Which models have 'J' type overdrive?
MkIV Spitfires from FH60001. All MkIVs were fitted with the 3-rail type gearbox.
Spitfire 1500's. All UK spec 1500s were fitted with the single-rail type gearbox. However, because USA spec vehicles had the 1500cc engine some time before the UK and other export countries, it is possible that there are some re-imported '1500s' that have a 3-rail type gearbox fitted as standard.

Are they the same overdrive unit?    - No.
Are all the parts interchangeable?    - No.
Are the adaptor plates the same?    - No.

Although outwardly they appear the same, (as are the vast majority of components), overdrive units for the 1500 (with single-rail gearbox) were fitted with a much improved 'Oil Pressure Relief Valve' system, which cannot be fitted to the original spec MkIV 'J' type overdrive used on 3-rail type gearboxes.
Also, due to the different gear selector system and gear lever mounting, 3-rail type gearboxes and single-rail type gearboxes each have their own specific 'overdrive to gearbox' adaptor plate.

Can I fit a 1500 unit to a MkIV?
Should I fit a MkIV unit to a 1500?
Our reconditioned (exchange) 'J' type overdrive units are suitable for both single-rail and 3-rail type gearboxes, but, you MUST use the correct gearbox adaptor plate.

'J' Type Overdrive Re-Builds
Overdrives require specialist knowledge to dismantle & re-build, and are normally beyond the ability of the DIY enthusiast, we therefore strongly recommend the fitting of a reconditioned exchange unit.
However, if you do intend to recondition your own unit, please contact us with the parts you require, and we may be able to supply them from stock.
Important
All our Overdrive units are supplied on a strict 'like for like' exchange basis.
Your old exchange units must be undamaged and be in a totally serviceable condition.
All overdrives are supplied less solenoid, output flange, adaptor plate & speedo drive. Refer to listings for details.

Overdrive Unit
Reconditioned exchange overdrive units are supplied less solenoid, output flange, adaptor plate & speedo drive.
Overdrive Unit Only ('J' type) - (1) - RKC684R
All models.

Gear Oil
Unipart EP90 (0.5 litre) - (ar) - GGL190

Adaptor Plate & Fittings

Single Rail type Gearbox
Adaptor Plate (overdrive to gearbox) - (1) - RKC634
Gasket Set - (1) - RL1571
Includes all necessary gaskets.

Gaskets;
Adaptor Plate to Gearbox - (1) - 22G1420
Main case to Adaptor Plate - (1) - 37H1901
Sump/Filter Cover - (1) - NKC76
Main Case to Brake Ring - (1) - NKC86
Main Case to Rear Case - (1) - NKC87

Detent/Plunger - (1) - 22G1421
Cap (retaining) - (1) - 22G1947
'O' Ring/Seal (selector shaft) - (1) - TRS912
Setscrew (adaptor to gearbox) - (8) - UKC4811
Washer (spring) - (8) - GHF332

3 Rail type Gearbox
Adaptor Plate (overdrive to gearbox) - (1) - 313085
Gasket Set - (1) - RL1576
Includes all necessary gaskets.

Gaskets;
Adaptor Plate to Gearbox - (1) - 106437
Main Case to Adaptor Plate - (1) - 37H1901
Sump/Filter Cover - (1) - NKC76
Main Case to Brake Ring - (1) - NKC86
Main Case to Rear Case - (1) - NKC87

Setscrew (adaptor to gearbox) - (8) - UKC4811
Washer (spring) - (8) - GHF332

The following parts are not illustrated

Fasteners (adaptor plate to gearbox);
Triumph used alternative fastening methods for locating the adaptor plate to the gearbox, it is down to personal choice.
Use either 7 setscrews, or 5 studs & 2 setscrews, or 7 studs.
Setscrew - (ar) - SH605071
Stud - (ar) - 132115
Nut - (ar) - GHF201
Washer (spring) - (7) - GHF332

Main Case - Solenoid & Fittings



Main Case - (1) - NKC19
Gasket (main case to brake ring) - (1) - NKC86
Brake Ring - (1) - NKC10

Stud (main to rear case);
Short (set of 4) - (1) - NKC58

Nut (for studs) - (6) - GHF201
Washer (spring) - (4) - GHF332
Washer (flat) - (2) - NKC89
Filter (pressure) - (1) - NKC23
Washer (for filter) - (1) - NKC11
Plug (threaded) - (1) - NKC24
Filter (suction) - (1) - NKC53
Cover (sump) - (1) - NKC54
Gasket (sump) - (1) - NKC76
Screw (sump cover) - (6) - SH604051
Washer - (6) - NKC110
Plug (threaded) - (1) - NKC97
Washer (for plug NKC97) - (1) - NKC96

Solenoid;
New - (1) - NKC41
Reconditioned - (1) - NKC41R

Earth Lead - (1) - NKC67
Gasket (main case to adaptor) - (1) - 37H1901
Retaining Spring (cam) - (1) - 137308
Spring Clip - (1) - 159503
Cam (oil pump) - (1) - 159505
Woodruff Key - (1) - KW316
Bridge Piece (set of 2) - (1) - 500587
Piston - (1) - NKC21
'O' Ring (piston) - (1) - NKC99A
Plug (relief valve) - (1) - NKC93
Spring (for plug NKC93) - (1) - NKC94
Ball Bearing (for plug NKC93) - (BLS105) -
Studs (main case to adaptor) - (8) - NKC57
Nut (for studs NKC57) - (8) - GHF200
Washer (for studs NKC57) - (8) - GHF331

Oil Relief Valve & Pump

Single Rail type Gearbox
Dash Pot Plug Kit - (1) - NKC13
'O' Ring Only (dash pot) - (1) - NKC91
Oil Relief Valve Kit - (1) - AAU1388
'O' Ring - (1) - RTC1949
'O' Ring - (2) - NKC92
'O' Ring - (1) - NKC102A
Plug Kit (pump) - (1) - NKC26A
'O' Ring - (1) - NKC101
Non-Return Valve Kit - (1) - NKC29A
Pump Body - (1) - NKC25
'O' Ring - (1) - NKC100
Plunger Kit - (1) - NKC28

3 Rail type Gearbox
Dash Pot Plug Kit - (1) - NKC13
'O' Ring Only (dash pot) - (1) - NKC91
Dash Pot Piston Kit - (1) - NKC15
Piston Kit (relief valve) - (1) - NKC33
Spring Only - (1) - NKC104
Sleeve (dashpot) - (1) - NKC14
'O' Ring - (2) - NKC92
Body (relief valve) - (1) - NKC30
Plug Kit (pump) - (1) - NKC26A
'O' Ring - (1) - NKC101A
Non-Return Valve Kit - (1) - NKC29A
Pump Body - (1) - NKC25
'O' Ring - (1) - NKC100
Plunger Kit - (1) - NKC28

Annulus - Cone Clutch & Sunwheel



Sun Wheel - (1) - NKC55
Cone Clutch - (1) - NKC40
Bearing Carrier - (1) - NKC62
Bearing - (1) - NKC63
Stud (set of 4) - (1) - NKC109
Spring - (4) - NKC12
Snap Ring (bearing) - (1) - NKC84
Circlip (annulus) - (1) - NKC85
Circlip (sun wheel) - (1) - NKC83
Bearing (front input) - (1) - SP74G
Locates on annulus shaft in rear case.
Annulus - (1) - NKC9
Thrust Washer - (1) - NKC79
Free-Wheel Assembly - (1) - BAU2061A
Rollers (set of 12) - (1) - 506063
Snap Ring/Spring - (1) - 513208
Oil Thrower - (1) - NKC20
Snap Ring - (1) - NKC77
Planet Gear & Carrier - (1) - AEU1051

Rear Case & Fittings



Bearing (front input) - (1) - SP74G
Locates on to annulus shaft in rear case.
Gasket (rear case brake ring) - (1) - NKC87

Gear (speedo drive);
Locates on mainshaft.
For 3.63:1 diff ratio - (1) - NKC45
For 3.89:1 diff ratio - (1) - NKC46

Spacer - (1) - NKC78

Rear Case;
Single-Rail Gearbox - (1) - AAU1387
3-Rail gearbox - (1) - NKC38

Bearing (rear output) - (1) - 513897
Oil Seal (rear casing/output) - (1) - NKC39
Drive Flange - (1) - 160286
Washer - (1) - NKC82A
Nut (nyloc) - (1) - NKC81

The following parts are not illustrated

Stud (main case to rear case);
Short (set of 4) - (1) - NKC58
Long - (2) - NKC59

Nut (for studs) - (6) - GHF201
Washer (spring) - (4) - GHF332
Washer (flat) - (2) - NKC89

Speedo Drive & Cable



Speedometer cable;
RHD Vehicles - (1) - 156316
LHD Vehicles - (1) - GSD273

Angle Drive - (1) - 120694

Speedo Drive Pinion;
For 3.63:1 diff ratio - (1) - AEU1578
For 3.89:1 diff ratio - (1) - NKC49

'O' Ring/Seal - (1) - NKC106
Housing/Bearing - (1) - NKC42
Speedo drive pinion.
Bush/Seal - (1) - NKC105A
Adaptor (angle drive) - (1) - NKC43
Screw - (1) - SH604041
Star Washer - (1) - GHF331

Gear (speedo drive);
For 3.63:1 diff ratio - (1) - NKC45
For 3.89:1 diff ratio - (1) - NKC46



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