Alternator replacement on 87 GT

derangedsheep · Post by **derangedsheep** » Mon Jun 11, 2007 9:35 pm

So I'm finally getting around to fixing the bad alternator on my GT. I figured that while I'm in there, I might as well put the 88 style alternator in since it's really not any extra work.

I ordered the replacement plug and this alternator (link here). The alternator came today and I'm a little confused. The alternator was in the Autolite box, which was in the box that it was shipped to PartsAmerica in, and that box was put in a box and shipped to me. The box that it was sent to PartsAmerica in has 1357-5-7 written on it, which is the correct part number for what I ordered. However, the sticker on the alternator has 7912507 on it. That part number is this.

The mounting points are at 180*, the plug that I bought fits the connector on the alternator, and the pulley is a 5 rib (which I think is correct, yes?). I'm wondering if perhaps I was sent the wrong alternator though.

Any input?

lucky · Post by **lucky** » Mon Jun 11, 2007 9:43 pm

the parts chain i work for owns partsamerica.com, i'll try and cross reference both tomorrow at work, see if i can offer any assistance.

derangedsheep · Post by **derangedsheep** » Mon Jun 11, 2007 10:42 pm

Upon further inspection of the part, I noticed that the alternator box has the part number 7912507 on it. But, the sticker on the alternator with the part number 7912507, has a sticker underneith with the correct part number, 1352-5-7.

I'm thinking that maybe Autolite changed the part number. Run the numbers tomorrow if you can though, I don't want to tear the car apart to find out that it's the wrong part.

The Dark Side of Will · Tue Jun 12, 2007 6:18 am

Getting the alternator out isn't really tearing the car apart.

However, you should not ASSUME that the alternator will come out without a fight. The aluminum bracket has a nasty tendency to let go of its threads when you unscrew the upper bolt. You'll have to remove the bracket (not terribly difficult) and have it helicoiled if this happens.

Installing Rodney Dickmans alternator bracket reinforcement would be a good idea while it's out.

Kohburn · Post by **Kohburn** » Tue Jun 12, 2007 7:24 am

The Dark Side of Will wrote:Getting the alternator out isn't really tearing the car apart.

However, you should not ASSUME that the alternator will come out without a fight. The aluminum bracket has a nasty tendency to let go of its threads when you unscrew the upper bolt. You'll have to remove the bracket (not terribly difficult) and have it helicoiled if this happens.

Installing Rodney Dickmans alternator bracket reinforcement would be a good idea while it's out.

or use a longer bolt with a nut on the end and never worry about siezed or stripped threads again ;P

derangedsheep · Post by **derangedsheep** » Tue Jun 12, 2007 1:40 pm

The Dark Side of Will wrote:Getting the alternator out isn't really tearing the car apart.

However, you should not ASSUME that the alternator will come out without a fight. The aluminum bracket has a nasty tendency to let go of its threads when you unscrew the upper bolt. You'll have to remove the bracket (not terribly difficult) and have it helicoiled if this happens.

Installing Rodney Dickmans alternator bracket reinforcement would be a good idea while it's out.

I know it's not really tearing the car apart, but I have an auto, so I have to take apart a lot more than if it was a manual. I never assume anything to be easy when working on any car, but especially with Fieros.

I was thinking about getting Rodney's bracket, but does it really make that much of a difference?

Fastback86 · Post by **Fastback86** » Tue Jun 12, 2007 1:49 pm

Yeah, get Rodney's reinforcement. Its really easy to break the stock bracket trying to get the bolt tight enough so the belt stays tight and doesn't squeel. Ask me how I know.

Kohburn · Post by **Kohburn** » Tue Jun 12, 2007 2:12 pm

Fastback86 wrote:Yeah, get Rodney's reinforcement. Its really easy to break the stock bracket trying to get the bolt tight enough so the belt stays tight and doesn't squeel. Ask me how I know.

out of the 6 i've owned i've never had that problem. yes to the belt losening over time, but that was from stretching not from the alternator possition bolt slipping

p8ntman442 · Post by **p8ntman442** » Tue Jun 12, 2007 6:02 pm

:withstupid:

Fastback86 · Post by **Fastback86** » Tue Jun 12, 2007 8:19 pm

Its only happened to me once, but it did happen. I'm not using Rodney's bracket, though, just a large washer to spread out the load.

Kohburn · Post by **Kohburn** » Wed Jun 13, 2007 11:05 am

i swear one of the best upgrades to a stock v8 is a propper belt tensioner that doesn't cause the belt to get stretched out but maintains tension.

lucky · Post by **lucky** » Wed Jun 13, 2007 5:07 pm

crossed those numbers for ya
135757 didn't come up as anything
7912507 came up as 88 pontiac fiero as well as a couple other vehicles

derangedsheep · Post by **derangedsheep** » Wed Jun 13, 2007 6:50 pm

Ok, the part number must have changed and the website didnt update yet or something. Thanks.

lucky · Post by **lucky** » Fri Jun 15, 2007 6:46 pm

no prob

lucky · Post by **lucky** » Sun Jun 24, 2007 1:58 pm

the early style has a 2 wire connector, while the later has a 4 wire, what do you hook the others up to?

derangedsheep · Post by **derangedsheep** » Sun Jun 24, 2007 5:06 pm

I'm having a bit of a hold up with this replacement. I got the old alternator out without too much trouble. But when comparing the 87 alternator with the 88 alternator I see that the 88 has a larger pulley on it. I measured them with a tape measure (from the outer lip) and the 87 pulley is 2-1/8" while the 88 pulley is 2-5/8". What's the deal? Should I switch the pulleys or is the bigger pulley the reason that the 88 alternator puts out more at idle and it should be left alone?

lucky80 wrote:the early style has a 2 wire connector, while the later has a 4 wire, what do you hook the others up to?

The later style has 4 ports on the plug, but the replacement wiring harness has only 3 wires. And, of those three wires, only 2 are used (one is cut off). There is a small writeup on the conversion on Old Europe that shows an easy way to do the wiring. Link: http://www.fiero.com/forum/Archives/Arch ... 73614.html

lucky · Post by **lucky** » Sun Jun 24, 2007 5:24 pm

i was looking at alts today, as the tension bolt's broken off in my housing,
where i work we list the same belt as running the alt on both the 87 and 88
it's a 5k413 or 5050413 depending on brand. if the crank pulley on both motors is the same o.d. the larger alternator pulley will make it spin slower than the smaller pulley would, but the smaller pulley causes less parasitic horsepower drain on the engine. underdriving an alternator usually doesn't cause much drop-off in power output, and since the 88 puts out 105 amps while the 87 w/ac 94 amps (wo/ac 78 amps), underdriving it would seem the way to go. although only changing one pulley won't free up tons of hp anyway as full underdrive kits usually only free up 5-7 hp on the average motor.

the number of windings of copper around the magnets dictates power output, but rotational speed is also a factor. i was looking at a powermaster today that is the same size as the 88 but puts out 140 amps.
If it wasn't $200 i probably would have considered it more.

i checked out that link and it doesn't even have one of the wires that's already on the 86 :scratch:

derangedsheep · Post by **derangedsheep** » Sun Jun 24, 2007 5:35 pm

Are you sure the larger pulley will spin it slower? I thought it would spin it faster since an underdrive pulley is smaller but makes your accessories spin slower.

Either way, I don't know what to do about the different sized pulleys. If I have to switch them its not a big deal, I'll take it to work tomorrow and have one of the shop guys hit it with an impact gun and switch them. I'll also bead blast the old pulley to get any built up shit out of the grooves.

EDIT: I have the Dayco Poly Cog 5050413 belt, I replaced it when I did my water pump maybe 2000 miles (and 2 years) ago.

lucky · Post by **lucky** » Sun Jun 24, 2007 5:50 pm

think about a 10 speed bicycle
the smaller the gear you're on, the faster you're going with the same rate of pedaling. smaller secondary pulley, higher rate of spin. (also the same reason a camshaft spins half as fast as a crankshaft)

edit: thinking about that, it's more work to get going in a higher gear on a bike, but once you're going its easier to pedal. I thought underdrive pulleys were smaller, but now i'm not sure.
one thing though, it definitely won't hurt the alt to leave the bigger pulley on it.

derangedsheep · Post by **derangedsheep** » Sun Jun 24, 2007 6:12 pm

I wouldnt think it would hurt the alternator. I'm just worried about it putting out enough at idle. If I calculated correctly, the new pulley should have 1.57" more circumference than the old pulley. So I could probably just get a belt thats 2" bigger and it should be fine.