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Re: [Spits] OD checking

To: Spitfires@autox.team.net
Subject: Re: [Spits] OD checking
From: <jimmuller@rcn.com>
Date: Thu, 20 Nov 2008 12:29:14 -0500 (EST)
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
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