I just got an '89 GT 5.0 / 5-spd, and I was driving it around this weekend... This being my first performance car, I was getting on it rather hard (up to about 5200rpm in 1st/2nd accelerating).

While taking a corner I downshifted from 3rd to 2nd, and unfortunately it shifted rather hard (I'm still working on matching rpm's) the car bucked slightly, but at the same moment that I engaged the clutch I heard a loud metal "CLANG." I worried slightly about this but chalked it up to suspension noise (bump-steer kit).

A few hours later I was driving in 5th doing about 60 on the highway (~2000rpm)- suddenly I lost all accessories, voltage dropped, and the temp began to rise rapidly. I managed to get off the road before it overheated, and spent the next 4 hours getting towed back to town (needed 2 tow trucks due to NJ turnpike regulation)

Anyway, when I popped to hood to take a look, I found that the alternator pulley had basically torn itself apart - it seemed to be a cast aluminum pulley, and fell apart into chunks when I touched it. The reason everything else stopped is because I threw the drive belt. The pulley is completely sheared off from the alternator shaft, with a large chunk of it missing and a crack that propagated all the way out to the rim of the pulley. Could a hard shift have caused such a catastrophic failure?

According to the previous owner, the alternator is a Ford Racing 90 amp alternator that's about 4-5 years old. I've already ordered an entire replacement unit, even though the current one still seems to rotate freely when I turn it by hand. I'm paranoid that it may have been sticking or seized.

I should note that I noticed appreciable voltage fluctuation when doing things like stepping on the brakes (just from the lights...).


I went with a Summit 100-amp alternator, fits Ford 2G brackets. Should I be checking anything else in there to make sure there was no damage elsewhere in the engine compartment? I'm planning to change this thing myself (2 bolts and a new serpentine belt - how hard can it be?) and am paranoid about missing something.

EDIT:

The alternator arrives tomorrow and I'll be adding a 4-gauge charge wire with a 175 amp fuse link in it... Even though 100 amps doesn't seem like a lot more than the stock 75 amps, it's important to remember that power dissipated as heat in a wire increases with current SQUARED ( P=I^2*R ). That means that there would be 54% more power being dissipated through the stock 10 AWG cable. Keep in mind that a 90 amp alternator would still be about 31% more power than the stock 75 amps. The 4 AWG upgrade significantly lowers the resistance of the wire compensating for the increase in (possible) current.

I'm adding some pics of the destroyed pulley. It seems like the Ford Racing 90-amp alternator is still good. The spindle still turns and as far as I can tell the fan and rotor are still spinning freely inside. I'll probably have it tested and maybe keep it as a spare if it's ok. I'm wondering if there was too much tension on the belt before, causing the pulley to shatter...

 

I would think the belt would slip before transmitting enough force to destroy the alternator pulley. Besides, you don't hear about people dumping the clutch at 5000 rpms at the dragstrip and breaking pulleys.

May have been a poorly crafted pulley. May have been damaged somehow by previous owner.

Do the research on the 100 amp conversions and make sure it's just a diff belt and bolt size.

My voltage drops a bit when using power windows and a slight bit when the brake lights are activated.

 

Thanks - I've been reading that if you put a much beefier alternator in these cars, you have to replace the charge wire running to the starter relay with a thicker gauge wire (like 4 or 6 gauge). I would PREFER not to do this, so I tried to get something that was close to what's in there now. It has a 90-amp at the moment and I figured 100-amp isn't that much more. Of course, P=I^2*R, so the amount of power dissipated in the wire would go up by about 19%... that might be a concern. That would be almost 45% more than the stock 75-amp if my calculations are correct, which may warrant a new wire.

 

this thread requires pics... i gotta see this one

 

I'll take some when I get home tonight... the metal on the pulley itself is so degraded that it almost looks like shredded lead or pewter , certainly not quality aluminum!

 

PA Performance, who I got all of my electrical stuff from, recommends a heavier duty power cable with 90 amp conversions but requires it with 130 amp conversions.

The line is really easy to install if you have a post style alternator. I can't remember if the stock alternator has a post on the back, but the power wires on the stock set up go into the alternator via a plastic connector. With the upgraded cable you need a post to bolt the terminal to.

 

From the reading I've done, I'd need to run about 7 feet of wire... This goes from the alternator negative to the negative on the starter relay, right? Where exactly is that, is it near the ignition coil? It would be nice if I didn't have to find my way through the firewall and into the dash...

 

PICS! Go to the tech articles and read up on the 3g upgrade.

 

I'm thinking about it, but considering I've actually had the car in DRIVEABLE condition for about 24 hours (put plates on Saturday, broke down Sunday), I'm kind of impatient to get it back on the road... I don't know what I'd have to do in terms of dremeling the bracket to make a 3G fit/etc. I've already ordered this 100amp which I think will be sufficient for now... (I don't even have the fogs in so there isn't much electrical equipment on the car)

Apart from this freakish alternator failure, everything should be 100%, so hopefully I'll be back on the road by Thursday/Friday (driving my Taurus around in the meantime is a real drag )

 

The starter solenoid is on the driver's side fender on my car, right near the ignition coil. The cable only needs to be so long as to run it from the solenoid to the radiator support, underneath the air intake, then to the back of the alternator. I used a cutoff wheel and notched the alternator bracket in a whole 1-2 minutes. Even left the bracket in the car and just covered the motor or other important part with a towel to block out metal shavings.