise that you'd have to modify the Subaru half-shafts or mounting flanges make it fit under a 510.

 
5. Now remove the Nissan stubs from the stock 510 differential (using the impact wrench or breaker bar / vise grip and a regular deep socket), and bolt them in place of the Subaru ones you removed, using the 510 stub axle bolts.  DO NOT use an impact wrench to tighten these, as they will strip.  Just tighten them "snug" using a breaker bar or ratchet.  You do not even need to use loc-tite on the stub axle bolts.  Everything else (driveshaft, half-shafts, etc.) just bolts right up.

 
6. Re-mount the new differential back under your 510, re-connect the half-shaft u-joints, exhaust system, e-brake cables, brake hoses, etc.  Make sure all your bolts are tight!  Be sure your differential fluid is topped off  (use 0.8 liters or 1.7 pints of new high-performance fluid made for LSDs) before you drive.  Some of us have had good luck with regular Redline 75w90 synthetic with 1/2 a bottle of GM LSD additive added to the lube.  Some prefer the Ford Motorsport LSD additive.  Others report that using Royal Purple differential oil with LSD friction modifier increased their breakaway torque, causing their car to drag the inside tire around a slow corner.  Still others prefer to use genuine Subaru LSD oil.  Torque the fill / drain plugs to 32 ft-lbs after coating them with anti-seize.  Putting the rear of the car up on jack stands allows for you to put in a little extra fluid:  just fill until fluid leaks out of the (top) fill hole.  Should you need a new rear cover gasket, Subaru sells them for less than $3.00 each.  Should you need new seals for your LSD, these seem to be cheaper from Nissan.  Nissan Part Numbers:  Front Seal 38189-U3000 List $11.81 Net $10.04.  Side Seals 38342-21000 List $7.91 Net $6.72.  Torque cover bolts to 22 ft-lbs.  Also note that the plastic vent on the top of the case can weep a bit of fluid at times, especially with very spirited driving.  If you use your car for autocrossing or track days, I'd change the LSD fluid every year.  It's cheap insurance to protect your LSD investment..  

 
7. Now Enjoy!  Be aware that LSDs are a bit noisier than stock units and that they can make your 510 push (understeer) a bit more than an open unit.

The clutch-pack Subaru 3.70 LSDs are around and available used for less than $300, though they can be hard to find.  Be persistent.  I have yet to see a stock Subaru 3.90 clutch-pack LSD.  Almost any older 4WD Turbo Subaru can have an LSD (look at Brats, Legacys, RXs, XTs, Loyales, GL-10s, etc.), but it seems that the more loaded the car, the more likely you'll find one.

Subaru Spotter's Guide:

It might help you as you wander through salvage yards if you knew what these older Subarus looked like.
Click the text below each picture for a larger view

              Brat                       RX Turbo Coupe           Loyale / GL Sedan

       Loyale / GL Wagon        XT Coupe                        XT-6 Coupe

       Legacy Sedan        1991 Legacy Sports Sedan    Legacy Wagon
                                              (Viscous LSD)

Feel free to correct me where I'm wrong, or to add/elaborate where I've left something out.  Don't bother calling Subaru and asking them about this stuff.  I've done that many, many times, and more often than not, they have given me inaccurate information.  Of course, you could just buy a complete Subaru LSD from them (for $800),  from NISMO (also $800), or install aftermarket LSD units ($500-$3,000), but junkyards are more fun, and they are much happier on my wallet.

© 1998-2004 By Kurt Hafer.  For private use only, may not be distributed without permission.

Last Revised 3/31/04 by Kurt Hafer