Speedo is miles out

[Jackmansell]

hello there, its been in for a while but iv just dealt with it, but my 1408 tpm speedo is at least 10mph slow now that i have a type E gearbox and a 3.89 diff, i thought a 1408 would have been close to correct? it always read a little over 2/3 mph when i had the original 4.22 diff in, what other speedo would i use?

[graham1957]

in the early 60s the 1098 cc morris 1000 had a gold face speedo 0/90 mph and 1376 tpm, that may be nearer. maybe some one on here can calculate it for you? i have some of this variaty if you are stuck. sorry i cant work it out its a bit beyond me , flocks of sheep are my speciality!!

[bmcecosse]

1376/1408 are near enough the same thing... What is a 'type E' gearbox? I And what tyres are on the car?

[mike.perry]

There is a list of speedos on http://seriesmm.mmoc.org.uk Car Ident, speedometers

[bmcecosse]

Is it a constant 10 mph across the whole range - or 10 mph at 30 mph true/ 20 mph at 60 mph true etc..... A much better guide is to compare the the odometer reading over a known correct 10 mile run. If the 10 mph is 'constant' across the dial range - then that is easily corrected by carefully repositioning the needle on the spindle. Simples !

[twincamman]

If the 'Type E' gearbox you are referring to is a Ford box, then it was designed to work with a 1000tpm speedo. The correct reading is obtained by swapping the speedo drive gears. These are still available from Burton Power. I suggest you contact them and they should be able to advise which ones you need.

[IslipMinor]

If the 'Type E' is the Ford 4-spd 'Rocket' box, then a common speedo drive ratio is 22:8 or 2.75. IF this is the box that you are using AND you have standard 145/80 x 14 tyres, the correct speedo TPM with a 3.89 axle ratio (Marina?) is 1229. With a 1408 speedo head, it would be around 13% slow.

Is this what you have?

[Jackmansell]

sorry fellas been busy, yes it is indeed the type E ford box (4 speed early version of the type 9) and the axle is out of an RS2000, the speed around 40 reads as 30 but as you increase the speed it is out more, 60 is around 45 and 70 is around 50, so it must be the tpm being wrong, so if i get a different speedo with a lower tpm that should work?

[bmcecosse]

There is a Mini speedo at 1294 which will work well if the calcs above are correct.

[philthehill]

Jack
Speedo issues aside what are your thoughts and comments on the 4 speed all synchro type E Ford gearbox now that you have it installed in your Minor?

Phil

[IslipMinor]

Some that might be suitable on eBay:

1280 tpm http://www.ebay.co.uk/itm/Classic-Mini- ... SwT5tWM6t1

1280 tpm http://www.ebay.co.uk/itm/Classic-Mk2-a ... Swl9BWM6eE

1240 tpm http://www.ebay.co.uk/itm/Classic-Mini- ... SwT6pVh-76

1248 tpm http://www.ebay.co.uk/itm/CLASSIC-MINI- ... Sw5ZBWJ5vl

There are others, but silly minimum/BIN prices!

[Jackmansell]

thanks guys ill keep my eye out for one! i forgot to say i have 15" miniltes and 175/65 tyres on but they work out as only 5mm larger in diameter than the original wheels so i guess its really irrelevant. Phil i have to say you're spot on, its a joy to drive, all gears are slick and that quickshift i had off of you is like a bolt action rifle! i also added a high tensile brass seat for the selector fork so its even more slick. i do have a few bearing whirrs but i will rebuild it next year, nothing too major i just thought id throw it in and hope they were fine. had to mess with the crossmember bracket but got it to work in the end.

[twincamman]

You can get a 1000tpm speedo here:-
http://www.europaspares.com/interior-pa ... meter.html

You'll need the 130mph one

[IslipMinor]

15" minilites and 175/65

175/65 x 15 are really quite big tyres - the speedo tpm with the Ford box and 3.89 axle is 1191.

[bmcecosse]

A 1000 tpm speedo is no use - if the reported speedo variations from true speed are correct.

[Jackmansell]

a tyre calculation thing online says my new wheels are only 0.8% larger than the original ones so i dont sseses its makinsg tshat much difference

[bmcecosse]

It matters not - your reported speed variation will be corrected (more or less) by fitting a 1294 (or similar) speedo.

[IslipMinor]

I have checked a number of different tyre calculation sites and they all say that 175/65 x 15 tyres are around 3.5% larger than the standard 145/80 x 14. Are the new tyres 175/65 x 15?? What site are you using?

[Jackmansell]

cheers BMC, and one called tiresize.com gave the following result[frame][/frame]

[John Naylor]

These tyre calculators are ok for approx comparisons but don't take them too seriously. They tend to use pi (3.1417 approx) to calculate the circumference which might work for a solid tyre but certainly not for a radial tyre. A radial has a 'flat bit at the bottom' and it is a little more complex than that. The radial tyre has a rigid belt that is its rolling circumference, this is just beneath the tread and the generally accepted constant is 3.05 times the unloaded diameter. This explains why the depth of tread, and tyre wear, doesn't affect the speedo reading. Another complication is the fact that the aspect ratio (i.e. the '80' in
155/80 R14) is a nominal value and will vary between tyre manufacturers eg. the actual aspect ratio could be 82. Remember also that our cars were supplied on 5.20 14" cross plies and speedos related to that tyre type and size, certainly not to oversize 155/80 R14's!