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Speedometer problem

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leo

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I need help with a speedometer problem on a 74 1/2 MGB.

I have searched the forum and can not find a problem similar to mine.

My original speedo and another one bought on Ebay both, when installed, record mileage but will not indicate speed. Both cable ends look good, and both speedos work correctly when spun by a drill. When driving with the speedo removed, the cable turns and I can't stop it with my fingers. The transmission is a later (I think 76) OD, so I would expect the speed to be slightly inacurate, but the needle doesn't move at all. Any ideas?
 
If it records mileage, that makes it tough to figure what the problem is. I'm not privy as to the inter workings of the speedometer, but did you use the non overdrive cable? The cable for an overdrive tranny is longer than the one for the standard 4 speed. If you used the one for the standard transmission, it might not be recessing into the speedometer far enough. Also, even with the OD cable, if the outer casing is stretched, that could cause the cable to be a little short. It's the recording of the mileage that stumps me. Maybe someone else has experienced this same problem. PJ
 
Gotta be the speedo head, and you got two non-working ones. If all is as you describe, it HAS to be the instrument.

bummer.
 
Could the armature winding in the speedo be burned out?
 
DrEntropy said:
Gotta be the speedo head, and you got two non-working ones. If all is as you describe, it HAS to be the instrument.

bummer.
Click to expand...

But Doc, he says they work well when spun with a drill. If the head was bad, they wouldn't work at all, would they?
 
Are you using an angle drive or hooking the cable directly to the speedo?
 
You're right, Paul... my bad. I ~did~ read it, then promptly lost my mind. Sorry, leo. My attention span was apparently about equal to that of a gnat yesterday.
 
Did the original speedo ever work correctlyhooked up as presently?
 
The original speedo has not worked since I bought the car last year.

I am thinking that my next move will be to hook the drill to the tranny end of the cable and see if anything happens, but it will be next week before I can get to that.
 
I missed that too! ::looks sheepish::
 
I'm guessing the cable is being pinched just enough that there's not enough 'force' to turn the speedo head....get a used angle drive & try that before you go any farther.....especially after you try to turn the cable (hooked to the speedo) from the tranny end.
 
It's kinda weird the mileage counter goes, but the needle doesn't. THAT's why I was blamin' the instrument. But if it does wind up with a drill, I'm at a loss to explain.
 
I suppose my next question is "where does your speedo cable exit the firewall?"
 
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