There is a shift fork in the starter which pushes / pulls the starter pinion gear / Bendix in and out when the solenoid is energized. Normally the return spring will pull the Bendix back with no movement (your 1/8" slack). It could be the return spring is weak or the fork is excessively worn where it fits into the Bendix hub. I don't think 1/8" is enough to cause your problem, but it is an indication of a problem.


I would do a bench test of the starter using the battery or a 12vdc source and watch the bendix action. It should drive out upon powering the BATT and S terminals on the starter and pull back upon removal of power. Put it in a vice to hold it.
You can measure the resistance (OHMS) between the S and R terminals and should have infinite resistance. The plunger contact disc (washer) is forced back by the electro magnetic pull of the solenoid to make contact with the BATT terminal with the field coil terminal and power the starter motor.
Although the Bendix sticking in the flywheel is what I would think is the most common cause of your symptom, the solenoid return spring failure would cause it also. The copper contact disc (washer) would have to be stuck to the BATT terminal and also the field coil terminal, which I have never found as a problem.
If the starter works normally with a bench test, you need to check the wiring to the starter switch and also the starter switch. There is another Thread on here now which had nearly the same problem. Be sure to power the system only long enough to check voltages or you may fry the harness if you have a short in the wiring.

 

Mr. Goodwrench is much smarter than I am, check out section 6Y of the Chevrolet Chassis Service Manual for starter testing and rebuild.
https://www.workshopservicemanual.co...-repair-manual

 

Here are some shots of the inner workings. I had this starter laying around and when I bench tested it, it was sluggish kicking in the solenoid actuator.
I have never taken one of these apart but I thought what the heck. With a little YouTube help I dug in. Cleaned everything up (armature, degreased the innards, etc.) lubed what I could and lo and behold the darn thing worked when I put it back together. I made a small disc to spread the brushes to ease placing the housing down over the armature. There's probably a trade secret for doing that but I took the "woodworking" route.

Maybe this will be of some help if you decide to tackle the rebuild.
Dave Z

 

Bench tested the starter. 12.6 volts from a fully charged automotive battery applied across 'BATT' and 'S' terminals. No motion of gear whatsoever. Then measured the resistance across the 'S' and 'R' terminals: none

After reading section 6Y of the shop manual, it appears that the gear sliding probably indicates worn internal starter components, so just replacing the Bendix is not a complete solution. While I probably could rebuild it with time and patience, I'm sure I'll never have to rebuild another, so its a skill I don't really need. I'll let a pro do it.

I'll buy a cheap temporary starter, install it, and send this one to the firm Mike recommended for real re-build. Hopefully it won't be like the "re-build" I supposedly already got from the firm I mentioned above.

Thanks all,
Mike

 

Most rebuilds and even new starters are built in Mexico, China, or other countries without concern for quality.
I try to use Standard Motor Products' best quality parts. They sell two grades, the lower grade to compete with the foreign stuff and a high grade for those wanting durability. Their warrantee of each reflects the quality of the parts. Their parts are available at NAPA and other quality FLAPS.
I rebuild starters and alternators myself, primarily to have a warm and fuzzy about the parts used. Less than 1/2 hour to freshen up a starter if the major components are good. But, the good parts may cost as much as the cheap rebuilt starters.
If you have zero resistance across the S and R terminals, you also need a solenoid as it is shorted. If it has infinite resistance, it may be good.
Ron

 

Mike,
Surely there is a shop local to you that can rebuild your starter for you. Google "Starter-Alternator-Generator Reuild services near me". I bet you'll find a shop or two that has been in business for decades and can turn your original starter around in a couple of days. Just be sure to tell them you want to keep your original, dated case.

 

Leif, thanks, I'll have a replacement here on Wednesday, and have it in the car in a hour or so. So, there's no hurry to rebuild the original. Unfortunately, capable auto shops up here on the remote shores of northern Lake Michigan are few and far between, with few mechanics familiar with old car parts. The closest one is close to an hour drive away, and given my results with Chevy Cool, without knowing a given shop's capability, I'm hesitant to use one. M.Geiger and I go way back and spent many moons cruising Woodward and working on cars together, so I trust his judgement. Though the shop he recommended is four hours from here, its 300 yards from my office, so I'll just send it to the office and, if I ask nice, the guys will take it over and monitor the process. I do go to the Detroit area reasonably often, so it'll likely be ready next time I visit the office.