A Remedy for Slow Overdrive Engagement (A type)

by Graham Stretch

A while ago I replied to a mail talking about slow A type O/D engagement, stating that mine took forever to engage. I timed it Friday at 3 miles (genuine ones) at 60MPH from flicking the switch to full engagement and about 2 miles before anything happened at all.

I then came home and followed the workshop manual fix which reads: "Access to the operating valve plug is gained by the removal of the console tray and the rubber grommet forward of the gear lever. Operate the solenoid several times to release hydraulic pressure. Unscrew the valve plug and with the aid of a small magnet, remove the spring plunger and ball. Taking care to avoid damaging the valve seating, remove the valve by inserting a piece of stiff wire down its centre and drawing it up. Ensure that the small hole which breaks through from the centre drilling at the bottom of the valve is not blocked. this hole exhausts oil from the operating cylinders when the valve is moved to its direct drive position.

If necessary the ball can be re-seated as follows: Place the ball on a block of wood, position the seat of the operating valve on the ball and give the valve a sharp gentle tap. Clean the valve seat in the casing, place the ball on its seat and gently tap the ball with a copper drift. avoid tapping the ball too hard otherwise the mouth of the hole will be closed slightly and prevent reassembly of the valve.

Seems easy enough right? Wrong, the plug is about six inches away from the hole and on such an angle that the hole could have been 2" to the right to make it visible. Take out the gearstick grommet plate and you have somewhere to look and shine the torch while you work through the other hole. Take the bits out with a magnet works, how do you get them back? Precision bombing! You hold them in long nose pliers and let go when your sixth sense tells you.

Re-seating the valve rod, use several very light blows from the hammer to re-form the shape then spin it with your fingers to generate a slight polishing of the seat, leaves a slight "witness ring" on the seat. to re-seat the ball down the hole you will need something like 3/8" rod with about a 15 degree bend in it to get it in the hole in the box and out the hole in the tunnel so you can hit it. The result as ever is a job with about an hour time budget that takes three hours, the effect is that an O/D that took three miles now only takes about 30 feet or a couple of seconds, verdict, well worth the effort.

The above was for a 2000 2500 saloon but I dare say the job is just as awkward on a TR or any other car fitted with an A type O/D.


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