How to Tell an Open Differential from a Limited-Slip

The fastest practical check: safely lift both driven wheels, place the transmission in neutral, release the parking brake, and spin one wheel by hand. If the opposite wheel turns the same direction or resists strongly, you likely have a limited-slip differential (LSD); if it turns freely in the opposite direction, it’s almost certainly an open differential. You can also confirm by decoding axle/build codes, tags on the housing, or the service manual. Below is a detailed guide covering driveway tests, visual clues, road-test behavior, and electronic-system caveats.

What’s the Difference—and Why It Matters

An open differential splits torque equally but sends power to the wheel with the least resistance, which can leave one wheel spinning on low grip. A limited-slip differential still allows speed difference between wheels in a turn but biases torque to the wheel with more traction through clutches, gears, viscous fluid, or electronically controlled clutches. Knowing which you have affects diagnostics, fluid choice, and how the vehicle behaves in poor traction and hard cornering.

Safety and Tools

Before any physical test, prepare basic gear and follow safety steps to protect yourself and your vehicle.

• Floor jack and rated jack stands (never rely on a jack alone)
• Wheel chocks for the non-driven axle
• Work gloves and eye protection
• Owner’s manual or service info for jacking points and drivetrain specifics
• Scan tool (optional) to check for electronic LSD/traction-control settings

These basics let you conduct a controlled, repeatable test without relying solely on road feel or guesswork.

Method 1: The Jack-and-Spin Driveway Test

This is the most direct physical test for open versus limited-slip on RWD and FWD vehicles. It can work on AWD/4WD too, but read the caveats below.

1. Chock the non-driven wheels. Lift the driven axle so both driven wheels are off the ground. Support securely on jack stands.
2. Put transmission in neutral (or N for automatics). Release the parking brake. Disable auto-hold features.
3. Spin one wheel by hand and observe the other wheel:
   

   • If the opposite wheel turns the opposite direction easily and freely, it’s almost certainly an open differential.
   • If the opposite wheel turns the same direction, resists turning, or requires noticeably more force, you likely have an LSD.

4. Repeat in both directions; note effort and behavior.
5. For vehicles with electronic traction control/eLSD, switch traction/stability control fully off to avoid brake intervention during testing. Ignition off may be required for some eLSDs; consult the manual.

The key indicator is torque bias: an LSD will couple the wheels enough to resist opposite-direction freewheeling. Open diffs reverse the other wheel with minimal resistance. If results are ambiguous, move to visual and information checks.

Interpreting Results and Caveats

Results differ by LSD type and vehicle setup.

• Clutch-type LSD: Often turns the opposite wheel the same direction or shows clear resistance. May feel “grabby.”
• Helical/Torsen: May allow some reverse motion initially but builds resistance under load. On a lift with no load, coupling can feel weaker than a clutch LSD.
• Viscous LSD: Behavior can be subtle when cold; slight delay before coupling is normal.
• Electronic LSD (eLSD): Uses an actuator to preload clutches. With ignition off, some act like open diffs; others retain mechanical preload. Check the manual.
• AWD/4WD: Center/diff couplings can mask results. Lifting only one corner can load the center diff or coupler—lift both wheels of the tested axle and follow the manufacturer’s procedure.
• Brake-based “torque vectoring” (not a true LSD): With ignition on, the ABS may brake a spinning wheel to mimic LSD. Disable traction control to avoid a false positive.

If your vehicle uses advanced AWD or brake-based torque vectoring, the driveway test should be paired with code/tag verification to be conclusive.

Method 2: Visual and Information Checks

Automakers often encode differential type in labels, tags, or build sheets. These clues can quickly confirm what’s fitted from the factory.

• Axle tags/labels: Metal tags bolted to the diff cover or stickers on the housing may list ratio and type (e.g., “LSD,” “S,” “Trac-Lok,” “Torsen”).
• Door-jamb/RPO codes: Many brands list axle codes on the VIN sticker or build sheet. Examples:
  

  • Ford: Two-digit axle code in the driver door jamb; cross-reference with Ford charts to see “open” vs “limited-slip.”
  • GM: RPO codes on the service parts label; note G80 indicates a locking differential in most trucks (a locker, not a clutch LSD). In some cars, separate codes denote LSD; verify by model/year.
  • Stellantis (Jeep/Ram): “Trac-Lok,” “Anti-Spin,” or specific sales codes in the build sheet denote LSD.
  • BMW/MINI: Option codes or “Torsen” notes on FWD-based platforms; M models often use active M differentials (electronically controlled clutch LSD).

• Service manual: Look for terms such as “limited-slip,” “torque-biasing,” “Torsen,” “helical,” “clutch pack,” or “electronically controlled diff.”
• Fluid labels: A sticker warning to use “friction modifier” or “LSD additive” strongly indicates a clutch-type LSD.
• Aftermarket signs: Finned performance covers, additional wiring/actuators on the diff, or receipts for LSD installs can be clues.

Codes and tags are especially useful when electronic systems complicate physical testing or when on-lift behavior is inconclusive.

Method 3: Road-Test Clues

Behavior in low-traction or cornering can hint at differential type. Use a safe, legal area and moderate throttle.

• “One-wheel peel”: On a straight, low-traction launch, a single black mark or one wheel spinning wildly suggests an open diff.
• Inside-wheel spin exiting tight corners: More common with open diffs; LSDs usually reduce this and improve drive out of corners.
• Chatter on tight, slow turns: A clutch LSD with incorrect or old fluid can chatter; open diffs are typically silent. Proper friction modifier usually cures it.
• Stability/traction control behavior: If disabling traction control improves traction out of corners, you may rely on brake-based vectoring rather than a true LSD.
• ABS activity under throttle on uneven surfaces: Frequent single-wheel braking to simulate torque transfer suggests you have an open diff with electronic aid.

Road feel can support your conclusion, but it’s not definitive on modern cars where electronics can mask mechanical differences.

Method 4: Scan Tool and Electronic Systems

Modern vehicles often integrate the diff with control modules. A scan tool or settings menu can identify what you have.

• Drive mode menus: Options like “eLSD,” “Active Diff,” “M Differential,” or “Rear Diff Lock” indicate non-open behavior.
• Module presence: A dedicated differential control module or rear drive unit listing in a scan tool suggests an electronically controlled clutch pack.
• Live data: Some tools show diff clutch command or axle torque bias in real time.
• DTCs: Fault codes related to differential actuators, pressure solenoids, or yaw/torque vectoring systems imply electronic intervention capability.

Electronic confirmation is valuable where the mechanical test is inconclusive or where the diff behavior depends on ignition state or selected modes.

Common Pitfalls and Myths

A few misconceptions can lead you astray when identifying your differential.

• Myth: Spinning both wheels in the air always means LSD. Fact: Brake-based systems can mimic this with ignition on.
• Myth: All “G80” GM axles are LSDs. Fact: In most GM trucks, G80 is an automatic locker, not a clutch LSD.
• Pitfall: Testing only one wheel off the ground on AWD/4WD vehicles can load the center diff or coupler—use manufacturer procedures.
• Pitfall: Cold viscous LSDs may act open until warmed.
• Pitfall: Worn clutch LSDs can behave like open diffs; fluid service or rebuild may be needed.

Knowing these traps helps you interpret test results accurately and avoid damaging sensitive driveline components.

Quick Reference: What You Might Have

Here’s how the common systems behave and what they mean.

• Open differential: Opposite wheel spins freely in reverse direction on a lift; simplest, cheapest, least traction when one wheel is unloaded.
• Limited-slip (clutch/helical/viscous): Shows coupling on a lift; biases torque to the wheel with grip; needs specific fluid (clutch types).
• Electronic LSD (clutch with actuator): Mechanically biases torque, commanded by ECU; behavior may change with modes/ignition.
• Locker (automatic/selectable): Mechanically locks both wheels together under certain conditions or on command; not the same as LSD.
• Brake-based vectoring: Open diff with ABS braking to send torque across; can feel like LSD in light use but not mechanically the same.

Each system has distinct behavior and maintenance needs; identifying the correct one informs proper service and expectations.

Maintenance Note

If you confirm an LSD, use the specified gear oil and friction modifier. Incorrect fluid can cause chatter, premature wear, or degraded torque bias. For eLSDs, observe change intervals and spec exactly—some use unique fluids for the clutch pack and hypoid gears.

Summary

Lift both driven wheels and perform the hand-spin test: opposite wheel spinning freely in reverse direction indicates an open diff; same-direction rotation or strong resistance points to an LSD. Confirm with axle tags, build codes, or the service manual, especially on vehicles with electronic traction aids or eLSDs. Road-test behavior and scan-tool data can further corroborate your findings. Proper identification ensures correct maintenance and realistic expectations for traction and handling.

How do you tell the difference between a slip diff and a limited slip diff?

The open diff results in the inside tire spinning while the outside tire has plenty of grip. In contrast, the LSD works by locking the diff as soon as the inside wheel starts to spin, distributing power to both tires and causing a controlled slide. In terms of drifting, open differentials can be a major issue.

How do I know if my differential is open or limited slip?

To identify a limited slip differential (LSD), safely lift one drive wheel off the ground and spin it. If the opposite wheel on the same axle spins in the same direction, you have an LSD. If the opposite wheel spins in the opposite direction, it’s an open differential. You can also look for an “LS” code or tag on the differential housing, check the vehicle’s build sheet, or consult the owner’s manual.
 
This video explains the difference between open and limited slip differentials and shows them in action: 1mAustin CoulsonYouTube · Feb 23, 2019
Method 1: The Two-Wheel Test (Recommended)

1. 1. Safety first: Safely support the vehicle by placing jack stands under the rear (or front for a FWD vehicle) and ensure the vehicle is in neutral. 
2. 2. Lift and block: Lift the two drive wheels off the ground using a jack. Block the wheels that remain on the ground to prevent the car from rolling. 
3. 3. Spin a wheel: Spin one of the drive wheels by hand. 
4. 4. Observe the other wheel:
   • Limited Slip Differential (LSD): The other drive wheel will spin in the same direction as the wheel you are turning. 
   • Open Differential: The other drive wheel will spin in the opposite direction. 

Method 2: Check the Decal/Code 

1. Locate the differential: Find the differential housing on the rear (or front) of the vehicle. 
2. Look for a tag: Check for a small metal tag or sticker on the differential. 
3. Identify the code: If the vehicle has an LSD, the code on the tag will typically include an “LS” (e.g., 4L10). 

Method 3: Check Vehicle Documentation

1. 1. Consult the owner’s manual: Opens in new tabThe owner’s manual will list the vehicle’s specifications, including the type of differential. 
2. 2. Check the build sheet: Opens in new tabIf you have access to the vehicle’s original build sheet or options list, it will confirm if an LSD was factory-installed. 

What does a limited-slip differential look like?

A limited slip differential (LSD) itself is an internal component, so you can’t “see” it from the outside of a car unless you’re looking inside the differential housing. However, you can visually identify one by checking for an “L” in the differential code on a tab on its casing, or by performing a wheel-spinning test where both rear wheels turn in the same direction. Inside, LSDs typically feature clutch packs, viscous fluid with discs, or helical gear mechanisms to transfer power to the wheel with grip.
 
This video shows the internal components of a limited slip differential, including clutch packs: 53sSabin Civil EngineeringYouTube · May 1, 2014
What to look for externally

• Differential Code: Look for a metal tag or stamped code on the differential housing. If it contains an “L,” such as “4L10” or “3L73,” it indicates a limited slip differential. 
• Wheel Spinning Test: With the car in neutral, the front wheels blocked, and the emergency brake off, raise the rear wheels off the ground. Try to rotate one of the rear wheels. 
  • Limited Slip: If the other rear wheel turns in the same direction, you likely have an LSD. 
  • Open Differential: If the other wheel turns in the opposite direction, it is a standard open differential. 

This video demonstrates the wheel spinning test to differentiate between a limited slip and an open differential: 55sChrisFixYouTube · Nov 26, 2012
What to look for internally

• Clutch Packs: Opens in new tabSome LSDs use multiple friction and steel clutch discs, similar to those in a motorcycle’s wet clutch. These discs are stacked and compressed to lock the wheels together and transfer torque. 
• Viscous Coupling: Opens in new tabOther types, called viscous or speed-sensitive differentials, use a fluid-filled cylindrical chamber with stacked perforated discs. The fluid warms and expands from the friction of the spinning discs, causing them to “block” the speed difference between the wheels. 
• Helical Gears: Opens in new tabSome systems, like helical limited-slip differentials, use helical gears that push against the inside of the case when one wheel begins to slip, thereby locking everything together and distributing torque. 

How do you tell what type of differential you have?

To tell the type of differential, safely lift and support the drive wheels off the ground, place the vehicle in neutral, and then spin one wheel while observing the other. If the opposite wheel spins in the opposite direction, you have an open differential. If the opposite wheel spins in the same direction, you have a limited-slip or locking differential. 
This video demonstrates the test for identifying open versus limited-slip differentials: 59sCatfish MotorsportsYouTube · Jan 11, 2024
1. Prepare the Vehicle

• Lift and Support: Safely jack up the vehicle and support both rear (or front, depending on whether the car is front-wheel or rear-wheel drive) drive wheels off the ground with jack stands. 
• Neutral: Ensure the vehicle is in neutral. 
• Block Wheels: Block the non-drive wheels to prevent the vehicle from rolling. 

2. Perform the Wheel Spin Test

• Spin a Wheel: With the drive wheels in the air, spin one of them by hand. 
• Observe the Opposite Wheel: Watch the other drive wheel. 
  • Opposite Rotation: If the other wheel spins in the opposite direction of the wheel you’re spinning, you have an open differential. 
  • Same Direction Rotation: If the other wheel spins in the same direction, you have a limited-slip (LSD) or locking differential. 

3. Other Methods

• Vehicle Tags: Opens in new tabSome vehicles have a tag on the differential housing that might indicate the type, possibly with an “L” for limited-slip. 
• Vehicle Options: Opens in new tabCheck your vehicle’s owner’s manual or the “Service Parts Identification” sticker on the door or glove box for RPO (Regular Production Option) codes, which can identify the differential. 
• Visual Inspection: Opens in new tabYou may be able to identify the type by observing the number of cover bolts or the shape of the differential housing.