gearbox question

Is there any reason why I can't use a gearbox from an Atlas into a 1972 Commando other than it wont require the big washer on the top mounting bolt. The box is marked NA something something something. I went through 3 gearboxes..the forth actually retained both bearings. I have 3 cases where the bearings drop out easily at room temp.

You can if you change the mainshaft to the longer Cdo mainshaft.

Slick

OK..it's in.

seattle##gs said:

OK..it's in.

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The whole gearbox?
Or just the main shaft ?

The whole gearbox. A struggle because the top boss is full length and does not require the usual commando washer.

You'll need a Commando outer cover, as the clutch cable entry point is in a different position, but this not much of problem.

already done it.

So I put everything back into the box. With a dial indicator on the felt oil seal area of 4th gear it reads a .004 variation. I can feel the gear dragging as I turn it by hand. About 2/3rd of the circle drags then frees up for the other 1/3rd. Turning the main shaft by hand has a similar result. I paid close attention to keeping everything clean and making sure the bearings went in easily and all the way. Comparing the old high gear bearing to the new one, the old one has more of a radiussed bearing both on the outer race and on the inner race so there might be some sort of conflict with the high gear radius and the bearing radius. I turned the bearing by hand when I installed it but it's possible nothing would show up until the mainshaft is installed. Next move is to remove all the gears and layshaft, reinstall the mainshaft and see if it's still dragging. Then pull out the new bearing and install the old one and see what happens. I'm getting tired of working on this box.

The high gear "felt area" (see above) has an .004 wobble. I swapped it with another high gear, also used, and it has only a .001 wobble. Any ideas? Is it poor manufacturing? This has nothing to do with the bushings inside.

Did you read through the thread I linked in your other thread about this? Do you completely understand where the problem was found? Can I help clarify any of the reasons for orbiting?
Have you inspected for signs of contact on unintended surfaces?

seattle##gs said:

So I put everything back into the box. With a dial indicator on the felt oil seal area of 4th gear it reads a .004 variation. I can feel the gear dragging as I turn it by hand. About 2/3rd of the circle drags then frees up for the other 1/3rd. Turning the main shaft by hand has a similar result. I paid close attention to keeping everything clean and making sure the bearings went in easily and all the way. Comparing the old high gear bearing to the new one, the old one has more of a radiussed bearing both on the outer race and on the inner race so there might be some sort of conflict with the high gear radius and the bearing radius. I turned the bearing by hand when I installed it but it's possible nothing would show up until the mainshaft is installed. Next move is to remove all the gears and layshaft, reinstall the mainshaft and see if it's still dragging. Then pull out the new bearing and install the old one and see what happens. I'm getting tired of working on this box.

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Yes, just the sleeve gear, sprocket and nut, main shaft, inner cover with gasket, bearing and all nuts, and main shaft nut all at least well snugged. If that's all smooth, then check runout (to see if main shaft is bent).

That FOUR GRAND runout of the sleeve gear is your smoking gun.


It has nothing to do with the mainshaft straightness, or lack of thereof.

"Comparing the old high gear bearing to the new one, the old one has more of a radiussed bearing both on the outer race and on the inner race so there might be some sort of conflict with the high gear radius and the bearing radius."

When I returned the bearing to the distributor/retailer with a note saying "not fit for purpose"
they never responded, nor acknowledged, and this because the maker does not understand how this stuff works.

In case it is not abundantly clear by now,


THROW AWAY the bearing, and replace it with one suitable for this application.

I did read your previous thread, otherwise I would never dream this problem existed. So tonight I pull out the bearing, swap it for one with the correct radius and see if my problems go away. Never in 40 some years have I ever run into this.

concours said:

That FOUR GRAND runout of the sleeve gear is your smoking gun.


It has nothing to do with the mainshaft straightness, or lack of thereof.

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Possibly not in this thread - I could be crossing the gearboxes he's fighting since he has been battling bent main shafts, and bearings loose in the housing in various threads and in emails and calls to me...

The test I described is worthwhile and one I do each time I build a gearbox now. I got burned once by a bent main shaft and have found a few more using that so I didn't get burned.

seattle##gs said:

I did read your previous thread, otherwise I would never dream this problem existed. So tonight I pull out the bearing, swap it for one with the correct radius and see if my problems go away. Never in 40 some years have I ever run into this.

Click to expand...

That's because we're old, and we remember when parts were made to do the job.
Measuring tools don't lie.

It's a new age.... parts are now copied, many times poorly, never even once being checked if they actually do what they are meant to.

marshg246 said:

Possibly not in this thread - I could be crossing the gearboxes he's fighting since he has been battling bent main shafts, and bearings loose in the housing in various threads and in emails and calls to me...

The test I described is worthwhile and one I do each time I build a gearbox now. I got burned once by a bent main shaft and have found a few more using that so I didn't get burned.

Click to expand...

Add the sleeve gear runout check too. 30 seconds.

I'll be gone for a week and a half, then back on the project. After that I need to inspect the transmission in the Atlas and find out why the shifting into first gear is slowly getting worse. A good job for December.

UPDATE...I replaced the sleeve gear bearing. The mainshaft now turns easily like it should...no intermittent stiffness. The sprocket also turns freely. This is with the GB emptied out of all gears and shifter forks. Nothing except the sleeve gear and the mainshaft tightened on right side. I then installed the gears etc and things were still running fairly smoothly. A bit more drag because of the gears but nothing to worry about. THEN... I installed the kickstart spring and the sprocket became much stiffer to turn by hand. The mainshaft was still easy to turn and consistent through the full revolution. I pulled off the spring and the sprocket returned to normal. I found I could push the KS shaft by hand and it would cause the GB to drag as felt through the sprocket.. All bearings and bushings have been replaced. The sleeve gear bearing has the correct radius. The GB shifts well by hand. This is a new one to me. I could probably run it like this but something is not right.
I have noticed that, while trying to put on the inner GB cover the shifter shaft was not lining up in the hole. I have rolled the shaft on a sheet of glass and it appears to be straight. Tomorrow I will pull out the shifter forks and shaft and see if installing the KS spring causes a drag. I have examined the forks and there is no noticeable problems.
Changing the sleeve gear bearing did help. The mainshaft turns freely all the time now. Something to watch out for in the future