South Bend 9a QCGB binding issue

[Bklimek]

I'm in the process of cleaning up a 9a that looked like it set in the back of an auto shop of about 50 years. When I bought it, I could tell it had likely been tipped at one point because the heads were broken off of both gear box levers. I wasn't super concerned because it was VERY cheap and I had a spare set of gear box levers from a previous rebuild a few years back. Fast forward a few months and I've got this new machine up and running sans QCGB. When I reassembled the gearbox after cleaning and repainting I noticed that in most of the lever positions the entire gear box binds up. I've gone over it thoroughly at this point and I'm pretty certain everything is assembled properly. The input out output shafts/gears spin smoothly. Both of the levers are a little difficult to engage and almost seem like they mesh too tightly and bind up the rest of the gear train when pushed all the way in. Everything I've been able to find makes it look like the castings/part #'s for these levers didn't really change, but it almost seems like they don't fit quite right. From what I can tell the levers are from the early 40's, I don't have any data on the machine they came from but they have a smooth unknurled top with a single rib that I've only seen on other machines from that time period. The rest of the gear box is from the mid 50's. I realize this is a pretty niche issue, but is there a possibility that the casting for these levers changed just enough that they're no longer compatible in that time period? I just don't see any other possible issues at this point and I don't have access to another set of levers to try. I really appreciate any input or ideas that anyone has. Thanks.

 

[texasgeartrain]

If you disengage the tumblers, does the rest of the gears spin ok ?

And if you bring the tumblers up so that the gears engage, but pins not locked in, does it spin ok ?

I would start at tumbler gears, and begin to engage while wiggling the gears back and forth to feel the gear back lash. Most likely those, but you can check every mating gear this way to see what has no backlash.

Keep in mind, that while they probably had a jig set up for the bores and such, these were not cnc'd, to be identical to inside a thou, across every machine made. A lot of parts may be sort of unique to each machine. The tumblers may need "adjustment" to fit, engage, and have nice gear backlash.

Just as an example, maybe the tumblers need to be removed. Remove the gears and short shafts from tumbler arm. Add bushings to the bore in tumber arm, and re-bore at a little off-set. I don't know without seeing it, but you might need some modification for it to work.

 

[10KPete]

If it fell over and bent the levers then one or more of the shafts may be bent. Check those first! Don't make any 'adjustments' until all the parts are correct.

 

[Bklimek]

If you disengage the tumblers, does the rest of the gears spin ok ?

Yes, without the tumblers engaged everything spins fine. The large and small gears as well as the tumbler shaft also turn freely.

And if you bring the tumblers up so that the gears engage, but pins not locked in, does it spin ok ?

Yes. Basically I can creep up on the tumbler pin hole and there will be a point ( maybe 1/2 way over the pin hole) where I'll get good mesh and backlash and everything seems to turn smoothly.

I would start at tumbler gears, and begin to engage while wiggling the gears back and forth to feel the gear back lash. Most likely those, but you can check every mating gear this way to see what has no backlash.

Keep in mind, that while they probably had a jig set up for the bores and such, these were not cnc'd, to be identical to inside a thou, across every machine made. A lot of parts may be sort of unique to each machine. The tumblers may need "adjustment" to fit, engage, and have nice gear backlash.

I don't really know much about how parts like this would have been made at that time, but I kinda wondered if it could be something like that. Small changes in the jig/alignment and drilling process over a couple of decades resulting in parts that are kinda a custom fit.

Just as an example, maybe the tumblers need to be removed. Remove the gears and short shafts from tumbler arm. Add bushings to the bore in tumbler arm, and re-bore at a little off-set. I don't know without seeing it, but you might need some modification for it to work.

That makes sense and based on what I'm seeing this is likely what I'll have to try and figure out how to do to make this work.

Thanks very much for the help, I just didn't have enough experience to even know if I was on the right track.
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[Bklimek]

If it fell over and bent the levers then one or more of the shafts may be bent. Check those first! Don't make any 'adjustments' until all the parts are correct.

That's totally valid. There were other parts damaged in the fall, but they've either been repaired or replaced at this point. As far as I can tell, with the exception of the tumbler handles the rest of the QCGB is okay. None of the gears have visible damage and the shafts are running true.