Triumph Spitfire Overdrive Unit
J Type Overdrives
Which Models have J type overdrive?
MkIV Spitfires from FH60001
All MkIVs were fitted with the 3-rail type gearbox.
All UK spec 1500s were fitted with the single-rail type gearbox. However, because USA specification vehicles had the 1500cc engine sometime 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 a 3-rail type gearboxes. Also, due to the different gear selector system and gear level 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.
Reconditioned exchange overdrive units are supplies less solenoid, output flange, adaptor plate & speedo drive.