“J” Type Overdrive Unit- All Models
April, 1973
A new “J” Type Overdrive Unit is currently being incorporated on the Triumph range of vehicles; consequently, the “A” and “D” Types will be discontinued. Incorporation of the “J” Type Unit was effective commencing with the following vehicle identification numbers:
| Model | Vehicle Ident. # | Color | Number | Part # | Working Pressure |
| Stag | LE 20857 | Yellow | 115837 | 312377 | 510-540 |
| TR-6 | CF 1 | Blue | 115838 | 313242 | 430-460 |
| Spitfire | * | Lilac | 115840 | 313305 | 320-350 |
| GT-6 | * | Lt. Green | 115850 | 313304 | 350-380 |
* – Estimated incorporation — Late February, 1973
Hydraulic Pressure Test
When running in direct drive, a residual pressure of 20 lbs. per square inch maintains the overdrive unit in a primed condition and provides lubrication. When overdrive is selected, the hydraulic pressure is increased to within the figures quoted above,
To check the operating pressures:
1. Check that the gearbox oil level is correct.
2. Remove the hexagon headed plug adjacent to the solenoid and fit hydraulic pressure gauge L188A together with the adaptor L188A-2.
3. Jack up the rear wheels and run the transmission at approximately 25 m.p.h.
Note 1. When in direct drive the residual pressure reading should be approximately 20 lb./in.
Note 2. When the overdrive is engaged, the pressure should be as specified.
Interchangeability Of Parts
“J” Type Overdrive parts are not interchangeable with those for “A” or “D” Type Units.