Im stumped

So, little history

Small block chevy tbi engine. Rear mounted battery.  

A few months ago, it began cranking slow. Eventually stopped wanting to crank at all. I thought battery was goung bad. Changed battery despite it testing good at tge parts store.  No change in cranking speed, but began cranking again. Next, cleaned all ground connections, as well as the power side connections that were easy. Same slow cranking behavior.  Only thing i haven't tested or physically took out is the starter. 

It turns slow, clicks like a dead battery, lights  in interior flicker in time to the clicks, but continues to spin the engine most the time and the truck will start.

I still think its battery cables, but dont want to keep guessing. I need this thing fixed asap, as i need to use this truck to fix my truck.  

What does this sound like to y'all? Cables, starter, something different?

Use some long jumper cables to bypass the battery cables and see if it improves.  

check your grounds. How did you run them? Most remote battery setups from the factory use a ground from the battery to the body of the car. I would start with looking at the condition of the cable, it's mount on the body, and then to the ground strap on the engine and it's mounting point to the body. With a remote battery, those cables are passing more power and are more important to getting the engine running

Good call. I can't do it from topside, so after work ill try this.

It just doesn't act like a bad starter. But, i may be wrong. 

A starter that's failing could cause the lights to flicker because when it stops spinning it'll be a dead short and draw a ton of current. But I think PMRs suggestion is a good troubleshooting step!

In reply to mad_machine :

2 gauge to frame from battery. 8 gauge to body from battery. 8 gauge from engine to body. 4 gauge from engine to frame.  All grounds were taken apart, cleaned, dialectical grease, and new star washers, and reinstalled.  I did not check ohms of resistance through the cables. 

Ran into similar problem on challenge c4.  Turned out to be hot terminal on starter was internally loose.  Starter shop fixed it for about $20 but could be an easy DIY. External symptom was slightly loose hot terminal when you wiggled by hand event though battery cable bolt was tight.

Batter was moved from stock underhand location to right rear passenger compartment.  2 ga cable used to relocate that was 7 feet of cable.  No problems after terminal repaired.

YMMV

Don't discount the starter.  My wife's TSX behaved exactly like a dead or dying battery that wouldn't hold a charge, even after I replaced the 6-year-old battery with a brand new one.  When running alternator showed plenty of charging.  But seriously, it acted exactly like you are describing until I replaced the starter.

same as PMRacing,  From whatever source, Straight to Starter + pole

 I don't like the ground cable sizing off the battery.  

Starter, solenoid, or low voltage going to the solenoid pull in circuit.

Google "how to test voltage drop" that should get you a lot closer.

I had an old chevy truck with a small block and headers that were close to the starter. As it methodically baked the starter it would crank slower and slower until it acted like the battery was dead. Usually had to change the starter once a year.

Have you checked the hot side at the starter? 

Most SBC setups pull power for... pretty much everything... off of the solenoid. If there's a corrosion issue there it will act as you described.

Your description sounds exactly like my V8 944's starting issue.  Internal corrosion in starter plus one broken brush spring were the culprits.  Took it to local rebuilder, $65 included new bearing and bushing plus brushes and springs.  The guy asked me if it was used on a boat, because he had never seen a car starter with that much corrosion in it.

gearheadmb said:

Google "how to test voltage drop" that should get you a lot closer.

This. Also has the engine block been painted or is there rust between the starter body and block? 

How old are the battery cables, particularly the positive? They can corrode from the inside while looking fairly new outside. 

All good suggestions guys. As soon as i get dinner with the family and the munchkin to bed, im going to go do a thorough diagnostics job and see what we find. The simple fixes didnt, so its time to dig. Will update as i go.

Straight jumper  cables made no difference in starter speed or sound. Fresh battery: no change. Tightened all the bilts, added a braided ground strap from starter to frame. No change. 

Looks like last thing is starter itself. Right?

Patrick said:

 I don't like the ground cable sizing off the battery.  

Forgot to mention the 4 gauge from battery to frame. 

Someday all cables will be redone with bmw 7 series cables. Just not noe.

sad to say, I think you narrowed it down.

Holy crap starters got expensive.  50 bucks for the old style, 100+ for the late 90s style. 

And our guy in town that rebuilt starters apparently died last year, and the shop clised. Dangit.

The gear reduction starters are great. You should really get one of those if you can!

Found one on Amazon for less than the 1 year warranty direct drive units from the lical parts store. 47 shipped. Vs 60 at AutoZone (cheapest in town)

Dusterbd13 said:

Patrick said:

 I don't like the ground cable sizing off the battery.  

Forgot to mention the 4 gauge from battery to frame. 

Someday all cables will be redone with bmw 7 series cables. Just not noe.

I like the C class Mercedes. The sheathing protecting the cable is a lot better quality than I've seen on BMWs.