21 replies to this topic

[dklawson]

Graeme, since Austin1987 knows he has a 10 MPH error, making the alignment marks and repositioning the needle by 10 MPH lower should get his speedo right where it needs to be and provide the hairspring preload at the same time.

 

If I remember correctly, there should be a tiny dot on the gauge face just below the stop pin.  That is where the needle should rest if it is on the "wrong" side of the needle stop pin.  I have never trusted that with 50+ year old gauges the stop position is still that dot.

[GraemeC]

I don't think I agree - if his speedo is showing 10mph with no input then there is no preload at that rest point.  Repositioning the needle 10mph lower will mean it reads zero, but still no preload.  It needs to be 12-15 mph lower to introduce the preload.

 

I worked in a Ford gauge factory in a previous life and despite it being some 40 years on from the Smiths design, very little was any different in how they worked.  Unless you started looking at the stepper motor driven ones.

[dklawson]

I see your argument about the preload but the OP has also reported that the gauge is off (10 MPH too high) across the range. By adding more than 10 MPH of correction just to insure you have preload on the spring means that the gauge will now read low by whatever additional preload is added.

[Austin1987]

Tried to get the needle off as directed but it is really stuck on. Is it normally very hard to lift off?

[dklawson]

Yes.  They are usually pressed onto the spindle very tightly so they won't move.  That's why I told you not to twist the needle.

 

If using a dinner fork under the needle did not work, your next best method is more difficult.  With two small, long shank flat blade screwdrivers resting on the screw heads securing the center of the gauge face you can sometimes lever the speedometer needle off.  You have to get both screwdrivers on the center most part of the needle hub and resting on the screw heads to provide leverage.

[Austin1987]

I have now got it off and replaced the needle at the white mark before the stop, I will get the dash built tomorrow and have a road test. I will let you know how I get on.

[Austin1987]

OK so today I fitted the speedo back in the car and all worked fine but the speed was still slightly out. I found that I put the needle on in-line with the white mark but the weight of the needle then dropped it further down so the trick is to have the needle placed just above this mark so when you let go it drops to it, then the pre load is correct and the speed is near enough spot on. I will have another road test later but it seems to have solver the problem.

Thank you to all for your help.