[TR] Tranny Questions

Randall TR3driver at ca.rr.com
Thu Jun 29 04:00:24 MDT 2017


> Would low tranny fluid cause second to 
> pop out or that
> is an internal gearbox issue? 

Most likely an internal issue.  But it certainly won't hurt to top it up and
try again.

>  The relay 
> looks new.  The
> solenoid looks old and I wonder if it is seized from non use. 

Not likely to be seized, IMO.  And if it was, it would probably be burned
out as well.  But you obviously need to deal with getting power to it first.

When the original relay on TS39781LO finally died, I had several
replacements (including a fairly expensive reproduction) fail within a year
of installation.  They would still look new (of course), and even pass a
continuity test; but wouldn't conduct the jolt of current required to move
the A type OD solenoid.  

The solenoid has two windings internally, a very low resistance "pull-in"
winding that is active only until the solenoid moves and a higher resistance
"holding" winding that remains active after it moves.  The pull-in winding
draws close to 20 amps.

So, you've checked that one side of the relay coil gets power when the
ignition and OD switches are on.  Next step would be to double-check that
the other side of the relay coil gets grounded when in 2nd, 3rd or 4th gear.
(It is possible to have one and not the other, so check all 3.)  If there is
12v across the coil, and 12v across the contacts; the relay is bad no matter
how new it looks.

What finally worked for me was to add a small diode to the relay output, to
help absorb the inductive kickback from the solenoid and reduce arcing at
the relay contacts.  With the diode, my cheap "Made in China" brand relay
has lasted several decades (and even got moved to my current TR3).  I used a
1N4004 diode, because that's what I had handy (Radio Shack used to sell 25
of them for a couple of bucks); but almost any small power diode should do.
The 1N4004 is rated 1 amp and 200 volts IIRC; but anything rated over
perhaps 0.5 amp and 30 volts should work.

>  Can I pull solenoid and wire 
> and bench test it
> by connecting power to wire connector?  

You can do that; but it's probably better to do it on the car.  You need a
power source that can deliver the 20 amps (my bench supply is a bit of a
brute but would pop it's breaker if I tried that).  Most if not all battery
chargers won't do, as they don't regulate the output voltage well enough.
And you have to be careful not to have the solenoid plunger out too far.

-- Randall



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