the speedo stopped working on the barch. It was suggested that it was the sender unit so a unit was bought - no change. after close investigation it turns out the pinion? in the gear box is broken. replacement gearbox or rebuild? is there any advice about the merits of either option and what if I continue to drive it without doing anything? and why would the pinion or whatever break in the first place?
Technical speedo problem
- Thread starter babybee
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Technical speedo problem
I cant comment on the repair BB as I'm new to the Barchetta myself. I would obviously try to have it fixed but continue to drive it in the meantime. The speedometer isnt part of the MOT so nobody would know. You could use the rev counter to judge your speed and someone on here will have the same tyres/wheels to give you the approx revs in certain gears. TBH, I dont think my speedo is all that accurate anyway.
Steve
Steve
Did the mechanic not say if the pinion can be changed without stripping the gearbox down?
Looking at the parts cd, it's only about £15 for the part.
Bumble - according to sat-nav, my Barchetta speedo is 2mph out from zero all the way up to .... er .... motorway speeds.
Looking at the parts cd, it's only about £15 for the part.
Bumble - according to sat-nav, my Barchetta speedo is 2mph out from zero all the way up to .... er .... motorway speeds.
Hi all thanks for the comments - the mechanic said that the speedo drive inside the gear box seems to have broken away so the sender is not being driven round. Apparently the offending part is plastic and so will probably do no harm to the rest of the box. and I don't think the part can be changed without invasive surgery. If needed speeds can be got from the satnav.
if you have ABS then you could consider using one of the ABS sensor signals as a source of speed information. This is perfectly possible but would require a little bit of electronics to sense, amplify and calibrate to road speed.
The ABS system knows exactly how fast the car is travelling as a matter of design function. The Fiat Examiner dignostic tool can read/display true road speed from the ABS sensors.
The ABS system knows exactly how fast the car is travelling as a matter of design function. The Fiat Examiner dignostic tool can read/display true road speed from the ABS sensors.
hi all. i had problem with needles, i removed them and did not mark zerro position. one way to adjust is to push them all around clockwise until you feel preasure, then push it a little more and release them to spin back to zerro position. repeat that until neddle is on right position. this is not 100% correct way, but it works.
very intrigueing solution I will look into it - is it too much to ask if the signals would then be routed through the existing speedo dial?
with ABS there are 'n' teeth (possibly 50 or more) per wheel revolution. I have no idea if there is a standard for this, but I suspect there may be. You can count the teeth yourself.
The gearbox speedo drive sensor comes off the final drive so will produce 'm' pulses per wheel rev. If you are dead lucky then 'n' and 'm' per wheel rev are the same. If not then hopefully 'n' is greater than 'm' by a sensible figure (like 2x, 4x, 32x etc.)
The divided signal is sent into the existing gearbox sensor pickup cable.
I have one reservation with tapping into the ABS sensor signal. The connection you make, ideally with a propper 'Y' cable, must NOT interfere with the ABS wheel sensor signal.
This sensor produces small pulses from a fairly high impedance source. This means that you pickup circuit MUST NOT load the signal. Any medium to major degradation in the ABS signal to the ABS control unit will make the ABS unit think the wheel is locked when you are breaking and thus release the braking to that wheel. Far from ideal and hopefully the remaining 3 wheels will be sufficient.
There may be a buffered and relayed ABS pulse signal to the ECU / body computer that would be safer to tap into. Grounds for more research.
The gearbox speedo drive sensor comes off the final drive so will produce 'm' pulses per wheel rev. If you are dead lucky then 'n' and 'm' per wheel rev are the same. If not then hopefully 'n' is greater than 'm' by a sensible figure (like 2x, 4x, 32x etc.)
The divided signal is sent into the existing gearbox sensor pickup cable.
I have one reservation with tapping into the ABS sensor signal. The connection you make, ideally with a propper 'Y' cable, must NOT interfere with the ABS wheel sensor signal.
This sensor produces small pulses from a fairly high impedance source. This means that you pickup circuit MUST NOT load the signal. Any medium to major degradation in the ABS signal to the ABS control unit will make the ABS unit think the wheel is locked when you are breaking and thus release the braking to that wheel. Far from ideal and hopefully the remaining 3 wheels will be sufficient.
There may be a buffered and relayed ABS pulse signal to the ECU / body computer that would be safer to tap into. Grounds for more research.
larkim
Established member
Is the mileage not stuck too? I had a panda once on which the speedo stopped working. And at the same time the odometer ceased working too. There wasn't too much risk on the motorway with "incorrect" speeds (it was a plain 1000 Panda), but driving past cameras in 30-limits was a "best guess" trick. Presumably having a non-working odometer IS an MOT fail (though how they'd tell, I don't know!)
Matt
hi there !
take a look in this thread ... https://www.fiatforum.com/barchetta/439509-speedo-stopped-working.html
take a look in this thread ... https://www.fiatforum.com/barchetta/439509-speedo-stopped-working.html
