JASO MB oils are formulated to deliver low clutch frictional performance.  The intent of the specification is to provide enhanced fuel economy performance for non-wet clutch applications.  These applications generally use external centrifugal clutches and Continuously Variable Transmissions (CVTs); for example: scooters.

The main physical, chemical and clutch frictional requirements, according to the current version of the standard (JASO T903:2023), for JASO MB oils are shown below:

Physical and Chemical

Requirement Methods Unit Limit
Sulphated Ash D874/JIS K 2272 % mass 1.2 max.
Phosphorus D4951/JPI-5S-38 % mass ≥0.08 and ≤0.10
Molybdenum D4951/JPI-5S-38 ppm Report
Foaming Tendency (foaming/settling)      
  Sequence I


D892/JIS K 2518


mL 10/0 max.
  Sequence II mL 50/0 max.
  Sequence III mL 10/0 max.
Evaporation Loss (NOACK)   % mass 15 max.

Shear Stability

(Kinematic viscosity (100°C) after test)

D5800/JPI-5S-41 mm2

xW-30 : 9.0 min.

xW-40 : 12.0 min.

xW-50 : 15.0 min.

Others : Stay in grade

High Temperature High Shear (HTHS) viscosity ASTM D62781 mPas 2.9 min.

Note 1 : Test shall be conducted by diesel injector method using the standard test conditions (30 cycles)

Clutch Test Friction Properties (JASO T 903:2023(Annex A))

Property JASO MB
Dynamic Friction Index (DFI) ≥0.40 and ≤1.35
Static Friction Index (SFI) ≥0.40 and ≤1.45
Stop Time Index (STI) ≥0.40 and ≤1.40

Note : MB shall be within the MB range for each of the three indices (DFI, SFI, and STI), or two indices shall be in the MB range and one index shall be in the MA range, or one index shall be in the MB range and two indices shall be within the MA range.

Submitter may On-File register an oil which satisfies the MB specification when one or more of the indices conform to the MB limits.

The significance of the indices:

Dynamic Friction Index (DFI) Measure of clutch feel and how progressively power transfers during clutch engagement
Static Friction Index (SFI) Measure of closed clutch pack torque handling capacity – resistance to clutch slip under high-torque “break-away” conditions
Stop Time Index (STI) Measure of how quickly the clutch engages

For more information on JASO MB, contact your Lubrizol representative.