Overdrive

[Davesunderland]

Hello all, ive just bought Mr Spacey's 1953 Jupiter Reg No 705 YUE, and a wonderful thing it is. Since collecting the car on Wednesday afternoon ive done around 150 fun miles only to be curtailed by the wet weather. Any way I was wondering about overdrive kits, and have had a rumage around on the forum and was wondering if anyone could shed some light on whether there are kits available and whether its a big job?
Also, are there any club meets in the North coming up?
Cheers

[Drummond Black]

Dave, An overdrive transforms the Jupiter. It gives it an increased cruising speed or cuts engine speed and the car runs quieter. I fitted one to my Jupiter six years ago.
Less engine wear, improved fuel consumption and seven forward gears !!!!!!!!

I chose an LH model which was fitted to MGB's. It is a tough unit and can take a lot of punishment. I made all the parts to allow the unit to fit onto the Jupiter Gearbox.
Unless you have access to good machining facilities then better to go the route of fitting a D type Laycock Unit. You do have to rebuild the gearbox with a modified main shaft. JOAC can supply an adaptor plate which then bolts on to the back of the Gearbox casting. You do require to either lengthen the front prop shaft by about 2 inches or fit a 2 Inch spacer on the Overdrive output shaft. Suggest you speak with Dave Twiggers at Overdrive Spares in Rugby who can give you lots of advice and most of the parts. I have masses of info regarding fitting to the Jupiter. Drop me a PM if you wish any advice.

Drummond
Scottish Section

[Keith Clements]

Dave,
My preferred fitting is and was not to modify gearbox as that means you are tied to a gearbox. Instead I replaced the rear prop shaft with the overdrive and shorter prop. I can thus change back to standard in an hour as I did at some race circuits depending on gearing requirements and the extra weight of the OD. However this did mean some cutting of the battery box and floor support as well as increasing the angle through which the universal joints travel and restraining the back axle from going into full droop.
This setup proved satisfactory on many gruelling rallies. Now that smaller units are available from OD spares my next attempt would be to replace the front propshaft rather than the rear as it is mechanically a preferred solution.

Electrically I have the unit connected by some relays and switches on the reverse gear and the clutch and a toggle switch. In this way use in reverse is prohibited and the unit is taking out of OD when the clutch is depressed which allows more sensible and quicker downshift. The toggle swich flips it into overdrive on command but immediately primes the clutch switch to take it out of overdrive. This priming can be overridden and the unit kept in OD by leaving the toggle switch in the ON position. Very occasionally such a change down say from OD top to OD third is better, rather than OD top to either top (with no gear change just clutch depression) or third (with gear change). The change down with just the clutch tickle is fast and there is no loss of power (so useful on hill climbs) and change up back to top with OD can be made at full power.

My unit also works in first and second although I would never dare to use first or OD first, OD second is really good, giving a full power change up when you really need it, even though it does strain the transmission somewhat.

[Frank Woolley]

Dave,
I fitted a Laycock overdrive behind the gearbox replacing the Front Propeller Shaft. This enabled me to remove the overdrive, as like Keith, I used the car for various competition events.
A short stubby prop shaft is needed to go between the gearbox and the overdrive. The flooring has to be cut to allow clearance for the top of the overdrive. The overdrive is held in position by rubber mounts and brackets that clamp to the chassis tubes. I have a layout drawing if you are interested. This was fitted in the early 90's and is still working today.
The operation of the overdrive was simply a push button that operated the overdrive and a relay to hold it memorized with a limit switch connected to the clutch pedal to break the circuit when you used the clutch.
Personally, I think the system of attaching the overdrive to the gearbox is the best and most proven method and parts are available.

Frank Woolley

[Frank Woolley]

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I attach drawing assembly layout and photograph of installation of overdrive unit.

[Davesunderland]

Thanks for this.

i think I'll favour the Laycock unit and bits and pieces supplied by overdrive spares, with a view to fitting it over winter, as i dont see myself using the Jupiter for any competing.

After doing a few more miles in the car, it will be nice to have the extra overdrive ratio's for "spirited" driving as well as a longer top gear.

Thanks again, and I'll let you know how I get on.

Cheers

[Edmund Nankivell]

Dave

JOAC do an adapter plate for an overdrive for the Jupiter. Contact Tony Mumby for one should you want one.
I have an overdrive on one of my Jupiters and would never be with out one. It is a Laycock D-type.
A company called OD Spares overhauls them
Edmund Nankivell

[Greg Jackson]

Hi, I would like a overdrive fitted to my Jupiter , ANY OFFERS TO FIT ONE , Greg Jackson

[Keith Clements]

Greg, depends how soon you want it.

My life looks very busy until next June and no doubt something will come along by then to fill 2014 as well. But If you get all the parts together and get your car down to the Jowett Health and Beauty Shop we can try and arrange a fitting session.

[Smithgrove]

Hi
I'm a fairly new Jupiter owner (December 2012) based in Bradford and am really enjoying getting to grip with the intricacies of the Jowett machinery. The car is great fun to drive, particularly now I've sorted out the brakes and as I hear that an overdrive truly adds to the driving experience, I'm thinking about installing one as my winter project. Are there any restrictions to the type of Laycock overdrive to be fitted. I've seen various types around and wondered if a J type will be suitable. Also, how available and where would I source the modified gearbox mainshaft?

Regards, Mike S. (Smithgrove)

[Drummond Black]

Dave Twiggers at Overdrive Spares in Rugby will sort you out with the majority of the parts.

Drummond ( Scotland )

[Chris Spencer]

Hi Mike - welcome to Jowett talk, nice to hear you are enjoying Jowett ownership - link pasted below for overdrive spares at Rugby - just double click on it and it will take you to their website - Regards Chris

http://www.odspares.com/