Replacement Gen 1 altenator

[sarge1]

Well, I pulled a bad rookie move pulling off my Gen 1 altenator and broke the casing where it bolts to the attachment bracket while trying to loosen a rusty bolt. Perhaps a little liquid wrench would have been a good idea in 5 degree temps and rusty old bolts. Threads were stripping out as I removed the bolt and it split the casing through the threads, leaving it unable to be put back on even if I had it rebuilt, as I had planned.

Gen 2 is fine (casing that is) and I'm getting it rebuilt. My question is I am going to buy the new replacement that the Wiki mentions: Autozone part # DL 7157. My question is in the Wiki it states it's a 78 amp altenator but when I looked it up, it says it is 100 amp. Anyone know if this is still the correct replacement?

Duralast/Alternator (DL7157) | Alternator | 1975 Cadillac Deville 8 Cylinders S 8.2L FI | AutoZone.com_

I'm an electrical dimwit which leads to:

Question 2:
On the back of my Gen 1 is a small m80 size cylinder that was not wired to anything since I bought the truck about 4 months ago that I am aware of. When I was taking the alt off, I noticed a small remnant of wire under the nut closest to the altenator, seperated from the red and other wire(exciter wire?)that looks like it may have at one time been wired to it but looked to have long since corroded/broke off. Truck ran for a couple months without any connection to the little cylinder. What is the small cylinder and will my new altenator have one and need to be wired up? Sorry to be long winded.

 

[D T]

I think you are refering to a condenser,that removes interference ,for the millitary radios

 

[Warthog]

The 7157 is a good replacement for the DRIVER SIDE alternator. Please mark it so no one in the future will try to install it on the passenger side.

The cylinder is a capasitor/noise suppressor for the military radios. No need to reinstall it.

 

[sarge1]

The 7157 is a good replacement for the DRIVER SIDE alternator. Please mark it so no one in the future will try to install it on the passenger side.

The cylinder is a capasitor/noise suppressor for the military radios. No need to reinstall it.

Thanks for the help guys. I already marked them, although it's easy to see the difference with a big ass chunk of metal tore off Gen 1 anyway.

Hopefully when I get the new one and the other rebuilt, my charging issue will go away. I still have another issue as my Gen 1 light has been really dim during starting process and didn't come on at all one day. Later when I was going home, voltage dropped gradually down to almost nothing, then I hit a bump and BAM! back up to the tick mark in the green section instantly. My headlights looked like the sun for the rest of the trip home. I thought I could just do some hunting around and find a wiring/connection issue somewhere the next morning.

Next morning.....not enough juice to start it, with Gen 1 light dim again during start up process. And that's where it's at.

Hopefully my lack of charging hasn't ruined my front battery as both batteries are new as of the day after I bought the truck. I've got them in the garage and charged them both for about 18 hours.

Should I get them tested at the parts store before I try to run the truck again I suppose? As they sit on the garage floor, the rear battery measures 12.63v and the front battery is only showing 11.74v. That's not good is it. Replace the low one, neither or both? Thanks a lot for your help, trying to save from spending more than I need to at this point.

 

[mtn man]

Just had the autozone 7157 'caddy' alternator for only 2 months... and it went out. It worked for a little while, but the strain was more than it could bare. Since it was under warranty I was able to get the refund... went ahead and picked up a 'junk' gen from a old CUCV and had it rebuilt... in the end I hadmoney left over and my lights have never worked better... charging at a solid 14.4. Good thing about the OE alternator is they can be swapped if needed since both are isolated ground. Those batteries should be OK, but cold is hard on them. I would get them off the floor at least on a rubber mat cause no one wants to lay around on a cold concrete floor.

 

[sarge1]

I've got them sitting on the brackets that hold them down when they are in the truck, so they aren't really sitting on the concrete. The lower volt reading in the front one should be o.k? Thought I remembered hearing a whle back on here that if a battery read under 12v after charging several hours that it was junk.

 

[Warthog]

Sounds like the 11v battery may be dead. After a good charge, have it load tested to see if a cell is dead.

Back yo your alternator. Do you still have the old busted one? Is the case broken on the front half or the rear half? If it is the front half, you may be able to use the front half from the 7157 alternator and the rear of the old one to make a new isolated ground alternator.

 

[sarge1]

It's the front bolt hole that cracked so I may try what you suggest. I had planned on keeping the old one anyway. I'll take the 11v battery to have it checked, but I don't have a good feeling about it. Those things get expensive buying them every couple months. Warthog, thanks a lot for your help I know you see a lot of stuff come up that is similar to one another but for us rookies, we can't help but to ask even after searching and reading a lot, just to make sure we don't waste money we don't have. You are very helpful with your advice

 

[Buckmaw]

O'Reily Part Number: 01-0136
1975 Caddy Commercial - 100amp alternator

I've had pretty good luck with this and it has a lifetime warranty.

This will work but the pulley is a tiny bit smaller than the stock one so you will adjust it out almost to the end of the stops.

Other handy part numbers:

Diode: 1876797
Rectifier 1875645
Borg/Warner Rectifier SC117

 

[sarge1]

Quick follow up question:

I bought the replacement Duralast unit from the FAQ's to replace my Gen 1. It came with a smaller pulley on it than my stocker. Assuming it will still retain proper belt tension without going to the end of the stop on my adjustment bracket, will the smaller pulley matter in the scheme of things? I would think that it would be spinning faster and therefore possibly be charging at a different/higher rate than my Gen 2 that still has the bigger stock pulley on it.

Is there any reason having the different sized pulley on my Gen 1 compromise my batterie(s) or charging system in general before I put them back in? I still have my old Gen 1 and could swap pulleys if I need to but just thought I would ask before I did anything with it.

 

[sarge1]

Bump for my last question please? Anyone know?

 

[ragedracer]

To the best of my knowledge, RPM does not affect voltage. All alternators have a voltage regulator, which keeps the voltage constant regardless of RPM. A smaller pulley on one shouldn't make any difference in the voltage.

 

[sarge1]

Thanks, appreciate it

 

[BIG_RED]

^ I agree, the smaller pulley won't hurt anything. Alternators are voltage regulated and put out the amount of power that the electrical system asks of them, regaurdless of engine RPM (within reason.. at 100 rpm it won't give you much juice.) My truck has to be revved a bit to get the alt lights to go out.. My guess because my diesel idles quite low. Once they get going, they work great.

Also, "GEN1 and GEN2" lights shoud:
- light up when you turn key to run
- shut off once the engine is running (might need to rev it a bit)

If they do not do exactly that, something is wrong. Don't drive far till you figure out what, or you might get stranded.

Good Luck.

 

[Barrman]

The only thing the smaller pulley is really going to effect is the belt size. You probably need a shorter one now.

 

[sarge1]

I'm hoping I won't need to buy another belt as the ones I have are only a couple months old. It was near the middle of the adjustment before so hopefully it can still keep good tension without getting to the end of the stop. We'll see in a couple days hopefully.

 

[sarge1]

Have I mentioned yet that I hate working on electrical stuff? Love CUCV's and hate electrical work; what a rotten combination.

So today, my only day off I get for God knows when I finally am getting to finish getting my altenators back on. The Gen 2 bench tested fine and went back on. I put the Duralast 7175 replacement from the Wiki on the Gen 1 side. It is not isolated ground, and only has a hole with a bolt that goes into it to put the ground wire on. I thought this wasn't a problem.

I got everything hooked back up and when I go to install the negative cable on the front battery, I have now smoked a fusable link that is connected to the rear battery cable that runs to the firewall right in front of the drivers side. I get no sparks at all until I go to hook up the negative cable on the front battery; then it's the 4th of July. I hooked the batteries back up in the correct order: pos rear, pos front, neg rear, neg front.

Is my ground on my new Gen 1 maybe causing this? I'm afraid I am going to run out of daylight before I can get it running and it's frustrating.

 

[Warthog]

Just asking, do youown a volt/ohm meter and know how to use it?

Did you check the negative ground post on GEN2. You need to check to see if the case and the ground post are isolated from each other.

Also how did you connect the wires to GEN2? The red w/white strip goes to the negative terminal.

 

[davidkroberts]

im not sure about your current problem but i had a simlar issue with the GEN1 light dimming and then running very low voltage ended up being the electrical connection on the firewall beside the glowplug relay. The hotwire coming from altenator wasnt making enough of a connection to get back to the battery fully. The bumping around occasionally would give it enough of a connection to make the problem come and go. The wire looked fine from the outside but if you gave it a tug it came off in your hand.

 

[sarge1]

Just asking, do youown a volt/ohm meter and know how to use it?

I do own a multimeter but I am brand new to using them. Only personally checked batteries at this point, which I replaced my front that had a dead cell already. My other is still holding charge and is only 3 months old.

Did you check the negative ground post on GEN2. You need to check to see if the case and the ground post are isolated from each other.

My Gen 2 was not rebuilt, it is the way it came off the truck. The Gen 1 is the only one I swapped out.

Also how did you connect the wires to GEN2? The red w/white strip goes to the negative terminal.

The wires are the same way they were when the truck was running fine and had the batteries removed twice before without the sparking issue. I don't have any red wires w/white stripe, I have a large red going to the negative post and a large red along with a small red, that has a grey/faded black wire connected to it that that connects to the red(positive?) post on Gen 2. Does this sound like a bad wiring issue from before I owned it? Just bought it a few months ago but ran great until my charging issues with Gen1 came up.

im not sure about your current problem but i had a simlar issue with the GEN1 light dimming and then running very low voltage ended up being the electrical connection on the firewall beside the glowplug relay. The hotwire coming from altenator wasnt making enough of a connection to get back to the battery fully. The bumping around occasionally would give it enough of a connection to make the problem come and go. The wire looked fine from the outside but if you gave it a tug it came off in your hand.

I think this is the area I'm frying my fusable connectors now. On the firewall on the drivers side right? I can't help but think my new Gen1 altenator's configuration with the ground being bolted to the back of the case instead of the way the OEM one was is causing my issue. I don't know, this electrical stuff shouldn't be that tough I know but I have trouble understanding it and knowing how to check things. I read the TM's until I'm blue in the face and just wonder if someone at Ft. McCoy monkeyed with the wiring and it's not what it should be...

thanks for all your input guys, I would have no chance without you