Citroen speedometer

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algieuk
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Citroen speedometer

Post by algieuk »

I've just bought a Xantia 1.9D (non-turbo) and have discovered the speedo reads 20% slow. The odomoter is also 20% slow which suggests to me that the drive ratio is wrong.
The car may have had a replacement gearbox, and I'm wondering if Xantia's all had the same drive ratio, or were some of them different. Alternately the speedo head may have been changed.
Whatever the reason I need to know what ratio drives havve been fitted, and to what vehicles, so I can get the right one.
Can anyone enlighten me?
TIA
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Post by JohnD »

There's a difference in ratios between turbo and non-turbo gearboxes. Maybe yours has been changed. Turbo 5th is .658:1 and non-turbo 5th is .800:1 or .757:1
Dave Burns
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Post by Dave Burns »

The only things that matter here are the speedo drive gear ratios and the tyre sizes, neither the engine or gearbox have any real bearing on this except in that as stated, a box may have been fitted from a car using a different size tyre.
I think an error of 20% is caused by something other than the speedo drive gear being wrong though.
The correct tyre size for a 1.9SD is either 165/70/14 or 185/65/14 according to the owners manual not sure about the 1.9D.
These tyres have theoretical diameters of 586.6mm and 596.1mm respectively.
For your speedo to read 20% slower than actual you would need tyres in the region of 700 to 715mm diameter and to allready have the correct drive gear fitted for your car and tyre size.
The largest tyre fitted to the Xantia is 205/60/15 with a theoretical diameter of 627mm, now the differences between this and the 165 and 185 are only 7% and 5.5% respectively, so it would appear that a discrepancy of 20% would be well outside the range of any available drive gear.
A drive gear designed for larger tyres and being driven by smaller ones would show the oposit and give an increase in displayed speed over actual speed.
Looks like your speedo head could be stuffed, or another possibility that the box was indeed changed and was from a different type of car alltogether with even smaller wheels and tyres, but I doubt it.
Dave
algieuk
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Post by algieuk »

Thanks guys. That's pretty much what I thought. The only thing that suggests to me it is the drive ratio though is that the odometer, which is a purely mechanical device is out by exactly the same amount as the speedo which is a spring/eddy current drag device, and for them to both vary to the same degree is extreme co-indidence.
So I think what I really need to find out is how many teeth should there be on speedo drive pinion? When I am sure that is right then if there is still a fault it has to be the speedo. Any ideas as to how many teeth anyone?
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