Discussion of OEM Alternators, replacements, and Importance of cleaning mounting point ground. Importance and method of tightening, and retightening, belt and electrical connections.
During production, two different alternators were installed at the factory. Earlier cars, up to approximately VIN 4539 per bulletin ST-26-11/81, were equipped with the Ducellier unit rated at 80 amps. This unit, in addition to being somewhat undersized for the application, were known to be more failure-prone than the later units. The second design alternator, installed in cars after approximately VIN 4539, was a Motorola (France) unit rated at 90 amps. This is a much more robust unit than the Ducellier but at this time repair parts for it are hard to come by. 90 amps is still marginal capacity with all accessories and headlights operating. The alternator belt
PN 102442 is the same for both alternators.
In the picture below, the alternator on the left is the later Motorola unit. The alternator on the right is the earlier Ducillier unit.
There is a slight wiring difference between the two factory alternators. The early Ducellier alternator has two light-gauge control wires (brown/yellow stripe and solid brown) that are connected to the alternator with a plug connector. The Motorola alternator has only one control wire (brown/yellow stripe). Often early cars were converted to the later alternator, leaving a solid brown wire disconnected and either cut or taped off. All designs also have a very heavy wiring connection consisting of 3 12-gauge wires paralleled together in a single lug at either end for flexibility. The heavy wire in all cases connects to the starter, which is in turn connected to the battery. The negative (ground) connection is through the mounting bracket bolted to the passenger side cylinder head.
The tension bracket was changed slightly and the slip joint moved from the alternator end of the bracket to the engine end of the bracket with the later alternators.
Over the years, there have been several other alternators offered in the aftermarket. The preferred Alternator
PN 110101, the one now sold by DeLorean Motor Company, is a Delco-designed alternator, specifically designed to fit the DeLorean application with the original belt and very slight wiring modification. This unit is conservatively rated at 120 amps, sufficient for the DeLorean application. This alternator is supplied with a new belt and hardware. This alternator uses a connector plug for the control wiring, and the single control wire is connected to the brown/yellow wire in the harness.
When replacing an alternator of any type, there are several things to be very careful with during the installation.
1 - DISCONNECT THE BATTERY. Should be obvious, but sometimes it isn't.
2 - Take the mounting bracket off the engine and clean the back side of the bracket, the mounting boss on the head, and if possible replace at least one of the 8 mm mounting bolts. At least clean it up. Clean up all mounting hardware.
3 - Be sure to tighten the main power lug (the three heavy brown wires) snugly, but not tight enough to break the stud off. Recheck this connection when you change the oil filter.
4 - Set the correct belt tension. Nominally the belt should be tight enough that the belt will deflect 1/2 inch when pressing with your finger. A better indication is to try to turn the alternator main shaft clockwise with a wrench. You should see the belt turn the engine slightly rather than slip at the alternator pulley. Too tight is better than too loose. A loose belt will slip under load and greatly diminish the output of the alternator just when you need it the most.
5 - If doing belt replacement, we recommend replacing the Air Conditioner Compressor belt
PN 105505 at the same time, as it needs to be removed to replace the alternator belt.
The # 1 Reason for Premature Alternator Failure Including "No Output" Is a Slipping V-Belt!
In the good old days when all cars needed was a 40-60 amp alternator, slipping belts were not a common problem. Now that we need 100 amps and up, it has become a real issue. The higher the amperage, the more resistance an alternator has, and it takes more power to turn the pulley. Therefore the belt has to be tighter to prevent slippage.Signs of belt slipping:
- Little or no output, discharged battery
- Pulley extremely hot and starting to discolor
- Pulley extremely hot and starting to discolor,
- Rust on alternator shaft
- Belt dust collecting on fan and front alternator housing >Belt sticking to pulley or belt glazed or cracked
- Belt riding too deep in pulley groove
- Bearing noise
- Most of the time the alternator belt doesn’t make a squealing noise when slipping.
Written 8/5/2016 DAS, slipping belt advisory added 10/2/2020 JE
Revised 1/13/2022 ET (formatting and links)