Alternator replacement on 87 GT

lucky · Post by **lucky** » Sun Jun 24, 2007 6:29 pm

you can get a belt that's 1.5" bigger if it's in production.
dayco belt are easily coded
5050413 50/5/0413
first 2 digits 50=single sided serpentine
60=double sided serpentine
third digit number of ribs 3,4,5,6,7, or 8
last four, total length of belt in inches with one decimal. 0413 is a 41.3" belt. so an 1.5" bigger belt is a 5050428, but a 5050430 is a fairly common belt and only 1.52" longer than stock and very close to the 1.57" difference in pulley diameter. don't forget though that you can probably use the same belt and just be not as far from the block on the tensioner. the alt has a lot of adjustment space.

i really don't see the larger pulley as any kind of an issue at all with power output. without knowing if the crank and waterpump pulleys are the same diameter on the 87 and 88 though it's not possible to be 100% certain what the change in rotational speed will be.

derangedsheep · Post by **derangedsheep** » Sun Jun 24, 2007 6:57 pm

Yeah I played around with the part numbers and found a belt that is 1.25" larger which may work. I probably cant use the factory size belt though, I pushed the alternator all the way in on its bracket and still had trouble getting the belt off as it seemed fairly small.

One more thing, I bought a replacement positive battery cable at Advance that was 40" long (as per the computer's listing). I was going to get a new negative cable too but the system lists the negative cable as being 35" long which I know is way too long to just go to that bolt at the head. What length should the negative cable be? Fierostore lists theirs as being 23".

I guess now would be a good time to replace the cable that goes from the junction block to the alternator as well, yes? Anyone know off hand what size that is?

lucky · Post by **lucky** » Sun Jun 24, 2007 7:58 pm

i just put a tape measure to the neg cable i pulled off my 87gt a couple days ago and it is 35" long. don't know if its stock or not, but i can tell you it's not from advance, our autocraft sereis cables are only black or red and this ones blue. the battery positive cable from the same car is a 10 guage wire.

Edit: i can also tell you that the advance APAL system doesn't always list
direct fit replacement battery cables, sometimes it's the closest fit we have in production, but i've never had any complaints from customers who seemed to know what they were doing.

derangedsheep · Post by **derangedsheep** » Sun Jun 24, 2007 8:51 pm

EDIT: It just occured to me. At some point, the previous owner had the alternator replaced. I remember he told me that it was replaced. I wonder if my new alternator has the correct size pulley and the old alternator has the wrong pulley. Can someone measure their alt pulley for me? I think I may just use it with the slightly larger pulley.

I think I will just pull the existing negative cable out of the car, measure it, and go to Advance and get one that is closest to that length.

As far as the wire that goes to the post on the back of the alternator. I want to replace it. I think its about a 10ga wire. Correct me if I'm wrong, but I think it goes from that post to the little junction block by the battery, although I haven't followed it back to be sure. Now I have a bunch of 8ga amp wiring, can I use that to replace it? It says on the sheathing that it's oil resistant and good for temps -20F to 220F.

lucky · Post by **lucky** » Tue Jun 26, 2007 5:33 pm

yeah, it looks about 10 ga, i wouldn't see any reason why that cable wouldn't work, especially with that heat rating.

what about the other wire on the plug tho, i know the 1 terminal on the delcotron plug is a positive input to prime the alt (so to speak), but what's the 2 wire?

derangedsheep · Post by **derangedsheep** » Tue Jun 26, 2007 9:43 pm

Theres the thin wire (brown) that I believe gets the signal from the dash light to excite the alternator (whatever excite means, maybe it gets it "in the mood") and the other wire, the red one, connects to the same wire that connects to the stud on the alternator.

derangedsheep · Post by **derangedsheep** » Wed Jun 27, 2007 10:04 pm

derangedsheep wrote:Can someone measure their alt pulley for me?

lucky · Post by **lucky** » Fri Jun 29, 2007 5:43 pm

the pulley on my 86gt is 2 5/8"

on my other question, the alt on my 86 2.8 has a cable to the battery AND 2 wires on the harness (Delcotron 1-2) the pic in the link you posted is a four wire alt (one Batt, 3 harness) that only has 3 wires hooked to the car, 2 of which are connected to the battery cable, not using one of the factory wires on the car. that's where i'm confused.

Boscolingus · Post by **Boscolingus** » Fri Jun 29, 2007 5:58 pm

sounds like the difference between a CS and SI series alternator,

CS = "Cool Shit"

SI - "Shitty Innards"

thats how I remember which is better :la:

derangedsheep · Post by **derangedsheep** » Sat Jun 30, 2007 12:58 am

lucky80 wrote:the pulley on my 86gt is 2 5/8"

Awesome. Then I think the alternator that was in there had the wrong size pulley on it.

lucky80 wrote: on my other question, the alt on my 86 2.8 has a cable to the battery AND 2 wires on the harness (Delcotron 1-2) the pic in the link you posted is a four wire alt (one Batt, 3 harness) that only has 3 wires hooked to the car, 2 of which are connected to the battery cable, not using one of the factory wires on the car. that's where i'm confused.

Pull away some of the loom on the harness that goes to your alternator. Of the wires on the plug, the thicker, red one splices into the one that goes to the alt stud, and then runs up to the battery. The other wire goes to the dash light (I think).

On the 88 style alternator, there are 4 pins, but you only need to hook up two. The one brown one to go to the dashboard, and the red one that hooks into the wire off the stud and runs up to the dash.

If I get some time, I'm going to try work on it some more tomorrow afternoon. I'll try to take some pictures of the wiring.

derangedsheep · Post by **derangedsheep** » Sun Jul 01, 2007 12:40 am

No time to work on it Saturday, so I'll be working on it Sunday. Question though. The wire from the alt stud to the junction block, I want to replace it. Does that wire have fusible links? If yes, where would I get replacements, or, could I somehow splice the one from the original cable into the new cable or something? And if I should go buy new ones, what do I buy?

derangedsheep · Post by **derangedsheep** » Mon Jul 02, 2007 6:27 pm

Checked out Ogre's Cave and hes got a thing about sizing fusible links. Now the wire I am going to use is 8ga. So by his sizing chart (use a link 4 sizes smaller) I would want a 12ga, correct?

Problem is, I cant find 12ga. Only 14ga and 16ga. Would a 14 work? The factory wire is (I think) a 10ga, so 14 would be correct for that one.

derangedsheep · Post by **derangedsheep** » Mon Jul 09, 2007 6:51 pm

Finished it yesterday. Runs good. The idle is much more solid now than it used to be. I cleaned up the wires around the battery/water pump/c500 area and it looks pretty good. Now I just have to fix my brakes. Anyone know why it would make a hissing noise (almost like air escaping) when I hit the brakes? It stops fine, though it does have a pretty low pedal like it has since I got it.