Spool, locker, and limited slip? What's the diff?

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Spool, locker, and limited slip are all different types of differential systems used in off-road vehicles. Here's a breakdown of each:

SPOOL: A spool is a type of differential that completely locks both drive wheels together, essentially making them turn at the same speed. It provides maximum traction to both wheels at all times but eliminates any differential action. This means that during turns, the wheels cannot rotate at different speeds, which can make the vehicle difficult to maneuver and can cause tire scrubbing and stress on drivetrain components.

Pros
  • Maximum traction: A spool provides equal power distribution to both wheels, ensuring maximum traction in off-road situations.
  • Simple and robust: Spools have a simple design with no moving parts, making them durable and less prone to mechanical failures.
Cons:
  • Poor maneuverability: Since both wheels are locked together, a spool can make it difficult to turn the vehicle. It causes tire scrubbing, which can put stress on the drivetrain components.
  • On-road handling issues: The lack of differentiation during turns can lead to instability and tire wear on paved surfaces.
  • Locker: A locker, also known as a differential locker or locking differential, is a mechanism that can be engaged or disengaged to lock the differential and provide equal torque distribution to both wheels. When engaged, it effectively "locks" the differential, allowing both wheels to spin at the same speed regardless of traction differences. This provides excellent off-road traction but can still allow for differentiation during turns, allowing for better maneuverability compared to a spool
Pros:


  • Selective engagement: Lockers can be engaged or disengaged as needed, allowing the driver to control when maximum traction is required.
  • Improved off-road capability: Lockers provide excellent traction and help overcome obstacles by distributing power equally to both wheels when engaged.
Cons:
  • Reduced maneuverability: Similar to spools, lockers can affect maneuverability during turns, especially in tight spaces or on slippery surfaces.
  • Potential for drivetrain stress: The sudden engagement or disengagement of a locker can cause stress on drivetrain components.

  1. Limited Slip Differential (LSD): A limited slip differential is designed to distribute torque between the drive wheels while allowing some differentiation. It uses various mechanical or hydraulic mechanisms to send power to the wheel with better traction while still allowing some speed differentiation during turns. The goal is to strike a balance between traction and maneuverability. Limited slip differentials are commonly found in many production vehicles and provide improved traction compared to open differentials without the complete locking of a spool or locker.
Pros:
  1. Improved traction: LSDs transfer power to the wheel with better traction, providing enhanced grip in off-road and slippery conditions.
  2. Better maneuverability: LSDs allow for differentiation during turns, enabling better maneuverability and reduced tire scrubbing.
  3. Suitable for daily driving: LSDs offer a good balance between off-road capability and on-road handling, making them suitable for everyday use
Cons:
  1. Less traction than lockers/spools: While LSDs provide improved traction, they may not offer the same level of maximum traction as lockers or spools.
  2. Complexity: LSDs have more mechanical components compared to spools or lockers, which can increase the chances of mechanical failures or maintenance requirements.

Photos to follow

Anyone have anything to add?

What type of Differential is in your truck?

E
 
Haven’t used it yet but when I had AJ set up my 3rd member at EWR he suggested a wavetrac. Don’t see them mentioned often but they’re USA made and a lifetime warranty I believe.

 
it falls into the spool category but you forgot the good old Lincoln locker (welded diff)
great for a temp solution to a axel you don't care for ,but as soon as it breaks you are S.O.L
 
I guess it really comes down to what type of Off-Road use you plan to do with the truck.

On my current truck it has a factory limited slip. Plenty good for a non-caged fun runner.

On my other truck that I plan to drive quite a bit harder and 95% dirt I really like have my detroit locker. I wouldn't mind a spool either. It's just rad to have more 'control' over what the vehicle will be doing. You basically don't have to guess if the rear is going to be locked or not. You know that if you hit the gas the rear end will come around.
 
I absolutely love my spool. I did it for the reasons Steve mentioned, but also to know I'll be fully locked going into a steep/precarious incline is confidence inspiring. Additionally, I have a budget full floater with 31 spline axles. I know they aren't terribly strong, so the spool gives me some peace of mind knowing I'll be able to get home if I break an axle
 
I guess it really comes down to what type of Off-Road use you plan to do with the truck.

On my current truck it has a factory limited slip. Plenty good for a non-caged fun runner.

On my other truck that I plan to drive quite a bit harder and 95% dirt I really like have my detroit locker. I wouldn't mind a spool either. It's just rad to have more 'control' over what the vehicle will be doing. You basically don't have to guess if the rear is going to be locked or not. You know that if you hit the gas the rear end will come around.
if you want a 35 spline spool let me know. will make you a deal you cant say no too.
 
I have a Detroit locker and it sucks on the street. It unpredictably locks up on the street and causes a scene. It's great in the dirt and worth the sacrifice, provided the truck is not a daily. When I build a 9", I'll go with a spool since I mainly drive the truck to, from, and in the desert.
 
Lunch box locker in my 8.8. Locks up when needed, unlocks on the street when not needed and does everything I ask of it. I do far too much rock crawling to use a limited slip and far too much street driving to do a spool. Not to mention it’s cheap and does the job very well. Only time I want a selectable is in the front axle. That way I can have reg 4wd when running at speed in the dez without a whole bunch of torque steer and shit turning but have a locked up front end when I go crawling
 
I have a Detroit locker and it sucks on the street. It unpredictably locks up on the street and causes a scene. It's great in the dirt and worth the sacrifice, provided the truck is not a daily. When I build a 9", I'll go with a spool since I mainly drive the truck to, from, and in the desert.
Based on my experiences with Detroit’s lockers, they are only unlocked when coasting or very lightly maintaining speed. As soon as torque is applied they BANG and full spool engaged. It takes a bit to get used to driving them on the street because you have to build up speed to coast through turns or it will chirp the tires on you
 
Based on my experiences with Detroit’s lockers, they are only unlocked when coasting or very lightly maintaining speed. As soon as torque is applied they BANG and full spool engaged. It takes a bit to get used to driving them on the street because you have to build up speed to coast through turns or it will chirp the tires on you
The moving turns are okay, it’s turning from a stop on the street that it’s nearly impossible not to chirp the tires. Parking lot speeds and torque don’t lock it up, so the locker has that advantage over the spool.
 
the page that this was hosted on is down but I found ErikB Toyota Diff Page. Dude is a legend... from Pirate4x4 ora

Tons of great info here for us Toyota Dorks.

Breif Toyota 4x4 history/definition of terms (for North America):

  • '79-85 pickups and 4Runners had front live-axle, leaf-spring suspensions.
  • '86-95 4Runners, '86-95.5 mini-trucks, and '93-'98 T100's have torsion bar Independent Front Suspensions (IFS).
  • '96-up 4Runners, '95.5-up Tacoma's, and 2000-up Tundra's, Sequoia's and FJ Cruiser's have coil-sprung IFS.
  • "First genereation" 4Runners are '84-89, 2nd gen are '90-95, 3rd gen are '96-03, and 4th gen are '03-up.
  • "Mini-trucks" are Toyota pickups prior to the '95.5 model year change to the "Tacoma."
    The "mini-trucks" are also known as the "Hilux" in other parts of the world.
What type of differential does my Toyota 4x4 have? (top)

  • '79-85 Truck or 4runner: Front, Rear
  • '85-95 4cyl Truck or 4Runner (non-turbo): Front, Rear
  • '86-87 Turbo 4cyl Truck or 4Runner: Front, Rear
  • '88-95 V6 Truck or 4Runner: Front, Rear
  • '95.5-up Tacoma: Front, Rear
  • '96-up 4Runner: Front, Rear
  • Tacoma "TRD", Tacoma "PreRunner" 4x2, or
    3rd gen. 4Runner w/ factory electric locking diff option: Front, Rear
  • '93-98 T100 (2wd and 4wd): Front, Rear
  • '00-06 Tundra or Sequoia (2wd and 4wd): Front, Rear
  • '07+ Tundra 4.7L V8: Front, Rear
  • '07+ Tundra 5.7L V8: Front, Rear
What's my gear ratio? There are several ways figure it out: (top)

  • If you think your axle gearing has not been changed since it left the factory, you can read and decode the "axle code" from your vehicle information plate. Off-road.com has some pretty good information how to do this HERE (scroll down to the section titled "Gearing").
  • If your differential has been removed so that you can see and count the teeth on the gears, you can divide the number of teeth on the ring gear by the number of teeth on the pinion gear to come up with their ratio. For example, 41/10 gives you a 4.10:1 gear ratio (the most common stock ratio).
  • To verify gear ratios w/ the diffs on the vehicle, there is the "spin and count"method:
    For "open" diffs:
    • Block the tires at one end of the vehicle to keep it from rolling, and then jack up a tire on the other end.
    • Place the transmission in neutral and release the parking brake if you are checking the rear diff.
    • Spin the tire exactly TWO full revolutions while at the same time counting exactly how many revolutions the driveshaft spins (marking the driveshaft and tires beforehand will make it easier to count revolutions).
    • The number of revolutions the driveshaft spins is your gear ratio.
      If it spins just over 4 times, then the ratio is probably 4.10; 4-1/3 = 4.30; 4-1/2 = 4.56; just under 5 = 4.88; 5-1/3 = 5.29, etc.
    • For limited slip (LSD or "posi"), locking differentials, spools, etc.:
    • With these types of diffs, you won't be able to turn one tire w/o the tire on the opposite side of the axle turning with it.
    • In this case, follow the directions above except raise both tires off the ground and turn them exactly ONE full revolution while counting driveshaft revolutions.
    • Again, the number of driveshaft revolutions is your gear ratio as mentioned above.
Toyota Axle Widths: (top)
(all widths are measured wms-wms, wms=wheel mounting surface)

  • '79-85 front axle~ 55.5", rear axle~ 55"
  • '86-95 front IFS~ 59", rear axle~ 58.5"
  • Tacoma 4x4, '96-up 4runner front IFS~ ???, rear axle- 60"
  • T100 front IFS~ 65", rear axle~ 66.75"
  • Tundra front/rear~ ??
  • '90-97 Landcruiser FJ-80/FZJ-80 front axle~ 63.5"
 
* Another tidbit: 2wd 4runners, Tacoma PreRunners, T100's, and Tundra's use 6-lug wheels- same as the 4x4's
(the other 2wd's use 5-lug)

Front Differentials (top)
'79-85 Trucks and 4Runners all have 4-cylinder engines and use what most call the 4cyl 8" diff in the front (the same one they use in the rear)- see "4cyl 8" diff" below.
The 7.5" IFS diff
'86-95 IFS trucks and 4Runners, and all '93-98 T100s use a 7.5" front diff that is offset to the passenger's side. Later models came with ADD (Automatic Differential Disconnect) which uses a vacuum actuated mechanism to disconnect the drivers side axle shaft from the differential. Carriers and gear sets are interchangeable between the two different versions (and also happen to be the same as used in the 2wd Toyota pickup 7.5" diffs). One difference between ADD and non-ADD diffs is that the carrier in an ADD differential has needle bearings supporting the axle shafts at the differential. The non-ADD diffs did not have this bearing and sometimes the passenger side axle flange wears the carrier and becomes loose or wobbly, eventually causing oil leaks, noise, and possible spider gear damage. ADD and non-ADD diffs are swappable as are most of their parts. This makes it possible to change your ADD diff to non-ADD by simply swapping parts as I've done in the picture to the right. This is desirable to some people since some of the ADD stubs are smaller diameter than the non-ADD stubs and are therefore slightly weaker.
- Passenger's side
- Low pinion
- 27 spline axles
* This diff is based on the 2wd pickup 7.5" rear diff- same internals, different housing.
Late-model 7.5" diff
'95-03 Tacoma, '00-04 Tundra, ?? Sequoia's, and 96-02 4Runners have a high-pinion 7.5" IFS front diff offset to the drivers side. The high-pinion design is used so that the rack and pinion steering and anti-sway bar on these vehicles can run under the front driveshaft. The housing is a unique bolt-together design. The carrier inside is exactly the same as the '86-95 IFS diffs, so LSD's and lockers for it are also the same. However, since this is a high-pinion diff, the gears for it are different (reverse-cut) than the earlier diff. There is an ADD and non-ADD version of this diff as well.
These diffs use different gear sets than the earlier IFS diff because of the high-pinion design.
- Driver's side
- High pinion
- 27 spline axles
- Bolt-together "clamshell" housing design.
8" IFS diff
'03+ 4runner, '04+ Tacoma, FJ Cruiser, '05-07 Tundra, ?? Sequoia: 8" IFS diff.
- Driver's side
- Mid-pinion
- Clamshell housing
- 30 spline axles
- Carrier break: 3.91 and up, 3.73 and down.
Posted by RockKrawler of Allpro Offroad 1-25-07
"The front differential is an 8" mid pinion IFS that uses a gear not available through the common aftermarket. It is the same as the Non-US Toyota Prado front differential. The only current ratios available are 4.56 from Toyota OEM Japan and 4.88 from Mossiero in Italy. All Pro has 4.56 OEM Toyota Gears in stock, and 4.88 on the way in.
Front install kits are also not available from the common aftermarket. It uses the rear 86-95 V6 pinion bearings, but everything else is unique to the FJ/Prado. All Pro has gathered the parts together and can assemble a kit for you by special order, and have preassembled kits in the works. No solid spacers are available for the front differential
One last thing - there is a case break on the front differential. This means there are 2 different cases, or differential offsets: one that fits 3.73 and down, and the other that fits 3.91 and up. So if you have an Automatic FJ with 3.73 gears and want to go to a 3.91, 4.56 or 4.88 ratio, you need an open diff from a stick shift wth the factory 3.91, or you can change to an aftermarket diff like an ARB and get yourself some extra traction at the same time.
The Hi-pinion 8" diff
‘90-97 Landcruiser (FJ-80 and FZJ-80) uses a high pinion, reverse-cut front diff based on the V6/Turbo rear diff. The high pinion design allows the steering on these vehicles to run behind the axle and under the driveshaft. Carriers (i.e. lockers, LSD's) from the 8" V6/Turbo diffs can be installed (direct bolt-in) in the hi-pinion diff. The entire diff is also a direct bolt-in to all front and rear axles that use an 8" diff.
This diff is desirable to some straight-axle mini-truck and 4runner owners for a couple of reasons. First, the reverse-cut design of the gears is stronger than simply using a rear diff and gears up front as the factory did since its not using the weaker "coast" side of the gears when driving forward. For this reason, this diff is generally only used in the front axle. Second, the hi-pinion design gives very good ground clearance for the pinion and driveshaft as well as improves driveshaft operating angles.
In North America, almost all of these diffs came from the factory with 4.10 gears. Aftermarket gears for this diff are more expensive than most since they are either imported or custom made in limited quantities. At this time 4.88 and 5.29 are the only aftermarket ratios available.


 
Rear Differentials (top)
3rds.jpg (94577 bytes)
8" Diff Housing (3rd member) Identification
4cyl has 3 ribs on each side. V6/Turbo has 4 ribs on each side and the trapezoid shaped top rib. T100/Tundra/Tacoma diff has the characteristic bearing truss.
Note- Starting in about '96, the V6 diffs started using a casting that looks nearly the same as the T100/Tundra casting from the outside. However, it doesn't have the trussed bearing cap on the inside, and the outside uses the smaller 8mm mounting studs.
axlehousings.jpg (74442 bytes)
Axle Housing Identification
4cyl/V6/E-locker has a dome-shaped cover. Diff uses 8mm studs with 12mm nuts.
T100/Tundra/non-TRD Tacoma has deeper, blocky cover to accomodate the bearing truss. Diff uses 10mm studs with 14mm nuts.
The 4cyl 8" diff
All pre-'95 4-cylinder 4wd mini-trucks & 4Runners use the Toyota 8" 2-pinion differential front and rear (except turbo models). This is known as the "4cyl diff." This diff is by far the most common diff in older Toyotas.
- Ten 10mm ring gear bolts
- 27 spline pinion
- 2-pinion carrier (case)
- V6 carriers can be used in this diff if the correct bearings are used
* LPH/SPH gear info: http://www.pirate4x4.com/forum/showpost.php?p=1478223&postcount=73
** 4cyl diffs are swappable with the V6 and high pinion diffs.
The V6/Turbo 8" diff
'86-95 4cyl Turbo and V6* trucks and 4runners, and ALL '96+ 4Runners use the Toyota 8" 4-pinion differential in the rear. This diff is known as the "V6/Turbo diff."
- Stronger housing than the 4cyl diff
- Larger carrier bearings than the 4cyl diff
- 30 spline axles
- 27 spline pinion (pre-'96)
- Ten 10mm ring gear bolts
- 8mm axle housing studs with 12mm nuts
- 4-pinion carrier (case)
- 4cyl 8" diff carriers (cases) do not fit without custom carrier bearing adapters ($), try Inchworm Gear
- A few pre-'96 V6 trucks and 4runners have been found to have come with the 4cyl style diff from the factory. Nobody knows why.
* LPH/SPH gear info: http://www.pirate4x4.com/forum/showpost.php?p=1478223&postcount=73
'96-up 4runner V6 diffs:
- new improved housing that looks the same as the T100/Tundra/Tacoma diff on the outside, internals are all the same as the regular V6 diff
- 30 spline pinion on OEM gears, swap pinion flange to 27 spline to use aftermarket gears
The FACTORY 4.88 V6 diff is unique!
- Axle code G144, white pinion paint code,
- generally came in 92-95 trucks/4runners with V6, auto tranny, 31" tires, and tow package.
- Housing offsets pinion towards ring gear, allowing ring gear to be thinner
- OEM Toyota gears are the ONLY gears that fit this diff due to the thinner ring gear. All other gear sets have thicker ring gears and do not fit.
- The carrier (case) is the same as the V6 diffs, so normal V6 lockers, LSD's, etc. will work in this diff
** V6 diffs are swappable with 4cyl and high pinion diffs
All 2wd and 4wd T100's, '00-06 Tundra's, and ?? Sequoia's use a newer/stronger 8" 2-pinion diff. Tacoma 4x4's and Tacoma PreRunner's that don't come with the electric locker (aka "non-TRD), as well as V6 Tacoma 4x2's also came with this diff.
This diff commonly and mistakenly called an 8.4" or 8.25" diff, possibly to imply its extra strength. The ring gear actually measures 8". The extra strength of this diff comes from the bearing cap/truss and large diameter pinion gear shaft.
LSD's available is the TRD/Kazuma clutch-type 3-pinion LSD, the OEM 4-pinion Tundra TRD LSD, and the Detroit Trutrac.
Lockers available are the Powertrax "Lock-right," "No-Slip," ARB Air Locker, Detroit Softlocker.
This diff cannot be fitted to an older style 8" axle because it uses a larger diameter mounting bolt pattern and because more space inside the housing necessary to accommodate the large bearing cap. The different bolt pattern also makes it very impractical to swap in an electric locking Toyota diff (the whole mounting flange would have to be re-done using a special jig).
- Carrier bearing truss and newer housing adds significant strength over V6 and 4cyl diffs
- Uses V6 carrier bearings, larger pinion bearings
- Uses shims for backlash adjustment instead of threaded adjusters
- Twelve 12mm Ring gear bolts
- 10mm axle housing studs with 14mm nuts
- 30 splilne axles
- 30 spline pinion
* 4Runners do NOT use this diff at all. Late-model 4Runners still use the V6 8" diff above.
** This diff is NOT swappable with V6, 4cyl, high-pinion, or electric locking diffs. This diff cannot be fitted to an older style 8" axle because it uses a larger diameter mounting bolt pattern and because more space inside the housing necessary to accommodate the large bearing cap.
Tundra 9.5"'07+ Tundra 4.7L V8, Sequoia?
Tundra 10.5"
131_0801_09_z+2007_toyota_tundra+rear_ring_gear.jpg
'07+ Tundra 5.4L V8, Sequoia?
http://www.4wheeloffroad.com/techarticles/drivetrain/2007_toyota_tundra_rear_axle/index.html
 
Toyota Electric-Locking Differentials (top)
Electric Locker
A factory option on 3rd Gen. 4Runners, Tacoma 4x4's, and Tacoma PreRunner 4x2's is an electric locking rear differential. This diff is a 4-pinon design based on the Turbo/V6 8" diff and uses the same gear sets and bearings (except for the large bearing near the locking mechanism).
These locking diffs can be retrofitted into 8" diff axles if the axle housing is modified (see this article for more info). It cannot be easily retrofitted into a T100/Tundra or open-diff Tacoma style axle housing because the mounting bolt pattern is smaller. It "could" be done by an axle builder by doing major work to the mounting flange, but that is not really a practical option.
- 30 spline pinion on OEM gears, swap pinion flange to 27 spline to use aftermarket gears
Hi-pinion Electric Locker
A factory option on ‘93-97 Landcruiser FZJ-80's is a hi-pinion electric locking front differential. It can be installed into modified 8" axle housings, similar to the 4Runner/Tacoma locker mentioned above. The reverse-cut gear sets for this diff are the same as for the standard hi-pinion diff mentioned earlier.
These vehicles also had an optional 8.875" REAR electric locker. This one has been retrofitted into other Landcruiser models with considerable effort (see this article), but it doesn't appear to be compatible with any non-Landcruiser vehicles.
Electric Locker Info
Toyota Electric Locker Links: (sorry some of this is very old)
-4x4wire's electric locker installation article
-Mike Carter's E-locker install
-Ken Emanuel's E-locker install
-Ed & Judy's E-locker install
-Carl Whitmore's CJ2a w/ dual hi-pinion electric lockers
-Landcruiser FJ80 rear locker into FJ55 front
Tacoma/4runner- "The Grey Wire Mod" to allow the factory locker to be engaged w/o being in 4-lowhttps://web.archive.org/web/2022030...ebtag=tacomaterritory&msg=10468.1&find=Search
- 4x4wire
- CustomTacos.com
- Offroaders.com
InchwormGear.com is a great vendor who has a lot of E-locker parts and experience.
Toyota Electric Locker E-mail Threads:
(lots of good info in these old emails)
-Karl Bellve and myself
-Scott Muir and myself
-Carl Whitmore (taken from the Toy4x4 list)
Home-fabbed wiring to control a Toyota Electric Locker using relays:
(click to enlarge)

Designed by Scott Muir, drawn by Karl Bellve and I
Special Thanks to Karl Bellve and Scott Muir for all the help with the electric locker info!

I would also like to thank Sean (aka "GearMan") at River City Differentials. He has been very helpful and doesn't seem to mind answering my many questions. He and his shop are highly recommended by members of the Toy4x4 mailing list Pirate4x4.com BBS, and others. Let him know his info is being put to good use!
River City Differentials
Rancho Cordova, CA
(916) 852-7109

"ZUK" also has a great Toyota diff info web page with a ton of practical gear install info:

http://gearinstalls.com/
 
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