Low voltage in reverse

[danielb927]

Hey FABO,

It's been a long time since I've posted! As I've been living with no garage the past 3.5 years I hadn't gotten around to much in the way of car work--that is, until last weekend. Finally swapped out my cracked & clogged stock radiator for a shiny 3-row champion unit. While I was at it, went ahead and switched pulleys to the correct non-AC setup.

On to my question. Since putting on new pulleys, the voltage drops down to ~12 volts when I put the car in reverse(also drops in drive, but not as much). Reverse is probably at around 700 rpm. As I had problems getting the single-groove pulley pressed onto the alternator during the swap, I tried a new alt tonight but with no effect.

The new crank pulley for water pump/alternator seems smaller than the old setup, so is this just the max the alternator can put out at 700 RPM now? Or some other fixable problem that others have seen? Other factors in play: did the ammeter bypass about a year ago and added headlight relays, but the issue does seem worse with headlights on.

 

[brian6pac]

https://www.summitracing.com/parts/dcc-3690731/overview/

 

[danielb927]

Is that regulator in particular going to solve the issue, or is this just as sign that my current one is bad?

 

[dirty white boy]

smaller crank pulley slowed down your alt and water pump can ether put bigger crank pulley or smaller alt pulley...

 

[67Dart273]

What size are the crank/ alternator pulleys? Is the alternator a roundback or squareback?

 

[danielb927]

Crank pulley is the Bouchillon performance 2-groove, 6-9/16" diameter (here). I'm not changing that, as it's the correct setup for non-AC and matched with the water pump pulley (6-7/8").

Alternator is an Ultima unit from O'Reilly (here), looks like squareback I suppose? Don't know pulley diameter but will try to measure tonight.