Help me diagnose my 1979 Ford Pickup.

March 15, 2011 1:34 PM

I have a 1979 Ford F100, which once belonged to my father. Since he passed away, it's served as a backup vehicle for an array of relatives, and now it's my turn. Yesterday, I got into the truck and turned the key, and I heard a single "clunk" (not a click-click-click), as if something started moving and then froze up. I tried again, with the same result. The next time, I got a kind of whirring sound, like something spinning free. It's a continuous whirring, rather than a series of attempts to catch. Lights and radio work fine. Jumping it didn't help. I didn't try to roll it off, because I'm loathe to leave it at the bottom of the hill in my slighty sketchy neighborhood; I'll probably try that this weekend, when I can get some help. The battery is relatively new. It started easily up until yesterday.

I have some experience with cars that won't start; I know what a dead or weak battery sounds like, and so on, but I've never heard this combination of distress calls.

Also, maybe of interest: when I got the truck, the fuel system was clogged with gunk, and I had it cleaned out and replace the gas tank and the carburetor. Don't know if that's relevant or not.

Any advice appreciated.

posted by steambadger to travel & transportation (10 answers total)

Starter is shot.
posted by Thorzdad at 1:42 PM on March 15, 2011

The whirring you hear is the armature spinning free inside the starter housing. It isn't extending to engage with the flywheel.
posted by Thorzdad at 1:44 PM on March 15, 2011

The great news is that it's really easy to remove and replace the starter on a Ford pickup of this vintage.

Disconnect the battery + post first, then climb underneath, disconnect the wires from the starter, then unbolt it. It should be just three bolts.

Any auto repair shop will be able to diagnose the starter, the solenoid, or the gear that engages the flywheel.
posted by Kakkerlak at 1:53 PM on March 15, 2011

Sounds like the starter motor.

The clunk was the starter motor trying, but failing, to engage with the flywheel, because it was failing to push it's drive gear forward into full mesh.

The whirring was the starter motor spinning freely without meshing at all.

The good news is that this is usually a very cheap, quick and easy repair, because it is a very common problem. It might be as simple as a corroded or broken connection to the motor. If not, the entire starter motor assembly can be replaced with a rebuilt one for not much more.

Here. example, is an entire rebuilt starter motor for $32.

http://www.partsgeek.com/catalog/1979/ford/f100/engine_electrical/starter.html
posted by CynicalKnight at 1:56 PM on March 15, 2011

i agree that this sounds like the starter, if not just the starter solenoid. both easy to replace as mentioned above. In the meantime if you require the use of the truck, use a rubber mallet and bang on the starter motor. sometimes cruft can build up in there, and banging can get it to engage the flywheel the next time you give it a whirl. If that doesn't work, you can try straight up jumping the leads on the starter motor itself. take a long flat-bladed screwdriver (plastic handled of course!) and with the key turned to the 'start position' (CAR NOT IN GEAR) connect the two posts with your screwdriver. should fire right up!
posted by Bohemia Mountain at 3:04 PM on March 15, 2011 [2 favorites]

Try Bohemia Mountains suggestions first. I was shown the Hammer/Mallet trick by a AAA guy once.
The other thing i would do in my old Mustang was cross the screws on the solenoid with a screwdriver to try as well. It could just be the solenoid. That is a $6 fix. I remember doing that once in a sketchy part of Santa Ana ( Hey its where the best food is ) and people looked at me as if i was stealing the car.
posted by stuartmm at 3:13 PM on March 15, 2011

Thanks, everybody. Sounds like a consensus.
posted by steambadger at 4:08 PM on March 15, 2011

Yes, definitely try hitting the starter with a hammer.
posted by BeerFilter at 5:16 PM on March 15, 2011

If something is spinning, the mallet probably won't help.
The thunk is the solenoid. If you have power and no thunk and nothing else, it's the whole starter.
If you have a thunk and nothing else, then it indicates that the contacts in the starter motor are worn and it stopped at a place where it can't make contact to move the motor. Hitting it with the hammer is usually enough to make the starter move to a place where the contacts work.
If you have whirring and no thunk, it's the solenoid.

You've had both problems in a short period of time. Sounds like time for a rebuilt starter motor assembly.
posted by plinth at 5:33 PM on March 15, 2011

I was going to say that sounds like a discharged battery. First it had enough power to engage the solenoid, but not enough to turn the engine. Then, it didn't have enough power to engage the solenoid, and the starter was able to weakly freewheel.

(Test: turn on a dome light or some other light inside the cab. Then turn on the headlights. A fully charged battery should fire the headlights right up, and the interior light will dim slightly. A discharged (or failed) battery will fire the headlights slowly and the interior light will dim significantly.)

If the battery is new, could the alternator be bad? That would be my first guess. The test here would probably be to jump-start the truck. If it fires right up, it is doubtful the starter is no good.
posted by gjc at 5:26 AM on March 16, 2011