aaz with a 92 tach reading to high

[R.O.R-2.0]

ok... i bet no ac too...

what ive found is due to removing the ac out of it, running a smaller belt.. the alt spins faster..

this is why the tach is off.. say close to 2k at idle??

how to fix.. no idea.. dakota digital thinggy?? i have same issue on my toaster with its tach.. and mykes tdi coupe does too..

so interested in how you fix!! sadly i am no help.. but if your getting around 2k with no ac thats why..

also never seen a tach set up like that.. got maf built into it by chance??

if the big pulley, and small pulley dont change size, then how does the alternator spin faster?

doesnt make sense..

the alt should be turning the same speed weither the belt is 5" long, or 5 feet long, or 5 miles long for that matter..

i dont get it??

Yet it still does it, every time.....

what still does? what were you responding to? kinda confusing reply..

[nathan_b]

I was replying to:

 "if the big pulley, and small pulley dont change size, then how does the alternator spin faster?

doesnt make sense..

the alt should be turning the same speed weither the belt is 5" long, or 5 feet long, or 5 miles long for that matter..

i dont get it??"

[R.O.R-2.0]

I was replying to:

 "if the big pulley, and small pulley dont change size, then how does the alternator spin faster?

doesnt make sense..

the alt should be turning the same speed weither the belt is 5" long, or 5 feet long, or 5 miles long for that matter..

i dont get it??"

thats like saying a longer driveline changes your rear end gears..

[nathan_b]

yet it does change the alt speed... every time lol

[R.O.R-2.0]

yet it does change the alt speed... every time lol

well, would someone mind telling me WHY, rather than just stating that it changes the speed? i still cant wrap my head around this..

if the crank pulley, and the alternator pulley are staying the same size, and the speed increase is not simply from the lack of an a/c pump, then why does the BELT actually change the speed of things?

i just dont get it. the belt transmits power, it has nothing to do with the speed of things.. a different belt should not change drive ratios.

could someone provide something more than an "it does" explanation? PLEASE?!

[vanagonturbo]

I have never seen a tach driven from a signal from an alternator on a diesel before (I think only VW does it),

My Mercedes Box truck has the tach driven from the alternator...

[R.O.R-2.0]

I have never seen a tach driven from a signal from an alternator on a diesel before (I think only VW does it),

My Mercedes Box truck has the tach driven from the alternator...

Alot of diesels in boats are driven like this. ive even seen some with a cable drive off the alternator like the old corvettes.

[vanagonturbo]

I think I remember old gasser Mercedes also being cable driven tachs.. anyway, not relevant I guess..

[R.O.R-2.0]

so, nobody knows if/why the change of a belt size makes the alternator spin faster/slower?

Nathan, you know it makes a difference, so would you please explain to me WHAT makes the difference? why does the alt spin faster when the BELT is the only thing that has changed?

[vanbcguy]

'cuz it stops slipping...

[92EcoDiesel Jetta]

so, nobody knows if/why the change of a belt size makes the alternator spin faster/slower?

Nathan, you know it makes a difference, so would you please explain to me WHAT makes the difference? why does the alt spin faster when the BELT is the only thing that has changed?

Changing belt size does not make the alternator spin faster/slower. Changing the pulley size does!

[vanagonturbo]

'cuz it stops slipping...

This seems like the most plausible explanation..

[fatmobile]

adjusting the bottom left potentiometer brought my rpm down its still slightly high a but its a hell of alot closer now. thinking about putting my own potentiometer in places of the original.
thanks for the advice
Colton

That potentiometer is just a fine adjustment.
 You'd have to change the resistor in parallel with the pot to change much,.. seems like lowering the resistance lowers the tach.
Probably a 13k in there now.

[carrizog60]

does the passat 35i tachos have that adjustement?

[nathan_b]

so, nobody knows if/why the change of a belt size makes the alternator spin faster/slower?

Nathan, you know it makes a difference, so would you please explain to me WHAT makes the difference? why does the alt spin faster when the BELT is the only thing that has changed?

the best way I have wrapped my head around it was to think of the whole belt as a "pulley," make the pulley significantly smaller and the rpm increases relative to the crank. It's just one of those things I guess, I'll admit ROR, I dont REALLY know either, lol.