Speedo Issues

[IronMike]

My 85 325e is experiencing a new symptom. The Speedo has a mind of its own and starts and stops at will. I think there is a connection issue but I need to determine where. Before you all start giving some recommendations, let me give you some history of what has been done.

This past summer, I had two speedo units rebuilt with all the solder connections reflowed. I installed one of the units and it worked fine most of the fall until this past December when it started misbehaving. At that time the speedo would slowly drop in speed over a period of 5-10 minutes to the point it was not registering any speed at all regardless of the speed I was actually driving. So.... I removed the SI Boad and replaced the batteries and reassembled the instrument cluster. Everything worked as it should for about 3-4 weeks when the local temperature dropped into the single digits. When that happened the speedo unit would not work for for 2-3 miles or what appeared enough time for the car to warm up. After a short time, the speedo would come to life and everything would work fine. Well, after about 2 weeks, the unit stopped altogether. At times I was able to slap the dash, and the unit would come to life.

Today on my way from work, the unit was totally dead, and then I happened to push the lower left portion of the instrument cluster. When I did this, the speedo immediately came to life and functioned properly.

So, there is loose connection somewhere that I need to fine and repair. I would welcome any insights. By the way, I think I've had the instrument cluster out 15-20 times over the last 12 months as I've worked on these issues. I'm getting pretty familiar with this part of the car.

Thanks in advance!

Mike

 

[IronMike]

Quick follow-up to my initial post.

Last night the temperature dropped 30 plus degrees so when I drove to work this morning it was in the single digits. As you expect, the speedo would not come to life. During my 42 mile drive I was able to get 'signs' of life where the speedo would occasionally spike to my actual driving speed (done by pushing the cluster at different points) but I was never able to get it to stay on and function as it was designed to.

 

[E30m42cab]

Next time you take it out, get a whole used used instrument cluster and swap out the tach to keep your odometer, and be done with it. If the thing works properly, you're good, if it doesn't, it's your wiring...
If it weren't for the fact that it works when you touch it, I'd think your SI board batteries were in need of replacement... esp. when cold. I doubt it's your speed sensor on the diff.

 

[jrt67ss350]

I bet it's a bad solder joint on the back of the instrument cluster where one of the wiring harness plugs is soldered to the circuit board. I had a similar intermittent problem with a turn signal indicator light in the cluster of my 87 that would spring back to life if you pressed on the cluster in certain areas. The solder joints on the circuit board of these clusters are notorious for cracking and subsequently failing to make a good connection. If it's a solder joint, it's easily fixed with a soldering iron.

 

[E30m42cab]

Justin makes a rare appearance and as usual, he's got the right answer!!! Too bad we don't see you too much any more. Dan, Joseph, and I are trying to hold down the E30 forum without you!!

How's the pontiac holding up?

 

[IronMike]

I bet it's a bad solder joint on the back of the instrument cluster where one of the wiring harness plugs is soldered to the circuit board. I had a similar intermittent problem with a turn signal indicator light in the cluster of my 87 that would spring back to life if you pressed on the cluster in certain areas. The solder joints on the circuit board of these clusters are notorious for cracking and subsequently failing to make a good connection. If it's a solder joint, it's easily fixed with a soldering iron.

Thanks for the input Justin. In this case the problem was not a bad solder joint. I had two separate speedo units resodered this summer and I was getting the smae symptoms with both of them. So in my mind the problem was in the
white multi-pin connector that attached to the back of the cluster. So a couple of weeks ago I took the cluster out and took a couple of slim plastic strips I could use as wedges. When I reconnected the multi-pin plug to the cluster I also inserted these 'wedges' thereby removing any play that may have existed. Guess what?? The speedo is working like normal and we've even had some single digit morning commutes. I'm pleased its working as it should!!

Mike