368
Overdrive on third gear - when was it discontinued on the MGBGTV8?
An enquiry from a writer compiling a buying guide to British sportscars included the comment in a draft guide to buying an MGBGTV8 the note "overdrive only on top". With the help of Peter Beadle, Victor Smith clarifies some of the myths. (Jul 07)

The MGBGTV8 was launched in August 1973 w
ith overdrive on both third and fourth gears available at the flick of the left hand stalk switch on the steering column. It is a very convenient feature which gives the model superb mid range flexibility, but using overdrive in third gear needs care as the overdrive unit can suffer damage from high torque from the V8 engine. Unlike many cars fitted with overdrive since the 1970s, the overdrive switch on the MGBGTV8 is not automatically overridden as you select a lower gear from either top or third so, unless you move the stalk switch to the "O/D off" position, overdrive will automatically cut in again shortly after you select third gear under power. The punishment the overdrive unit can suffer in that case is not good news, so most V8 enthusiasts with overdrive still available on third pay particular attention to disengaging overdrive as you go down the gears.

This problem was seen in the months following the launch as the Factory at Abingdon received many reports that MGBGTV8s were appearing at MG dealers with a damaged overdrive usually requiring a replacement unit under warranty. Peter Beadle, who was parts manager at University Motors at Epsom at the time, recalls that to overcome the problem "the gearbox plunger isolation switch 22B727 and selector 22B726 were fitted to gearboxes from gearbox A 1404 onwards due to the number of overdrive units they were having to replace under warranty. It was not done to save the gearbox as is sometimes believed." The effect of this modification was to remove the overdrive option from third gear so overdrive was then only available on top gear. Prior to that change the parts were plunger isolation switch 22B406 and selector 22B386.

Over the years many V8 enthusiasts have been puzzled over quite when overdrive on third was discontinued because it is clear that cars with chassis numbers (or Car Nos.) of up to at least GD2D1 1200 and probably slightly higher have overdrive on third (and are known to have had that option from new) whereas much earlier cars do not. Peter Beadle suggests the answer to that puzzle is that whilst the modification was made to on production cars from gearbox A 1404, many of the cars going in for overdrive warranty work had the modification made then so they emerged with overdrive on only top gear. The approach to the warranty work was that as an "engine and gearbox out takes 10 hours, then let's do the modification" and avoid a recurrence of the problem. So

as the cars that went in for overdrive warranty work were inevitably earlier cars, they are running around today with overdrive only on top. But that still leaves the question of when was the modification made in the production run at the Factory. Sadly the handwritten copy of the Factory production control records made by the late Geoff Allen in the final weeks before the MG Plant closed does not record gearbox numbers so they cannot be cross-referenced to chassis numbers.

Even if we can identify an MGBGTV8 with gearbox A 1404 or one near that number, the change point will be uncertain because engines and gearboxes were not fitted to each car on the production line so that engine, gearbox and chassis numbers align in a perfect sequence. Geoff Allen was well placed to know this as both the former V8 Historian and Archivist and someone who had worked at MG for over 27 years, much of the time in Rectifications Department. Geoff noted that most of the chassis number (known as Car Nos. with this model) change points often quoted have to be seen as flexible as changed parts were applied to production cars by both the assembly line rectifiers and by Rectifications Department, often using whatever was available. So it would be quite possible for an old part to be fitted after a quoted chassis number change point.

To illustrate this Geoff mentioned there was also a tendency for odd boxes of parts to turn up from time to time and he related the tale of one example when a box of fifty rear bumpers AHH 6261 with number plate illuminators in the overriders was discovered underneath a bench and were used after the change point at GD2D1 1248 when the new rear bumper with illuminators on the bumper BHH1525 was introduced. So quoted change points are not reliable as there was often considerable overlap in parts actually fitted on the line or during work in rectifications! When I discussed the likely chassis number change point for discontinuing overdrive on third with Geoff some years ago, he felt it was difficult to say with any certainty but it was likely to be somewhere around GD2D1 1175 or possibly later.

Well I know my V8 (Harvest Gold 1089) and Bryan Ditchman's (Bracken 1012) both have overdrive on third, and have from new, but to try and identify the change point by chassis number a little better we are running a simple survey of members on the V8BB. It will be interesting to see what we find! But at least the myth that overdrive on third was discontinued early in the production run can be laid to rest - in fact overdrive was available on both third and fourth gears on a major part (probably over 60%) of the chrome bumper MGBGTV8s.
Survey
To try and identify the change point by chassis number when the overdrive on third gear was discontinued, we are running a simple survey of members on the V8BB. It will be interesting to see what we find! But at least the myth that overdrive on third was discontinued early in the production run can be laid to rest - in fact overdrive was available on both third and fourth gears on a major part (probably over 60%) of the chrome bumper MGBGTV8s.

So could members with a Factory MGBGTV8 please post replies to three questions on the V8BB or email them to me at victorsmith((atat))v8register.net substituting @ for ((atat)) in the usual way:

What is the colour and car number of your V8? The Car No is in the form GD2D1 NNNN G where "NNNN" is a two, three or four digit number and can be found on a small plate fixed to the inside of the offside inner wing adjacent to the oil filter. Mine is Harvest Gold 1089 for example as the Car No is GD2D1 1089 G.

Did the car have overdrive on third gear originally?

Does the car have overdrive on third gear now?
If your V8 does not have overdrive on third gear, have you any records of the overdrive being the subject of warranty work? If so do you know when that work was done and where?

Please either complete the convenient online survey form or send your responses to Victor Smith or post them on the V8BB. The results of this survey are available on the V8 website. (13.7.07)