[TR] TR3A Overdrive Switches

[Ibsen Dow]

Thanks Randall for the insight...I suspect that there may be dirt on the ball
seat or ball not seating properly. That seems like the next step, since I have
already re-aligned the solenoid plunger assy and it seems to be an easy way of
checking.

Regards,
Ibsen
  ----- Original Message -----
  From: Randall
  To: triumphs at autox.team.net
  Sent: Friday, July 25, 2008 10:41 AM
  Subject: Re: [TR] TR3A Overdrive Switches


  > What should the operating pressure be?

  It varies with which OD you have, and which engine it's behind.
  Unfortunately I can't lay my hands on the factory spec for a TR3A offhand,
  but several sources give it as 350-370 psi so that's probably correct.  The
  early TR2 unit (OD only on 3-4) took more pressure (420-445) as it had
  smaller operating pistons, and the TR6 unit took more because of the
  increased torque it had to handle (450) and its smaller accumulator.

  > I understand that if you attached a
  > gauge to the overdrive unit, you can measure the pressure.

  True, but it takes a special adapter.  It's also best to use a liquid
filled
  gauge, as the pressure pulsations caused by the pump will eventually damage
  a standard gauge.  There's a fellow that sells the gauge and adapter on
eBay
  occasionally, but I don't recall his name offhand.  Be sure you get the
  A-type version, as the J-type is different.

  > If the pressure is down, is it the sealing o ring where the gauge goes
  > that may be leaking off some pressure?

  I'm not sure what O-ring you are talking about here, Ibsen.  There is a
flat
  fiber washer where the gauge attaches (to an A-type), but if that were
  leaking, you would see the oil running out from it.

  The most common leaks that cause low pressure in 2nd gear, IMO, are the
pump
  non-return valve; and the piston rings on the accumulator and operating
  pistons (which were metal on the original TR3A units).  But there are other
  possibilities, like the ball in the operating valve not seating into the
  casting with the unit disengaged.

  There was an article written by "Mr. Finespanner" (Del Border) about the
  non-return valve; which you might still be able to find on the web.
However
  it seems to be missing from its original repository on the Team.Net server.
  If you can't find it, let me know and I'll email you a copy.

  Randall
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