1986 944 NA speedometer question

[dcarlson]

noticed it occasionally seems to stick at bottom until I tap it - works OK after that .. Car has been sitting all winter and just getting out last couple days - my understanding there is no cable to lube - is there anythiing ls to check or is this normal on a 120,000 or so unit? thanks for any insight .
PS: had the odometer gear replacement thing done 2 years ago. All else working OK.

[OK-944]

Not sure if this will help...but I replaced the odometer gear on my 87 na (so would be the same setup as yours), which involved very gently removing the speedometer needle. My first thought in your case was that there may be some interference between the speedo shaft and the speedo gauge faceplate, but at least for my car this is not the case...as the faceplate opening is a bit larger than the shaft itself.

But again...the removal and installation of the speedometer needle was very delicate...and my guess is that it might be possible to put a slight bend in the shaft upon re-installation. You may want to look very closely at where the speedo shaft enters through the faceplate to see if the faceplate opening is indeed evenly concentric with the shaft...and if not, then there may be some interference between the shaft and faceplate - which I would imaging could be repaired by removing the needle, and very (very!) gently bending the needle. To be honest though, this would be my very last resort...the thing is delicate!

Another possibility is that there may be something about the speedo shaft bearing itself...like a bit of loose material (even dust...it would not take much) somewhere on the shaft below the faceplate, or in the bearing itself.

I suppose that there could be a bit of dried up lubricant in the bearing or on the bottom of the shaft itself...but I'd be very careful about re-applying anything. I would think either some watch oil or a bit of WD-40, which is appropriately thin, but sometimes it needs a bit of filtering (coffee filter is good) prior to applying.

Clarks garage has a decent tutorial on speedometer gauge disassembly, and if you cannot find this, let me know and I can email this to you. Good luck, and if you do try to tackle this yourself, be super careful with the needle, and do your best to keep dust out of the gauge interior.

[peteb]

Hi,

My '86 has this problem. After not being driving for a while the speedometer may stick at zero. A tap on the speedometer "fixes" the problem. I may go months without seeing the trouble again.

You are correct that there is not a speed cable. Late cars have an electronic speedometer. Does your odometer still work? I could see mine turning while the speedometer was stuck a zero. This is proof there is a speed signal getting to the speedometer electronics.

I'm fairly sure the trouble is in the connections to the moving armature coil/spring assembly. I have no 100% proof. I couldn't find a specific problem when I had my speedometer out of the dash. Not a mechanical sticking issue for me. Everything moves freely. No obvious trouble with the circuit board/driver electronics. I'm just kind of guessing based on my experience with analog meters and not finding other problems.

There are four electrical connections between the moving and stationary parts of the speedometer with clock springs in between. They are all delicate so I didn't attempt any rework for the risk of breaking the speedometer. What may happen is the the connections pick up some corrosion after sitting and go bad. Any movement such as a tap, makes a connection. After that the movement of the speedometer keeps the connection good until the car is parked for awhile again.

I'm ignoring the problem for now. I did pick up a spare instrument cluster as a backup in case of a complete failure.

All part of the fun with old cars..

Peter