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I am now driving my 4BT powered mid 70's 3/4ton 4WD Chassis with 36 Ford Cab. Sometimes the motor won't start--the starter will only click and I have to jump it. I have a 780 CCA car battery--so the other day I added another battery with the same specs. I wired them so the positive goes to the positive and negative goes to the negative (2nd battery going to first battery--first battery positive goes to starter and the negative is grounded to frame). The batteries are located by the rear axle on the frame so it's about 7 feet of cable. I am wondering if I have big enough batteries and should I go to series 65 truck batteries. Also, I am wondering if my cable needs to be increased in size. Anybody else had experiences along these lines? Otherwise, I think the 4BT is gonna be wonderful (tranny is 700R4 beefed to the gills). Thanks, Dan Smith, South Dakota
 

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The batteries should be at least 800 cc per Cummins ,now the cables need to be 1/0 or 2/0 the bigger the better.
I use welding cable and lugs and HD term like on tractors or heavy equipment.
The best way to to battery cables if your running two .

Pos 1 to pos 2 than to starter , neg to frame and to block

The main thing is to make sure the neg have a good ground
 

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(2nd battery going to first battery--first battery positive goes to starter and the negative is grounded to frame). The batteries are located by the rear axle on the frame so it's about 7 feet of cable. I am wondering if I have big enough batteries and should I go to series 65 truck batteries. Also, I am wondering if my cable needs to be increased in size.
You can check your cabling to see if it's up to task by doing what's called a voltage drop test:

Grab your multimeter, set it to DC Volts at the lowest scale that can handle 14V or so (for most, this is 20V). Hook the thing in parallel to the cable / circuit you want to test.

For example, if testing the negative side of the equation, hook the negative lead of the meter DIRECTLY to the negative post of the battery, and then the positive lead of the meter DIRECTLY to the body of the starter or the engine block. Checking the positive side is similar, positive meter to positive post of battery, negative meter to the big stud on the starter where the positive battery cable attaches. If you hook the meter backwards, no problem on most digitals (you'll get a negative reading, though..) but could cook your analog meter types.. And it is CRITICAL for this testing that connections be directly to the battery posts / endpoints or else you're not really testing things.. Here's where those 20' meter leads come in handy.

Once the meter is hooked, disconnect the fuel solenoid so the engine will not start, then crank the thing while observing the meter reading. You should NOT see anything over .6 volts. (Yes, .6, as in just over half a volt...) And that's not the greatest, really. You want it to be less. If it's over that, you've either got bad connections or insufficient cable sizing. You can work your way back to battery or to block with one of the test leads to try to find the bad connection or cable.

When running battery cables, if at all possible, run a cable from the negative of the battery(s) DIRECTLY to the block. (And cables from battery negative to frame and body, or from block to frame and body...) Every connection in the path from battery(s) to your load (starter, in this case) is a two-fold problem: One, there will be loss, even if it's not that great. Two, it's a potential failure point, whether from vibration / fatigue or corrosion.

If you do decide to run negative through the frame to the engine instead, make sure that you use VERY beefy cable from battery(s) to frame and from frame to engine.

And.. Anywhere you connect a cable, be it frame or block, needs to be absolutely clean and free of paint / rust / other impediments. Once you have the connections on, tight, and tested you can paint over them to protect 'em.


I'm going to go out on a limb and say it's likely on the negative side of the circuit that you'll find problems: If you hook up jumpers the way I do, namely direct to battery on the vehicle / battery doing the jumping, positive clamp to positive battery post and negative clamp to big hunk of engine block on vehicle being jumped, then what you're doing is bypassing / augmenting the negative side of the circuit as well as bringing another battery to the party..
 

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Starter

I would check your starter and starter solonoid. I think you have more than enough amps of power. If your starter or the solonoid is bad they will draw all the amps your battery has and when you jump it that is the push for the little extra Amps it need. That is a very common problem with chevy startes and i have seen it many times. I know your starter is not a chevy starter but the same applys. Brushes or solonoid are bad.. On my chevy convershion i am only running the stock group 34 battery at only 600 amps and i have no problem at all turning it over. The starter that i got with my engine was a pretty new reman. If you cranked the starter alot on the first start up and used it hard they over heat and the windings get bad and require alot more amp's to do there job.
 

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My Cummins Shop manual under'
Specifications Page E-22
B3.9 Engine
Minimum Recommend Battery Capacity at 0 Degrees F

With Light Accessories 12 vdc Starter 625CCA

With Heavy Accesorries 12 vdc Starter 800 CCA

MInimum Allowable Resistance of Starting Circuit with 12 VDC
Starter .0012 ohms

LIght accessories include Alternator, Pwer Steering Pump and disengaged clutch

Heavy Accessories include, Hydraulic Pump, Torque Convertor

Paul
 

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Sticker in my truck. Indicates 650CCA as a minimum. I had I think 750 or 800CCA in the truck that had no problems. I agree with the wire size relation to length possible issue, but mostly with the starter possible issue.

 

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My donor van had an almost new Interstate 950cca that I transfered to my truck. Left the interior light on 15 hours or so a couple of times, still spun it up like crazy.
Carl

1979 F-250 crew cab 4 x 4
4 bta with modified H1C
Separate cooling system for JWAC
Cold air intake
ZF S5-42 5 speed
Borg Warner 1356 x-case
Dana 60 rear
Dana 44 front
3.54 gears
255/85R16 tires (33.5x10.5)
Hydroboost steering and brakes
Custom 40 gal. fuel tank
Much more later
 

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My donor van had an almost new Interstate 950cca that I transfered to my truck. Left the interior light on 15 hours or so a couple of times, still spun it up like crazy.
Carl
CCA has nothing to do with how long the battery last. You would be looking capacity, it will be a AH capacity. 50AH means it can put out 50 amps for an hour, or 5 amps for 10 hours.
 

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Machman wrote a very good article on how to test the starting circuit. It allows you to troubleshoot exactly where the problem is at. I haven't seen anybody use that method in years due to most mechanics are not good at manually troubleshooting. My father showed me the same method when I was learning how to use a VOA meter (Simpson 360).
 

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My father showed me the same method when I was learning how to use a VOA meter (Simpson 360).

Ah, yes..

I, too, lost my innocence to a Simpson meter. Dad's had several over the years. I really liked the analog ones in the wooden cases that had the meter, leads, etc. all tucked away nice and neat.

Dang, now I'm getting all misty-eyed thinking back.. Good times.. Good times.. :dustin:
 

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My recommendation, if you have the room, is a Group 31 battery. The fleet that I work on has been using them for the last 20+ years on our large four cylinder diesels. We use one battery to start the 3.9L/4.0L Perkins. The users don't always use the cold-start systems (even in the cold of winter). Most of the smaller diesels came with Group 27 batteries, but we're upgrading them to Group 31s along the way.
 
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