Dim dash lights… Yah, I know this has been covered a billion and one times and there are many solutions but I did find some interesting facts I thought I would share. That said, it’s always irritated me that the OEM set-up works as poorly as it does. I’ve always seen the lights dim at idle and go brighter on acceleration. Probably like everybody else! So, I set out to find a root cause. I installed a voltage gauge about 6-8 months ago and have been monitoring it regularly. I had never changed the alternator and was not sure how old it was but it typically put out about 10-11 volts at idle and approximately 14 volts at speed (say 1,500 RPM+). I figured it was just old and the brushes were likely tired and didn’t think too much about it. I’ve always just sort of told myself that when I replace it, the readings will be better and should solve the issue (meaning the lights will be constant, not necessarily ultra bright). Last week I got some bearing/rotational noise in the engine and sure enough it turned out to be the alternator. I went down to my local parts store and sourced a remanufactured unit. I went ahead and installed the alternator this weekend. Low and behold, the voltage was a tad lower at idle than the old alternator and a tad higher at speed!! What gives??? All of it got me thinking that something’s just not right and the likelihood of getting a bad part of the shelf was minimal. Especially taking into consideration how wide spread the problem is. Knowing this, I decided to call the manufacturer and get the operating specifications for the unit. The parts store (national chain) did not list the information anywhere! These are my findings and calculations: Per the manufacture, the alternators minimum operating RPM is 1250, its maximum operating RPM is 6500 and their recommended idle speed is 644 RPM for my application. Measuring out the diameters of the pulley’s, we can calculate how fast the alternator is spinning compared to the engine RPM. The crank pulley on my car (72 Maverick with the 200cid engine) is 6.75 inches. The alternator pulley on the remanufactured unit measures is 2.68 inches. OEM recommended idle speeds (per Classic Inlines) Manual: 500-550 (rpm), Automatic: 475-500 (rpm) The chart below depicts the results: For those of us who drive automatics, the OEM idle speed is not fast enough to meet the minimum manufactures operating requirements! Thus, the output is below 12 volts and we will never achieve the required voltage to operate the lights or other instruments as per Ford’s original design. If we were to set the idle speed, per the alternators manufactures recommendations, the alternator would be churning out at a whopping 1,622.01 RPM’s at idle! (and slamming into drive or reverse) Solutions: We’ll, likely the best solution is to install a later type of alternator that’s internally regulated or the myriad of bulb changes and painting schemas others have come up with etc… Doing the math, I think I’m going to go with an under drive pulley at the alternator. The minimum diameter pulley to achieve the minimum operating RPM (1250) will be 2.57 inches. I’ll likely source a 2.5 inch pulley that will spin the alternator at 1350 RPM’s at the OEM idle speed, this should solve the diming issues at idle! If anybody see’s any problems with my logic or calculations let me know! I used the below calculator to figure out much of the math. http://culvermotor.com/Engineering-Formulas/Pulley-and-RPM-Calculator.html Thought I would pass on the info! kb
If you are using the original mechanical regulator that is likely part of your problem, the electronic replacements do a better job... Bringing up the idle another 50/75 RPM till alt is putting out isn't going to hurt anything... My Comet idles around 650/700 RPM, the C4 doesn't slam into gear...
My regulator has been replaced at some point, it’s not the original. My idle speed is set at approximately 480 rpm. At that speed, the alternator is mechanically incapable of producing enough electricity with or with any type of regulator. To my knowledge, the regulator only controls the maximum electricity available and bleeds off any excess current to keep the electrical system within its operating range. By changing the pulley, I will be increasing the alternators rotation by approximately 200 rpm delivering a constant 12 volt stream even at 475 rpm engine idle.
I like it! It sounds worth looking into. Let us know the real-world results when you get your pulley swapped. Are there any other Ford pulleys that are that small?
Don't know?? I was just searching for a v-belt pulley with a shaft diameter 17 millimeters or .669in. inside diameter with an outside diameter of 2.5 inches. The closest I found so far is a .664/2.25, I think that may be a little aggressive at 1425 alternator rpm (found at Summit Racing). I just started searching, we'll see what I can find!
Well good luck but I consider 475 RPM far to slow for any engine... I always idle my stock stuff around 550 to 600 RPM and never had a issue(been doing it 48+ years, not gonna change now)... For something with a moderate cam and a small converter, 700-900 is the norm...
The Maverick came with type 3 pulley, Part Number C5TZ 10344-K The Maverick 2 sheave pulley, type 6, is the same diameter as the single sheave pulley, Part Number C5TZ 10344-L A= 2.84 B= .670 C= .38 E= 1.015 67 and earlier...some came with a smaller pulley but they are type 6 pulley Part Number C5TZ 10344-E You can find this pulley on a 240 Big Six. A= 2.63 B= .670 C= .38 E= 1.56 F= .65 I agree with Tom...Jack up the rpm. My 250 idles around 725
I also agree w/ Tom; I have never had a car idle @475. My stock DD, computer controlled 06 Buick, 99 Windstar idle more than 475. B4 I went thru the changing of pulleys I wud increase the idle and see how that works. My Comet idles abt 800 w/ mild cam, stock converter, don't slam into gear.
Hey Kevin, go chat with these guys http://www.autoairmarineelectric.net/ they should at the least be able to get you the pulley your looking for. one other thing to consider is the increased resistances of the wiring harness being 42 years old. their is a wire that senses the system voltage. im not sure on the stock harness where it goes, i suspect just to the battery post on the starter solenoid, but its what the voltage regulator looks at to regulate the voltage output. on my old car i had originally had that wire on the out put wire of my alt (3g) and had relatively low system voltage. i then moved this wire to under the dash to after the ignition switch and saw a good increase in the system voltage. as for the dim lights, when i did the headlight relay up grade, my lights got much brighter. before the up grade the difference at idle and cruising was pretty drastic. after the upgrade it was minimal.
