AC Aceca Bristol - fitting an ex Derek Hughes overdrive unit

[Glen Smytheman]

Hi all from NZ - last question for the day....

I am looking at the possibility of fitting a Derek Hughes designed overdrive unit to my Aceca Bristol gearbox.  I understand that there were some 110 of these units that were made.  I have factory overdrive in my Ace and its great for long distance driving.  I just wanted to know if anyone else has fitted a Derek Hughes overdrive unit to an Ace/Aceca and how they have found it works compared to standard/factory overdrive and also how easy it was to fit. 

Many thanks from down under for anyone that can share their experience.

Glen Smytheman

[B.P.Bird]

Glen,
Sounds interesting, having never heard of the Derek Hughes overdrive unit I am about as useful as the proverbial chocolate ashtray, however do tell us more: Who, where, what ?
The slippery Aceca would possibly benefit from an O/D unit more than an Ace, have to consider the percentage effect on RPM though, as the Bristol sports engine will not be so happy pulling a high gear ratio. Remembering a misspent youth and my Aceca Bristol the 100D2 seemed to be delighted to spend all day at 5,000 RPM and more, so any thought of economy or restful cruising never entered my empty head....
Barrie
P.S. Didn't have a 70 MPH limit or Points on Licences then

[Glen Smytheman]

Hi Barrie,

The links below will give some background.  This kit has been fitted to many Bristol 6 cylinder cars and means you can keep the original gearbox and don't need to alter gearbox mounts etc to fit an overdrive.  I have two spare overdrive gearboxes that I could fit but this conversion may be an easier way to get an overdrive fitted.  I also have access to a diff fitted with crown wheel and pinion that is the correct match for an overdrive in an Aceca, so it should be quite a nice machine.  My ace is super with overdrive gearbox for long distance touring - drops revs by about 500.

https://bristoloda.org/category/people/

Derek wrote many articles for Bristol owners and sourced many difficult to find parts some of which he had made at his own expense. He is best known for his overdrive conversion for early Bristol cars. He was the first to do it spending long periods working out the shape of the casting so the conversion could be fitted with hardly any alteration to the car. He had to organise patterns, castings and machining then doing any extra work himself. He did of course make all the electrical bits himself at home. He made over 110 conversions.

Links to cars for sale are as follows that have been fitted with the overdrive conversion.
https://www.carandclassic.com/car/C1723434
https://www.historics.co.uk/auction/lot/lot-217---1954-bristol-403/?lot=9070&sd=1