Slow crank issue

My 84 has a slow crank issue going on, looking for advice please.

Here is what I know so far:
-Truck will somewhat slow crank, but it will eventually start on a cold start
-Occasionally the truck will spin backwards a tad when I let off the starter as if there is too much compression built up (timing maybe?)
-Truck will only slow crank and not get any momentum or start after it is shut off once its warmed up
-If I let it cool down for a while it will again have a slow crank but it is fast enough to start again
-Battery is 12.6v (725CCA)
-When attempting to crank the battery drops to 9v (normal I think)
-I have cleaned/filed/saned all battery terminals and main wire connections from the battery, to ground, to the starter
-When I attempt to jump the truck to another vehicle it still has the same exact slow crank symptom
-If I move the battery over to the 85 she cranks fine (so battery is good)

So my suspicion is starter because that is the only thing left right?  Is there anything else on these trucks ignition wise that could cause a slow crank other than a starter such as voltage regulator, or ignition module?  I was going to pull the starter and have it tested today but just did not have enough time and wanted to see what you guys thought before I pull it tomorrow.

I think you have one of three problems. Here they are in my estimation of decreasing probability:

1. Bad Cable: You may have a problem with a cable, which is fairly common. Do the Electrical/Voltage Drop Test to find out.
2. Bad Starter: It could be a bad starter as the bearings (bushings actually) wear and the armature drags on the field, so the starter's power is consumed just overcoming its own friction, which increases as the temp goes up due to expansion, which causes more friction, which raises the temp, which.....
3. Too much initial timing advance on the engine.

I agree with Gary. My truck would slow crank, but only when warm, because of timing advance.

Check the battery and cables. Also some parts stores will check your battery and starter for you.

What’s your static timing set at? Do you know?

No I do not know, I have not messed with the timing on the 84.  I did learn quite a bit setting the timing on the 85 though so I will check out timing on the 84 to see.  Just another item to add to the list for the project.

Dropping to 9V on a start is the low side of normal. I would check your engine ground first. Many times, they become " non-existent" . . over the years. You need a good ground, good connections at the end of the cable and a good clean connection where it bolts to the truck frame or sheet metal. I would take all loose, clean and reinstall.

jstone4646 wrote

Battery is 12.6v (725CCA)

That's nearly a volt lower than it should be.

jstone4646 wrote

When attempting to crank the battery drops to 9v

That's also more than a volt lower than normal.

jstone4646 wrote

I have cleaned/filed/saned all battery terminals and main wire connections from the battery, to ground, to the starter

A file is the wrong tool to use on any electrical terminal.  It removes so much metal, and can change the shape of the terminal so much that it makes the connection worse.

jstone4646 wrote

When I attempt to jump the truck to another vehicle it still has the same exact slow crank symptom

Even when warm?  You said without the jump, it doesn't crank warm.

jstone4646 wrote

If I move the battery over to the 85 she cranks fine (so battery is good)

That's not a valid test of the battery.  The only test Ford, most automakers, & most battery mfrs. accept is this brand & type:

jstone4646 wrote

...that is the only thing left right?

Not even close.  You didn't post any pics of the battery, the terminals, the starter, the cables, the meter you're using, the engine-running voltage at the battery OR the alternator...

Click this & read all the captions:

jstone4646 wrote

Is there anything else on these trucks ignition wise that could cause a slow crank...?

No, the ignition system has barely any impact on cranking.  It's mainly dictated by the starting system & the engine.  But the charging system has a big impact on the condition of the battery, which is in the starting system.

SUCCESS UPDATE:  So my boy went to auto zone last night and had the starter tested, auto zone reported the test was good.  This morning I put that starter back in the truck and the same thing, slow crank.  I started noticing a smell coming from the engine bay, crawled under the truck and discovered it was the starter that was smelling (think burnt electrical smell).  Took it back to auto zone and sure enough it tested good.  When it came out of the tester it was so incredibly hot I could not even pick it up and their tester cubby smelled like a series of burnt electronics.  Bought a new one, put it in, truck cranks just fine....case closed, finally!

I ended up going back to auto zone and purchasing all new wiring, relay to starter, relay to batter, ground wire, etc.  The old wiring worked fine but it was so nasty looking I decided to replace it anyways.

Congrat's!!!!  

It's a good feeling when you fix a nagging problem like that.  Well done.

jstone4646 wrote

...went to auto zone...  Bought a new one, put it in, truck cranks just fine....case closed, finally!

I hope so, but I doubt it.  Zone parts are rarely a "final fix".  More often, they're just wastes of time & money.  But 2 of them almost killed me on separate occasions.