Overdrive In General

Dolomite overdrive

In general all Laycock overdrive units of a type (ie D and J type) are the same - you could pull one out of a Transit van, Volvo, Reliant Scimitar etc and if could be used on a Triumph with the right adapter plates. There are some subtle ratio differences but none that you'd really notice. Adapter plates are available to fit a J type to Herald 3 and single rail boxes. If you see a Laycock overdrive on a box, any box, it's a good thing to save.
Although the overdrive is a separate unit it needs to mate, via an adapter plate, to a box intended for overdrive. You can't just plonk an overdrive onto a non-overdrive box, the output shaft is different
A Dolly 1300 single rail gearbox with a J type will go into a Herald 13/60 - you need a mounting plate and rubber mount. A special clutch plate (the splines are different) but it's a Marina 1.3 plate I think. The prop needs to be a special length too, a standard one won't do. The box should come with a lever and overdrive switch on top - you need a little wiring but there's no relay involved in a J Type so it's fairly straight forward to do. If you want to make it look like a factory Vitesse fit then you'll need a two stalk cowl for the column and a switch - both are remade but at a price. the switch is about £40, can't remember what the cowl costs. It all goes in nicely and there's loads of room fo rthe box and overdrive. You can change a solenoid without jacking up anything. You can even change the tail seal and housing with the box in the car - been there and done all that.
Overdrive on a Herald is great, next to electronic ignition it was the single most impressive modification I did. It's not the same driving experience as in a GT6 or Vitesse with overdrive, you can't really power through the change into overdrive but it's excellent for relaxed cruising. It makes the Herald happy at motorway speeds and makes B road driving in third and overdrive a nice experience again.
If you can get yourself a list of the parts you need and acquire them from autojumbles, eBay etc and do it for less than the £600 odd for a complete kit then it makes it even better.

By : Jason Chinn, 16-Sep-2004, 03:00pm on TSSC

See also: Overdrive Conversion Kit, Canley Classics

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