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Re: Overdrive on 77 MGB

To: Tom McLaughlin <tomm@ti.com>
Subject: Re: Overdrive on 77 MGB
From: Robert Allen <boballen@sky.net>
Date: Thu, 02 Oct 1997 20:03:46 +0100
Tom McLaughlin wrote:
> 
> Anyone get a chance to look at this in the Haynes manual.  Don't mean to be
> a pest, but I don't want to put this back together unless the solenoid is
> correct.  Any help would be appreciated.....

Okay, okay, quit being a pest. I went out to the garage and personally
removed my solenoid (last week, resting comfortably in a baggy) just to
deal with your problems.

> I pulled the solenoid and if I apply 12v and ground the body, it will suck
> the plunger in.  It takes some force to get the plunger to come back out
> (slap the thing against my hand).  Should this be difficult to get out or
> should it slide out easily once power is not applied? (Is there a residual
> magnetic field that holds it in?)  It seems to be in good shape.

The plunger on mine will flop back and forth -- there is no resistance
in any position. When power is applied it the plunger moves out, not in.

> Now for the "strange" question.  The solenoid looks different from the one
> in the Haynes manual.  There looks to be an added part on the top of the
> solenoid housing.  I think I'll try to draw it...
> 
>         _
>       _|_|_ <-------This is not on my solenoid, but it is on the picture.
>      |     |
>    __|_____|__
>    |          |
>    |          |
>    |          |
>    |          |
>    |          |
>    |__________|||----------
> 
> Hope that looks OK when I send it.

REF: '69CGT w/LH overdrive -- same as late model 'B's.

>From the Haynes MGB 62 thru 80 (c)'89 manual, page 135, figure 19.1(b).

The little talliwacker (tech term) hanging down off the solenoid is not
on mine from the '69CGT. Except for the talliwacker, figure 19.1(c) is
accurate.

Referencing fig 19.1(c), the parts are (L to R) electrical solenoid,
operating valve plunger, valve ball, and operating valve.

The valve plunger has a single O-ring at the tip although it is grooved
at the base for a second O-ring. The base of the plunger (the thick part
that goes in the solenoid) is grooved along one side presumably to
prevent a suction bind.

The operating valve has a large O-ring around the base and a second,
smaller O-ring at the end of a short, hollow shaft. The end of the shaft
has a hole. The other side of the hole is a seating surface for the
ball. There is a relief hole on the side of the valve to bleed off oil
pressure when the solenoid is not engaged.

The great talliwacker controversey is that a small hat at the end of the
valve shaft is evident in the Hanyes photo (and my 'C' manual) but is
not present in my valve -- that's where the hole is.

With the electrical solenoid sitting wire-down on the bench, the
operating plunger is a simple slid fit into the solenoid. It will easily
seat to the bottom of the solenoid by gravity. When the solenoid is
energised, the operating pluger moves no more than 1/4 of an inch up out
of the solenoid and stops.

While the solenoid is energized, the plunger will not move. It reamins,
ah, erect about 1/4 inch off the bottom. Removing the voltage and the
operating plunger will again fall to the bottom of the solenoid.

When your solenoid is energised and your plunger is fully erect, it may
not come quite as high as mine. That's just a curse I have to live
with...

And thats how mine works.
-- 
Bob Allen, Kansas City, '69CGT, '75TR6, '61Elva(?)
"The last manufacturer to service the masochistic needs of sports car
owners was BMC, which persisted in building the Stone Age MGA until it
became some sort of four-wheeled fossil." -- Car & Driver, May 1966

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