Lotus Elan

DETAILED REPORT Five Speed ISUZU

PostPost by: Kiwi elan +2 » Sun Jan 17, 2010 4:09 am

Five Speed ISUZU Gearbox into an Elan.

The ends did justify the means…

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This is a reasonably comprehensive report on my experience of putting the Isuzu Five Speed Gearbox into my Elan because I found first hand information to assist me difficult to come by. There were many people who knew people who heard of something and someone saw something once that might have been but … well I gave up looking and asking for help and rightly or wrongly just did it my way.

The box I used came from what in New Zealand is called a Holden Gemini SLX 1984. I live in Auckland, New Zealand so the pool of possibilities is a little smaller than some other countries.

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I’m sure there are many names in many countries but the gearbox itself looked like this before I attacked it. Quite a sweet looking unit and so easy to visualise this suspended in the fork of an Elan chassis.

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There are several variations that I have seen including the one below with an extended gear shift quadrant that reportedly came from an Isuzu Piazza 2.0 twin cam. Although the box and gears may be suitable the gearshift on this unit is obviously an issue.

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There appears to be many generations of the box with a huge range of subtly differing ratios as well as a Diesel and a Petrol version. The Photo#3 shows the starter motor bulge in the bell housing in a position of about two o’clock when viewed from the tail whereas Photo#4 it is on the other side. I have seen a Diesel origin Gearbox which had the fuel pump on the engine using the 2 o’clock spot and therefore requiring the starter to be repositioned to the Ten o’clock location. Other different variations I have spotted appear to have a Steel Sandwich plate in the centre of the gearbox (as seen in Photo #4) in the place of the Aluminium Sandwich Plate that is in the generation of box that I used.

The correspondence I had read from as many places as I could find it covers people making up an adapter plate to mate the front of the integrated Isuzu Bell to the rear of the Ford / Lotus Block. I didn’t like this option and did it another way for several reasons. I had recently gone to great effort to make my heater work significantly better and I was reluctant to affect the Heater Hose area with the Bell of the Isuzu Box which had its starter bulge exactly in line with my heater hoses. If I were to take a bite out of the Bell to accommodate the Heater Hoses and another bite to accommodate my Starter Motor where I needed it to be I would have weakened the bell significantly structurally and visually. The adapter plate option I had read about involved cars used in Australia for racing so I presume a heater as you sprint down the back straight and into the hairpin is not a high priority. I guess the Diesel version that has its starter bulge in the ten o’clock position could suit better in the best interests of warm feet in the winter. Another reason I went in a different direction was that to cut off the Isuzu Bell meant I could retain the Lotus clutch and Slave Cylinder etc and thereby leave the Motor and Clutch 99% unchanged. In fact the only differences are that I have a 17mm inside diameter spigot bush slipped into the Flywheel instead of the usual and the clutch plate spline has been changed.

This is my Gear Box after I altered the Gear Stick in length, thickness and angle but before I cut off the bell.

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And here is a shot showing the section removed and what fell out of the inside.

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This is a beautiful design in the way that all the gears are mounted on the Sandwich Plate and therefore did not require to be individually removed or separated in any way. While the gearbox was split I took the opportunity to replace the input and output bearings and seals.

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The cut face was Milled to exactly the same plain as the surface the bearing retainer mounted to with the exception of the two protruding mounts that Isuzu use for the Clutch pivot pin mounting positions. I reshaped the outer area of these two mounting points to 20mm diameter and 10mm proud and used them to assist in locating and mounting the Ford Bell Housing. Before any math wizard points out that I left the two protrusions exactly the same height as the plate is thick and therefore it couldn’t possible tighten down correctly I will point out that there is a paper gasket around the bearing that provides the clearance.

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This is the Isuzu Input Bearing Retainer and Input Shaft / Clutch bearing support as seen in place in Photo #6.

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The reverse side of the Isuzu Input Bearing Retainer and Input Shaft / Clutch bearing support.


And now I have come to the end of the maximum allowable attachments so I will attempt to add part 2 in the next section. Bare with me while I negotiate the system.
Last edited by Kiwi elan +2 on Sun Jan 17, 2010 10:47 am, edited 6 times in total.
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PostPost by: Kiwi elan +2 » Sun Jan 17, 2010 4:31 am

Five Speed ISUZU Gearbox into an Elan. PART 2

Now comes the tricky bit. I created a CAD drawing of an adapter plate that would go between the Cut face of the Isuzu G/Box and the back face of the Ford Bell Housing that would pick up the important parts of each and the drawing looked like this.

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For the Computing illiterate CAD stands for “Computer Added Design” and in this case it is a drawing that can be formed into a three dimensional model. The file (in this case 2.5MB in size) can be saved onto a compact disc or memory stick and loaded into a computer controlled Lath or Mill and zip zap when the pieces have stopped flying you have a 3D shape that hopefully looks like what you were planning. I took my memory stick and a lump of Ali along to the friendly neighbourhood machine shop and had it cut out of a 35mm by 220mm x 250mm block of grade 7075 Aluminium. This grade is reportedly stronger and machines better than some of the other grades. The dominant flat area is 10mm thick. When cut out I added the Clutch support snout from a length of stainless steel tube and it looked like this.

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This adapter plate could then be sat on the bell housing to drill the extra holes required to mount it. Two holes were already available but the other six just required drilling in the locations indicated by the plate. The bolts are all through bolts being that they all pass though the Bell and the Plate and screw directly into factory created pre-existing pre-threaded holes in the Gearbox. Any pre-existing gaskets were still required but no more and no less.

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If you bolted it all together you end up with one of these.

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As you can see there are eight bolts holding the Bell to the Box as well as the horns from the original Isuzu Clutch fork pivot points and the Aluminium plate contour that protrudes though the Ford Bell to be flush on the Clutch side which makes for a very tidy, very strong and perfectly aligned package. The two lower pre-existing bell housing mounting holes as you can see are not used. On the Gearbox side the Aluminium plate locates on the input bearing and contours to the other shapes of the Isuzu box to make the three become very much one unit without the need for welding which has many problems due to heat, distortion and stress points. The input shaft is completely unaltered; it’s the correct length only requiring the 17mm inside diameter spigot bush slipped up the fly wheel. The Isuzu input spline is a relatively common 24 tooth but not the same as the Lotus however this is easily solved by just getting your Clutch Plate of choice fitted with the Isuzu centre spline by your Clutch Shop and slip it back under your Borg & Beck. Presto, the pressure plate and clutch compound remains what you have grown to love and admire.

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My car is intended to be a daily drive and as such I have a need for reliability and to survive the riggers of modern traffic issues. While the original Isuzu unmolested Box was sitting on the floor of the garage the gear change felt great as do all Japanese Boxes and much better than the feel you get from the forty year old Lotus Semi Close. After the Gear stick was altered to simulate the Lotus length and angle the feel became more notchy attributable to the decreased leverage of the shorter stick but still retained a slightly better feel than the Lotus box.

The mounting cross member from the Elan Gearbox fits the Isuzu Box if it is rotated 180 degrees and add two 35mm easily obtainable rubber mounts. The mounts I used can be seen in photos # 18 & 20 and are allegedly gearbox mounts from a BMW. It’s just a 35mm thick rubber centre bobbin with a bolt out each end and all the holes line up perfectly.

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The drive shaft tube is the same length as the original Lotus Shaft although the Gearbox exit spline and its immediate universal has been changed. When I purchased my gearbox I also got the Isuzu drive shaft so I removed the gearbox exit spline at the universal and fitted it to my spare lotus drive shaft. The two Diff end plates and drive shafts in the picture below are unaltered original Lotus just the output spline and its immediate universal has been changed on the Isuzu shaft (closest to the camera in photo 20)

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Here endith PART 2. Bare with me...
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PostPost by: Kiwi elan +2 » Sun Jan 17, 2010 4:42 am

Five Speed ISUZU Gearbox into an Elan. PART 3

The Speedo Cable that I ultimately used was the original Lotus / Smiths cable. The 90 degree that is fitted to the Lotus Gearbox output will screw to the Isuzu Gearbox output and with minimal alteration works great. I just created the square profile on the inside of the Isuzu drive wheel and shorted the length of the 90 degree to fit inside the Chassis without touching the sides.

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If you look at the photo above and compare to the photo below you will see that I had to shorten it once it came to fitting into the chassis. The speed reading is not a lot different to what I had before but I can’t help you regarding accuracy because my speed read incorrectly prior and it is incorrect still. If you really want to know how big your speeding ticket is going to be ask the cop.

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The end result is the Gear Shift Lever in exactly the same place as original but if you could look really closely you would spot the number 5 atop the knob along with the other more common numbers.

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To fit the Isuzu Gearbox has many plus and a few minus points and a lot of the beauty is in the eye of the beholder. What suits one person will not necessarily suit the other. I am not so much into racing but enjoy the cars handling and agility on a daily basis so to cope with today’s traffic requirements is more important to me than tradition or racing ratios. Advantages of a five speed to me are a lower more comfortable open road / motorway RPM. It has moved from near 3500 to near 3000 at 100 KPH ( 62 MPH ) and this is a big thing for me for noise and engine longevity. My perverted logic suggests that a motor has a finite number of revolutions to perform in its life time so why waste them when cruising on the motorway. The Japanese have been making excellent road going gearbox units for many decades and I for one are prepared to accept that for road cars they know what ratios are ideal. I am using my Elan on the motorways that didn’t exist when my Lotus was born and in bumper to bumper stop start and crawling traffic, hill starts and the other obstacles modern motoring throws at us and for me in my situation the Isuzu Five Speed ratios are near perfect. The extra low first is wonderful on hill starts and crawling traffic and the overdrive brings a tranquillity to the car at speed. If you’re a purist then good for you and I’m surprised you’re still reading. If you’re into racing then this isn’t the correct ratios. If you have a bottomless bank account then you may find something better on the market elsewhere. However if you’re ears are open to the five speed debate and have questions around the Isuzu option then I hope this is providing some answers.

The relative ratios as I understand them to be are…
Gearbox Type..........1st........2nd........3rd.......4th.....5th........Rev
My Isuzu................3.77.......2.31.......1.40......1.......0.81......3.87
Lotus Five Speed.....3.20.......2.01.......1.37......1.......0.80......3.47
Lotus Standard........3.54......2.40........1.41......1..................3.96
Lotus Semi Close......2.97......2.01........1.40......1..................3.32
Lotus Close Ratio.....2.51......1.64........1.23.......1..................2.81

Not terribly relevant but someone may want to know what Diff ratio I run and it’s currently the standard 3.77 which I do intend to change to a 3.55 when I happen to locate a good one. Not urgent and if it never happens then c’est la vie (so be it). Having stated the relative ratios it should be mentioned that there are more different Isuzu ratios than you can poke a stick at. Everywhere you look you will find different numbers but realistically the recommendation from me would be for these gearboxes to be used on the road so the subtle variations become academic.

It requires a lot of work and a sprinkling of money to cut off the Bell and make an adapter plate to take the Ford bell as I have done but for me it was the correct move. I enjoyed the learning and the challenge of tackling a problem in a new way. I have access to a lath and mill so I could handle some of the fiddly things myself. The key to this was my CAD production of the adapter plate. It cost me around $900 New Zealand Dollars ( at time of writing about $670 US ) just to cut out the shape from a thick slab of grade 7075 Aluminium which itself cost around $250 NZ. The gearbox you could expect to pay between just few dollars to a couple of hundred. The replacement input and output bearings and seals total around $150 and the spigot bush and clutch re-spline and the drive shaft modification if you do the math the all up cost for this strong well designed gearbox is actually quite reasonable.

I am very happy with the way it works. I have several thousand trouble free miles on the clock since the heart transplant. The shift feel is more notchy than I would have expected courtesy of the very short shift lever however I like it and it is a small improvement on the original Lotus/Ford box feel. So many things lined up without alteration or fitted together when you wouldn’t have expected it was uncanny.

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If there are any enthusiastic individuals out there that want to give this a try and wish to obtain a copy of my CAD drawing I am unsure what to do about that. I have spent much time and effort tweaking it to produce what I believe is a very tidy item and it can even be easily altered to accommodate a concentric actuated clutch if desired. The problem I have is that everything I have needed to get my car running nice I have paid market value for and as much as I would like to help any Elan fan I don’t know what to do about compensating my hard work. You can get a fully operational and free CAD program that will allow you to create your own model from
http://www.rhino3d.com/
and this one even has tutorials to teach you how to model. I thoroughly recommend this FREE program because I have used it several times to learn and create models. There are no hooks or drawbacks with this evaluation version other than the limit of only being able to save your creations 25 times but even then the program still functions perfectly for viewing and learning. I don’t wish to profiteer from this but equally why should I give it away when people didn’t just give me things that I needed. The intent of putting this information out here is not to move people in this direction but to just inform because I had a real hard job trying to shorten my learning process. It would suit me perfectly well if nobody wanted to do with an Isuzu what I have done. Much of this information would be relevant regardless of however you shoe horned the Isuzu Box into the car anyway and if you give it some thought yourself you may well find a better way than this. Go forth and build a better mouse trap. Circumcise the gearbox or not it still performs well.

Make of it what you will and if you’re ever in my part of town and get overtaken on the motorway by a slow revving Elan most likely on the wrong side of the speed limit…
it may just be thanks to Mr Isuzu. Bless em…

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I think it looks great (but I’m bias)
Regards Maurice Cain
[email protected]
Auckland, New Zealand

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Last edited by Kiwi elan +2 on Sun Jan 17, 2010 6:36 am, edited 3 times in total.
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PostPost by: Kiwi elan +2 » Sun Jan 17, 2010 5:52 am

Five Speed ISUZU Gearbox into an Elan. PART 4


Now for some useful excerpts from the service manual of a gearbox of this type.
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Last edited by Kiwi elan +2 on Sat Jan 23, 2010 3:23 am, edited 3 times in total.
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PostPost by: Kiwi elan +2 » Sun Jan 17, 2010 6:24 am

Five Speed ISUZU Gearbox into an Elan. PART 5

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PLEASE NOTE THE OIL USED IN THE GEARBOX IS MOTOR OIL

I originally put Castrol 20-50 in my Gearbox which is what I use in my Engine along with a little “ Red Line engine oil break-in additive” which adds many of the desirable things the greenes and econuts have had removed from the “modern” more environmentally friendly oils. I have since changed my gearbox to Castrol 10-40 with a splash of Red Line and the synchromesh works better on this.

I have now clocked 15000 very happy miles and would not change a thing if I were to do it all again...
Except maybe go a little slower past the many traffic enforcement officers I have come to meet. :oops:
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PostPost by: Tonyw » Sun Jan 17, 2010 7:17 am

Kiwi Elan,

This is without doubt the best and most well thought out five speed conversion I have seen to date you are to be congratulated. There will be the knockers no doubt who will criticise the ratios and in some parts of the globe the availability of the Isuzu box but I for one take my hat of to you. The other alternatives are expensive and generally unavailable while yours is relatively inexpensive and potentially readily available.

Do you know if your plate design is common to all of the various Isuzu boxes? If you are willing to either have some adapter plates made or willing to sell a copy of your DWG or CAD file please let me know as i would be keen to do this mod to my car while the body is off the frame.

Well done.

Regards,

Tony W
Second childhood? no just an extension of my first.
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PostPost by: mikealdren » Sun Jan 17, 2010 7:54 am

A really great and inspiring post, congratulations and many thanks.
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PostPost by: Higs » Sun Jan 17, 2010 9:34 am

A great post - thanks for putting in the effort to write it up so clearly.

You are to be congratulated on a well engineered conversion.

All in all a very enjoyable read. As my Plus 2 is getting down to the chassis, I might well be discussing this with you some more!

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PostPost by: john.p.clegg » Sun Jan 17, 2010 9:45 am

Well done...a good read..

John :wink:
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PostPost by: rennbaron » Sun Jan 17, 2010 10:38 am

...

this is an awesome forum! It´s full of worthwhile information!

but you established a new level of posting.. great!
...even for me, who would not change to 5 speed... ;-))

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PostPost by: GrUmPyBoDgEr » Sun Jan 17, 2010 11:47 am

I'd also like to add my congratulations.
What a phenomenal amount of ingenuity & Engineering in that transformation & a truly remarkable report.
You have set a Milestone; my deepest respect Sir.

Cheers
John

PS Luv your Avatar also :lol:
Beware of the Illuminati


Editor: On Sunday morning, February 8th 2015, Derek "John" Pelly AKA GrumpyBodger passed away genuinely peacefully at Weston Hospicecare, Weston Super Mare. He will be missed.
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PostPost by: smo17003 » Sun Jan 17, 2010 12:21 pm

What a fantastic read. If there was a prize for post of the year you've won it already.
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PostPost by: bcmc33 » Sun Jan 17, 2010 1:17 pm

Maurice,

A very impressive piece of work and presentation – my congratulations.

However, these were a couple of thoughts that came to mind when reading your dissertation:

1. The cotton reel gearbox supports won’t last 5 minutes. I think you will need to make an adapter in order to fit the standard Ford type mount.
2. With all the effort put in, I was surpised you did not use a modern concentric clutch slave cylinder instead of retaining the old lever method.

I have no knowledge of this gearbox and wonder if there was a European version. Does anyone out there know?
Brian Clarke
(1972 Sprint 5 EFI)

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PostPost by: johnc » Sun Jan 17, 2010 3:50 pm

Maurice,

Thank you for just doing it, and thank you for sharing how you did it. You are an inspiration.

A masterful design and implementation, and an excellent presentation!

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PostPost by: elansprint » Sun Jan 17, 2010 4:36 pm

Maurice what a fantastic piece of work i am not sure what the cost of perfecting the adaptor plate was but may i suggest if you wish to offer it for sale ask the question on this forum see what the response is i am sure anyone goiung this way would be prepared to offer some cash by Paypal for a copy of the file? Only problem i see is not sure of the gearbox availability in Europe.
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