DETAILED REPORT Five Speed ISUZU

[AussieJohn]

I drove an S4 in Sydney about 15 years ago with this box and did not find the ratios any problem; it was a lovely car to drive. I am wondering if theory and practice dont always line up?

[Lincoln62]

I have no knowledge of this gearbox and wonder if there was a European version. Does anyone out there know?

The Isuzu/Holden Gemini was a development of the Germen Opel Kadett. That might be a good place to start.

Peter
66S2

[Kiwi elan +2]

Thanks for the good words and feed back.

I have just added into Parts 4 & 5 some useful excerpts from the service manual of a gearbox of this type.

[msd1107]

Maurice,

Is there a page 97 in the manual? The words do not seem to flow well without it.

And was there a tooth count of the gears anywhere in the manual?

David
1968 36/7988

[msd1107]

AussieJohn,

I am sure there were no problems shifting the gearbox you drove in Sidney 15 years ago. After all, this was a production gearbox. But if you had had a toolbox full of optional gears, and you had swapped them individually and jointly into your gearbox, you would have seen the difference each change made.

I know. I originally developed the rationale for gearbox ratio staging more than 50 years ago. I had a gearbox that was in several different models, and perusing the factory parts manual I noticed that the gears came with different tooth counts, varying by one tooth, depending on the model in which they were installed.

So I got some different gears. One by one, I put them in, and evaluated the changes. Every gear change altered the shifting feel noticably, even though it was only a one tooth difference. I wound up changing 4 of the gears, changing the gear ratios from a wide ratio 2.778 1st with steep drops between gears to a mid-close ratio 2.5 1st with even drops between gears. This was a much more pleasant gearbox to use, even though owners had used the standard ratios without complaint for years.

This was the impetus behind the design of the first gearbox program, more than 35 years ago, written in FORTRAN on punch cards. And for the current program as an Excel spreadsheet.

And also the impetus for the virtual test drive of multiple gearboxes that was posted earlier in this thread and also in the 5-speed and 6-speed thread. If you are going to make a major change, and have to live with the results of the change, it is probably good to make the optimum change, especially if you can evaluate different options for suitability or optimality. Otherwise, you will drive around in blissful ignorance of how you could have improved the driving experience.

For instance, looking at the maintenance manual Maurice posted, it appears 5th gear is replaceable. The Isuzu Twincam has the highest 1st gear, but a too close 5th gear. Replace 5th with the pair of gears from the Piazza Turbo, and you get a better staged set of gears, and a taller 5th gear also.

Just my opinion. Shift the gearbox that pleases you the most.

David
1968 36/7988

[jabingb]

David,
Although I did not program Fortran with any appreciable facility, the mention of your accomplishment with punched card programming resonates with the good old days doing machine and AutoCode on a 1401. Back to the thread, props to Maurice for resuscitating this somewhat dormant option with such clarity.
Jerry

[Kiwi elan +2]

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 added another page to the area that shows the pages from the manual showing the recommended oil.

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.

[bcmc33]

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 added another page to the area that shows the pages from the manual showing the recommended oil.

Interesting.............

I've just had my Lotus 5 speed box stripped and rebuilt by the best known UK lotus 5 speed guru as the 2nd and 3rd gear synchros didn't work without double-de-clutching.
When I asked what the problem was - "you used the wrong oil", was the answer.
I made no mention of Redline MTL that was such an improvement on the 4 speed that I assumed would do the same for the 5 speed - "you've used synthetic oil - bad idea - the gear set was designed for standard engine oil" was his final comment.
He agreed that the use of engine 10w40 running-in oil is probably a good idea.

[cabc26b]

Gents

On the topic of motor oil - Try the motul dinosaur based 10-40 motorcycle oil -has the higher level or ZDDP still in it plus additive packages for gears and stability .

g

[rgh0]

I dont think a good quality synthetic gear oil of the right viscosity and friction characteristics can be a bad idea for any gear box and will certainly be better than almost any standard mineral oil be it an engine oil formulation or a gear box oil formulation. The guy you talked to is probably very good at bolting gearboxes back together but he does not sound like a lubrication engineer to me.

I certainly believe Redline MTL is an excellent oil for the Lotus 5 speed and it improved the performance of mine in speed and smoothness of changes and in the ability of the relativly weak syncros to match speeds on down changes. Its temperature stability means it maintains its excellent charactersitics over a large operatiing range of loads and temperatures and over an extended time period. Read the comprehensive technical information Redline provide on their web site, they talk there about why the use of engine oils in a gear box is generally not a great idea

Using engine oil in a gear box is always a compromise and a clever and cheap option adopted by those excellent engineers at BMC who made Colin Chapman look like a spendthrift who threw hand fulls of gold around when building his cars.

cheers
Rohan

[Famous Frank]

Kiwi Elan +2,
What a mnagnificent article. Thank you. I've been wanting and thinking hard about 5 speeds for years, and with the restoration of my S2 moving along, I've been giving it thought daily. I must admit, I've been thinking steadily about the T5, but your article has me seriously thinking about an Isuzu box. I'll be looking for one and should I find one, I'll be back in touch with you. I'll be using a 3:77 rear which would be easier withyour ratio's or the other box listed with the 3.1 first gear would be even better as I like doing 1st gear burn outs!!! Again, many thanks for a wonderful job and article!

Famous Frank

[alexblack13]

Run the box in 1st before changing to the Redline. The Lotus 5 speed box Baulk rings are steel and can take a while to bed in. Mr B (I trust him!) said use a good 20/50 1st as the box was designed to run in engine oil (Maxi!!) Run it in on that then a good synthetic will be fine..

Dont shoot the messenger!!

Alex..

[gjz30075]

Nothing really to add here except I remember my '63 MGB had motor oil as recommended for the gearbox.

Greg Z

[Sarah Ryan]

Ive been running a this box in my sprint witha 3.5 diff for a few years now. The box are pretty bullit proof but it's not a simple swap. The best box was the one used in the Holden Piazza (rare as & guys who drive this car have most of the spares locked away) in that it nearly matched the Lotus ratios except for first. The next best choice was the one used in the Holden Gemini diesel TD.
Modifications to make it fit was to fabricate an adaptor plate so the bell housing mounts to the Elan block & modify the spigot bearing to accept the Isuzu input shaft. The bell housing needs to have the starter cut out & relocated on the opposite side & a plate to fill the that void.
I used a Saab centre Slave cylinder & fabricated brackets to run the fluid. The prop shaft needs to be modified (a little shorter I think) as some of the the Isuzu gearbox's had either fine or corse output splines. I got a new one made so I could keep the original Lotus unit. The rear gear box mount was from a Toyota as the Lotus one will not adapt.

The alloy speedo drive output on the Holden needs to be recut to accept the Lotus speedo drive. This is not a five minute exercise & the Lotus chassis may need a couple of hits with a hammer so the speedo drive can clear it. Another choice where these gearbox's were used was in early versions of the Holden Rodeo. Your speedo will need to be recalibrated as the Isuzu speedo drive ratio will give a false reading but that is a different subject accounting for diffs & tyre sizes etc.

The manual does recommend engine oil but I changed that to synthetic & its works fine. Nowdays parts for these gearbox's are becomming rare with Syncros now longer available.

All in all it works atreat & the overdrive on fifth with my 3.5 diff makes distance touring a pleasant trip. Good luck to all!

[mikealdren]

a clever and cheap option adopted by those excellent engineers at BMC who made Colin Chapman look like a spendthrift

Rohan,
Not sure they really were, Ford took a mini to Dagenham and did a cost analysis on it. They concluded that they couldn't build it and make money and continued with the Cortina. BMC proved that Ford were right.

Mike