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Chicagoland MG Club: Driveline
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  Chicagoland MG Club:Driveline
Just a Simple Wrench
by Ann & Jake Snyder

That Good Old Feeling

All winter long we had been worrying about the rubber-bumpered MGBGT which was stored safely away from salt. The problem was the overdrive, which made the most unlikely of events true: “If for any reason the overdrive does not disengage,” reads the caution in the handbook, which may or may not be in your glovebox, “do not reverse the car otherwise extensive damage may result”. The disengagement of an overdrive was never before a problem of which we had really heard or experienced. The overwhelmingly common problem was that an overdrive would not engage, thereby providing hours of pleasant thought and patient endeavor until this most coveted of options was able to work its magic again. The problem with the GT was that the overdrive had taken miles and miles to disengage in November, before it was stored. What if we had had to back up before it dropped out?

It is interesting how you notice immediately when the overdrive switch is flicked to the “out” position and the overdrive is still engaged. There should always be a bit of a lurch, just as when the overdrive is switched in. Not feeling the lurch sets you on guard, and constant concern dogs you until the overdrive does drop out. Our concern was so severe that we drove the last week of November without the overdrive, and did not even attempt to use it this spring, promising ourselves that we could quickly rectify the fault. During the last technical session we attended, we had asked Mr. John H. Twist about the failure to release. We were told that the failure of the overdrive to disengage could probably be traced to the pressure relief valve sticking or the solenoid valve sticking, both of which are accessible from beneath the gearbox and without removing the unit from the car. The really priceless bits of information were that the O-rings are fractional-inch and therefore available from a good local hardware store and that the ball in the solenoid is 3/16 inch in diameter. We had previously purchased the O-rings from a vendor, but bought two more ball bearings for the grand price of fifteen cents each at a hardware store.

It was time for the annual drain and refill of the gearbox, and we drove the car until the oil was nicely warm. It is essential to get a good working height between the car and the floor for the mechanic’s comfort, and the important second safety rule must be remembered: Never get under a car that is supported on concrete blocks - invest in steel jack stands. Concrete blocks have been known to suddenly disintegrate, leaving the prostrate MGB owner in a cloud of dust and a puddle of grease (his or her own). The drain plug was removed, and the hot oil gushed into the drain pan with a loud sigh from the vent on top of the gearbox. Good sign, this sighing, meaning that we had not plugged up the breather with a bolt by mistake as we have done sometimes. The drain plug was replaced, and tightened to final torque, just to make certain that we did not fill a gearbox with a loose plug. Next came the overdrive filter cover, and we tapped it free with a plastic hammer, being careful not to bend the pickup tube which locates in a depression in the cover. Another pint of hot oil cascaded out and into the drain pan. Replacing the filter was simple, greasing it liberally and fitting it over the pickup tube. After cleaning the magnets inside the cover with paint thinner (the first safety rule is not to use gasoline or lacquer thinner to clean parts), we attached the cover with the old screws but with new #10 internal toothed lock washers.

Next we emptied the drain pan and put it under the gearbox to catch the little things that jump out. The pressure relief valve is under the hex nut, and it came out with no real problem, and the three O-rings were simple to replace. The solenoid was a little more difficult. After removed the square cover and the old gasket, the solenoid just would not come out. We were tempted to pull on the power lead, but the replacement cost of fifty dollars made this route seem rash. Eventually, the plunger dropped out and we were able to pull the solenoid down using the plunger hole and fit the new O-rings. Unfortunately, the ball bearing was on top of the plunger, and we never did find it. The ball bearing even managed to fall outside of the eighteen-inch drain pan, and we have only the certainty that the overdrive could not have engaged without that ball bearing to convince us that it was ever there. In fact, till the afternoon was over, we had lost two ball bearings in a similar fashion.

Refilling a gearbox has always been a slow process, but this time we had one of those “super turkey basters” made of aluminum with a plunger at the back and a hose at the front that cost seven or eight dollars. It sucked up half a quart of Castrol 20-50 at a time, and the seven-pint refill took only ten minutes.

Time for a test drive, just to make certain that the overdrive did not stay engaged anymore. Limited success! Not only did the overdrive not stay engaged, it did not engage at all. Wonderful! Life is good! We have achieved a warm, cozy feeling of knowing we have a problem that we have had many times before. We wonder if the third ball bearing escaped, as well.

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