First of all my batter is brand new. My alternator died around a month ago. I replaced it with a used (s4) alternator. This alternator died within two weeks of purchase. Are these alternators that shitty? What causes alternator failure? Could frequent redlines and an overtightened belt break it without causing any noise? Should I get another used one or get an "OEM replacement"?

 

You bought a used alternator, which means you have no idea what its history was in the first place. Get a high-end reman one from somewhere like Napa, or go with one from Mazda. Don't bother with the cheap remans since the workmanship will match the price. 2 brand new kragen alternators I bought had bad voltage regulators.

 

Used parts are a crap shot.
I don't trust anything reman short of the Mazda dealer.
Yes, they are the most expensive, but I'm tired of dealing with "lifetime warranties" from the big chain stores.

Overtighten belts will cause the bearings to fail.
Overly frequent redlines will cause the bearings to fail.


-Ted

 

see if there is a local shop and have it rebuilt.

 

It could also be that you tightend the belt too much, not hard to do and will KILL the alt FAST.

I did it to mine for just a little bit (maybe half an hour of run time, and it is now louder then it was before).

 

How tight should you tighten it? Should you be able to twist the belt 90 degrees or something? Pull it tight by hand?

 

A friend told me it was a soft short somewhere between the alternator, battery and starter. Could this cause the alternators to fail?

 

I think your overly tighting your alt belt.
+ never buy used parts like that haha =D unless you have to.

 

Seems after the first failure, you would go to the small plug on the back of the alternator and see if there is switched voltage to the BLACK/WHITE wire. Like turn the key on/off and see if it comes and goes.

Then see if the WHITE/BLACK wire, WHEN THE PLUG IS CONNECTED TO THE ALT, and key is ON, has approx 3vdc on it. You'd have to backprobe that WHITE/BLACK wire to do that.

IF both of the above are right.........got me why the alternator went bad, IF the alternator was lined up with the other pulleys etc and belt on tight enough.

Maybe check the large terminal of the alt with the engine at idle, with a meter, to see what the output is. Close to fourteen volts should do it.

 

As a rule of thumb, push down on the widest span and deflection should be about 1/2".


-Ted

 

mixing the s5 car with s4 alt and vice versa is a no- no without wiring mods
the s4 needs a key switched IG sorce, the s5 needs to see battery DC full time

with them **** about, the s4 alt on a s5 car will stay on, and cook out while draining the battery

**** about the other way can bring about an overcharge condition