Hi All Driving my '92 348 on some rough cobbled streets recently my speedo decided it prefers smoother surfaces and took itself on a holiday. Driving as slow as possible given the surface, all was fine until I heard a few 1980s-style beepy sounds from the dash with which the speedo stopped working. It felt like I may have momentarily lost power for a second too, though I have had no such issue since (so could have been my reaction to thinking the car was about to stop working hours from home and needing to collect someone to get to a wedding!). Whilst driving for the next hour or so, a large bump would get the speedo working again and with the next bump it would stop working. During the hour the moments of operation reduced and eventually stopped, and the speedo has remained inactive since. I've searched the existing 'speedo not working' threads and it was usually the sensor having failed, so I've had the sensor by the left rear wheel checked and was told it's fine. It seems logical (to my simple mind) that some wires in the dash became loose and finally came apart during that thrilling hour of bump hunting and avoiding. I've loosened the dash console and checked the tightness of all the screws there, and the connections seemed good. So I guess the loose wires may be inside the speedo/odometer unit. My question is: can I take that apart without interfering with the actual odometer mechanics or anything else getting upset? I'm talking about the screws holding the white cylindrical unit to the grey unit in the attached photo. Also, any other ideas? Thanks very much. Image Unavailable, Please Login
My Spider did this too. It was a the sending unit, but not at the wheel. I think it was in the engine compartment somewhere.
You could try Palo Alto Speedometer, perhaps it is the gauge itself. The speedo sending unit is the most common issue we see though.
My question is: can I take that apart without interfering with the actual odometer mechanics or anything else getting upset? I'm talking about the screws holding the white cylindrical unit to the grey unit in the attached photo. Also, any other ideas? Yes, you can take it apart with out worry about hurting anything. But I doubt you will find anything wrong without the proper test equipment. This speedo is a sort of hybrid. Its only partly electronic. It receives a frequency modulated signal from the sending unit near the LH side of the transaxle. As the speed goes up, the signal frequency goes up. The speedo receives this signal and converts it to a voltage that drives a small motor that in turn rotates the odometers and generates a magnetic field to move the needle much like the physical cables of old used to. The problem usually lies in either the electronic circuit or the motor itself where the bushings can wear out. From your description, I'd guess your problem is in the electronic circuit. A good speedo shop that specializes in speedos of this type can usually fix the problem. Motors on the other hand are no longer available so you'd have to find a decent old core for that. I have an old core but the motor is shot. However, the circuit board is likely still good if you can't find something near you.
Probably more info than you'll ever want to know or need? Right here http://www.ferrarichat.com/forum/348-355-sponsored-bradan/503511-348-speedo-burned-internals.html On mine, however, I found a shorted seatbelt ECU that was frying the Speedo's circuit board.
Thank you guys, very helpful and much appreciated. Good to understand how the system actually works as well Jerry - thanks for explaining. I'll set about checking the sending unit or then trying to track down someone who can test the electronic circuit. Will report back in due course...
Thanks Wade - our posts crossed just now - that link is well beyond anything I'll be attempting but certainly informative for anyone so minded! Curious that your seatbelt ecu caused the damage, and keeps me wondering of the extent of damage caused to my circuitry by driving through the centre of one city. Tip of the day: avoid central Milan in your 348!
The seatbelts ECUs are for the US spec "mouse motor" system. So, not an issue with Euro cars. The wiring isn't specified in work shop manual diagrams either. But take a look at Connector 115 (left side of the engine bay). It's a common point of failure and both speedo sensor wires pass through it. I was getting stray voltage through mine but this link provides a description and breakdown. http://www.ferrarichat.com/forum/348-355-sponsored-bradan/505341-348-quick-voltage-check-connector-115-pin-2-a.html Which makes sense; a loose/broken connector will be effected by jounce, bounce and jiggle (or is that wiggle?). . Image Unavailable, Please Login
Yes, you can remove the white rear cover without disturbing the mechanical portion of the speedo, but at some point you will need to pull the knob off of the odometer reset shaft, which can be a bit unnerving as it takes some force to remove it. The sender is the most likely culprit but it wasn't the complete solution in my case. I do have a few parts kits available to replace most of the components on the speedo drive board but no idea how much they'd cost to ship to you. Good luck and let us know what you find. This is apparently a pretty common problem but the cause is not always easily identified.
Thanks Mike. I need to catch a few hours to get stuck in to all this... In the meantime, just having to wait for GPS to catch up with me!
