Diesel Tach Help

[nchinca]

Okay - I bought a cluster out of a medium duty truck with an 8.2. I liked it because it had a tach and fuel gauge, along with an air pressure gauge. I have all the gauges hooked up. It took a lot of searching, but I finally figured out how to hook up the diesel tach to the alternator. Now the tach is totally off. I know it has to do with pulleys and windings and probably a bunch of other crap I am clueless about.

My question is: Is there any way I can calibrate the tach at home? I saw a tab on the rear of the tach that looks like it can be put into another position (but it did not help). Is there any place I can find out different pulley ratios or any other calibration help to make it right?

Oh yeah, this is in a gas truck.

I have searched the forum with no luck. I have searched the internet with no luck. Please help me!!!!!

 

[Russell]

Have you tried connecting it to the HEI cap's "TACH" terminal instead of the alternator's rectifier?

 

[nchinca]

Yeah,

I tried, but there was no reaction on the tack. I read that the factory one reads off of the alternator, and that is where I have had the most luck.

 

[Blue85]

Do you have access to the AC voltage on your alternator? You may need to open the alternator and add a wire on the stator side of the rectifiers. You could also try to find a diesel alternator with the Tach terminal on it. Of course, this all depends on having the ability to calibrate the tach. Otherwise you will have to calculate the right pulley size to make it work right and this might not be the right size pulley for optimum charging. I would think that a diesel would have a smaller alternator pulley (or larger crank pulley) than a gas truck since the rev range is lower.

If you give up you could splice the guts from an aftermarket tach in behind the Tach face in your gauge cluster and run it from the distributor.

 

[nchinca]

I got the non rectified ac voltage stud coming out of the back of my alternator and I get some reading on the alternator, but it is off. I am trying to figure out how to get the right pulley ratio, or if I can recalibrate the tach on my own. Thanks a lot for the help.