BCM Community

On another thread someone was advised to check the starter current draw because even though they had new batteries and a new starter the bus still wouldn't start when hot.

I have the same problem. I have a new (rebuilt) starter and all new cables going directly from the starter to the batteries, having moved the batteries closer to the engine.. I have 2 8D's that are older but still in decent shape(I think) The last time this happened (a month or so ago) I called a tow truck  who gave me a boost and the bus started right away. This made me think that maybe the batteries were weak and wouldn't hold a charge. So I let them sit for a couple of weeks thinking they would drain down if they were bad but no such luck
So I want to do the current  draw test on the starter while cranking.

What equipment do I need to do this test. I have a good digital voltmeter. Keeping in mind that the starter is a "bear" to get at on a GM 4106 can this test be done at the batteries or do you have to be at the starter.i.e. the other end of the battery cables.

Thanks for your help.

Fred Mc

GM PD4106

Is the starter motor "rebuilt", "remanufactured" or "new" ?
It is possible that the starter motor could be defective, you would have to check the current draw on it while cranking.

Might want to first have your batts "load tested" - FWIW

You need a clamp on digital ampmeter. Fluke makes one. You also might be able to get an optional clamp on device only that plugs into your existing digital meter.
Richard

How would you use the clamp on ammeter. Does it smply clamp on to a stater cable?

Thanks

Fred Mc.

I just noticed a couple of days ago that Sears has a clamp on AC-DC meter for $69.00.  I think it was good to 400 amps.

Len

What would I be looking for results wise? How much of a draw would indicate a bad starter?

Thanks

Fred Mc.

There are small and relatively inexpensive guages out there made for testing starter draw current which you simply place on the battery cable to the starter and have someone crank the engine.  It gives a relative amperage draw reading on the face of the guage.  I have two of them in my toolbox down at the barn.  Since it's 5:30 AM it's not likely that I'll go down there now...but I will check later to see if I can offer more info...such as a brand, etc.  My best guess is that I bought at least one of them from NAPA.

FWIW

Bob

Fred Mc, when I was trying to find out what our starter on our 4106 drew while cranking, I checked it on our Link, which reads up to 500 amps. The reading was right near 400 amps when cranking at a normal speed. As I recall, it was around 9.5 volts when cranking.

If the engine slows down for any reason while cranking, the amperage will climb very rapidly. If you get slow cranking and the current doesn't go WAY over 400 amps, the resistance in your cranking circuit is too high.

Higher voltage would mean the starter isn't taking the current; lower would mean that the battery system is not delivering enough power. Either condition will lead to damage.

Good luck.

Tom Caffrey
Suncatcher
Ketchikan, Alaska

Before you mess with starter current give the batteries a good load test at any parts store.

The batteries are probably the problem.

If you checked all grounds (often over looked) and all connections id buy a load tester, just put it on the batteries and put the load on it , it will tell you if the batteries are at fault, they are easy to use.
Frank allen
4106

To load test an 8D battery you have to put on a minimum load of 500 amps. A small  load tester for car batteries willl not give you a valid test.

A DD starter does not have an internal ground. Your ground cable should go to the insulated ground bolt on the end of the starter, then to the engine cradle, and then to chassis. The bus manufactrurer may go to the chassis first but this  introduces more connections in the high current circuit.  When drawing high current, very small resitances in terminals and connections cause a serious voltage drop at the load.

Stan, I rewired my batteries, after moving them closer to the starter,and ran a ground cable directly from the starter to the batteries thus eliminating all the other connections. Same with the positive cable.

Fred Mc.

Quote from: Fred Mc on July 07, 2006, 10:44:16 PM
Stan, I rewired my batteries, after moving them closer to the starter,and ran a ground cable directly from the starter to the batteries thus eliminating all the other connections. Same with the positive cable.
Fred Mc.

Fred did you also run a chassis ground ?  Running it straight to the starter is great but other areas (instruments, distribution panels, lights, control panel, etc.) get there ground directly from the chassis I've seen where problems arose when engine swaps were done and someone elimnated or forgot to ground the chassis back!  Let us know ! BK (using Huck.A.Buck's computer at the moment)  ;D

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