Alternate 5 speed gearbox

[dougie]

At the risk of being thrashed with a limp lettuce leaf.
Has any one fitted or considered a modern 5 speed gearbox to their Jupiter?
I am wanting to do a lot more competition and just don't think the Jowett box is going to be up to it.
I am covering my head awaiting your response.

[Forumadmin]

Yes Alan Fishburn has. I think Chris knows some details.

[Chris Spencer]

Alan described the conversion to me but I have yet to attempt it - I do have it in mind for when I build the 'Spenbitza Jupiter' - the gearbox to use is the Ford Type 9 which will give you gearing quite close to the original Jupiter box but of course with the all important addition of a fifth gear. The conversion requires a 25mm alloy spacer plate to be made up to bolt between the Jupiter bellhousing and the new gearbox - the clutch plate requires making up from the type 9 centre spline mated to the plate and the outer friction ring of the Jupiter - sounds complex but in reality is straight forward - just drill the rivets out of the original plate that secures the centre and re-rivet the Ford centre. Modifications to the engine mountings on the front of the chassis rails require rebating by 25mm has the Ford box sits slightly higher than the original Jowett box (In doing so you are lowering the engine / centre of gravity on the car - so its all good - just watch the sump clearence). The gearbox mounting will require modification to support the Ford box along with the propshaft - with the Ford box being longer in the tailshaft plus a suitable output flange on the UJ will have to be sought in order to match the Ford one on the new box. The new box is floor change - I have no doubt that should you have time to burn and acres of patience that you could build a suitable column change adaption but this would be far easier said than done.

The type 9 Ford box was fitted to European models of the Ford Sierra, last series of the Ford Granada & the Ford Scorpio - I am advised that the Scorpio box is of a better build quality - these are readily available if you know where to look - unsure what the non European equivalent models of the above utilised the same drive train but they must be out there. The only other alternatives are to fit an independent overdrive unit but then you are adding weight - I understand that the Ford box is lighter than the original Jupiter gearbox. So not a straight forward fit and certainly not for the purists but a worthwhile conversion if you are looking at stretching the legs of a Jupiter.

N.B. Alans Fishburn's prototype Jupiter fitted with this conversion has been placed for sale with a UK auction house - I will list it in the February Jowetts for sale in the car & parts section of Jowett talk over the next 24 hours.

[dougie]

Thankyou Chris.
I think this is what Brian Holmes has done to his car.

[Andrew Henshall]

I can confirm that Brian H has a Ford Sierra 5-speed T9 gearbox in his Jupiter.

These T9 gearboxes are a bit rare in Australia because the Sierra has never been sold here. However, Eurospeed Motorsport in Brisbane sells secondhand T9 units with a 6 mth guarantee for A$880 + GST. They have various options for rebuilt units & conversions priced accordingly. I have no connection with this company.

Cheers,

Andrew Henshall
JCCA Victorian State Representative

[dougie]

Thanks Andrew.
I'm having a look around.
I have a spare engine with bell housing to work from.

[Greg Jackson]

Jupiters racing now with a Jowett gear box and 130 bhp with no problems

[AmilcarJohn]

Agree -it seems strange to me that people consider this. Jupiters still seem to be treated as 'old bangers' to be fixed up with whatever comes to hand. I don't see Bugatti owners fitting Sierra gearboxes, despite constant competition usage and several hundred BHP...

Please do modify your car -that's a big part of the fun -but retain the major components as designed.

Just my personal opinion!

[Forumadmin]

What is required is a service to rebuild Jowett boxes to the desired specification. I am frequently asked to recommend someone to rebuild engines and boxes. They usually blink when I ask how much they want to pay. I do not know how much it would cost to rebuild a Jowett box to take 130bhp, but I suspect a few thousand pounds, as you would probably need to design and make many of the components as well as modify more modern components. This is what every (competitive) racing classic car has to do. Very little of the original metal is left.
You must be prepared for any component pushed outside its sedentary limits to break and, via trial and error, get a reliable machine.

It is far easier to take a component that was originally designed for that power, and has had many years of development with service in tens of thousands of vehicles.

All that said, I am a great believer in getting the most out of the Jowett engineering and restoring it to at least its original specification after 70 years of wear. But then if I want to drive up the motorway at the legal speed limit all day I would not expect the 1950 engineering to do that. But it would be quite happy 10mph slower, as our drive across the US showed.

[AmilcarJohn]

I would say that if you have the resources and skills to extract 130BHP from a Jowett engine, then making the gearbox suit will be well within your capabilities.

Let's not forget that it's nice to drive funny old cars with all their failings- if we follow the 'much easier to...' argument we'd all be driving Nissan Micras.

[Forumadmin]

That is very true, and then you need to upgrade the brakes, wheels, tyres, ......it took me 30 years to get my Jup to where it is so that it can cruise along the German autobahns all day, climb the steepest hills, wind along the country roads and suffer snow, dust storms in the desert and torrential rain. What a great car! Josephine has non Jowett pistons and a period Laycock overdrive, but otherwise it is just Jowett.

[Andrew Henshall]

The Jowett gearbox in the Wylie Javelin special supercharged GP car has been reliable for many years and of course transmits far greater torque than the original Jowett flat four could develop. The trick is a complete set of close ratio straight cut gears manufactured by John Needham! Needhams are still in business in Melbourne (Australia) operating as "Old Gar Gearboxes Pty Ltd with John & son Ben doing the work.

Unfortunately, because Needham went as big as possible on PCD for the gears, he created an issue with the selectors, and this meant that it is possible to select reverse when changing down from second into first in the heat of the moment during competition coming into a hairpin corner. I guess it's even also possible when changing from fourth into third although far less likely. This is not an issue when doing sprint events as there are no down shifts during the run and you can take extreme care downshifting after the finishing line, but for a circuit race & hillclimbs, a solution had to be developed. The temporary solution was a blocking collar under the quadrant that blocks out reverse entirely. This worked fine during a race except if you had a spin and needed reverse, and I'm told it can be a pain in the pits.

[Chris Spencer]

Jupiters racing now with a Jowett gear box and 130 bhp with no problems

Please see next quote / comment

I would say that if you have the resources and skills to extract 130BHP from a Jowett engine, then making the gearbox suit will be well within your capabilities.

Well first you have to build an engine that will give you the said 130BHP and then engineer the gearbox to take the power output from the engine and transmit to the remaining drivetrain without the gearbox falling apart - if you left the gearbox original and tried to transmit 130BHP through a standard Jowett gearbox it would not last very long at all !!!
So regardless of what knowledge you hold and what equipment you have available alongside your skills the fact is that you will require deep pockets to build a Jowett engine & gearbox to a reliable 130BHP specification

I don't see Bugatti owners fitting Sierra gearboxes, despite constant competition usage and several hundred BHP...

Agreed - but how can you compare a Bugatti owner who has spent several hundred thousand on a car and is highly likely to have access to far greater expendable income than that of a Jowett owner who has spent £20,000 - £30,000 on a Jupiter (A Bugatti engine rebuild alone is well in excess of what a good Jupiter would cost you)

The comparisons are flawed - I am all for a original , well presented car. Equally I have several boxes of bits that have been collected from about 10 + cars - at some stage I build this up to resemble a Jupiter - it in my book will be a special and it will retain original Jowett engineering where I can, and where I can improve it - I will - I don't have deep pockets - I will not be going trophy hunting with it - but it will be built to drive and have some fun with - Each to their own

[dougie]

I am keeping low and covering my head with my hands.

[Keith Clements]

Promise I will not raise the subject in June. .....in front of cranky.....