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RE: TR4A transmission selector rails

To: "Jim Wallace" <jim.wallace@netscape.ca>, <triumphs@autox.team.net>
Subject: RE: TR4A transmission selector rails
From: "Randall" <tr3driver@comcast.net>
Date: Sun, 20 Feb 2005 15:19:35 -0800
> 1. Plunger with pointy tip, spring, and distance piece.

I believe, not certain, the pointy tip goes on the 3/4 rail.

> 2. Plunger with blunt tip (not from wear), spring, and distance piece

The reverse rail definitely gets a plunger, but again I'm not certain, only
think it gets the blunt plunger.

> 3. Ball bearing with heavier spring and no distance piece.

1/2 rail.

> The books, in two different
> drawings, indicate one plunger and two ball bearing setups, with the
> plunger for the reverse rail. To me it appears the wider detent in the
> reverse rail should accept the ball bearing.

There's a nice diagram, with part numbers, in the TRF TR6 catalog, Vol I.  It's
still available (unlike Vol II) and free ...

Both earlier and later versions of the gearbox used balls on both 1/2 and 3/4,
which probably explains why the factory diagrams show that configuration.  Just
a WAG, but I'd guess the change was to try to prevent complaints of jumping out
of gear.  Once that problem was solved with modified gearsets and strengthened
case, they went back to a ball on 3/4 to try to get a smoother shift.  Strictly
a guess, though, your mileage may definitely vary.

BTW, my TR4/A Bentley reprint mentions the change to a plunger on 3/4 (from
gearbox CT9899), but interestingly enough says it's identical to the plunger
used on reverse.  But the TRF catalog has different part numbers, so perhaps
that's an even later change.

One approach might be to see which plunger gives the recommended release load on
reverse.

HTH
Randall




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