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Have had HKY on the road for a couple of seasons and gone through (I hope) most of the teething troubles. Have just got out of running in and got on the motorway. Not being a cruel man have stuck to between 55 and 60, feeling that 3500-4000 RPm is kind whereas higher would be unfair on a continuous basis. Had a chat with Edmund and one or two others and then delved into axle ratios. I understand overdrive gives great flexibility, but in my humble opinion there is more to go wrong.
I have an e-mail from Salisbury Europe telling me categorically that the TR2A/3 did not use the 3HA, Also the Jag used the 4HA. Now I believe the Morgan Plus 4 used the 3HA throughout the 50's but have yet to confirm with Salisbury.
I went to see a TR axle specialist this AM, he confirmed the Salisbury e-mail, but showed me what was as close as I could see a CWP set that was designed for the MGA. Now I may be a mug but I have agreed to pay them to confirm (by stripping an old Axle I have knocking around) that the MGA ratio will fit. Then if they confirm this I have agreed they will fit a new CWP to that axle. These CWP's are imported from Germany, are brand new and cost £195.00 Plus VAT. They expect the labour to strip and fit to be around £400 plus VAT. Pricey yes, but guranteed not to moan when in use.
So they can get 4.55:1 4.3:1 4.1:1 3.9:1 and 3.77:1
I have a hankering to go for 3.9:1. Lots of folks run Jupiters on 4.1:1
I probably won't fit it this season but lets see what you all think, this of course assumes I get that option as the MGA cwp may not fit.
Any one have a Jupiter speedo that I could buy to recalibrate?
When it comes to 2, 4, 6 cylinder cars, I have little experiance, V8 I do...
2, 3 4 speed transmissions, wheel diameters etc etc
So I assume the same principles would apply.
1st thing is to decide what the car is to be used for 90% of the time...track, type of track, road, road town, open road, hilly or flat.
And how you personally drive the car, quick/zippy or granny foot.
The starting point is where the engine performs at...is it a bit cammy, higher rpm range or bottom end
If higher rpm range a low rear end 3.77 could make it bog off the line, sluggish on hills.
If engine is built for bottom end, cruising open road/ around town the lower ratio would be ideal.
If you want to have a play, and I dont know if possible on a jupiter, drop, borrow a set of much smaller (or larger) diameter tyres/rims on the rear...feel the difference and see if it suits your style of driving AND the engine.
Dropping 2 or 3 bags of cement into the car will also give u an idea/feel of what you want/need.
Factory specs on cars, espec pre 80s from the engine to the tyre size was very much a compromise for the widest possible customer base.
When these cars are built, engine specs to rear end, designed for your personal style of driving, the enjoyment feeling the car personally matched to YOU is worth every penny spent... and done right there are pleasant suprises
Hate having to refer back to my Camaro, but it is the only real example I have.
It is used as a daily driver, tow vechile, and being american V8 meant to be very thirsty.
I put a botton end low rpm cam (designed the custom profile myself) carb headers, compression ratios etc all to match...std 3 speed auto (cant afford the 4 speed I want ($5000) and low ratio diff (3.08)
This gave me a low stable idle rpm, Dont use 1/4 throttle on a damp road at an intersection (wheel spin)..lower open road cruise...and economy better than a modern 6 cylinder car, injected, computer contolled, and low emissions.
If I want to take to the drag strip, I swap the torque converter (1200 rpm ) or a 2500 rpm stall, and run a 13.8 sec in drive under 5000 rpm...ratyher respectable for a daily shopping basket.
If I change to a 4 speed auto, lower 1st, higher top, I will drop the 13.8 , and on the open road 60 mph rpms drop from 2400 rpms to 1600 to 1800 rpms
Gear ratios, diff, tyres size, engine are all one balanced package and individual to that car and driver.
Alastair, You are thinking along the right lines as I , am many like me, consider the Javelin & Jupiter to be " under geared ". It takes me back to my early Jowetteering days when I fitted an overdrive to my original Javelin. This was an A type Laycock de Normanville and the car also was fitted with a Jupiter axle ( 4.56 : 1 ratio ). At 4,500 RPM the road spead in O/D top was 96 MPH. It had a Jupiter engine fitted and could pull this comfortably. So the power is available. Yes - that was the same Javelin that your Dad & yourselfrescued from the M6 years ago. !!! ( The overdrive NEVER gave me any problems and I was cruel with it.
Regarding different axle ratios, I recall George Mitchell,s Javelin Reg No O11 which was fitted with one of the Le Mans axles. This was 4.11 :1 ratio. This ran very well and had a high cruising speed.
While over in Australia end of last year I drove Mike Allfreys Jupiter completeing about 600 miles over different types of terrain. This has a different axle ratio fitted. If memory serves me correctly it is 3.90 :1 .
I found it very different to drive compared to a standard Jupiter especiallly in traffic and at lower speeds. I had to use the gearbox much more than normally used to with my own car. ( Especially first Gear which we all try and use as little as possible ) But when out on the open road the difference is very noticeable. Get Mike into the debate before you decide, and maybe also some of the other Aus Jupiter owners who have also modified their ratio.
Tony George , from Western Australia , as like a few UK Jupiter owners, has opted for the Overdrive route and discussions with Tony has indicated that this gives him the best of both options.
I have decided to go the Overdrive option and I am nearly ready to fit the modified unit to the car. Should be finished by March. I have chosen the LH Laycock unit giving 22% reduction. It is a tough unit which was fitted to MGB,s and some Land Rovers. My calculations show that with an engine speed of 3500 RPM the road speed would equate to 73 MPH.
Keith Andrews is perfectly correct in saying that " what do you intend to use the car for," Like myself think of all those hills in your area.
I shall refrain from polling at this early stage of the debate.
Thanks chaps keep your thoughts a coming. Am not a speed merchant if it will sit comfortably at 70 Mph all day then I'm fine with that. Yes Derbyshire is not short of hills but I haven't found a hill that can't be taken in top (Traffic and bends permitting). I have been up Holme Moss from both sides.
Mike Allfrey knows this area (it would be good to get his and as many other opinions as possible) and I can take Ashbourne up to Fenny Bently in top at 55 MPH plus, prior of course to them reducing the speed limit to 50 Mph. So locally if I have to go down to third I shan't be too dissapointed provided distance driving is more relaxed.
Having driven Javelin and Jups with overdrives in many long rallies and races and of course normal driving I would recommend fitting. I have also driven Mike Alfrey's Jup.
The beauty of an overdrive is the quick change and reduction in loading on the gearbox which, with a lower ratio diff, would be increased. That is something to consider as the Jowett box is the weak part of the car.
That said, if you intend to do any motorway driving, a lower ratio would be useful and save the engine.
At one time, I also put a Javelin diff in the Jup and this made it very useful on hill climbs. My overdrive could be removed or replaced in under an hour, so on some circuits I would run with it and others without it. The overdrive adds weight!
We are very interested in your project. £600 is probably a good investment. I would watch out for that first gear though and be very careful if you are pulling away on hills with the 3.9.
Apparently the MGA CWP has a different pinion bearing diameter and to modify the housing to accept that we are going into the stratosphere with cost. So Bad news. Good news the 3HA was also used by the Healey fraternity. The Bad news, that was a different size pinion bearing as well. The jury is still out on the pinion size used by the 50's Morgan's. They definitley used the 3HA but my concern is the pinion bearing diameter.
So for all you gambling types, bets are off.
Thanks for the input. Will now consider an overdrive unit, but it won't be for a while yet.
Why dont you converse with Mike Allfrey in Melbourne. ? His method was to fit a totally different diff , complete with its casing and weld the Jowett axle tubes to it. It certainly works.
If an overdrive is going to be the final decision, I will let you have a few details, or talk direct with Tony Mumby. Overdrive spares in Rugby hava a Jowett gearbox main shaft machined down to take a D type overdrive.
The comment from Drummond about welding the Jowett axle tubes to a different diff reminds me that I heard recently that Jowetts apparently bought-in the diff assembly, complete in the housing from Salisbury and then manufactured and fitted the axle tubes etc. themselves.
So, doing this with a different diff would just be following good Jowett tradition?
Anybody else interested, I know the JOAC had 4.1:1 done some while ago, they were around £400.00 and had a tendancy to whine if not set just so!
I could approach the people I have been talking to if there is interest, as they speak directly to the importer for, Healey, MG and Triumph. It would seem like a good place to start.
See pictures of Mike Allfrey's diff mod. on a JUp in the Gallery. I think he used a Ford diff. Sorry cannot post link as Gallery is being particularly slow tonight!*$$$TOPIC
Sorry I am so late with joining in on this topic. We have had more than a week of temperatures from 38 C through to 45.4 C, and I have been a bit lazy computer-wise. I have also been fixing a speedometer drive gearbox in my Rover P6B -- why did they have to make that so complicated?
My experience with the higher ratio axle is basically, that I like it, however, there are a few points:
1. My gearbox is a Javelin wide ratio box. That probably explains Drummond's comments.
2. I am very gentle with first gear, Australian experience with close ratio boxes is that first gear suffered. Putting in a 4.11:1 crown wheel and pinion set has put me into the less tolerant first gear situation, although the cluster gear set is now running on full length roller bearings and the layshaft is properly supported at the front -- which should help.
3. I have a great affection for second and third gears in traffic with the 4.11:1 axle ratio.
4. In hill country, I change down a fair bit earlier than I used to. Once in third, with a heap of revs on, hills are treated with disdain.
5. If I had another life, I would opt for the overdrive setup, the way Tony George went about it.
6. I would not opt for 3.90:1, it was tempting as a Nissan Bluebird centre assembly would have fitted nicely between my axle tubes. Was advised that the Nissan diff is wear prone.
The diff centre I used was from a Ford Falcon XY (1972) ute (pickup) and is very strong.
Thanks for joining in Mike, whilst I understand about the Nissan Blubird being prone to wear, I couldn't quite decide if you meant you wouldn't touch the 3.9:1 because it was prone to wear or if you felt it a step too far.
Er I'm rather ignorant but am not familiar with Tony George or his application of an O/D, clues appreciated (not having one).
Am trying to weigh up the options and looking into the overdrive situation Drummond has pointed me toward this company:-
There are it seems three options if I read Drummonds e-mails to me rightly.
1 Type D which requires the adaptor Plate supplied by the club. Upside 350 GBP ish plus adaptor at 85GBP. Downside you need to modify the propshaft and cannot fit a standard box back in place as the mainshaft needs modding as well. Vic Boddy has a slant on this that means with slight mods you could drop a standard box straight back in if you wish.
2 Type LH Drummond picked one of these up (I guess it was the right price)and is about to fit it to his Jupiter, Upside price (I don't know) down side still major mods on gearbox.
Upside could remove and keep standard Jowett fittings, then modify another manufacturers propshaft (Keith Clements has used a reliant one). Thus return the car to original and use a standard Jowett box any time I chose. Downside 795 GBP, battery boxes need moving and a lot of faff.
I am tilting in favour of option 3 particularly when you suggest if you did it all again you would have gone for O/D Mike.
Further input from any or all gratefully recieved.
I also beefed up the Midship bearing rubbers with Silentblock type vibration insulators in place of the big rubbers so as to support the weight of the OD.
This had lots of use racing where it was changed on circuit (in less than an hour) to suit conditions and on 3000 mile Marathon competitions. Only reason to take it out was weight which arguably was negated by better weight distribution to rear and faster acceleration through gears plus higher top speed. No I cannot say whether my lap times were faster or slower with it in or out. I am not that good a test driver to do every corner the same!
