Gearbox rebuild

kanuckle · May 9, 2015

Hello,

The gearbox on my New Holland 914a mower was leaking oil so I decided to take it apart and rebuild it. It looked pretty straightforward in the owners manual! Once opened up, I found one of the bearings had completely disintegrated.

I've found the replacement bearings, but can't get the pulley of the end of the shaft to replace them. The manual calls the plate holding it on a "collet hub" but I haven't found very much information on how they work. In the pictures here, I've removed two small screws I thought were holding it on, but it still wouldn't budge. There are two smaller threaded holes in the plate, so I drove in two bolts hoping to push it off. It didn't seem to move and I broke off one of the bolts which you can see in the picture.

Any suggestions on how this collet hub works and how to get it off the shaft? Also, any suggestions on the best tool to remove the bearings? I don't have a press which I think would probably work. Any other options?

Thanks in advance

Dan

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Fawken · May 9, 2015

Heat up the pulley with a yellow torch. If you don't have a press you'll need a very strong vise to hold the pulley and then tap the shaft with a hammer. This works most of the time. I have bought brand new transmissions for mowers and post-hole diggers for $125-$150 from an outfit called Surplus Center.

kanuckle · May 9, 2015

Thanks for the reply Fawken. Trying again to get these images to work. . .

crazyal · May 9, 2015

Usually the way a collet hub works is there's a tapered sleeve that slides onto the shaft with a small split in it. The pulley hub is also tapered so as it's tightened onto the sleeve it compresses the sleeve so it will grip the shaft. It's not unusual for them to get a little rust and stick together. Looking at your pictures I would say that the pulley hub needs to be tapped towards the bearings to release it. In your second picture I think what you are seeing is the flange and the split in the sleeve.

This picture doesn't show the taper well and the bolts go through the pulley and thread into the flange. Your second picture would be from the other side.

To remove the bearing a bearing separator (also called a bearing splitter) would be what you want. They aren't too expensive from a place like Harbor freight or you might be able to rent one from a place like autozone. They work well with pullers so you don't need to use a hammer and damage the shaft.

banjodunn · May 10, 2015

G'day screw a bolt in opposite your broken one tight then with a good solid punch give it a good crack on the pulley hub on the side of the broken bolt it should pop off make sure yoou hit on the pulley hub not where the belts run.

Jon

kanuckle · May 12, 2015

Thanks for the suggestions guys.

I soaked it in diesel for a couple of days, then penetrating oil with no luck. I've tried whacking the pulley both toward the bearings and away. It just doesn't seem to move. I've screwed down a bolt into the one remaining threaded hole but again no movement.

The mower manual states "Loosen and remove the collet hub and pulley from the output shaft on the gearbox." This is before even opening the gearbox, so the only access you would have is what you see in pic #2 above.

Maybe I should get that broken screw out and try again with 2 bolts. I don't have an impact wrench so I'm just turning them down with a ratchet. Maybe the impact tool would break it free before the bolt snaps? Argggg. . .

kanuckle · May 12, 2015

Double post. . .

Oldtink · May 12, 2015

You need to get the broken stud out first. Otherwise you'll pushing the tapered bushing crooked and you'll have two broken studs to remove.
After you remove the broken stud (left hand drill bits are a blessing) Screw the two studs down evenly with just the slightest amount of pressure on each one. Like only an 1/8 of a turn each once they bottom out and just keep alternating back and forth. Same procedure when you put it back together. Certainly don't want or need an impact in either case.

flyerdan · May 12, 2015

If it's really stuck on there, as advised above remove the broken stud and put good bolts in each removal hole, snug it down and hit the center hub with a couple blasts of an air hammer with the dullest chisel (grind one flat if needed). I've found that will often break the rust bond when just applying puller force will tear things up or strip threads before the rust gives up. HF has air hammers all the time for around $8, worthwhile investment.

kanuckle · May 14, 2015

Thanks for the help guys!

I picked up some left hand drill bits and managed to get the broken stud out. I gave the centre hub a few sharp cracks with a hammer (don't have an air hammer) then drove in new bolts alternating slowly as suggested. After a few turns, something gave out and the pulley came loose.

Then after lots more penetrating oil spray, I hammered the pulley away from the bearings and the "collet hub" came off the shaft. Interesting there is a small steel "key" that locks the hub in place. I took a few pictures of the pieces so someone else may see how these things and come off. Hopefully I can get it back together.

Thanks again for the help!

Dan