Slow cranking when warm

[asappin]

1969 Bronco
302 stock engine
3 speed manual
Pertronix coil and ignition

Updates recently:
New single port vacuum advance
New PCV valve and hose (there was just an elbow to the carb but no valve previously)
New spark plugs

So after my bronco was warm one day I couldn’t get the starter to free up and it was stuck. It was not having any problem cold starting. I got it to crank by banging on it but soon replaced it with a new mini starter from Toms. Well it’s starting to have the same problem again so I feel like it’s more than just the starter. Cranks great cold but after driving it and warming it up when I turn it off and try to crank it’s like the starter is real slow to turn. Almost like a dead battery but I know the battery is good. I have long tube headers that the prior owner put on that split the engine mount around the frame on the starter side. Could this be a heat issue? Or is this timing related? Or is my starter bad? Makes me think not since it spins freely and cranks right up cold.

One note is that once the starter finally does turn when warm it cranks right up.

Help is greatly appreciated!

 

[rustbucket]

I would take it to an auto parts store and have the battery tested. It’s a sign of deterioration.


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[B RON CO]

Hi, the first thing I would do is clean up all the battery terminals and grounds. And make sure the cables are in good shape.
Good luck

 

[m_m70]

Hi, the first thing I would do is clean up all the battery terminals and grounds. And make sure the cables are in good shape.
Good luck

This ^ and what is your timing set to? Advanced too much can cause this issue as well...……..

 

[DirtDonk]

Those are the main highlights of this type of list asappin. All of the above and then some.

You will have to diagnose it at this point, because there are several components that can contribute, as you can see by the different answers.
Including your new starter in fact. Although I'd put that at the end of the list of possible culprits, we all get bad parts now and then. And starters are no different.
But because it's acting like it was before, is a reasonable reason to keep it down on the list.

1. You'll need to check your base timing. It's easiest to do, so could be first.

2. You'll need to wrap, coat, shield or otherwise block some of that heat from the headers. Depending on what brand/design they are, headers were the traditional bane of a starter's existence. Modern headers specifically for Broncos, especially the shorty variety, are not as prone to putting the hurt on a starter, and and older Fords are less susceptible than many of the older GM's, but they still have their issues.
Yours sound like the old Blackjack brand that was split up to go around the engine mount. I think there was one other brand that did that on some models, but for all I know it might have been a sister-brand owned by the same parent company.

3. What size are your battery cables? How old are they? If in doubt, change them out.
I like 2ga because it's just the bare amount of overkill, are easy to find these days, and not that expensive. Huge fan.
Even if the current ones are not the issue, giving yourself some leeway/headroom for an overheated starter is a good backup plan.

4. Traditionally, it's hardly ever the starter relay causing a slow start. But it's not impossible either, especially given the modern environment of piss-poor quality afforded to the lowly Ford starter relay these days.
So while you may not need to change yours, keep it in the back of your mind in case none of the other ideas pan out.

5. Being a stock engine, even a '69 does not have enough compression to be hard on a decent starter motor. But tuning issues can exaggerate things.
What prompted the new vacuum advance, and where do you have it connected?
What prompted the Pertronix ignition, and did you check timing after installing it? Check gap after installing it? Verified that you have a full 12v to the Red wire to the distributor?
These things don't normally cause a slow crank, but if they effect timing in just the wrong way, perhaps they can.

7. Glad you put a legit PCV valve in place. Is it for a Bronco, or just one for another vehicle? Was the carburetor tuned/jetted for the old way (full vacuum leak mode!) or was it just not running right that way before?
Just wondering if the carb needs any tweaking. Again, not likely to cause the issue unless there is some extreme issue going on, but it's worth looking into for the long term. And hey, you brought it up!;D

And last, how hot does the engine actually run? Is it a hot runner? Maybe getting super hot under the hood with those headers?
Anyway, there are your few things to check. Start wherever, but easiest first is fine too.

Good luck!

Paul

 

[SteveL]

Dont just look at the ends of the cables. Feel em along the insulation too. I've had em look fine but corrode under the insulation where it was powder on the inside.

 

[Crush]

also those headers are the old type. you just about have to remove the engine to get them off without cuttin the headers. they were also notorious for causing heat sink in the starters and greating the problem you descrribe. I would toss those pieces of crap and put manifolds or modern headers on there that give better clearance

 

[tbratz]

Mine started to do the same thing after about 2 years. I tried trouble shooting all the above suggestions and it still did it. I then broke down and bought a Motorcraft mini starter and no more hard starting. So, I guess my problem was with the starter itself.

 

[DirtDonk]

I'll have to agree with that assessment.
In my experience, when it works fine for a couple of years, then starts to do it either seldom at first and more later, or all at once, it's usually the inherent heat issue, but the starter was able to work with it for all that time and finally just deteriorated to the point it could not handle the heat any longer.
They get weaker as they get older, but heat is still the big killer.

Some starters will just get old, but I've never had that happen without the heat being the issue myself. In my case they would always just get inconsistent in their grabbing the ring gear of the flywheel. The starter would still spin normally, but not catch.
But in every rig with headers I worked on the starter would just finally get slower and slower until it could not longer turn over the engine when hot.

Paul

 

[asappin]

Thank you for all the replies. Sounds like I have a few things to try out. I think I need to cut off the old headers and run new headers that don’t run right up against the header. Maybe even look into adding a new starter after also.