Lotus Elan

Jim Clarks over/under drive

PostPost by: promotor » Thu Mar 14, 2019 12:34 pm

HAIRY wrote:I happily register an interested in an overdrive, were it to be developed to fit an Elan.

On an associated matter, three or four years ago MKF Engineering in East Sussex were reported in the motoring press to be developing a 5 speed cluster to fit within the Ford 2000e gearbox casting.

It may be that this was not a viable option, as The Daily Telegraph reported in August 2018 an illegal gun factory had been found on the MKF premises!

Should it be assumed that all Elan gearbox development work has stopped at MKF?

Does anyone have an information on other locations of the development of a 5 speed Ford 2000e gearbox?


It was a 5-speed gearbox with 5th gear as 1:1 so it wasn't an overdrive gearbox - just a close ratio box for low torque engines. Pretty much a step backwards in an Elan!
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PostPost by: denicholls2 » Thu Mar 14, 2019 1:57 pm

Slowtus wrote:Would it not be 'better' to find a 5/6 speed 'box you could fit in that small space?


It depends on whether you're looking for the next gear or a new set of ratios. I had two Mk III Spitfires with Laycock de Normanville overdrives and in my ignorant youth found them quirky. They did deliver over 40 mpg, though.

The available fives are not known for having great ratios. Overdrive, surely as used by Jim Clark, allows an ideal close-ratio set for maximum acceleration on the track and in the twisties (spacing between gears to match the torque curve) that is augmented by dropping the overall drive ratio to cruise quietly while still offering a downshift to third for passing. Provided that you don't need all of the ratios in play all of the time (and it's hard to think of a scenario where you would), it's a very nice combination that gets you (almost) a six-speed box.

Getting into overdrive is a button press and a thunk.

Lotus typically selected overall drive ratios to allow the redline in top, making for a whiney ride on interstates (particularly in Europas where those Webers are right behind your ears!) Overdrive is a wonderful solution to this problem. Even harder to fit to a transaxle though. :wink:
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PostPost by: baileyman » Thu Mar 14, 2019 3:27 pm

I keep wandering around industrial supply sites looking for something like "2 speed planetary gearbox". It appears that such things are commonly used in CNC tools to transition from rough to finish rotation speeds. The ratio change there is big. But these boxes are available in lots of sizes and specifications.

I am however surfing above my pay grade on this...

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PostPost by: Davidb » Thu Mar 14, 2019 3:44 pm

I will second the idea that finding a good five speed gearbox is the way to go!

Fitting a Laycock overdrive to an Elan could only be done with the body off the chassis. Fitting one to the back of the gearbox would entail a new mainshaft and rear housing. Fitting to the nose of the differential might be preferable. But this simply ignores the size issue!
Laycock overdrives are very reliable-I worked through the eighties in the busiest Volvo dealership in N.America and I don't recall one internal failure of an overdrive-but solenoids did occasionally fail. One thing a Laycock overdrive Will Not tolerate is operating in reverse-so a reverse switch is an absolute requirement.

A good five speed is the ZF S5 18/3 as fitted to many cars of the early seventies and should have been in the Elan Plus 2 I think. This box can be found in the Sunbeam Lotus, Maserati Twin Turbo, some Fiats and the Alfa Montreal plus others. Importantly, it was fitted to works Escorts for rallying so bellhousings are available.
There is small industry out there making close ratio, expensive gear sets for them but they are not required for road use. The version used in the Maserati is probably the most available since the Maseratis rusted away, however, that box has the worst ratios. The gears are pressed onto the laygear assembly and can be changed however. I acquired a box from an Alfa Montreal, quite cheaply. This has a 2.95:1 first gear but fifth is 0.87:1 which is not great as an overdrive (Montreal owners complain about fifth gear). I acquired the two gears used for the 0.80:1 fifth in a Lotus Sunbeam and fitted those during a major overhaul and the box was superb! Specialists who rebuild these boxes for racing throw away the 0.80:1 gears and I was given a set! Various gear shift locations are available. (I did not fit this in a Lotus)

I am pretty sure that Jim Clark's "overdrive" was a 3.55:1 diff ratio!!
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PostPost by: Slowtus » Thu Mar 14, 2019 5:10 pm

Just picked up on that Fiat point DavidB.
My Cortina, before I monstered it, came into my hands with a 1.8l Fiat Twin Cam and a 5 speed which,if memory serves felt like an overdrive when plopped into 5th gear.

Given the Cortina weighed a bit more than the Elan - though only marginally more than the Plus 2 - and had similar power, wheel size etc, this, the Fiat could be one way to go. Going from memory, the Fiat 'box was small and "looked" like it could fit into an Elan Chassis with minimal mods.

But that is going from memory so...

And I dunno if an overdrive unit really suits the character of the Elan...

Must buy me another Plus 2 so I can play with the number of gears I can stuff in there. :D
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PostPost by: h20hamelan » Thu Mar 14, 2019 8:28 pm

Yes, the Volvo unit works well. I have had 3 Volvo overdrives. Love them. They function wonderfully. And most important, for those of us striving to keep some semblance of originality. One over 400,000km. Another was always on the fritz. Not a solenoid, not the wiring, not the switch. Replaced unit, and all is well.

The ZF S5-18/3 box sounds good, and with close to the correct gearing, it also holds almost 200ft lb of torque? Probably one of the best options, one can be sourced rebuilt for £4,000
Gears : 1 = 2,3 / 2 = 1,8 / 3 = 1,36 / 4 = 1,14 / 5 = 1,0 / R = 2,82
The problem is/will be, bell housings (for a start). As only produced for the escort rally cars, there are few. Maybe you folk in the area of Europe could comment. It seems to me, either finding a bell housing from an escort. And having some built, unless somehow the mold is still in existence. Again, a production for those interested.
The Fiat 130, 131 is quite available here in N. America.

Has anyone ever fit a ZF S5-18/3 to an elan?

As to the over/under
I would hope that simple modification to the output of the overdrive, and simple modifications to the input of the differential nose cone. And splicing them together might also be an option?
Or a new casting of an adaptor.
Both would be a bit more of a tight fitting obstacle, in already tight confines. So it remains to be seen if the unit would fit.

Maybe there are other options, like the Gear Vendors. I suppose if one sticks with a manufacturer who is still in production, the reality of having support would be great.

Obvious, this is all very theoretical at this stage. It would be great if someone with a chassis could get their hands on a over drive, and try to make sense if with the nose cone removed. While keeping in mind, with the removal of the over/under output shaft. More length would be available. Further, if they had some access or live near a drive line, gear, or similar transmission shop.
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PostPost by: Davidb » Thu Mar 14, 2019 9:41 pm

h20hamelan: I had a bare chassis and two overdrive units-see photo.

The overdrive unit would need to be MUCH smaller. Here is a Triumph Spitfire gearbox with overdrive fitted: https://www.ebay.com/itm/Triumph-Spitfi ... 3116423495

The bellhousings are available for the ZF-Ford Kent engines-they still make them.
https://www.burtonpower.com/bellhousing ... -bh2a.html

As regards cost, I must be cheap but it seems to me that buying used and rebuilding yourself is the best way to go. I paid $700 for my ZF in good condition. I took it apart to check and to swap the fifth gears.

For those in the UK I can suggest a source of parts and technical help if needed.
PM me for info.

The T5 is cheap and available in N.America
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PostPost by: Davidb » Fri Mar 15, 2019 4:55 am

Looking at the Burtons catalogue tonight I would think that the Ford Type 9 gearbox is what we should be considering: A great selection of ratios is available and it has already been adapted to the Elan and Plus 2. The ZF is fifty year old technology after all-and expensive!

This issue has been covered many times on the forum--here is one discussion from ten years ago: lotus-gearbox-f37/twin-cam-bellhousing-anyone-t15954-105.html
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PostPost by: h20hamelan » Fri Mar 15, 2019 5:19 am

thanks Davidb
I had a great spirited drive on some of the local, fabulous roads in a 740 today. 3 hr of amazing fun.
The overdrive unit make these 55mph twisty roads much fun in a 740.
I can just imagine hitting the button, dropping down into a corner in an elan.
Somehow, it all just made sense to me.
Though, I suspect we will see a T5 in the elan.
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PostPost by: JonB » Fri Mar 15, 2019 8:56 am

Could an overdrive box be made to fit in the chassis? Say, a Triumph Spitfire o/d gearbox?
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PostPost by: jono » Fri Mar 15, 2019 9:16 am

Hairy/Promotor:

Since Mark Kinman was arrested for manufacturing illegal handguns MFK are no more!!

I managed to procure a close ratio gearset from him before his head was turned (or perhaps the gearboxes and Fast Ford stuff were just a 'cover') - it's nice if a little noisy as it's actually a semi helical!

It's a shame as he was a talented bloke (also responsible for the Caterham 6 speed box). If anyone could have productionised an overdrive unit for the Elan it would have been him.
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PostPost by: nmauduit » Fri Mar 15, 2019 12:00 pm

jono wrote:Hairy/Promotor:

Since Mark Kinman was arrested for manufacturing illegal handguns MFK are no more!!

I managed to procure a close ratio gearset from him before his head was turned (or perhaps the gearboxes and Fast Ford stuff were just a 'cover') - it's nice if a little noisy as it's actually a semi helical!

It's a shame as he was a talented bloke (also responsible for the Caterham 6 speed box). If anyone could have productionised an overdrive unit for the Elan it would have been him.


I was not so lucky and he (...) still has some parts I had sent him for machining a short block (work paid in advance - my bad to be trusty I guess) ... if anyone has an idea about how to recover at least my parts, I would highly appreciate. I've already written to the Police in Hailsham several months ago, in attempt to find out how to proceed or if a liquidator had been nominated, without reply so far...
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PostPost by: Davidb » Fri Mar 15, 2019 3:33 pm

JonB wrote:Could an overdrive box be made to fit in the chassis? Say, a Triumph Spitfire o/d gearbox?


JonB: I posted this link earlier to an advt for such a box-it shows how big the overdrive is--it is the same unit as fitted to Volvo 740s --Laycock J Type. https://www.ebay.ca/itm/Triumph-Spitfir ... 3116423495
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PostPost by: h20hamelan » Fri Mar 15, 2019 4:18 pm

I asked Dave at OdSpares

Some other questions.

1. Have you fitted an over drive to an elan?

2. For weight distribution, the rear would be better. If we could find 100 or so people who would buy one. Quaife and some others have said they would build it. There needs to be some research and development if it can be fitted to the rear of the old English differential. I think the Cortina, Escort, Capri people would also like the rear mounted over drive.

Cheers

"Hi we do not do any fitting of the units we have had people mount them solidly to the diff flange to flange and bracketed back so that everything moves together
regards Dave

Overdrive Spares"

I will continue to gather information. Hope to make progress!
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PostPost by: Davidb » Fri Mar 15, 2019 5:24 pm

20hamelan: So you are talking about designing, building, testing and marketing a new, small overdrive unit from scratch :shock:
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