correct tach pulley size

[azreark1]

so i bought a sunpro 52mm tach for my truck and got it wired up, hooked it up to the alternator and the thing works except at idle its showing my truck running at 3500rpms...now i KNOW this is wrong lol so i've read that the reason for this is the pulley size being wrong but i cant find anything about what the correct pulley size is...anybody have some light they can shed on this subject?

 

[NVW]

That tach may only work on gassers.

 

[azreark1]

well according to some other posts ive read, the pulse output is almost exactly the same as what the tach looks for in a gas engine but it was mentioned that different alternators sometimes come with different pulleys and will giv an incorrect reading.

 

[NVW]

That would be more variation than pulley size, I'm pretty sure 10% difference in pulley size gives 10% difference in tach reading.

 

[Matt Bachand]

Is that a TYPE - O where it says 3500, did you mean 350?

 

[vegtech]

Even if it was the wrong pulley 3500 or 530 would not be anywhere near the incorrect reading. IS set to 8 cylinders? I would say xot have a problem with the tach either it is wired wrong or its not for diesel. you would have to have a pulley the size of a quarter to get that reading

 

[azreark1]

ok yeah talking to my brother in law about it we both figured the tach might just be bad.

 

[minisub]

..

 

[NVW]

The tach is 52mm, he doesn't mention pulley size.

 

[azreark1]

in doing some research most modern tachs will run off either a coil signal or the alternator signal so thats why i was askin cuz mine was hooked up right but giving me a bad signal.

and no i dont know the pulley size.

 

[Matt Bachand]

A LOT of junk parts out there... I have an Glowshift fuel guauge that I just learned to live with 1/2 being full, and Full being empty.......... doh.

 

[96 OILBURNER]

I don't have the book in front of me right now, but there are 2 sizes 2 1/4" (57mm) and 2 7/16" (62mm). One is for pre 96, the other is for 96 and later. Can't remember which is which though.

 

[ak diesel driver]

odlaw has it in his garage

 

[JMJNet]

IIRC, 62mm. Gasser run on 57mm. I don't have the correct pulley size in mine.