Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Overdrive for 4 speed box

A question for the Morgan owners with the 4 speed gearboxes.

Has anyone fitted a remote overdrive unit such as is offered by Overdrive Spares in Rugby (and others)?

It may be an alternative to fitting a Ford T9 5 speed box and possibly not much more expensive than having a T9 box properly rebuilt and easy to remove if originality is an issue.

It may be a very tight fit even under a modified transmission tunnel.

Totally new to me but very interesting.

Had overdrive on my Spitfire 1500 many years ago,it was marvellous worked on 3rd and 4th gear.certainly would be nice on the Morgan, but as you say don't think it would be possible to fit around the tunnel.

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Barry 78 4/4 4 Seater

I would also be interested in any findings

The problem with fitting an overdrive to a non overdrive box is that you'll need a shorter output shaft to mate with the input on the overdrive, and a corresponding outer case instead of the standard tailshaft. It would be simpler to find an overdrive box that would fit, (with an adaptor plate) or stick with a five speed conversion. The four speed plus overdrive unit will also be heavier than a five speed box.

This photo shows how bulky it makes the rear of the gearbox:

Dave,
There should be no problems getting a competent prop shaft manufacturer to make a suitable input and output shaft, I have had standard and bespoke prop shafts made before. With regards to weight,the Ford T9 5 speed box is considerably heavier than the 4 speed, so I don't think there would be a weight penalty.

The main problem as I see it and without any careful measuring is whether the OD would fit in the confined space under a modified transmission tunnel even though the overdrive unit under 7" wide.

I'm another 4/4 1600 owner who would be very interested in your research results. I've read about the 5 speed conversion and it seems feasible but it would be good to know if overdrive is an alternative.

Wouldn't it be easier to just have the rear axle ratio changed, or just go with bigger tyres or wheels?

That is not the only problem Dave. The gearbox mounting points on the overdrive box are likely to be further back compared to the original, so it is highly unlikely that the gearbox cross member will line up with them. So it means cutting and repositioning the crossmember (best done when in total rebuild mode) , or making up a fabrication to mate the new mounts with the gearbox crossmember.

We used to look out for Humber Super Snipe overdrive gearboxes for Moss Boxed +4s. This was no simple conversion and involved all the problems mentioned above. I remember the first time John Macdonald raced a Super Sports fitted with 0/D and when braking heavily into Tower (first bend at Croft) the whole unit slid forward in the car nullifying the clutch travel and the water pump hit the radiator. It moved by more than a few inches. I will try to dig out some photos to show the differences.

Regarding the OP , I would definitely go for a 5 speed box every time.

That is not the only problem Dave. The gearbox mounting points on the overdrive box are likely to be further back compared to the original, so it is highly unlikely that the gearbox cross member will line up with them. So it means cutting and repositioning the crossmember (best done when in total rebuild mode) , or making up a fabrication to mate the new mounts with the gearbox crossmember.

Yes there would need to be fabrication of a longitudinal member between the 2 existing cross members to mount the OD unit, there is also a certain amount of metal fabrication to fit the T9 5 speed box

Regarding the OP , I would definitely go for a 5 speed box every time.

The 5 speed conversion is well proven and a good conversion however I think it worth looking at other options to achieve the same result, any engineer worth his salt would do so and its always easy to copy whats been done before.