Location: Lexington, KY
Posts: 218
My VIN: 16655
Check the tension on the alt belt... I've got one of Hervey's higher-amp alts and I'm becoming more convinced that the pulley on it is just ever so slightly too small such that there isn't enough adjustment in the bracket to tension it properly without having extended the slot so I can get more tension and that it slips slightly when the engine is colder or there's a higher load on the alt...Originally Posted by DMC3165
Posts: 1,068
The pulley is more than "ever so slightly" smaller. John's website lists a 90 inch belt "for Special T alternator" and a 95 inch belt "for stock Motorola or Ducy alternator." By using a smaller pulley he spins the alternator faster, increasing power output at any given engine RPM.
Bill Robertson
#5939
Location: Smithtown NY
Posts: 893
My VIN: Formerly 0774, Formerly 3165 twice
Club(s): (DMA) (LINY-DMC) (DCUK)
Yesterday afternoon I went through the entire car. I started with the alternator connections. There was some corrosion but very little. I also pulled off the main ground strap on the engine and cleaned up those contacts again as well. I also unplugged the red wire by the A/C unit and gave those contacts a quick cleaning. In the process I also pulled out every external lightbulb and cleaned up all those contacts as well. Most everything was pretty clean and showed only minimal amounts of oxidation if any at all.
In the end 4 hours later it made absolutely no difference at all. I do notice while driving at night the lights dim for 1/10 of a second with a quick drop and recovery on the volt gauge with the A/C on. This happens about every minute or so which I can only assume is the compressor cycling. So I'm thinking maybe the compressor is going bad? Will it draw heavily on the electrical system when they are starting to go bad?
Chris Piazza
1GR8STRY
Owner of 3165 by default
Location: Leonardtown, MD
Posts: 9,006
My VIN: 03572
The compressor clutch draws about 6 to 10 amps. But when the compressor kicks on it also loads the engine so at idle you may see a momentary drop in voltage because of the RPM drop.
My guess is your alternator has weak output power.
Location: Smithtown NY
Posts: 893
My VIN: Formerly 0774, Formerly 3165 twice
Club(s): (DMA) (LINY-DMC) (DCUK)
Someone is offering me a 140 amp DMCH alternator right now. I am hesitant to install such a high output unit in a car that was never designed for 140 amps. What are your opinions on this.
Chris Piazza
1GR8STRY
Owner of 3165 by default
Location: Leonardtown, MD
Posts: 9,006
My VIN: 03572
What I have heard of some of the high output alternators is they have low output at idle speed. I don't think John even sells them anymore.
Location: Northern NJ
Posts: 8,581
My VIN: 10757 1st place Concourse 1998
Alternators cannot put out their full, rated output at idle. Just because you did not find the bad connection does not mean you do not have one. You can use a voltmeter and look for large voltage drops while you are running your A/C. The A/C does a "double whammy" on your car's systems. Not only does it add a very large load onto the idling engine, it adds a LOT of electrical load all at once by using the heater fan, both cooling fans, and the clutch. While you are driving you can actually feel it in the gas pedal when the A/C cycles. You feel the car "pulling back" and slowing down. Start by having the battery load tested and the alternator checked. Then clean ALL of the "big" connections.
David Teitelbaum
Location: Fresno, CA.
Posts: 1,382
My VIN: 16409
I spoke to Toby about this low output at idle problem. He said Dave at DMCMW found a very good alternator shop locally that is making the latest iteration of alternators. Toby said they were designed to have good output at idle. I never had a problem with the Houston unit. I had some bad wiring going to the starter, which I thought was a bad alternator. I bought a D-110 to try and fix the problem, but the starter wires got burned on the exhaust manifold. (SPEC 1 manifolds, be sure you properly route your wires if you install a new exhaust system.) Once the wires were replaced, my battery light problem went away. I did notice that my volt gauge sat higher with Houston's unit.
Last edited by Chris 16409; 07-20-2011 at 11:34 AM.
Chris Miles
For Better or Worse I own a DeLorean!
1983 Grey Manual, VIN #16409, Fresno, California
Location: Northern NJ
Posts: 8,581
My VIN: 10757 1st place Concourse 1998
At idle, during periods of very high electrical loads, the battery is supposed to supplement the alternator. Not meant for long periods, more like stopping at a traffic light. Off-idle the alternator should be going fast enough to handle the loads. This works unless you have a chronically under-charged battery. If you use the car infrequently and the battery is never fully charged, the alternator will always be trying to recharge it. This puts an additional heavy strain on the whole electrical system and reduces the life of the battery and alternator. The answer is not a high output alternator. Get a trickle charger like a Battery Tender and if you do not use the car keep the battery fully charged with that so all the alternator has to do is handle the operating loads on the electrical system and not have to always recharge the battery. The only recharging the alternator should have to do to the battery is replace the power that was used up to start the motor. If that is all it has to do it can more easily handle the other loads on the electrical system.
David Teitelbaum
Location: Lexington, KY
Posts: 218
My VIN: 16655
*sigh* I wish that were more prominently stated on the site- like in bold with the alts in question that you must use a smaller belt. I wish it didn't require pulling the A/C belt to replace the alt belt. :/
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Dave M vin 03572
