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RE: [TR] TR4a transmystery

To: "Jim Wallace" <grandfatherjim@gmail.com>,
Subject: RE: [TR] TR4a transmystery
From: "Randall" <tr3driver@comcast.net>
Date: Fri, 8 Sep 2006 09:07:01 -0700
> a) In first, second, and third gears, the input shaft would only turn a few
> degrees and then come to a hard stop
> b) In fourth gear, the output shaft turns at the same rate as the input
> shaft
> c) In neutral, the output shaft turns at the same rate as the input shaft

Somehow, the output shaft is locked to the input shaft.  Can you confirm
visually that 4th gear is not engaged ?  If not 4th gear, then my next guess
would be that there is something wrong with the bearing between the two shafts.
Possibly one of the shafts is not properly seated into it's other bearing. or
the bearing not properly located in the case; forcing the shafts too close
together and locking the center bearing.

> OK, so then I disassembled all but the front cluster on the mainshaft,
> because I seriously don't want to deal with that circlip ever again. Then I
> saw where a thrust washer between second gear and its synchro cup seems to
> be preventing the two cone-surfaces from making contact - yet it is
> definitely shown that way in Haynes....coudl this be right?

No, not right.  That thrust washer should be much smaller than the synchro cup,
the cup doesn't touch the washer at all.  The shift hub should be able to press
the synchro cup into firm contact with the cone on the gear, well before
contacting the washer.  The thrust washer fits well down inside 2nd gear.  Kinda
sounds like you either have it assembled wrong, or your "top hat bushing" (aka
2nd gear bushing) is broken.

Note that there were several different revisions of all the 4-synchro parts over
the years (through TR6 and Stag).  Some of them will interchange, but many more
just look similar and won't interchange.  Is there any chance you have
mis-matched parts ?  You wouldn't be the first !  I've even heard stories of
professional rebuilders trying to use mismatched parts.

> Isn't the point
> of the cone shaped surfaces to make contact?

Yes.  When you start to shift into a gear, the first thing that happens is the
center of the shift hub forces the synchro cup into contact with the cone.  Then
the force from the shift fork overcomes the springs in the hub, and the outer
ring of the hub slides over the dog teeth on the cup & gear to complete the
shift.

Randall


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