Speedo Calibration

[Guest AndrewH]

Hi,

 

I am installing individual gauges in my Series 3a as my Sierra cluster whilst served me well is looking a bit tired. I plan to go for the ETB dials that look good value and offer everything I need.

 

I want to go for a mechanical speedo as I dont really want to have to go to the lengths I would need to to access the propshaft. But to calibrate properly I need to provide ETB with some measurements/ratios. I have trawled manuals and the web and go some of the info. but can find all I need and hoped someone reading this might be able to help.

 

I need:

 

Differential / final drive ratio

Speedometer cable worm and drive gear ratio inside the gearbox

 

I am running an unmodified type 9 (5 speed) gearbox and final drive from a 1.8ltr 87 Sierra with a 2.0ltr Pinto engine.

 

Any help gratefully received.

 

thanks

[Jez Morton]

I had the same thing in mind when I built my 2B, but I went for a Smiths telemetrix electronic speedo with a cable driven transducer so I didnt have mess in the tunnel. I had to get a speedo cable made to suit the transducer which was easy enough from Speedy cables. The electronic calibration is straight forward it requires pulses per mile to be programmed, Ford speedo cables turn 1000 turns per mile so if your trans and wheel rolling diameters are about the same as donor nothing complicated to work out, the transducer gives 4 pulses per rev so 4000 pulses per mile, easy. Passed SVA first time with 4000 set, speed was within 5%.

 

jez

[Guest turbo]

benefit to the leky one is it can go anywhere in the dash and pick up can be taken fromeither rear driveshaft which is easy to get to.

[niduncan]

I have an electronic VDO speedo in my Series 3 and use a sensor that is triggered by the 4 bolt heads on the propshaft to diff flange. This works perfectly. It is easy to hang a bracket off the monocoque to mount the sensor on. Nice and easy to calibrate, either drive a measured mile or use a Satnav. If you need any pictures then let me know.

[Guest 2bsprint]

I have used these before for calribration, not the cheapest option but it was spot on after they had done it

 

http://www.speedograph-richfield.com/html/...ation_form.html

 

 

Glynn

[Guest robinj66]

I prefer the electronic speedo but if you want a set of ETB gauges with a mechanical speedo get in touch as I have a set available

[Guest AndrewH]

I have an electronic VDO speedo in my Series 3 and use a sensor that is triggered by the 4 bolt heads on the propshaft to diff flange. This works perfectly. It is easy to hang a bracket off the monocoque to mount the sensor on. Nice and easy to calibrate, either drive a measured mile or use a Satnav. If you need any pictures then let me know.

 

Hi a picture would be great.

 

thanks

 

A

[Guest AndrewH]

I prefer the electronic speedo but if you want a set of ETB gauges with a mechanical speedo get in touch as I have a set available

 

Hi thanks. I will PM you.

[Snapperpaul]

The dificulty here is that the diff ratio on a 1.8 could either be a 3.92 or a 3.62 and you cant be sure unless you have the diff I.D. tag still attached or you have used both the gearbox and diff from the same donor and still have the VIN plate from the engine bay, this will have a code letter in box 10 Axle, that could tell you what you have.

The gearboxes had 3 different speedo gear drives for different diff/wheel/tyre combinations and i have no idea which one you have, you may have to remove it to find out, some were colour coded, i think.

When you have got all this info you will have to tell them the tyres you are putting on as no Sierra had 205 50 15 tyres as standard and used a Type 9 box (Cosworth had 205 50 15 on 7x15 wheels but used the T5 box).

 

Personally glueing 4 magnets to the rear prop flange and making up a bracket for the sensor then running some shielded twin core cable was not a bad job and calibration for any combination is very easy (if you can do the maths) and you can also change it to suit if you are a bit out.

[Guest AndrewH]

The dificulty here is that the diff ratio on a 1.8 could either be a 3.92 or a 3.62 and you cant be sure unless you have the diff I.D. tag still attached or you have used both the gearbox and diff from the same donor and still have the VIN plate from the engine bay, this will have a code letter in box 10 Axle, that could tell you what you have.

The gearboxes had 3 different speedo gear drives for different diff/wheel/tyre combinations and i have no idea which one you have, you may have to remove it to find out, some were colour coded, i think.

When you have got all this info you will have to tell them the tyres you are putting on as no Sierra had 205 50 15 tyres as standard and used a Type 9 box (Cosworth had 205 50 15 on 7x15 wheels but used the T5 box).

 

Personally glueing 4 magnets to the rear prop flange and making up a bracket for the sensor then running some shielded twin core cable was not a bad job and calibration for any combination is very easy (if you can do the maths) and you can also change it to suit if you are a bit out.

 

Ummm. nice and simple them! I think I might have to go down the cardboard circle and chalk route!

 

Thanks for the detailed response.

 

A

[niduncan]

Being able to easily recalibrate is a real bonus. I have tried 3 different ratio diffs and different combinations of wheels and tyres which all required the speedo to be recalibrated. Having a mechanical speedo would have made this impossible.

 

[ibrooks]

Diff ratio is easy. Raise one rear wheel and support it securely because you are about to get uder there (or an able assistant is). Now with the car in neutral grab hold of the prop-shaft and turn it until the raised wheel has spun two complete turns. How many turns did the prop-shaft go? slightly over three and a half or just under four? there are only so many possiblities and 3.62 or 3.92 are by far the most common. You watch for two turns of the wheel because the other wheel is stationary so the free wheel will spin twice as fast.

 

The speedo gears can be worked out in a rough and ready fashion with the same system. Spin the prop and watch the number of turns the speedo cable makes.

 

In both cases if you are unsure then multiplying the numbers by the same factor will let you get a more accurate "guess". Imagine the case of the prop to wheel - if you multiply by 10 then you will be looking for the difference between 36.2 and 39.2 rather than 3.62 and 3.92 (3 complete turns rather than a third of a turn).

 

However....... If your existing speedo is accurate (and you know it hasn't been re-calibrated). The chances are that the overall system is giving 1000 turns per mile at the speedo cable. The calibration number should be printed on the face of the speedo. Most manufacturers stuck to 1000 turns and changed the drive cogs in the gearbox for different combinations of differential, wheels and tyres.

 

Iain

[Guest AndrewH]

Diff ratio is easy. Raise one rear wheel and support it securely because you are about to get uder there (or an able assistant is). Now with the car in neutral grab hold of the prop-shaft and turn it until the raised wheel has spun two complete turns. How many turns did the prop-shaft go? slightly over three and a half or just under four? there are only so many possiblities and 3.62 or 3.92 are by far the most common. You watch for two turns of the wheel because the other wheel is stationary so the free wheel will spin twice as fast.

 

The speedo gears can be worked out in a rough and ready fashion with the same system. Spin the prop and watch the number of turns the speedo cable makes.

 

In both cases if you are unsure then multiplying the numbers by the same factor will let you get a more accurate "guess". Imagine the case of the prop to wheel - if you multiply by 10 then you will be looking for the difference between 36.2 and 39.2 rather than 3.62 and 3.92 (3 complete turns rather than a third of a turn).

 

However....... If your existing speedo is accurate (and you know it hasn't been re-calibrated). The chances are that the overall system is giving 1000 turns per mile at the speedo cable. The calibration number should be printed on the face of the speedo. Most manufacturers stuck to 1000 turns and changed the drive cogs in the gearbox for different combinations of differential, wheels and tyres.

 

Iain

 

Thanks Iain,

 

this is really helpful and makes perfect sense. cheers.

 

I think I will go down this route as I am really happy with my wheel and drive set up and dont envisage changing it so a mechanical speedo will work for my needs.

A