Tachometer not working - where should i start?

[richmason]

Greetings to the Forum,

This is my first post looking for assistance from the group. Please bear with me as I learn how to work on our new project - a 1986 LJ70 - without the benefit of my home garage back in the US (we are in Monrovia, Liberia).

The tach on my 2,4 l turbo diesel is stuck on about 2k revs. The needle doesn't move for anything - switching car on and off, changing engine speed, nothing. Should I start at the dashboard end of things or under the car with the tach sensor?

I do have some basic tools, including a digital multimeter. Once upon a while I had a decent amount of experience working on old Mercedes and VW diesels. This is my first Japanese project.

Many thanks for any and all assistance. This truck will be returning to the US with us if I can keep it from completely rusting out in the coastal salt air.

Cheers,
Rich

 

[kbushnz]

If it stuck in one position all the time even when off I would suggest the needle / mechanism is stuck.
They are finely balanced things and I have personally had small spiders build their homes in there and the webs jam it up...
Also it uses a magnet and attracts steel.. Could have some stray bits stuck in it....

 

[richmason]

Thanks Calvin. I'll pull it off and see what I find.

 

[richmason]

Tach is out but no obvious issues. How should I test it? Should the needle fall to zero from a spring or its weight? It holds in whatever position I move it to.

Thanks for any suggestions of next steps.

 

[kbushnz]

Tach is out but no obvious issues. How should I test it? Should the needle fall to zero from a spring or its weight? It holds in whatever position I move it to.

Thanks for any suggestions of next steps.

Have a look and see if the spring (looks like a watch spring) is attached..
You should be able to move the needle and it should go back to zero.
Its spring loaded...

If you can turn the needle to any position and it stays there it could be a broken spring. Or something is jamming it...

 

[richmason]

Fixed it but not sure why it worked

When I loosened the two screws that hold the faceplate on the tach, the needle went to zero and returned to zero under spring pressure. Tach works fine now. Not sure why it was binding. Thanks for the feedback and suggestions.

 

[kbushnz]

A Win !

 

[richmason]

Yeah, I understand completely why these trucks have such a fanatical following - it is just a joy to work on. A phillips screwdriver and a 10mm spanner can provide a day's entertainment. It reminds of me of the greatest car ever made - the 123 series Mercedes Benz diesel.