problems with tach / rpms

[lsansone]

first time post.

I have a couple of MV ( unimogs ) but this is my first m817. I cant tell what is going on with my tach.
When the engin is running the tach is very jumpy and if i give it some throttle it will spin right around to 3 or 4 k . There is no way that these engines rev that quickly. It does seem to idle around 600 -700.

took apart the cable and cleaned it up. looks like someone greased up the cable or put some oil in it. I cleaned it out and the tach runs a little better, but still seems to be able to rev way to high for the little amount of throttle I am giving it. any ideas

thanks

 

[Floridianson]

first time post.

I have a couple of MV ( unimogs ) but this is my first m817. I cant tell what is going on with my tach.
When the engin is running the tach is very jumpy and if i give it some throttle it will spin right around to 3 or 4 k . There is no way that these engines rev that quickly. It does seem to idle around 600 -700.

took apart the cable and cleaned it up. looks like someone greased up the cable or put some oil in it. I cleaned it out and the tach runs a little better, but still seems to be able to rev way to high for the little amount of throttle I am giving it. any ideas

thanks

Welcome and you will make friends here. I would make friends and I bet someone close will let you use a good tac and if the problem goes away you got it.

 

[jwaller]

Id swap the tach for another. I have several new ones I can sell cheap.

 

[bigmike]

My new M818 had no speedo and a very jumpy, inconsistent tach. I followed the TM closely to troubleshoot.

I took the cables off at the origin. Using a power drill, I tested the cables and guages and they worked fine. I found that the end of the cable gets worn down so much it spins inside the transfer case or I.P. I tested this by pushing some metal around on the tach cable end and it started working just fine. I'm thinking about rebuilding that cable end with J.B. weld otherwise I'll be changing the cables.

I would perform the same test and keep the drill at a steady speed. If the tach still jumps it's probably the tach but still could be the cable.

 

[lsansone]

update
put new gauge in the truck and the problem is solved

lou