(This information was taken from http://kmhafer.datsun510.com/Subaru.htm All of this information is credited toward Kurt Hafer and is being used by his permission. This is very good information about differentials and how to identify the different types from Subaru models.)
Last Revised 2/10/03
Disclaimer: I have no affiliation with Nissan or Subaru, and have gathered the information presented below to assist other Datsun 510 enthusiasts. While I have attempted to present only accurate information, inadvertent errors do occur. Please let me know if you have found any errors or can add any new information to this FAQ.
is a Limited Slip, and what are the different types?
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.
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. There are several variations on a theme here, which are very well discussed on Gordon Glasgow's LSD tech page (http://www.gordon-glasgow.org/lsdtech.html), but I will briefly list them below:
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.
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) units, like the Subaru LSD, viscous fluid units (as used in the early Miata, Sentra SE-R, 240sx, 300zx, and '91-92 Subaru Legacy turbo 4WD sedans), and the mechanical torque-sensing units like the Quaife and the Gleason-Torsen (the latter come in the '94 and newer Mazda Miatas and 3rd generation RX-7s). All of these combine the streetability of an open differential with the advantages of a locked differential.
The Quaife and Gleason-Torsen units are probably the best, as they have no clutch plates to wear out and do not have the delay in locking up that some report with the viscous fluid units. However, there are no applications that easily fit under a 510, and they are very expensive (Miata Gleason-Torsen units are $1200 used, $3000 new). 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 case that sells for $850 new. Ted Hedman has one of these in his 200hp Autech-powered SR20DE 510.
Viscous units are popular in that they have no clutches to wear out, and locking characteristics can theoretically be changed by varying the viscous fluid properties. The downside is both the delay in lock-up mentioned earlier, as well as the limited availability in applications that fit 510s. Subaru USA lists the '91-'92 Legacy 4WD Turbo 4 dr sport sedans as having a viscous 3.9 LSD option. These LSDs have their half-shaft axle stubs held in with internal C-ring retainer clips, not bolts as described below. 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.
The Salisbury (Clutch-Type) 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). 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 shim thicknesses, 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 BRE 510s had breakaway settings adjusted to 150 ft-lbs. Anything under 100 ft-lbs should be fine for a dual-purpose street car.
What kind of Differential came in my 510?
Stock 1968-73 Datsun 510 sedans came with a nice independent rear suspension setup using half-shafts and u-joints, unlike many cars of their era. The 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. 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. The R-180 units (for which a Quaife LSD unit is available) are a direct bolt-in under a 510. These diffs can be found under z-cars, 720 4x4 truck front diffs, and 4 cylinder 200sx cars. The R-200 is huge, and about 50lbs heavier than an R-160. It may require sledgehammer mods to the spare tire well and possible moustache bar mods to fit under a 510. It can be done, but isn't 100% bolt in like the R-160 units, and you have to think about what to do for half-shafts. Viscous R-200 LSD units may be sourced from 240sx, 300z, and Infiniti J30s, with JDM units being preferred over US units for their beefier innards. My 300+hp 510 has yet to break the stock Subaru R-160 LSD. This FAQ will not discuss the R-180 or R-200 conversions further.
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 rearend 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 1986. Cars which used the R-160 include the BRAT, Loyale, GL, RX, XT, and first generation Legacy. Most of these R-160 differentials are NOT limited-slip, but as they come in 3.70, 3.90, and 4.11 ratios, they are an attractive replacement unit for a tired 510 differential, and can often be purchased for less than $50. Installation 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 LSD candidates are the 4WD turbo cars, often with the 4AT (4 spd Auto) tranny. High-buck XT-6s, XT Turbos, and RX hatchback turbos also have them, and possibly even Brats. 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 Subaru LSDs, but never actually found one myself, nor seen one. As an aside, most Legacys have 4.11 R-160s that are non-LSD, 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.
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 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). As an aside, I'm not sure if the Subaru Impreza or Forester differentials are R-160s, or if they have and LSD option. I do know that they are Hitachi units. The cool finned aluminum cover off of the Impreza differentials would sure look nice under a 510, but I have no idea whether it would fit. 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
Sure Ways to Tell if it's an LSD: (Tell this to the salvage yard person!)
What if you find a 3.70 Subaru LSD, but want a 3.90 or 4.11 ratio? I have heard that the 3.70 Subaru units will fit inside the 510 R-160 cases, and that the 510 ring & pinions will fit inside the Subaru R-160 cases. I have not seen nor done this myself, so I cannot offer specifics, nor guarantee that this is the case. I am sure that Subaru LSD units will interchange inside all of the Subaru R-160 cases, using various Subaru R-160 ring & pinion ratios. I purchased a used Subaru 3.70 LSD unit and a used legacy 4.11 open R-160 differential and created 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 Subaru LSD unit's bolts could be used, and to set up the newly assembled unit with the correct tolerances. You MUST use either the Nissan Motorsports LSD 10mm x 1.25 ring gear bolt set (Part # 99996-D3100, bolts cost $8 each and you'll need 8 of them), or just BE SURE to use the bolts that came with the LSD unit, not the ones from the open differential whenever you do this or your LSD innards will chew themselves to pieces. List member 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, with no reported problems to date.
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 8 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.
NON-LSD units have the following Subaru part
numbers (look at the foil sticker for part number and ratio):
Which parts do I need to get?
Ideally, all you need is the 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.
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.
Listmember John Arnold reports that his stock 240Z halfshaft stub axles would NOT work with a Subaru LSD. The 510 and 240Z halfshaft stub axles appear to be the same (same 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 & stubaxles are the way to go unless you modify the placement of the dustshields.
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?
How do I install the Subaru LSD?
The Subaru 3.70 LSDs are around and available, though hard to find. Be persistent. I have yet to see a Stock Subaru 3.90 LSD. Almost any AWD 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 Subarus looked like.
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), or from NISMO (also $800), but junkyards are more fun, and they are much happier on my wallet.
Copyright 1998-2003 By Kurt Hafer. For private use only, may not be distributed without permission.
Last Revised 9/29/03 by Kurt Hafer (kmhafer at yahoo.com)