[TR] Transmission Locating Dowels

Randall tr3driver at ca.rr.com
Sat Mar 22 10:08:11 MST 2008


>  but only bolts and/or 
> studs between the backing plate and bell housing. There's two 
> studs side by side at 12 o'clock.

Bob, I'm not sure I follow you here ... but the original configuration used
two "dowel bolts" that served the purpose of both dowels and bolts.  They
had precision ground shanks that located (aligned) the bellhousing to the
backplate, plus heads & nuts to clamp the bellhousing to the backplate.
This was a change from earlier engines that used plain dowels; so I believe
the clamping function was added for extra strength.

I agree with Herman that the locating function is most important; to the
point that I'm convinced that lack of the correct bolts is a relatively
common cause of clutch and gearbox problems on these cars.  When I checked,
the dowel bolts were NLA from most vendors, except one that appeared to be
selling standard bolts.  Using a standard bolt is a really bad idea, IMO,
because they are made with undersize shanks that allow the gearbox to be out
of alignment with the crankshaft, possibly enough to cause problems
including premature failure of the bearing between the input and output
shafts inside the gearbox.  Without the dowels or dowel bolts; it's
virtually impossible to get this alignment right.  (When I bought my first
Stag, it had exactly this failure, for exactly this reason I believe.)

> if so, what's the options?

Probably easiest is to purchase standard dowels (3/8" as I recall) and put
them in the holes with a little Loctite to hold them into the plate.

There was also a discussion a few years back that there should be some
aircraft specification bolts with the precision ground shanks that would
work.  The part number AN176 was mentioned, tho I'm not sure if that is
right or not.  These are called "close tolerance" bolts by the aircraft
folk, and differ from the more common "relaxed fit" standard aircraft
hardware.

Or, what I did was to buy some "drill rod" from MMC, which I cut to length
and threaded for nuts on both ends.

Randall


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