my tach doesn't work when the engine is cold. it has been progressively getting worse, taking longer to work. i don't know if its the colder weather or the fact my truck is running cooler after fixing the fan clutch. its accompanied by a squeaky noise(not a belt, more like a bearing) under the hood at the time its about to kick back in. also reducing the electrical load; ie turning out the headlights or the heater fan, will make it come back on when its about heated up or squeaking. i figured it was the alternator going bad, i heard something about the tach not working till the alt heats up, here on the forums. does all this add up? thought i would run it by you guys. also what is the best way to go when replacing it , rebuild, heavier duty(if so what amps), a cheaper GM equivalent. advice would be appreciated.

 

I would check every pulley the belt wraps around, make sure they are nice and smooth. If the alternator is dying, you can tell by taking a flat head screwdriver and just put it along the sides of the alternator.

If the magnet is strong and holds the screw driver firmly, the alternator is good, if it is weak, then all you have to do is open up the alternator and change the brushes. They are like 5-10 bucks..

I always thought the speed sensor controlled the tach...

 

Yes your alt is going south, this winter it wont work at all.
Have yours rebuilt or buy a used one.
I am on my 3rd "new" one, first 2 from AutoZone and now this one from Advance Auto.
I would have more faith in a used high mile Rover alt than one of these POS rebuilt ones.

After the first of the year I am going to buy a used one and have it rebuilt by a local guy who can crank up the amps on it too.

GM ones are cheap but crap, they wont last 30k.
And keep in mind that the LR alt is water proof.

www.autosportsunlimited.com

 

Before you spend the BIG $$$'s, check your belt tensioner, if it is getting tires, and at your trucks age, it should be, then your belt won't remain tight causing less power to the alternator.
If you then think it is the alternator, take your truck to a local parts store and get it tested for free before replacing.
As Spike mentioned, try and find a local shop that will rebuild your alternator, not give you a remanufactured one cause most of those are never rebuilt completely right where a local shop can give you back all the parts from yours giving you some assurance that it has be rebuilt right.

 

if i have it rebuilt should i go for more amperage, what is the stock ampreage and how big should i go? i do have a big stereo amp and may want to add some more offroad lights in the future.

 

Stock DI alt amp's is 130? Mike will know better than I.

 

wow i was under the impression that a 100 amp alt was "heavy duty". well i will look into finding a local shop to rebuild it. thanks.