It seems that I need to replace that as well, because I will maybe destroy it when I dissamble the wheel hub
I am a bit confused, you are trying to identify your rear wheel bearing on a 4x4 conversion, the company that did the original conversion are no help, you have taken the bearing to match it up but are worried it may damage the ABS?
There are several types of ABS sensor operation depending on how it gets the signal.
Unless you short the terminals on the sensor at the wheel you are unlikely to damage the ABS pump/ECU which is the main expensive bit.
So do you know how your ABS sensor gets it's signal to send to the ABS computer?
Some use an external vane type thing that is registered by the sensor and some use a magnetic type that is usually in the end of the bearing in line with where the sensor pick up is fitted. It may not be obvious, just a black plastic ring where you would expect a built in oil seal on a bearing.
The first type shouldn't be a problem when ordering a bearing as most good nearing shops just take measurements and give you that bearing.
The second type is basically the same in that the shop measures it, the only difference is you ask them to supply the ABS version that has the magnetic ring in the end of it.
Normally if the bearing is thoroughly cleaned the numbers to recognise it are engraved in the metal at the ends.
If you are just going to ask for a fiat part from a stockist you are probably wasting your time, it needs to be a bearing specialist, not just someone who looks up Fiat in his book.
