[Healeys] speedo stuck at 78 MPH

[Bob Spidell]

Ira,

The speedo needle gets 'wound up' by the cable when moving, then a 
spiral 'watch spring' should return the needle to zero as the cable 
slows. I think you may have two problems, which may or may not be related:

1) The cable is driven by the angle drive, which is driven by a gear on 
you O/D output shaft. It should not spin--at least, I don't /think /it 
should--when you turn it at the speedo end, unless you've pulled it out 
of the angle drive. Since it's not moving at speed, the angle drive is 
probably TU.

2) There's a couple things I can think of offhand that could cause 
'non-return-to-zero;' the spring is busted, or something else is jammed 
in the speedo (the cable drives a magnet, which torques a metal plate to 
turn the needle; not much to break).

The speedos can be disassembled--the hardest part is getting the guts 
out with the odo zeroing knob in the way--and you could have a look. Or, 
you could send it to one of the gauge shops (Nisonger, West Valley, 
MoMa). I've attached the 'bible' on Smiths gauges in case you don't have it.

I don't think a tire change would make a 65-78MPH error, unless you've 
changed to 13-inch wheels ;).

Bob

On 6/11/2021 3:04 PM, i erbs via Healeys wrote:
> Any ideas on why my speedo is stuck at 78 MPH? my cable spins freely 
> when I remove it from the back of the speedo, but does not spin while 
> moving. I have not yet jacked it up to see if my angle drive is shit 
> or not. I need to replace it anyway as my speedo is off with new 
> tires. It said 78 , but I was really doing 65., Honest officer
> Ira Erbs
> Milwaukie,OR
> _______              _______
> (______ \____1959 BN4____/ _______)
> (_________________________)
>           BT7 engine and disk brakes
>
>
> 1967 MGB MG
>
> A racing car is an animal with a thousand adjustments. Mario Andretti
> Please excuse random auto corrects and misspelled words
>

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