[TR] Overdrive Update

Randall TR3driver at ca.rr.com
Mon Aug 7 10:47:57 MDT 2017

> Randall, this is a very interesting, simple and rather 
> brilliant, modification. Your custom nut is long enough to 
> bear on the transmission housing eliminating the need for a 
> hex wrench to secure the nut when rotating the socket head screw.   

It actually fits down into the space in the lever (where it is folded over),
doesn't touch the housing.

> In Terry's instance, if the slot in the lever arm requires 
> widening could this be the result of wear on the lever arm 
> slipping on the pin just enough to cause a groove to develop 
> on the pin so that the lever arm cannot securely and 
> adequately clamp the pin before the gap in the lever arm 
> closes? If this is happening, over time could this possibly 
> weaken the pin so it eventually fatigues and separates? 

The clamp doesn't have a lot of travel (as Terry learned), so I think not
being able to clamp the lever tight enough would be a problem long before
the shaft is weak enough to break.  But I don't have any experience with
that, so I don't really know.  And the shaft can be replaced, although
getting it drilled just right for the adjustment arm is probably tricky.
Might have to fill the existing hole in the housing and drill a new one.

BTW, TRF used to offer a replacement operating lever arm.  Probably they
still do.

> I am lost as to how the referenced "short pin" is used in the 
> adjustment lever unless it's used between the lever arm and 
> the pin to open the lever arm slot so the arm can compress on 
> the pin. 

The adjustment method given in the book involves inserting a 3/16" pin
through the adjustment lever on the other side, into a hole drilled in the
case.  Normally, a 3/16" drill bit works well, but the clearance is very
limited with the tunnel installed, no room for a drill bit.  What I found is
that, by cutting a 3/16" diameter pin just the right length (roughly 1/2",
I'm not sure of the exact dimension after all these years), I could put it
in with chain nose pliers and working underneath the car (without removing
the tunnel).  After 3 or 4 times through pulling the carpets, seats, tunnel,
etc. I was determined to find another way.

> I took a chance without researching it first and have 
> purchased a very low time 1964 or 1965 TR4 OD transmission 
> thinking I can use it in my 1959 TR3A. Any advice on 
> installing this transmission this will be truly appreciated. 

Should be fairly straightforward.  If you are installing the OD onto a TR3
gearbox, then it should just drop right in.

If you have the complete TR4 gearbox with OD, you need to slot the holes
where the rear motor mount attaches to the cross member.  The TR4 gearbox is
about 3/8" longer at the mounting points than the TR3 box (the extra length
allows for synchromesh on 1st gear).  In my case, I also had to bend the
stiffening tab on the cross member, but you might not need to do that.

The longer gearbox also moves the speedo cable attachment back a bit, so I
added a piece of fuel line to cushion it where it goes through the floor.
Both changes are visible here (I hope) http://imgur.com/0OJpiee

I had several other changes, because I used a TR6 main housing (which has a
much thicker mounting flange).  But I don't think they would apply with a
TR4 housing.

-- Randall

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