[Spits] speedometer stopped working

[Jim Muller]

On 10 Jan 2011 at 20:18, Grant Buss wrote:

>  I don't want to take the trans apart,unless it is
> a simple fix. I think you can't buy the part.

Whether it is a simple fix depends on what the problem is.  One might 
way that anything you do with the gearbox isn't simple.  But it 
really depends on what the problem is.

That the speedometer works at all and is more or less right at 60 
suggests it is something inside the speedometer.  I don't see how it 
would work at all if any part of the speedometer drive were broken.

That being said, there might be a relatively easy fix (compared to 
pulling the gearbox out).  The speedomoeter is driven by a plastic 
gear on the output shaft.  This turns a worm gear on a shaft held 
into the rear gearbox extension by a removable socket and into which 
the cable goes.  You might be able to see and even replace some of 
this if something is broken.

Spitbits.com has the plastic output shaft gears for at least the 
later Spitfire and GT6 boxes.

You need to remove the vertical dashboard support, the front carpet 
section, and the gearbox cover, all a bit of work but not hard.  Then 
you might be able to pull the worm gear holder out by removing the 
pin bolt that holds it in place (located just above the cable input 
hole).  This might give you enough access to let you see into the 
hole.  With a small light you might be able to see if the gear on the 
output shaft is broken.

If the gear is broken you can probably remove the rear extension from 
the gearbox without pulling the gearbox out.  Mind you, I've never 
done it with the gearbox in place but I see no reason why you can't.

Remove the driveshaft bolts and the nuts which hold the rear engine 
mount, then jack up the engine with a hydraulic jack and board under 
the oil pan.  Once the driveshaft flange is free you should be able 
to remove the rear pulley.  You should probably remove the shifter 
from the top too jsut go gain working space.  Remove the seven bolts 
which hold the extension in place.  Then with a soft mallet and/or 
suitable drift you can knock the rear extension off the back of the 
output shaft.  Voila!

Assembly is the reverse of dis-assembly.

It's, ah, a lot of work.

-- 
Jim Muller
jimmuller at rcn.com
'80 Spitfire, '70 GT6+