Topic: Problem With Speedo Drive

[ppetersan]

I have been on this forum for a while, but this is my first time posting as this is the first problem I have had that I hasn't already been addressed in a thread.

I have a 76 CB750F that i am making some modifications to. A while ago I bought an aftermarket headlight bucket that fits my headlight and stock speedometer.  When I first installed it, the speedo did not work so I ordered a new cable.  When I installed the new cable the speedometer still didn't work, so i figured it was the speedo drive, or gear box, as it is called in the manual.  I bought a used, but working, speedo drive on ebay and installed it last night - but the speedo still didn't work. 

There appears to be no problem with the mechanism.  And, when i align the tabs in the gearbox with the notches in gear box retainer, the mechanism spins.  However, when I attach the cable the speedo drive it  doesn't work and when I take the cable off the mechanism doesn't spin with the wheel anymore.  Im guessing the tabs in the drive are somehow slipping out of out of the notches in the retainer, but can't figure out how that's happening or how to fix.

There are so few moving parts it seems like this should be an easy fix, but I can't figure out why it isn't working.

Thanks for any help or suggestions.

[Rigid]

Pics?  you lost me on the tabs slipping part......

[ppetersan]

Unfortunately, I couldn't get a picture of the inside of the speedo drive and I can't seem to find an exploded view of the drive which shows me the name of the different parts within the drive, so I will try to explain the situation a little better. 

The speedometer drive is attached to the gear box retainer and the gear box retainer is attached to the hub.  The axle slides through the speedo drive and the drive sits against the gear box retainer.  they are attached to each other only by the pressure of the axle which holds the two pieces together.  The retainer has two notches in it and you can orient the wheel so the notches are at 12 o'clock and 6 o'clock.  The Speedo drive has corresponding tabs (for lack of a better word) which can also be oriented to 12 o'clock and 6 o'clock and when slipping the axle through the drive, the goal is to get the tabs of the drive into the notches of the retainer.  Since the retainer is fixed to the hub, when it spins, it spins the mechanism in the drive.

You can see the diagram of the front wheel on page 131 (at least in my manual), figure 13-1.  Unfortunately it doesn't show the inside of the drive, but you can kind of see the notches in the retainer.

Sorry for the confusion and I hope this helps a bit.

[Gonzowerke]

Pics?  you lost me on the tabs slipping part......

This is a drive plate from a 1978 K, which may be similar to the 76F. If not, then it is a flat plate with the two tabs bent down to interlock with flats machined on the hub. Post 1975(I think) had this style drive plate, and was anchored by a chrome cover with two recesses for the tabs that bolted on with the disc bolts.

[grcamna2]

Try moving the drive plate inside the hub & see if it is loose where it should be held tightly in the hub.

[Danno]

I believe your cable is not long enough inside the jacket or it is broken

or the speedo itself is stuck inside