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1981 CB400T: Wanting a sounding board for tachometer replacement

OUberLord

Member
Joined
Mar 13, 2023
Total Posts
44
Total likes
20
Location
Omaha, Nebraska, USA
I had my original tachometer die on me today. I'd noticed it started making some odd noises earlier in the day of riding. Closer to getting home the needle started acting erratically, then it laid at 0. Upon taking it apart the square void that the cable fits into is rounded off; I think the gauge has had some sort of internal failure and it bound up. I want to replace it, but I have a few options and I'm not sure which path I want to go down. Last year a buddy parted out the remnants of his old CM400 and I took the speedo / tacho from it (and promptly used the speedo to replace the one on my bike which failed last year). However, now that I could use the tachometer I have noticed that it's "stem" that the cable screws onto is loose and isn't firmly attached like it should. As I see it, my options are:
  1. Figure out if the spare I have is repairable / if that stem can be reattached (possibly just some epoxy?).
  2. Buy a used one off of eBay and roll the dice on it being any good (anywhere from $75 to $150).
  3. Buy a new one off of CMSNL ($254 shipped).
Anyone have any thoughts on any of these routes? Given that I just had the original speedometer fail and had to replace it, and now having the tachometer fail, I'm somewhat leery about trusting that anything used of the same era is going to last all that long, but maybe it was just something with these as they were on this bike / how it was stored before I got it.
 
Given that your speedo failed too, were the cables replaced with cheapies that had a smaller square shaft on the inner drive wire?

I think the numerical order of your options is prudent. Go for it.
 
Hmm. It's possible. They were both replaced with NICHE cables, but now that you mention it I really don't know if they are an exact fit.
 
I would follow your list and see where it goes. The cheaper electronic units aren't worth the money IMO. If you want to change speedo and tach to electronic then you might look at the Trail Tech Vapor, it's given me years of good service.
 
I had previously found a video of how to repair the tach and that is a bit of a known failure point in how my spare is right now. I'm hopeful I can just pop the gauge apart, get some JB Weld on it, and it'll be good as new.

I know you can get a mechanical to electrical conversion cable for the speedometer cable (I actually bought one back when I was considering going electronic when the speedometer failed). Is there something similar for the tachometer cable, or is it a lead that wraps around an ignition cable?
 
OUberLord said:
I had previously found a video of how to repair the tach and that is a bit of a known failure point in how my spare is right now. I'm hopeful I can just pop the gauge apart, get some JB Weld on it, and it'll be good as new.

I know you can get a mechanical to electrical conversion cable for the speedometer cable (I actually bought one back when I was considering going electronic when the speedometer failed). Is there something similar for the tachometer cable, or is it a lead that wraps around an ignition cable?
Click to expand...
You could try sending one or both out to either Foreign speedo in Cali or to Levine's down south somewhere (perhaps someone knows contact info) then use a cheap chainsaw tach (wraps around spark plug wire) in the interim.
No experience with conversion stuff.
 
OUberLord said:
I know you can get a mechanical to electrical conversion cable for the speedometer cable (I actually bought one back when I was considering going electronic when the speedometer failed). Is there something similar for the tachometer cable, or is it a lead that wraps around an ignition cable?
Click to expand...
It depends on the unit, the Vapor unit can be just the wire wrapped or connected to the coil wiring.
 
The (genuine) Koso electronic tachos have three means of getting the rpm signal.

Preferred method, for bikes with a CDI and existing electronic speedo, is to use the signal wire from the CDI to the tacho. This works fine on my CB600 engine.

Next best is piggyback connection to LT side of ignition coil.

If all else fails, wire wrapped around a plug lead.

For what it's worth, I've been running a genuine Koso unit on my CB600 for the best part of 20 years, and it has proved to be reliable and accurate, as well as expensive. I'm currently playing with a Chinese knock off Koso on a 175 engine, it remains to be seen how accurate that is, and how long it will last.
 
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