1990 348

How come my speedometer works sometimes and some times it just drops to zero and doesn't work?

 

Probably your speed sensor. The wire tends to break on the sensor and only sometimes make contact.

 

OiTBill; Welcome to Ferrari Chat!

Just in case you are not familiar with the system in your 348, here's how it works. There is no drive cable involved with the speedometer in your car, it's totally electronically operated. There is a sensor mounted on the transmission case at the back of the car, next to the inner end of the left axle. This sensor is reading the rotating speed of one of the inner gears, and translating it into an electronic signal. The signal is sent through two wires to the speedometer, where a circuit board reads the signal and drives the needle. The usual problem is that the sensor breaks down and sends an erratic signal (or no signal) to the speedo. There is at least a possibility that you have a bad connection at the pigtail plug next to the sensor, or at the twist connector near the top of the LR shock tower, or at the printed circuit board on the back of the instrument cluster. And you may have a problem with the speedo itself. Is the odometer working normally, or does it also stop working when the speedo stops?

There are a few basic checks you can make to be sure that the connections are clean and tight, but you probably have a bad sensor. My opinion.

 

Hi Jeff, do you know what year they start using the elctronically operated speed sesor? I wan't to know if my 84 308 QV is electronic or mechanical thank you.

 

They have been around a long time my '75 308 GT4 had a electronic speedo and your 308 does also. Regards,Vern

 

This little gizmo is screwed into the left side (driver side) of the gearbox:

http://www.ricambiamerica.com/product_info.php?products_id=193699
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How much does the speedo sensor run?

 

click da' link, mate!

 

Thanks for the info sir.

 

Crap... Sir.. am I that old. LOL Regards, Vern

 

I remember reading somewhere here that the speedo sensor produces a square wave?? Anyone know if it is a basic Hall Effect-type sensor?

 

Yes!

http://webpages.charter.net/aircover/348/1994Ferrari348Spider.html#Speedometer

 

Thanks for the reply's.