Colotti-Francis Gearbox

[ianh1968]

My Dad's old "Clive Trickey" book from 1966 mentions a
"Colotti-Francis 5-Speed"...

The only information that I can remember finding about this was
that the first gear was its weak point, and that it was rated at
about 75Bhp.

Has anyone got any more details on this, tooth counts, ratios, etc?

I am in the process of making an update to the "Ratios" spreadsheet
and would like to add in this historic set:

http://mk1-performance-conversions.co.u ... anical.htm

Release 005.Mk1 is bubbling under...

Ian

[JohnA]

Hi Ian

I found this in a 1964 tuning manual







John

[Astro]

Hi,

there is the story that such a gearbox was used by the group 5 Arden car from Jim Whitehouse. The problem was never the gearbox but the driver to have difficulties to get the right gear and to destroy the complete engine this way.

[59fan]

I have one in my pickup, the ratio's listed are for the 'fast road' gear set, you could get a 'race' set as well, I don't have access to the ratios for that to hand but will have when I get home from work this evening.

Its a very close box and the main issue I have found so far is going from 4th to 3rd and avoiding 1st, so I'm putting a gate on it.

Pictures of the internals are in 'Our cars and projects' look for 62 pickup. the 2nd page has a photo of the box prior to fitting.

Ian

[m1cH1]

Yes, there are the two types of the Colotti T.40 gearbox as mentioned before!
There were the more "race" set which had the ratio a normal four speed box would have in fourth in fifth. The ratios for this set are the ones given in the Trickey book above.

Then there was the second set, which was more a fast road or "gran turismo" gear set. It resembled more or less a close ratio four speed mini gearbox with a ratio of the fifth gear that was usable like an overdrive for fast cruising.

I´ve got some information about this set, which I found somewhere in the internet and saved it:

Code: Select all

Shift Pattern Colotti T.40 - Mini Cooper five speed gearbox:

R  2  4
|  |  |
|  |  |
1  3  5

Gear ratios and projected RPM in gears:

    Speed and RPM Calculator
    Gear set: 
    Gear            1        2        3        4        5        Final
    Ratios:     2.181    1.352    1.060    0.905    0.789        3.765

    Tyre Size:            165/65 x 10
    Tyre Diameter:        18.44 in
    Tyre Circumference:   57.93 in

    Gear   Mph per 1000 RPM   Mph @7000 RPM   Mph @6500 RPM
    --------------------------------------------------------
      1         6.68                47              43
      2        10.78                75              70
      3        13.75                96              89
      4        16.10               113             105
      5        18.47               129             120
    
     Mph             RPM (in Gears)
    -----------------------------------------------------
                1        2        3        4        5        
    -----------------------------------------------------
       5      748      464      364      311      271
      10     1497      928      727      621      541
      15     2245     1392     1091      932      812
      20     2994     1856     1455     1242     1083
      25     3742     2320     1819     1553     1354
      30     4491     2784     2182     1863     1624
      35     5239     3248     2546     2174     1895
      40     5987     3712     2910     2484     2166
      45              4175     3274     2795     2437
      50              4639     3637     3106     2707
      55              5103     4001     3416     2978
      60              5567     4365     3727     3249
      65              6031     4729     4037     3520
      70              6495     5092     4348     3790
      75                       5456     4658     4061
      80                       5820     4969     4332
      85                       6184     5279     4603
      90                                5590     4873
      95                                5901     5144
     100                                6211     5415
     105                                         5686
     110                                         5956
     115                                         6227
     120                                         6498
    
    Gear Change  RPM drop (change @7000)  RPM drop (change @6500)
    -------------------------------------------------------------
      1 -> 2         -2661 (to 4339)          -2471 (to 4029)
      2 -> 3         -1512 (to 5488)          -1404 (to 5096)
      3 -> 4         -1024 (to 5976)          -950 (to 5550)
      4 -> 5         -897 (to 6103)           -833 (to 5667)

Cheers, Mike

[ianh1968]

I think that I need to chew over these figures, because I think that
somewhere along the lines, something has got "lost in translation".

In John's book, we know that 5th is 1.0:1.
We also know that the gear lever position of
5th is as per 4th on a "normal" box... This is the position in a
standard box where the 1st and 3rd motion shafts are directly
locked together. The laygear would need 5 sets of teeth.
These would be the driven set, plus one for each of the 4
non-direct gears.

The ratios we have are:

Code: Select all

1st 2.96
2nd 1.73
3rd 1.35
4th 1.15
5th 1.00

Mike's figures are weird because none of the gears are
1.0:1, ie there is no direct drive...
For this to work, we would need a laygear with 6 meshings
on it, ie, the driven one, plus one for each of the 5 gears.

I am also not sure about achieving an 18.47mph top gear
with a 3.765 diff and 10" rims during the 1960's...

However, if we divide all of Mike's figures by 0.789, so that
5th becomes 1.0:1, we get:

Code: Select all

1st 2.764
2nd 1.713
3rd 1.343
4th 1.147
5th 1.000

We are back to something that looks fairly "normal"...
It much more resembles a slightly closer version of the
set in John's book.

Ideally what we really need here is a tooth-count!

Ian

[ianh1968]

Its a very close box and the main issue I have
found so far is going from 4th to 3rd and avoiding 1st

I have often wondered if a bias could be achieved inside the
gearbox itself by sliding suitable compression springs onto the
diagonal selection rod...

On a normal box, the reverse lamp switch is activated by this
rod, being pushed downwards towards the front. (I think!).

On the CF box, you would want to bias the lever TOWARDS
this direction as 1st and reverse are at the other end...

This would suggest to me that putting a compression spring
above the selector arm on the rod would do the trick.

Ian

[JohnA]

this is from a 1964 road test 1071 S
The ratios listed are slightly different and include over all speeds in the gears.

[59fan]

Mike,

That's the information that was on Ebay on the last Colotti box I bought, not sure if that was the original source though but its an exact copy, I must have bought that box 5/6 years ago, maybe more.

I have an advert for the gears somewhere that I will scan and post tomorrow.

Interestingly I thought I was running the overdrive gears, but 5th is definitely 1.0 now I'm driving it. I do have spare gears so could possibly count them, they are loose though and gearboxes are a black art to me but with some guidance I'm sure I can rustle up the information.

Ian

[mab01uk]

Random fact below!

The famous 1950/60's Racing Mechanic Alf Francis (the other half of Colotti-Francis) used to be my parents next door neighbour in the 1960's. I remember as a youngster he often arrived in Italian sports cars or sometimes in a race car transporter to visit his wife who lived in the new bungalow next to ours in the village of Charlwood near Gatwick Airport. He was very rarely at home but I often think now if only I had taken a few photos or asked him a few questions, especially after recently reading his famous book 'Alf Francis, Racing Mechanic'
http://www.velocetoday.com/lifestyle/lifestyle_36.php

[ianh1968]

JohnA has come up with two sets of ratios and it looks like only
1st and 2nd are different. This may rule out the S/GT method
of making a closer ratio set by adding a tooth to the 1st motion
gear...

There is also the question of "rounding" in the calculations,
and of course the possibility that they were all worked out
using log tables.

Code: Select all

       Road      Race
1st =  2.96  -  2.761
2nd =  1.73  -  1.702
3rd =  1.35  -  1.349
4th =  1.15  -  1.145
5th =  1.00  -  1.000

I do have spare gears so could possibly count them

I'd really like to know the tooth counts, I can confirm the calculated
ratios very easily and this would give me some nice data for the
"ratios" spreadsheet. This information would then be preserved for
future generations of "number-nerds"...

(The Other)
Ian

[251 ENG]

Hello Ian

I have a colotti in the shed somewhere , but has a broken gear .

There is also another box in there that I think is a 1960,s jack knight box , also broken.

Both are 5 speed dog box,s and in 22G 333 casings .

I will try and dig them out next week .

[m1cH1]

I'd really like to know the tooth counts, I can confirm the calculated
ratios very easily and this would give me some nice data for the
"ratios" spreadsheet. This information would then be preserved for
future generations of "number-nerds"...

Hi Ian,

I´ll have a look in my workshop later today, or tomorrow (As time permits.) There I have a box with one gearset of the type in question, which I had counted in the past, but didn´t make any notes. I´ll count the teeth again and post this info here. (When I remember it right, the gears had also the tooth counts written on their sides...)

Cheers, Mike

[m1cH1]

A few days late, but now I´ve finally counted the teeth of the gears. The result is the following:

Code: Select all

1st: 11/24
2nd: 17/23
3rd: 15/16
4th: 19/21
5th: 15/19
(tooth count of gear on mainshaft/gear on layshaft)

Then I transformed the ratios to decimals to compare them to the other ratios in this thread and they were the same as stated in the data I´ve posted a few posts ago. (@59fan: Yes, that was the information from ebay! (http://www.ebay.co.uk/itm/CLASSIC-MINI- ... 0724923618?))

Then I also began to be suspicious about these ratios. I looked at the gearbox, thought about the ways the torque gets transmitted - and then I realized what the mistake was! To make this explanation a bit better understandable I drew up a schematic of the box.



If one selects 1st, 2nd, 3rd or 4th gear, the torque goes from the input gear to the 1st motion shaft, then onto the layshaft and from there through the selected gear onto the main shaft / 3rd motion shaft and out to the diff through the diff pinion.
But if one selects 5th gear, 1st and 3rd motion shaft get locked together and thus the ratio of 5th is 1:1!

As the 5th gear is - like the 4th in a regular mini gearbox - an integral part of the 1st motion shaft, there is the 15/19 or 1:0.789 ratio influencing every ratio of 1st, 2nd, 3rd and 4th gear. You just have to divide them by 0.789 (like Ian suggested before!) and you´ll end up with much more plausible values:

Code: Select all

1st: 2.764 (152/55)
2nd: 1.713 (437/255)
3rd: 1.351 (304/225)
4th: 1.146 (361/315)
5th: 1.000

Resulting from this I think that the data posted on ebay is definitely completely wrong! (And I should´ve better checked it myself before posting it and thereby spreading wrong information...)

But then there is one thing I´ve always wondered about: Why should Colotti have offered two different gear sets with different ratios, but both under the same project number "T.40"? At this point I´m not completely convinced anymore that there definitely have been two variants. I´ve read for sure somewhere that there should have been two variants, but what if somebody used the same set of data (the one from ebay) and came to the same wrong conclusion I came to before? So I´ll check my small archive of all things Colotti sometime in the next days and try to locate where I found the info about the two different boxes... (Or does somebody in here know it for sure?)
The values from the Haynes book and from the posted article (Small Car, January 1965) are relatively close. So it´s highly possible that they didn´t calculate everything in fractions, but used already rounded decimals for calculating, or something similiar...

(EDIT: Changed some tooth counts, as I had them enumerated in the wrong order last night. Now they are definitely in the right order!)

[m1cH1]

I have an advert for the gears somewhere that I will scan and post tomorrow.

Would be great to see this advert! There are three different articles in period magazines known to me, but no period adverts up to now...
(And I bet there must have been some adverts in some of these magazines!)

Interestingly I thought I was running the overdrive gears, but 5th is definitely 1.0 now I'm driving it. I do have spare gears so could possibly count them, they are loose though and gearboxes are a black art to me but with some guidance I'm sure I can rustle up the information.

I think this shouldn´t be too hard to find out! The gearset I examined today had on all gears, except 1st and reverse an inscription made with some kind of electro-sparc engraver! Also seen previously on other gear sets from colotti. Seems to be something they do with every gear set they make...



It says for example 3°V 15/16 T 40 which means terzo velocità (->third gear), then the gear ratio of 3rd and Colottis project number. This makes identifying the gears relatively easy.
Now to the gears which have no inscription: The 1st gear is very good recognizable by it´s large bush, where the second gear sits on. And the reverse gear has a relatively huge diameter but is very narrow with teeth that have a less square profile than the other gears. Their gears look more like the small dog-teeth on regular (properly synchronized) mini gears. The same is valid for the reverse idler gear. It´s about the size of a regular mini one, but has also the relatively narrow dog-teeth.

[59fan]

Very interesting information, see below a picture of the advert I have.



This states that 2 sets had been available but by this stage clearly only one was available. The gear ratios quoted as its not very clear.

1st 2.761
2nd 1.702
3rd 1.349
4th 1.145
5th 1.000

[Falcone500]

Hi!

A friend of me is selling such a box in fully reconditioned order.
If someone is interested in it, pm me.

Cheers Marco

[ianh1968]

We are starting to get some good detail now - I think that some of the
anomalies with the previous information comes as a result of the
common perception that the "First Motion Shaft" IS "Top" Gear. Whether
this is 4th, as in a standard box, or 5th as in the CF boxes we are talking
about here.

It is true that the "shaft" part of the "First Motion Shaft" is used for "top"
gear. The "teeth" part of it, along with the corresponding driven teeth on
the layshaft are NOT part of the equation in "top" gear...

In all other instances, that is, first to third in a standard box, or first to
fourth in a CF-style box, the teeth on the "First Motion Shaft" drive the
laygear at a fixed ratio, from which all the non-direct gears are driven.

For the CF box with the approximately 2.76 first gear, the one we are
calling the "Race Set", the "First Motion Shaft" has 15 teeth, and the
meshing gear on the laygear that pairs with it has 19 teeth.

Now for the "nerdy" part:
Top gear is direct, there are no EFFECTIVE meshings of gears, the final
ratio through the box is therefore 1.000:1. (5th, in this case).

All other gears are driven from the laygear via a reduction ratio of
19/15 - The "Laygear Driven Teeth" divided by the "First Motion Shaft"
teeth. For the "Race" set, as per Mike's figures, this comes out as
1.26666. (with the 6 recurring).

The reciprocal of this figure is 0.7894 - Sound familiar? It should do
because this is the figure that has been quoted for 5th gear in the
incorrect figures previously published. This is because the author of
the original figures wrongly classifies the "First Motion Shaft"/"Laygear"
pairing as being "5th" gear... (Which it isn't!) (Mike, Should you edit/delete
that whole chunk of information out of your earlier post?).

Back to the maths (or math, if you are that way inclined...):
For each non-direct gear, the formula is:

Code: Select all

"Laygear Driven Teeth"     "Third Motion Shaft Driven Teeth"
----------------------  X  ---------------------------------  = Overall Gearbox Ratio
 "First Motion Shaft"           "Laygear Driving Teeth"

What we end up with is this:

Code: Select all

Colotti Francis Type 40 (T.40) "Race Set" # Edited @ 16:49 to add Type 40
1st Motion Shaft: 15
Laygear 19     Driven Gear
5th   Tooth Count Not Applicable, Direct 1.000:1 
4th     21  :  19 (19/15 x 19/21 = 1.146)
3rd     15  :  16 (19/15 x 16/15 = 1.351)
2nd     17  :  23 (19/15 x 23/17 = 1.714)
1st     11  :  24 (19/15 x 24/11 = 2.764)

JohnA's excellent scan gives first as 2.761, we have 2.764 here, and as an
experiment, I calculated the ratio using 3-figure logarithms and got 2.767...

The figures in the block above are definitely 100% correct - All the teeth on
all of the gears in the set were checked (Thanks, Mike!) and accordingly, any
minor variations in the quoted figures will be down to calculation method
and/or rounding.

I have updated my copy of the "Ratios" spreadsheet with this gearset, for those
interested, I have given it the short name of "5CFRC". The elusive "Road" set,
ie the one with the 2.96 first gear, has been provisionally added as "5CFRD" with
the data being fixed and as per JohnA's other scan. (JohnA, I hope that this is OK?).

At some point soon, "Release 005.Mk1" will appear on the main Mk1 website...
If anyone wants a "pre-release" version, please PM me.

My thanks go to everyone that has contributed to this thread, I really was not
expecting it to generate so much decent information. All we really need now
is an actual tooth count for the 2.96 first gear set, if it was actually produced...

Ian

[John Bull]

I had one, many years ago, but gave up on it because I could never get all 5 gears to select correctly. I gave it to a friend who was an airline pilot doing the Malta - UK route, as he said he thought he knew of someone who could fix it, but 30 years down the road, my friend has since been long gone, and I have no idea where the Colotti box is.

I've been running the normal SC/CR 4 speed ever since, and even with a fuel injected, 8 port 1500, it seems to cope well.

[e-type]

the company is still around, and you can get a new 5 speed, price is around 7000£ though

http://www.colotti.com/index.php/en/con ... 00100/home