Speedo problem

Hi all

Just wanted to see if anyone has heard of a problem my car has developed recently. Speedo and Odometer both did'nt work when we bought the car. I changed the sender unit and it fixed the problem. Recently though, after about an hour on the road the speedo starts to waver and bounce around and it gradually stops working altogether. After stopping for several hours for lunch or whatever, speedo works again and then the same thing happens again. This has happened consistently of late. Any ideas?


Thanks in advance

David

 

The first thing to check would be the connections and connectors to the speedometer. That being said it unfortunately sounds like the main chip on the speedo board is failing. Luckily a new and improved board is available now from Palo Alto Speedometer designed by a fellow fchatter.

 

I have exactly the same issue, a new sender is on the way. A new board did not solve my problem. Still jumps around and eventually dies. Could be a some sort of temperatur issue with a broken sender, as the speedo always works for the first couple of minutes?

 

My speedo presented the same behavior, but cleared up for almost 5 years after putting Birdman's fuse strip in. Then a couple months ago it started up again. I'd loose it for days to a week, it would come back for a while and go out again. Finally, it just stopped coming back to life. I changed the sender, but no luck. I guess the next step is the board; however, I've spent so much more of the last year under my car than in it, I'm going to depend on an iPhone speed ap for now so I can enjoy DRIVING my car for a little while before I tear it apart again.

 

Mine did exactly the same as the OP describes. Fine when cold , died usually after about 15-20 miles of running. A new sender cured it.

 

Mine had also done it but it was a bad connection due to an oil leak I once had getting into a lead connector.

 

Mine is an '88.5 328 GTS, but I had similar symptoms with my speedo. One thing different: after replacing the sender didn't solve the problem, I did find that a firm rap with my bare hand on the side of the binnacle, would often (but not always) bring the speedo back to life (temporarily, of course). Ultimately, I replaced the speedo in the instrument panel with an NOS one I bought online ($$$), and my problem has been gone for over a year now. Of course, I lost the miles on my original odometer, but my plan is to repair my original speedo with a new circuit board, roll the odometer forward to account for the couple thousand miles I've put on my car with the NOS speedo, then reinstall the original one, and I'll be back up to snuff.

So, in my case, it was definitely a failing circuit board in the speedo that was causing my problem.

I was working with an F-Chat veteran (Alhbln) who was designing a new speedo board for 308s, to help him revise his design to accommodate the 328s also. Last I'd checked in July of this year, Adrian was nearing the end of his development, and would be able to offer the new board soon. I think he has already put out the 308 board he was designing, so that might help you out. if you search here on F-Chat for 'speedometer 328' you'll find the thread where Adrian's development was chronicled.
Good luck!

 

My '85 GTSi did the exact same thing... speedo dropped out entirely last year. New sender unit ($$$) a couple months ago created the drop-out symptom around 20min into any drive. Worked again once everything was cooled back down. I'm planning to replace the speedo next.

 

Mine did the same (75 GT4). I rebuilt the sender a few times to no avail. I looked at the signal from the sender with an oscilloscope and found it was not sinking far enough down to trigger the speedo. Using advice from Alhbln I put a resistor between the signal line and ground and that fixed the problem. Also, check your battery ground strap. If the ground is bad, it will show up on the speedo first.

 

I hear ya!