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Author: Subject: Speedo Misbehaving
L1berator

posted on 30/3/21 at 01:34 PM Reply With Quote
Speedo Misbehaving

Good Afternoon,

I was wondering if someone could shed some light on an issue I have with my speedo. I have a Smiths International 80mm electronic gauge which was supplied as part of a full set from Kitspares. The sensor is mounted at the back of the tunnel and is activated by the 4 bolts holding the rear of the propshaft to the diff.

The speedo reads fine when starting the car off, but after few miles, as the speed increases, the speedo needle starts to drop, eventually reading too low or, in some cases, zero. When I stop the car and then pull away again (without having to switch the ignition off), the speedo works fine, and then the issue starts all over again.

I've checked the sensor and it's 1.5mm from the propshaft bolts (Caerbont recommend 1-2mm) , and is calibrated accurately. I've tried adjusting the distance and it doesn't seem to make any difference to the problem.

Has anyone seen anything like this, or have any ideas how to rectify it? It's very annoying...

Thanks,

Peter

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Slater

posted on 30/3/21 at 02:11 PM Reply With Quote
I recently had similar issue on a 2007 ETB speedo, needle would read 140 mph then 0....plus my LCD odo display was intermittent. I called ETB and explained, and ended up sending it back for a refurb, recieved it back and it's been perfect since. Good service! 67 quid including the postage. Think it was caused by dampness inside the gauge as the issue sometimes went away when I brought the gauge inside the house and put it in the airing cupboard.

I suggest you call Smiths and see if they can offer advice or refurb the gauge, then at least you will retain you mileage.





Why do they call Port Harcourt "The Garden City"?...... Becauase they can't spell Stramash.

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mcerd1

posted on 31/3/21 at 12:13 PM Reply With Quote
Don't know how much difference it makes but its worth considering that the bolt centres are not even on the sierra prop flange - it is a 90mm P.C.D. but they actually make a rectangular pattern (approx. 60x67mm) so maybe this could upset the speedo ?

if thats the case you'd need to move the sensor to somewhere it can get an even signal (like the driveshaft bolts if you have bolt-on ones)

or maybe fit a small trigger-wheel in-between the diff and the prop (although you'd probably need to get this made and fit longer M10x1.0 bolts too)
(you can actually get ones for the driveshaft pre-made linky, but the bolt heads should work in this case as the driveshafts have an even spacing)




the other thing that could cause an issue is vibration in the sensor mounting - how rigid is it ?
you could have the perfect gap when the car is at low speed but vibrates out of alignment at higher speeds..





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roadrunner

posted on 31/3/21 at 12:59 PM Reply With Quote
quote:
Originally posted by mcerd1
Don't know how much difference it makes but its worth considering that the bolt centres are not even on the sierra prop flange - it is a 90mm P.C.D. but they actually make a rectangular pattern (approx. 60x67mm) so maybe this could upset the speedo ?

if thats the case you'd need to move the sensor to somewhere it can get an even signal (like the driveshaft bolts if you have bolt-on ones)

or maybe fit a small trigger-wheel in-between the diff and the prop (although you'd probably need to get this made and fit longer M10x1.0 bolts too)
(you can actually get ones for the driveshaft pre-made linky, but the bolt heads should work in this case as the driveshafts have an even spacing)



By Joe, I think you've cracked it.

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02GF74

posted on 31/3/21 at 01:27 PM Reply With Quote
quote:
Originally posted by roadrunner
quote:
Originally posted by mcerd1
Don't know how much difference it makes but its worth considering that the bolt centres are not even on the sierra prop flange - it is a 90mm P.C.D. but they actually make a rectangular pattern (approx. 60x67mm) so maybe this could upset the speedo ?


By Joe, I think you've cracked it.


I'll be amazed if that works as it would be be a wee poor design.

You will have a reluctanc sensor; a magney with a coll wrapped around it. Any iron based object (steel bolts contain iron) passing through the magnetic field distorts it causing an electrical pulse in the coil.

The speedo should be edge detecting the electical pulses and counting them in a given time. If it requires them to be periodic which at a constant speed they are, then that's not clever.

By all means give it a shot.

Have you not considered using a sender the fits to the gearbox speedo drive? IMO that's the best solution.

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peterrosey

posted on 9/4/21 at 09:13 AM Reply With Quote
Is the mounting bracket entirely rigid - had a similar issue with a flexing bracket. At speed or over bumps it would just move a little and cause the speedo to drop out. Beefed up the bracket and no issues - they're very sensitive to the gap being kept constant.
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40inches

posted on 9/4/21 at 09:18 AM Reply With Quote
Had similar on mine, ok up to around 50mph then dropped to zero, moved the sensor from the prop to a drive shaft and re calibrated,
been fine since.

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Deckman001

posted on 10/4/21 at 10:20 AM Reply With Quote
I had a very similar issue, my sensor was glued to the tunnel and I have glued 6 small magnets on the prop shaft. It was driving me mad, working well when up on jack, but on the road is didn't work well.
It is now bolted a lot further back along the tunnel where the prop seams to be steady when rev'd and driven. I have also reduced the cable length and removed any excess cable behind the speedo , I have also removed an extension bit of cable that was used to make it look better. The sensor is now between 5-10mm away from the magnets and it seams so smooth I can't believe how good it now is after the little changes.

Mine is fitted to a live axle car so was a risky place in the tunnel due to the axle and prop moving up and down a little as well as being able to pivot slightly across as well, but it now feels perfect.( well it was on this mornings test drive testing the steering and speedo )

Jason

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02GF74

posted on 10/4/21 at 10:42 AM Reply With Quote
As I said earlier, don't waste time on bolt heads/magnets/brackets etc but do it properly by fitting Ford electronic sensor. I'll get critised for saying that as although many people have had success with that arrangement, you never read about people having problens with the Ford speedo sensor, which cannot be said about the former.

You'll need an adapter:
Burton popwer: 20 https://www.burtonpower.com/revotec-electronic-speedo-adaptor-ford-gearbox-revt9-a.html

plus a sensor:
10 https://www.ebay.co.uk/itm/Fiesta-MK3-Speedo-Sensor-genuine-Ford-94BB-9E731-CA/224330016313?hash=item343b1c6639:g:xjEAAOSwgAFgETC~
12.50 (China)https://www.ebay.co.uk/itm/Gearbox-Speedo-Speed-Sensor-For-Ford-Escort-1995-01-Fiesta-1995-02-Cougar-98-01/143724354106?fits=Car+Make%3AFord&am p;hash=item2176a39a3a:g:5UYAAOSwrwxfVfQr
13.70 UK https://www.ebay.co.uk/itm/Speedometer-Gearbox-Speedo-Sensor-For-Ford-Escort-Ka-Fiesta-Cougar-95BB-9E731-BA/254352576415?fits=Car+Make%3AFord&hash =item3b38984f9f:g:ikoAAOSw~5ZfhB3S

Total costs less than filling up the tank with petrol.

The only reason you would not do this is because there is not enough room for both items

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Deckman001

posted on 10/4/21 at 01:25 PM Reply With Quote
quote:
Originally posted by 02GF74
As I said earlier, don't waste time on bolt heads/magnets/brackets etc but do it properly by fitting Ford electronic sensor. I'll get critised for saying that as although many people have had success with that arrangement, you never read about people having problens with the Ford speedo sensor, which cannot be said about the former.

You'll need an adapter:
Burton popwer: 20 https://www.burtonpower.com/revotec-electronic-speedo-adaptor-ford-gearbox-revt9-a.html

plus a sensor:
10 https://www.ebay.co.uk/itm/Fiesta-MK3-Speedo-Sensor-genuine-Ford-94BB-9E731-CA/224330016313?hash=item343b1c6639:g:xjEAAOSwgAFgETC~
12.50 (China)https://www.ebay.co.uk/itm/Gearbox-Speedo-Speed-Sensor-For-Ford-Escort-1995-01-Fiesta-1995-02-Cougar-98-01/143724354106?fits=Car+Make%3AFord&am p;hash=item2176a39a3a:g:5UYAAOSwrwxfVfQr
13.70 UK https://www.ebay.co.uk/itm/Speedometer-Gearbox-Speedo-Sensor-For-Ford-Escort-Ka-Fiesta-Cougar-95BB-9E731-BA/254352576415?fits=Car+Make%3AFord&hash =item3b38984f9f:g:ikoAAOSw~5ZfhB3S

Total costs less than filling up the tank with petrol.

The only reason you would not do this is because there is not enough room for both items


The above was an option I was thinking about, but I was worried about getting the correct ratio sorted due to the correct diff ratio and wheel and tyre options?

Jason

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02GF74

posted on 10/4/21 at 05:41 PM Reply With Quote
After market speedos are programmable.

I had a Racetech speedo and from memory it requires the number of pulses per mile.

Depending on how many pulses the Ford sender produces per turn, you can work out the rest.

Otherwise just jack up one rear wheel, turn it through one revolution counting the pulses (and multiple by 2 due to diff action right?)

BTW I made my own sender so do not know what type the Ford one is i.e.reed switch (unlikely), inductive or Hall effect.

Oh, the other reason you wouldn't go this route is if the gearbox is not a Ford.

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Fozzo

posted on 1/5/21 at 05:28 PM Reply With Quote
Is this possible for an mX5 gearbox? I have the same issue on the prop shaft bolts.

The MX5 gearbox sender is electronic and has a 5v pulse - is this too much for the Racetech Speedometer?

Thanks in advance.

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