355 Speedometer trouble

Hi, I have trouble with the speedometer om my 98` F1. I got the sending unit on the gearbox changed at a major service oktober last year and hoped that it should cure the problem, but it didn`t help. The symptoms is that when I put the ignition on the needle is in the correct position, but when I start to drive it suddenly goes all the way around the meter and then ends up in a strange way down to the left and stays there, suddenly it can work for a short while, but then soon ends up dead again. I think it is an electrical failure. Any suggestions where to start looking...?

 

Are you getting any warning lights (suspension, Check Engine or F1)?

I'm not sure of the speedometer internal circuitry, but the speedo processes the signal from the gearbox sender and sends the data to the speedo needle (pointer) circuits and to other parts of the car. If there are no warning lights, perhaps the speedometer processing circuits are ok and just the needle drive circuits are bad.

 

Hi. Thanks for your reply! There are no warning lights and everything else work perfectly! How do I check if the needle circuit is bad, and what do I do to fix it?

 

I am a bit shocked you can drive the car. My F1 car speedo died and it would not allow any gear but first.

Off the top of my head, my approach would be:

1. Check the speed sensor and test or replace.
2. Check the wiring for pinches, breaks or corrosion
3. Pull the instrument pod and check / clean all the connections in the back.
4. Pull out the speedometer and lift the small circuit board out and touch up all the solder joints (this fixed mine)

 

Then it must be a speedometer needle drive circuit. Sorry, I don't know how you'd power just the needle.

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The signal going into the speedo goes to the needle circuit and to a frequency divider circuit. The divider circuit sends signals to the other systems (including the F1 system). I doubt it would be an input/output wiring problem or power problem because the divider circuit is working (you have no other faults). I'm assuming you drove long enough to generate a fault light and didn't stop the car straight away.

There are a few message threads on fixing speedometer internal problems, but I can't recall if the needle drive circuits were mentioned. Here is one of them (F348 speedo)

https://www.ferrarichat.com/forum/threads/348-speedo-burned-internals.503511/

 

I am not sure if this is completely related, but my 355 non-F1 has kind of the same problem: speedo needle works for about 10 minutes, then stops working.
I also get no warning lights, and all other meters work (if the odometer/tripmeter still works, I have not checked, but expect it not to work)
I suspect an increased resistance in the meter itself or the connections, and warming up the system (or gearbox?) leads to a resistance that is probably too high.
But have not found the time to take it all apart yet. (diagnosing/fixing my 550 takes up all of my time...)
When I have, and I know more, I will update in this topic so others might benefit.

 

Hi! Thanks for the replys. I´ll try to remove the dash pod (found a video on youtube and it seemed to be quite easy) and check the connections on the back of the speedometer. Hope this will fix it!

 

This may, or may not, help:

https://www.ferrarichat.com/forum/threads/speedo-died-which-sensor-is-it.600933/

 

Thanks! I have now checked the connections behind the speedometer but it didn`t help. I have booked an appointment with the workshop who did the service and changed the sensor and hope they can work it out. Can it be the meter itself?

 

It is most likely the meter. As I said earlier, if you are getting no warning lights, then the wiring is almost certainly ok. The speedometer is processing the sensor data properly and sending it to the other systems (and they are happy). All that can be broken is the internal needle drive part of the speedometer. Your workshop either needs to look inside the speedometer or replace it. It would probably be cheaper if you removed the speedometer yourself and took it to an instrument specialist.

 

Hi. Thanks for the information. This sound like o good theory! I will call an instrument specialist here in Norway tomorrow. I think I can do the job with removing it myself. To be continued....

 

Hi. I`ve removed the dashpod from the car and unscrewed the three small schrews that fastens the speedometer but how the h.... do I remove the odometer reset knob...?

 

with force... It's the same as the tacho knob

https://www.ferrarichat.com/forum/posts/147669157/

 

OK, thanks. that was that I was afraid of. It’s not a very good feeling to use force on these parts...

 

There is a place in Florida that fixes them but can not remember the name

 

Hi! I got the knob removed by using a hait drier and a little force. The speedometer is now sent to an instrument spesialist in Oslo here in Norway. Hope they can fix it!

 

Hi.
The speedometer shop here in Norway couldn’t fix it…. Managed to buy a brand new one from a company called Prosport in England so now erverything is working perfect. Considering to get a shop to set the milage on the new one to the same as the old one, but that now that must wait until the winter! Haven’t quite Image Unavailable, Please Login given up to fix the old one either, so if anyone has a recommandation for a good speedometer shop I would appreciate that!
Ola

 

Hi. You can try calling these guys:

https://speedycables.com/

 

Thanks, I have send them an request.

Ola