Round back w/1 field vs square back w/2

[Bandit360]

Clearance between the back of the alternator and the cylinder head forced me to put a 69 Coronet round back 60A one field alternator on my 69 Charger hemi project.  I still have the square back with two fields, but I need the shorter round back to fit (It's only about 1/4" shorter, but that will make all the difference).  But now I have only one field connection on the back of the alternator, and two wires (green field and DBL)  I know there is a way to solve this problem.  It would be even easier if I could find a round back at AutoZone with two fields (anybody know an application that uses this?) but NachoRT posted something about modification, and I'll follow that if I can't find another solution.  Anybody got any ideas?

Ray

[John_Kunkel]

Your '69 originally came with a single field alternator, are you saying the regulator has been upgraded to the '70 and later style or is the 2nd field wire simply grounded?

Here's the mod you're referring to:

[Bandit360]

Thanks John,

That's the mod I saw.  I was hoping someone knew an application for a round back with two fields, but i guess that is non-existent.  It appears my car has been modded with a 70/later setup, thus the DBL wire for the second field connection.  Not really sure I understand NachoRT's mod instructions.  I'll look at it a little closer when I get back from out of town.  Am I adding a second brush at the ground point?  reversing the ground connection?  I've gotta look closer, but gotta go to work now.

Ray

[Pete in NH]

Hi,

The round back with two field connections was used on 1970 and 1971 cars. If you ask for an alternator for a 71 Charger with A/C that should get you a two field connection, round back rated at 45 amps. But again, any 70-71 application will get you a two field wire round back.

[Bandit360]

I looked at the pictures on line from every parts store in Las Vegas for 70 and 71 chargers.  All two field alternators are pictured with square backs, which is the case for all 70/later alternators, even with two groove pulleys for air conditioning.  Except, I have a DuraLast 7001 from auto zone (searched for 69 Coronet) which actually is pictured as also fitting a 71 Charger, even though it has only one field connection.  Pretty sure that's not right, as all 70 and later had two.  I guess I'm going to figure out the mod John pictured above.  Doesn't look hard.

Ray

[Nacho-RT74]

Dual field began in mid 69 for C bodies still being round backs. 70 to all bodies. Last longed up to 71 as mentioned.

72s was the first year for square backs. THESE ARE SAME DIMENSIONS THAN ROUND BACKS... So there is not reason to not fit.

DON'T get confused with the lates 70s squarebacks, which are actually wider by a tad. ( couple of milimeters maybe ) than the earliers. These got stator hidden down the two alt ( front and back )  housings.

[Pete in NH]

The problem is these cars are 40+ years old now and there are fewer people around today that understand what parts are correct as they left the factory. Also, alternator rebuilders are trying to cover as many model years as possible with parts they have on hand. Despite what pictures may show, again from people who don't really know about these cars, a 71 alternator was a two field terminal round back. A square back might interchange but, a 71 car left the factory with a round back alternator. You might have to look around to find the correct alternator despite what the 20 something kid behind the counter and his computer are saying.

[John_Kunkel]

72s was the first year for square backs. THESE ARE SAME DIMENSIONS THAN ROUND BACKS... So there is not reason to not fit.

The OP has a Hemi. While the overall depth might be the same, the square-back has some "overhang" that won't clear the bulky Hemi head.

[Nacho-RT74]

I don't think this is the first case of somebody trying to fit a squareback onto an Hemi...

[Bandit360]

I performed the mod as Nacho described on the round back single field alternator I bought.  The square back two field alternator off the 383 I removed from the car wouldn't fit.  It is just that much longer than the round back, and the square part of the back hit the hemi cylinder head.  This is a Classic Auto Air Sanden replacement A/C compressor setup for  an A/C hemi car (I live in Las Vegas).  It now all fits with some massaging and the round back alternator.  Most hemi non air setups have the alternator mounted to different places farther forward on the water pump, but that won't work for a double groove air setup, (total of four grooves on the crank - 1 water pump, 1 PS, 2 A/C and alternator)

I did as NachoRT suggested and drilled a 1/2" hole through the rear case opposite the original ground brush location.  I had a vertical brush/insulator sitting right there on my old square back alternator, (which was only worth $10 as a core, so I kept it) -  (#2 brush/insulator in Nacho's excellent picture description). It fit easily in the drilled 1/2" hole and secured  in a newly drilled pilot hole.  Came out great.   Engine not yet started, because I'm not finished with other stuff, but soon, and I fully expect it to work.

Thanks for all your advice guys.  I'm as frustrated as many of you are when walking in to an auto parts store looking for a specific part for a highly modified car. (more on the mustang than this Charger). None of it is original. Starting the search for a serpentine belt under "69 Mustang" isn't going to yield any results.  Listen to what I'm asking for rather than the first words out of your mouth "Year, Make and Model".

[Nacho-RT74]

I just collected pics to describe the mod, never done by myself. BUT I have seen restored/remanufactured alts personally with that mod already done. Yes is pretty much easy to do. Just need to drill the hole meeting the rotor track ( same distance from center than the grounded brush )

[John_Kunkel]

I don't think this is the first case of somebody trying to fit a squareback onto an Hemi...

And maybe not the first to fail. 

[Nacho-RT74]

yes, well, maybe!!!

maybe the Hemi was dropped from the engine options on 72 because the alt was changed to square back ? LOL

[John_Kunkel]

The Hemi was dropped because of emissions standards. The introduction of the squareback at the same time is purely coincidence.

[Nacho-RT74]

it was just a joke LOL