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Speedo Jumpy ???

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George Zeck

George Zeck

Jedi Warrior
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Hi All -

My speedo jumps drastically when driving (typically 15-20 MPH range). I've been told (& obviously forget) I need to replace one item and it wasn't the speedo cable. Can someone point me in the right direction?

Tx-

George
 
Not much else to it, besides the speedo and the drive gears inside the transmission. The speedo on my TR3 was wavering worse than that, and the problem was entirely binding within the speedo head. Took me a couple of tries, but I finally got it smoothed out until now it only wavers 1 or 2 mph.

Not sure if your Sprite would be the same, but in the TR speedos the odometer and trip meter each have a dog moved by an eccentric shaft that in turn moves a gear one tooth at a time. The odo & trip mechanisms were so tight that every time a dog tried to move a gear, the speedo cable would wind up (causing a low reading), then once the gear was done moving the cable would unwind and cause a high reading. I had to completely disassemble the trip & odo to polish up all of the friction surfaces.

DSCF0015.jpg
 
I went through the same issue, I proved it was not the cable by running the speedo with a drill. A small square screw bit (robertson) in the drill works good. This is also a good way to calibrate the speedo.
 
This is one of those "Patience Grasshopper" moments taking a SMith's Speedo apart. With Bugsy I went the digital route using a Sigma Bicycle Speedo. Absolutely dead on accurate plus a fun project.
 
Isn't their something called a "drive gear"? Couldn't find anything on Moss's site. Maybe I am mixing this up with something else????
 
George Zeck said:
Isn't their something called a "drive gear"? Couldn't find anything on Moss's site. Maybe I am mixing this up with something else????
Click to expand...

Look on the gearbox page. Moss PN 461-810 They call it "Pinion, speedo drive" but it's the same thing. Unlikely to be the problem, IMO, but I guess it is possible.
 
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