Topic: Does anyone have experience repairing 400F gauges?

[eatpasta]

The tach that came on my CB400F doesnt work - and the one i bought off of eBay doesnt work....

    the cable is new and the bit in the middle of the cable spins while the engine is running so in theory, the tach should register if it works properly, no?

Im guessing there is something wrong internally with these and was wondering if anyone had any experience getting them apart and working on them....

 any tips?


 - cheers

 

[mattcb350f]

Check to see that the cable is spinning with the engine running at the tach end. Unscrew it and start it momentarily to see that it is indeed spinning.

.... just to make sure that the problem is not something else before diving into the tach 

 Matt.

[amemoryoncelost]

Mine kind of works, def. not accurate, it moves though. Gonna have to go through mine in awhile, anxious to see what the problem is so I can keep an eye out for it as well..

[kent400]

I've written a restoration guide detailing how to get these gauges apart and restore them. It's quite detailed with many images. At the moment it's with forum member Burmashave who has very kindly offered to get it in to the correct format and upload to the site. He hopes to get it done this weekend.

The images shown in the guide are 400f gauges but CB750f ones work the same way there are just bigger.

I've restored more 400f gauges than I care to remember and it's not often that I found one that does not work, they are a very simple device. The first thing to do is take it off the bike and to try turning the drive end with a match stick. The needle should move. If you can't turn the drive end of the tachometer then it is seized in the drive end, try some thin oil and leave it for a few hours. If it turns OK then the cable can't be properly inserted in the drive end.

Inside the tachometer and for that matter the speedometer there's a magnet. If the base is corroded on the inside rust flakes get attracted to the magnet and that causes a problem. How to deal with that is detailed in the guide.

As for tachometer accuracy, well none are 'spot on'. I just check them by driving them on a lathe against one I know is fairly accurate. The rust flake problem will certainly cause inaccuracy.

Hopefully once the guide is uploaded this will help you, certainly you will learn who to get the gauge apart and back together without destroying it.

[destroyer]

I've got a CB400f tach that I'm not gonna use in my rebuild.  Not even sure if it works, but you're welcome to it if you want to pay the shipping.

[swan]

How are you testing it? If I remember correctly, use a tach cable in a drill on REVERSE and see if it spins. If you rotate clockwise the needle will not move, causing you to think it does not work.

There are many threads on this forum and others on how to open these up. You can either carefully pry the bottom of the bezel ring or cut with a dremel and refit with glue when done. Either method works, but both are tricky. Tachs are easier to work on than speedo's.

I have a electronic versions of custom CB400f gauge faces if you want to print your own. Let me know.

[kent400]

To test them I use a cable and run them up with a lathe in reverse. I know what lathe rpm exates

[kent400]

Sorry about that a 'technical hitch' or maybe a Senior moment! Basically I know what speed the lathe is running at and what the tacho should read at the given lathe speed.

As you say you can cut the band and bond it back, really it's quite satisfactory but most people don't want to that. If you 'pry' the band off you need to careful it's not distorted, if it is it's very difficuilt to refit and the fact that it's been apart is obvious. The guide, when it appears on here will explain how to do that. I aim to get them apart and back together without any visable evidence.

As for the faces, I've had some professionally printed to replicate the original. They are printed on self adhesive vinyl. I've seen some of the custom faces and they look good. It just depends on how you want to restore them, I find that most people want to keep things as close to original as possible but thanks for the offer.

[eatpasta]

I've got a CB400f tach that I'm not gonna use in my rebuild.  Not even sure if it works, but you're welcome to it if you want to pay the shipping.

 That would be cool!  Ill send you a message.


 Thanks for the help guys - its appreciated!   I would like to see the guide for sure!  Those adhesive gauge faces are a great idea!!