1966 Monza: can't get speedo to work

[cooperplace]

this is the bike that I mistakenly thought was a 1964 GT. I'm assembling it having acquired it in pieces.

I can't get the speedo to work. With the front wheel up in the air, and spinning it, the speedo drive spins just fine. And if I grab the speedo cable and spin the square end with my finger, the speedo works fine. OK? So far so good.

But when I screw the speedo cable into the wheel, and the wheel spins the cable, in the same direction as I do with my hand, and faster, the speedo is dead. Nothing.

I'm having a lot of trouble understanding how this can be. Maybe I'm going mad. If anyone has another explanation as to why the speedo works when I spin its cable with my hand, but not by the wheel, I'd be really, really pleased to hear it.

[motoital]

I'm not 100% but it might have it something to do with the reduction gear in the front wheel. Are you getting a constant reading while you turn the cable or does the needle just jump? Count how many times the cable turns as you spin the wheel. Also maybe the drive head of the cable isn't seating into the speedo. Good luck!

[cooperplace]

well, the needle just jumps, but it works when I spin the cable. When it's spun by the wheel, nothing.

[JimF]

Jumpy needles are inherent on the speedometers, but they should register some nominal speed and then deflect to both sides of that speed.

Do you have a variable speed drill? Maybe you can chuck up the end of the cable and spin it with the drill. You could then spin it faster than you can by hand, more simulating the wheel speed.

If both the drill and the wheel fail to drive the speedometer the problem is either in the cable or speedometer. If the drill drives the speedometer but the wheel doesn't the problem is in the wheel.

Let's say the drill doesn't drive the speedometer either. I think you need to try another cable or another speedometer to isolate the problem. You might try taking the cable off and dripping some oil into the cable from the top so it runs down the inside of the sheath so as to lubricate the cable and perhaps dislodge any dirt inside.

What about the bends in the cable when secured at both ends? Could the cable inside be getting pinched?

Jim

[cooperplace]

Hi Jim,

great suggestion re the drill. Thank you. I'll try it out and come back with the answer. Will take a week or so because bike is now in frame shop.

Cheers

Peter.

[cooperplace]

the bike is back from the frame shop, so I put the cordless drill on the end of the speedo cable. It's the same effect as the wheel: the speedo doesn't work, no matter how fast or slow the drill turns the cable, or the direction.

But I can get the speedo to indicate a steady 20mph for a few seconds by turning the cable by hand.

I don't understand what's going on.

[motoital]

Did you select reverse when using the drill? It will just stay against the needle stop in the wrong direction. Also the drill might be spinning the speedo clutch to fast to get a grip. At 80mph the cable is spinning at about 3k and it isn't spun up as fast as a drill. They are pretty simple on the inside, see picture. I think it will work fine on the road as mine doesn't give a reading when I spin my front wheel either. Do you have any pictures of your bike?
Good luck!

[cooperplace]

yes, i tried the drill in both direction. Tried it slow, fast, in between. No speedo indication. Works fine when spun by hand.

I still don't get it. I guess I'll have to take the speedo apart.

The bike is in pieces. I post pics when I've got it back together.

[DucRedux]

Until last summer I had ridden my 450 MK3 for 5 years without a working speedometer following a partial restoration. The troubleshooting of the speedo problem proceeded just as you and forum members are describing. Frustrated by the the situation, I resorted to cutting off about 1/4 inch of cable sheathing and refitted the cable. The speedometer resumed working. I can now guess that some wear or misalignment had occurred at the ends on the drive and receiving pins where the cable's respective ends index and the deeper insertion did the trick.

[cooperplace]

that sounds good! I'll try it. Thank you.