Speedometer Sticking

[limalbeps]

Hi guys, I would appreciate any experience on an issue I have with a speedometer. I sent it off to be cleaned by a reputable instrument repairer and now that its returned, the speedo sticks at an indicated 80mph.   I resent it back to the repairer, who looked at the speedo again, bench tested and said that the speedo is not the issue.  He believes that its the sensor on the gearbox, but all was functioning fine before with the speedo.

 I have been scanning pelican and most of the posts with sender failure show issues at low speeds, whereas this is fine ( including trip and odometer ) until indicated 80 is reached.  I have tested the signal from the sender in the tunnel by the rear seats and I am getting resistance values.  It may be really bad luck that the sender failed whilst the speedo was out of the car, but I don't see any posts on the net that have a speedo sticking at  a high(ish) speed. Originally I though that the needle was stuck and sent the speedo back, but the repairer is adamant that the speedo is fine on the bench.  

I know the next step is the replace the sender, but I am feeling a bit sore after spending quite a lot to receive a clean, but now , non-working speedo and I would appreciate any input before spending pm the sender, or at least some logical explanation as to why a speedo would just stop indicating beyond a certain speed.  thanks 

[Phill]

My first thing to do would be to check all the earths, especially the one to the back of the Speedo. They do strange things when the earth is dodgy.

Edited May 30, 2020 by Phill

[SilverWT]

What do you mean by "stick at 80"?

Reads OK until you get to 80 then it stays there regardless of speed? Does it return to 0 when you turn the car off? Or, can you make it change from 80 by tapping the glass? 

[limalbeps]

At first it stuck, then I left it and it returned to zero. Subsequent trips, it has moved freely up to 80, but won’t move further, but drops back at lower speed. My first thought was that something mechanical was stopping the needle moving further around the clock....hence why I returned it to the repairer. However, he says that the movement is free. 
 

I’ll check the earths and see if I can get any joy

[limalbeps]

Update....went for a spin last night and the needle still sticks now from 70 onwards, but can be corrected by frantic tapping of the glass...does this indicate that it’s the gauge?

[SilverWT]

10 hours ago, limalbeps said:

Update....went for a spin last night and the needle still sticks now from 70 onwards, but can be corrected by frantic tapping of the glass...does this indicate that it’s the gauge?

I would certainly think so.

Mechanical intervention at the gauge has an effect, so most likely some sort of interference as the needle moves around.

Mark