Starter wouldn't engage - '71 911

[Jim727]

So there we were....

I was at one of my Veterans' dinners a couple of weekends ago. Drove the 911 - 2 hours each way of enjoyment. However! After the dining-in I went to start the 911 and... nothing. Headlights were bright with plenty of power, but the starter would not engage. There was the faintest of sounds as the solenoid tried to connect, but nothing. Now, I've had this problem before many years ago after a high-speed drive when attempting to start a heat-soaked engine. This time, however, the car had been sitting for five hours in 50-degree temps, so it doesn't have a heat-soak excuse.

Must have been a sight: me in a tux, another officer in a kilt and the security guard outside the Officer's Club pushing a 911 at 11:30 in the evening. It did start and I drove it home uneventfully. Just to be sure, I parked on a hill when I got home and tried the starter. Worked fine, and has worked fine ever since.

I'm not sure what happened, but I would like to kill the problem rather than experience it again. The starter is original, so it might be "tired". Any thoughts??

Thanks,
Jim

[rusnak]

I'm not sure what you mean, but if the starter did not spin at all, then it's likely that the pinion could not fully kick out. The Bosch starters have a safety feature that will prevent the starter from spinning until the solenoid kicks the gear out to engage the flywheel gear. Check the starter to make sure that the bolts are not loose, and the gear in good condition. I'd try to file the burrs off of the gear teeth if not, since this is likely causing the problem. Until you can get under the car, if you want to drive it in the meanwhile, the thing to do is the let the clutch out, and try shifting through the gears to use the gearbox to turn the flywheel a slight amount. The starter will kick right over and you'll be in business. The other thing you can try is to put it in gear, and nudge the car a little to turn the flywheel. Or you can use your alternator wrench from the toolkit, but that takes longer to do.

If it sounds as if it is spinning, but not catching, then the pinion is not fully extended, and it's probably a problem with the solenoid. Options are to rebuild the starter or buy a new or rebuilt one. I think buying a starter rebuilt by Bosch through their exchange program is the best option in that scenario.

[JCR]

Is it possibly an ignition switch issue?
I had the same problem on my 73... a very occasional "click" but no spin, no start.
Tried it after a few minutes and worked fine. I replaced the starter and the new one did the same thing, still only once in a great while. I know it isn't a battery issue.

[Jim727]

OK this all helps a lot. I wasn't sure of the sequence of things but being
Battery ==> Solenoid ==> Starter means that the solenoid has to be the problem. I can hear the low hum of it energizing, but no mechanical action. Starter does not spin. Flywheel is new.

Looks like I'll pull the starter and take the solenoid to our local electrical rebuild wizard. Might as well get the starter motor brushes done and have it cleaned up internally as well.

Thanks, all.
Jim

[carsngolf]

I've had this exact problem with a '65 and a '68. It mostly happened after a long drive. I'm still not certain where the problem lies, except I'm sure it is not the starter or solenoid. I finally ran a wire directly from the solenoid into the engine compartment where I could short it directly to a hot post. This has worked on both cars. It would seem the ignition switch is somehow involved but I'm not sure. If you ever pin it down, please post it as I know others have had the same exasperating experiences.
Good luck,
Jerry Weiland

[Walt Fricke]

Rusnak's diagnosis seems the most likely. And your conclusion - take starter w/solenoid to a shop - the best response.

There are other possibilities, though.

The main current path is battery hrough solenoid to starter. But it continues - starter to transmission to transmission ground strap to chassis to battery ground strap. Loose starter bolts (unlikely, I think) could mess this up. So could corrosion on either end of either of the ground straps, and the tranny one is most exposed. Fix is to remove and clean all contacting surfaces. But a quicker test is to clamp a jumper cable on one of the battery bolts (or anywhere on the tranny) and a suitable piece of the chassis and see if that makes any difference.

If the tranny to chassis ground really goes bad there can be some other bad effects, as there are usually some small ground wires hooking the engine to the chassis or battery ground, and they can't handle starter current and fry if they are the only path. If they are part of shielding of something else (points to CD, for instance), that can be a problem. Since your car runs, maybe a bad ground is low probability. But it is so easy to check.

But there is a second, much lower current, path: battery to ignition to solenoid, and thence to ground same as starter grounds. If there is too much resistance (or, of course, an open) in this path, the solenoid may not get enough current to do its thing. Which is two fold - connect the big starter cable to the starter, and shove the starter gear out to engage the flywheel ring gear. The positive part of this solenoid path has a fair number of connections in it (unlike the starter system where the battery cable is uninterrupted from battery connector to the ring terminal on the starter). All could introduce resistance.

I think the '71 has a multi-pin connector in the enging bay which connects all or most of the electrical connections to the engine to the rest of the system, and also connects the solenoid actuating wire. Then there are through bulkhead connectors up by the dash, and connections to the ignition switch. And the contacts inside the switch itself. All could introduce resistance, and some are unique to the solenoid's path.

So a test is to measure voltage at the battery with the starter engaged (but, one hopes for diagnostic purposes, not working), and then at the solenoid wire (a push-on connection) at the starter. A significant drop might indicate a problem along the way.

Another test of a "not enough solenoid current" theory is to jumper from the battery cable at the starter to the solenoid's puish-on connector. If the starter springs into life when otherwise it won't using the key, you've isoated the problem to something other than the starter most likely.

Obviously you need to take some care if you futz around diagnosing things so you don't ground a hot starter cable. And you don't really want the engine to start while doing any of this under the car, just turn over a little.

Let us hope this is not an intermittent. Those do incline one to the brute force methods of replacing everything that could possibly be invloved.

Taking the starter out is just enough work that I'd be inclined to do a couple of checks first.

Walt Fricke

[Jim727]

Thanks, Walt.

I'm afraid it is intermittent - SO intermittent that it has happened only twice in almost 35 years; once when hot and once when cold (the recent event). Hot, I understand the cause, but cold made me want to inquire.

The ground straps, etc., are good. The engine was out recently for a rebuild and the ground straps are new with well-cleaned attachment points. The stuff from the ignition switch to the start system is original, so there could be some crud in the way. Starter and solenoid are also original. My ongoing plan has been to clean up and de-corrode (is that a word?) the electrical connections throughout the car, but since this is new and could strand me somewhere I wanted to pop it to the top of the list. Looks like that will be cleaning all the connections from the battery to the solenoid. Then maybe treat the 38-year-old starter and solenoid to some tlc for good measure.

Jim