[Spits] OD checking

[jimmuller at rcn.com]

stiker2126 wrote about a newly-acquired Spitfire:
> strange shifter... has a slide button on the top of it...

Ah, excellent!  That's not strange, it's the original OD control (where, as some people claim, God and BL decreed it should be).  It would appear that this car already has OD.  Someone may have put an OD knob on a non-OD stalk, but it is unlikely.  The top of the knob pops off easily.  See if it has wires attached.

> its in rough shape.... rust has taken its toll...

Not a surprise.  As long as the frame is okay you are probably okay.  Floors and rockers can be replaced if you spend some money.  You don't want to fall through onto the roadway, of course.

> anybody know what to check for on an OD unit?

Mostly, does it work?  Does it engage and disengage okay?  The clutches inside can get worn but you have to take it apart to see.  The solenoid and various valve components can be removed for inspection.  Be aware that if the gearbox is running low on oil the OD will engage slowly, incompletely, or not at all.  Some conditions can make it stick on.  If that ever happens, do NOT roll or drive the car backwards, do NOT even push it by hand enough to force it to move backwards.  Doing so will damage or destroy the OD.  There are several reason this can happen, the most common being dirt stuck in an orifice so that pressure cannot escape from the engagement piston.  Waiting long enough is the typical cure, but it can always happen again and probably will until you clean things out and maybe replace the oil.

> does the rear end also have to be swapped?

It appears you are considering switching from non-OD to OD gearbox.  This does not require swapping the diff; the speedometer drive comes off just in front of the driveshaft output, so it will be right regardless of what is driving it.

OD and non-OD geraboxs different in the following ways:  different length driveshaft, different rear engine mount (actually at the rear of the OD unit, a vertical support and a flat crosspiece that sits across the frame members and is often forgotten when OD is pulled from a for-parts car), and I believe a longer speedometer cable with right-angle drive at the gearbox end.  The shift-lever support mechanism and external control rail are different too, but rather integrated into the whole package, so they aren't likely to be separated.

> He's going to put the OD in his spit 1500 if it's
> any good...

Ah, he's going to put this from a newly-=acquired Spitfire into one he already owns?  Did I miss a point somewhere?

Good luck with it!
--
Jim Muller