Tachometer Vixen

[vixen]

Yesterday I was checking my tachometer because it stoped working.
I was wondering if the tachometer on the S3 were the same type as on the S2.
Mine has Smiths number RVI 2431/00.

[daza]

Although I was switching from an impulse tacho to an electronic tacho, ETB Instruments replaced the internals of my rev counter. It saved having to source an alternative.

Darren

[Moto]

My S3 has Smiths instruments. The tacho is no. RVI 2417/00. It seems to work fine and to be accurate, but I have a bullet/2000e gearbox which may be different to yours.

However my understanding is that the original instruments in S3's were AC. As these are difficult to get hold of, many oweners have replaced with Smiths when the originals break.

Moto

Edited by Moto on Monday 31st October 17:25

Edited by Moto on Saturday 19th November 18:32

[tomtrout]

The tacho on my S2 is a Smiths (cortina style)RV1 2413/00. My speedo is also a Smiths which looks more like those fitted to MGs and doesn't match the face style of the tacho. I presume that Smiths made a matching speedo for Fords?

[thegamekeeper]

Original Vixen speedo and tacho were Cortina Mk2 GT with the speedo recalibrated from 13" wheels to 15"

[RCK974X]

Are you sure the speedo was recalibrated ?

Those gearboxes had different gear options for the speedo cable drive - my understanding was the all the classic Ford speedos from that era were calibrated at 1000 turns per mile....

Just sayin' ....

[thegamekeeper]

RCK974X said:

Are you sure the speedo was recalibrated ?

Those gearboxes had different gear options for the speedo cable drive - my understanding was the all the classic Ford speedos from that era were calibrated at 1000 turns per mile....

Just sayin' ....

Those gearboxes had dfferent gear options for speedo cable drive is in fact recalibration to accomodate the different final drive ratios and tyre profiles of classic Ford cars which all had 13" wheels

Ford Cortina GT had 165/82/13" tyres which covered 1833 mm for each revolution, TVR Vixen had 165/82/15" wheels which covered 2026mm per revolution. If the speedo was not recalibrated it would have been approx 11% wrong

[RCK974X]

(rolls up sleeves, spoiling for a fight.... Nah, - just joking....)

I agree, BUT.

The speedo in a Capri 2.8i (3.08:1) was ALSO 1000 turns per mile, as was the early Anglia 4.11:1)
and I know that the Type 9 5 speeder (and hence probably the 2000E box from which it came) had gears which allow for something like a 4.5:1 diff to a 2.8:1 for 13 inch wheels. On the basis that a Vixen has 15 inch wheels and a 4.1 diff, it actually falls more or less in the middle of this range.

Isn't it cheaper to order gearboxes with the right drive gears than get the speedos recal'ed....
Hmmmm... don't know actually.

Anyway The 5 speed type 9 box gears cover propshaft turns per mile from 4170 down to 2750.

My Vixen/tuscan with 3.7 TR6 diff, 2.8 V6, 5 speeder, and 15" tyres comes out at 3100 TPM more or less..... and I have a 1000 tpm speedo with 8 and 24 teeth drives (= 3% high)

[RCK974X]

Ok, now I'm on a roll.....

Rolling circumference of tyres can be estimated with a formula to give turns per mile, and then multiply by diff ratio to get prop turns per mile....

165x15 (TVR orig fitting) are around 813 turns per mile.

165.70x13 (typical ford fitting) are around 936.

so not that much difference.... a 4.1 in the Vixen (15") is equivalent to a 3.57 with the 13"..

formula is
Turns per mile calculation -

tyre specs are WDT/ASR-WHS

Where:

WDT = Thread width mm
ASR = Aspect Ratio number
WHS = Wheel size ins

then:
Rolling Diameter = 3.14159 x [(WDT x ASR/1270) + WHS]
i.e dia of wheel + two hieghts of tyre......
turns per mile 63360/Rolling dia 63360 = inches per mile
but 65261 works better (3% derate for tyre wall)

The 63360 does not allow for tyre wall distortion, so the turns per mile would be too low.
increase by 3%. gives approx correct values.

[thegamekeeper]

I used to fancy emigrating to New Zealand BUT I am now glad I didn,t. Its got to be worse than people say.


ps beforeYOU accuse me of being disdainful and acrimomious note the smilie

pps, if you had mentioned teeth and gear to Stan Kilcoyne in the late 1960,s he would have thought you were referring to his dentures and his clothes

[RCK974X]

OK...In the same spirit

I *could* get nasty, but I'll put it this way instead.....Us GEEKS are Everywhere !!

I'm from Manchester really, and buggered off to NZ when I decided the EU was a bloody stupid idea....

Honest, come to NZ it's truly beautiful, and they don't salt the roads, and you can bring in classic
cars duty free.....

(wasn't that info useful ?)

[Comadis]

the drive-gear of speedometers are located (accessable) in the gearbox.

the ratio of this drive must match the final-drive ratio (diff and wheels) and thats it.

there are several drive-ratio´s from ford available as ford used differnt final ratios (diffs) and tyre sizes.