[TR] Replacing TR2 gearbox with TR6 gearbox

Randall TR3driver at ca.rr.com
Thu Feb 21 02:06:08 MST 2013


> Hi!,What does one look for changing long door TR2 gearbox 
> with the later 1970
> TR6 overdrive gearbox.Ie clutch/driveshaft.

Keep your old clutch setup, it will work with the TR6 box.  You may need to
do something creative with the clutch slave cylinder mounting, as the TR6
box is thicker in that area.  On my TR3/A I just made up a shorter pushrod
to account for the difference (but it has the Girling slave instead of
Lockheed so your solution may be different).

I installed the TR2/3 brass bushings to carry the clutch operating shaft,
and added zerks so they could be greased.  Not necessary, but should reduce
wear in that area.

The driveshaft will bolt right up, the sliding spline has enough range to
cover the slight increase in overall length.  Be sure to replace the Nyloc
nuts.  I prefer to use all-metal lock nuts (aka Stover nuts) as I've found
that even new Nylocs will back off sometimes.  Note that the bolts are
specials but available from the usual suspects.

Slot the holes in the rear crossmember, to allow for the extra length (about
3/8" or one bolt width).  I also had to fold down the lip at the back so it
wouldn't rub on the mount.

You'll probably need longer studs and bolts on the back of the engine.  The
studs can't be too long though, or the output flange will hit the tunnel
when trying to R&R the gearbox with the engine still in the car.

Although not necessary, I swapped the TR6 shift linkage components into an
early top cover, so I could keep the dipstick.  If you do keep the TR6 top
cover, you'll probably want to install the TR2 shift lever, which may
require drilling out the holes on the sides.  The TR6 lever will work, but
is longer (and curved) and just looks odd to me.

Of course you'll need the OD wiring if you don't already have it, but that's
covered in the manual.  I added an in-line fuse in the hot wire to the
relay, so the fuse will open if the solenoid gets stuck in some manner and
the cutout contacts don't open.  Hopefully that will save the solenoid from
overheating and letting out the smoke.  Of course that means the OD will
drop out, potentially over-revving the engine, but I figure that will happen
anyway when the solenoid burns up and my engine doesn't seem to mind brief
excursions to 6k rpm.  I used an 8 amp "slow blow" fuse just because I've
got a bunch of them, but an ordinary 10 amp (or even 5 amp) fuse should do
fine.

The original relay lasted a long time; but replacements seemed to fail
quickly until I added a snubber diode from the load terminal to ground.  Not
being a stickler for originality (obviously), I just used an ordinary
Bosch/Tyco type automotive relay from the local parts store.

It's probably worth doing a pressure test on the OD, and replacing the
isolator switches before installing it in the car.  I put in an iffy switch
for 2nd gear and I'm regretting it now as it stopped working the other day.


-- Randall 


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