Patrick,
James is correct here. at low revs, the OD oil pump will not build up
enough pressure on the "J" type to engage the OD.
The OD units were not larger on the 2.5 engines. There were a number of
minor differences. The "J" type from a TR6 or 2.5 saloon will quite
happily fit on a Spitfire providing you have the correct rear casing.
There were a number of pressure release valve setups even for the two
"J" types used on Spitfires. ( single rail and 3 rail transmissions -
yes they were used on 73' 3 rail ). I have never found this to be a
problem.
Only other difference was the speedo drive gear ratios and the overall
drive ratio used on the 2.5 saloons.
Some Saloons used the "type 28" ( 28% reduction ) "J" type where the
"type 25" was used on the Sports range. All are interchangable providing
you have the correct rear casing with correct mounts. In fact, the lower
mounts are the same, the top mounts only hold the remote change used on
the single rail Spit Transmission.
Hope this clears it up.
Peter Cebalo
73' Spitfire ( converted to OD from a type 25 saloon... )
Auckland New Zealand
>While the J-type overdrive was used on 2.5l engines they were also larger
>units, same type of unit, but not the same ones. Again they were only used
>at higher rpms where torque was not a problem, you had the enertia of the
>vehicle to fight that.
>Patrick Bowen
>- -----Original Message-----
>From: James Carpenter
>Subject: Re: Wiring Spitfire Overdrive
>Having seen the inside of one of these things torque is NOT a problem, they
>coped with the 2.5LPI engin didn't they! These things are rely STRONG! The
>reason you don't get them on 1st and 2nd is you can pull away from start in
>1st or 2nd. At thoes speeds the main shaft is turning realy slowly, and you
>don't get much oil pressure in the thing. So it wont work when instructed.
>James
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