Author Topic: Clutch safety switch cable  (Read 385 times)

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Offline 74CB750K4

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Clutch safety switch cable
« on: March 07, 2021, 11:40:05 AM »
Clutch safety switch cable pops out, as seen below. Easy enough to just pop back in. But is this supposed to be attached as one unit so to speak, this cable shouldn't pop off like this I assume. The connections are being made and if unplugged and in gear it won't start unless clutch is engaged. Maybe a bit of super glue to hold it in place?

1974 CB750 K4 Flake Sunrise Orange

Offline bryanj

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Re: Clutch safety switch cable
« Reply #1 on: March 07, 2021, 11:55:20 AM »
Should not pop apart, theyare easy enoug t replace, just remove clutch lever and thread cable in from lever side till switch locks in.
If you cant find a xlutch switch a front brake light switch from one on the drum braked 125 will do the same job even if wire colours different
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

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Offline Bodi

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Re: Clutch safety switch cable
« Reply #2 on: March 08, 2021, 06:24:06 AM »
Where's the switch? The wires should be attached to a cylindrical "push button" switch that connects the two wires together when the clutch is disengaged... as far as I know all Hondas switch ground so at least the wires can't blow a fuse by touching metal.
The switch goes in from the lever side so it won't be pushed out by the lever or pulled out from the cable side. Remove the clutch lever and it should push out using a screwdriver or blunt tool. Possibly you can solder those wires back onto the switch terminals and have a working switch again.
Or just jumper the switch wires and remember not to start the engine in gear without disengaging the clutch.
Assuming this is a K4, the starter should work when the engine is in neutral. There are two ways Honda enabled the starter when either in neutral or with clutch disengaged (or both) - either an SSU, a somewhat complicated electronic module, or a simple diode from the neutral switch to the solenoid ground (the diode is to isolate the neutral light from the clutch switch so it isn't on whenever the clutch is disengaged). I don't know which they used on a K4. The clutch switch directly enables the starter either way, and it's nice to be able to start an engine stalled in gear as the transmission is not often cooperative when asked to shift gears on a stopped engine.
The SSU is too complicated to try and explain, a failure can disable the neutral start capability but with the clutch lever pulled it should still run the starter. Same with the diode but it's very simple (and easy + cheap to replace) - failure will either disable neutral only starting (diode failed open) or have that neutral light activated by both the neutral switch and the clutch lever (diode failed short).

Offline 74CB750K4

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Re: Clutch safety switch cable
« Reply #3 on: March 08, 2021, 06:54:07 AM »
Switch is in there, just appears that this cable was pulled apart from the switch at some point.  It's always been like this since I rode it in the early 2000's, I just made sure it was plugged in.  When plugged in or unplugged, it works like it should either allowing it to start only when clutch is engaged out of neutral or not work when unplugged and only starts when in neutral.  I think for the K4 the safety unit is the one with a photocell, not diode, and have read posts about what happens when that unit eventually fails.

I think for now a dab of glue to hold the cable in is what I'm gonna do until I replace the cable.  I do not want to jump anything to bypass it.
1974 CB750 K4 Flake Sunrise Orange

Offline Maltboy

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Re: Clutch safety switch cable
« Reply #4 on: March 08, 2021, 07:02:38 AM »
VintageCB750.com sells the switch for 6 bucks.  NOS is about $17 on eBay.