MFactory Helical Limited Slip Differential for D15/D16

MFactory Helical Limited Slip Differential - Honda D Series

Spinning one wheel coming out of corners in your D series Civic or CRX and getting smoked by cars with LSDs? The MFactory helical LSD splits power between both wheels instead of sending all the torque to whichever wheel has less grip. I've run MFactory helical diffs in my D series track cars for years because they work and they don't need constant rebuilds like clutch-type LSDs. Your stock open diff sends 100% of power to the wheel with the least traction. That's why you're one-wheel-pegging it and going nowhere. The MFactory helical LSD can transfer up to 75% of torque to the wheel with more grip. You're getting way better corner exit traction and you're actually putting power down instead of spinning one tire.

Here's Why Open Diffs Are Garbage for Track Use

Your stock D series diff is an open differential. When you're cornering hard and one wheel lifts or loses traction, all the power goes to that wheel. The wheel with traction gets nothing. You're spinning the inside wheel and the car's not accelerating. An open diff works fine for street driving where you're not pushing the car, but on track it's useless. Every time you're trying to put power down coming out of a corner, you're spinning one wheel. The MFactory helical LSD uses gear geometry to split power between both wheels based on which wheel has more traction. When one wheel starts to slip, the diff transfers torque to the other wheel automatically. No clutch packs, no preload springs, just gears doing their thing. You get predictable power delivery and way better corner exit speed.

Helical LSD vs. Clutch-Type LSD

Most aftermarket LSDs are clutch-type (like Cusco or OBX). They use clutch packs that wear out and need rebuilds every few years. You're also supposed to run special diff fluid with friction modifiers. The MFactory helical LSD uses gears instead of clutches. There's nothing to wear out and you don't need special fluids. Just run regular gear oil and forget about it. I've got 5+ years and probably 100+ track days on my MFactory diff and it still works like new. Clutch-type diffs also change your steering feel because they bind up under certain conditions. The helical diff doesn't bind, so your steering feels normal.

Forged Japanese Steel, Not Cast Garbage

The MFactory diff's made from forged Japanese SAE 4320 and SAE 9310 steel. That's way stronger than cast steel or cheap Chinese forgings. The gears are double-tempered and cryogenically treated (super sub-zero treatment) for extra toughness. MFactory also shot-peens the gears to increase surface hardness. The diff's designed to handle drag racing shock loads, so it'll survive anything you throw at it on a road course or autocross. The gear geometry's designed to minimize parasitic drivetrain losses. MFactory claims their diffs transfer 1-2% more power to the wheels than competitors' diffs. That's not a huge number, but every bit helps.

Four Variants Based on Differential Bearing Size

MFactory makes four different D series LSDs based on differential bearing size and engine type. You MUST order the correct variant for your transmission or it won't fit.

Variant 1: D15/D16 35mm Differential Bearing (White Speedo Gear)

• Fits: L3, S20, S40, S4C transmissions with white speedometer gear and A00/A000 case stamp
• Engines: D15B, D15B7, D15B8, D16A6, D16Z6, D16Y5, D16Y7 (with 35mm bearing transmissions)
• Vehicles: 1988-2000 Civic DX/LX/EX/Si/HX, CRX DX/Si, Del Sol S/Si (with white speedo gear)

Variant 2: D15/D16 40mm Differential Bearing (Black Speedo Gear)

• Fits: L3, S20, S40, S4C transmissions with black speedometer gear and B00/B000 case stamp
• Engines: D15B, D15B7, D16Z6, D16Y8, D16Y7 (with 40mm bearing transmissions)
• Vehicles: 1989-2000 Civic DX/LX/EX, 1996-2000 Civic EX (D16Y8 - most common), 1999-2000 Civic Si, Del Sol VTEC (with black speedo gear)

Variant 3: DOHC ZC Engine

• Fits: S1, A1 transmissions (DOHC ZC only)
• Engines: ZC DOHC (1.6L dual overhead cam, JDM engine)
• Vehicles: 1988-1991 Civic/CRX with JDM DOHC ZC engine swap (ZC never sold in USA)

Variant 4: D17A Engine

• Fits: SLXA, SLXM transmissions (D17 cable transmissions)
• Engines: D17A1, D17A2, D17A6
• Vehicles: 2001-2005 Civic DX/LX/EX (7th gen, NOT EP3 Si which uses K20A3)

How to Identify Your Differential Bearing Size

If you've got a D15 or D16 engine, you need to figure out if you've got 35mm or 40mm differential bearings. Here's how:

Method 1 - Check Speedometer Gear Color:

• Remove your vehicle speed sensor (VSS) from the transmission
• Look at the speedometer gear inside the transmission case
• Black gear = 40mm bearing (order Variant 2)
• White gear = 35mm bearing (order Variant 1)

Method 2 - Check Transmission Case Stamp:

• Look for a stamp on your transmission case near the transmission code
• B00 or B000 stamp = 40mm bearing (order Variant 2)
• A00 or A000 stamp = 35mm bearing (order Variant 1)

What You Get

• MFactory helical limited slip differential (choose correct variant)
• Forged Japanese SAE 4320/9310 steel construction
• Double-tempered and super sub-zero treated
• Shot-peened gears for increased surface hardness
• Up to 75% torque transfer to one wheel
• No clutch packs (maintenance-free)
• Works with standard gear oil (no special fluids)
• No steering bind or adverse effects
• Brighton-Best hardware included
• Lifetime globally transferable warranty
• Power rating: supports up to 1000+ whp

Note: Ordering the wrong variant will result in the differential NOT fitting. The 35mm and 40mm bearings are NOT interchangeable. Verify your bearing size before ordering by checking your speedometer gear color or transmission case stamp. If you're not sure which variant you need, remove your VSS and look at the speedo gear color, that's the easiest way to tell. Installation requires pulling your transmission and opening the diff. If you've never done diff work, get a shop to install it. The diff supports up to 1000+ whp, so it'll handle any D series build you throw at it.

*Images show the D17A variant. Other LSD variants may differ from what is depicted in the images.