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Gordan

Is there "acceptable side play" on BGB shafts?

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Gordan

Looking at a tractor that has a BGB with no gear lash, no end play on either shaft, and no side play on the output shaft, but a small, barely perceptible amount of side play on the input shaft. And I do mean barely perceptible; certainly nothing one can see. I've never actually felt what a new BGB feels like, only what a worse one is like, so I'm not sure whether this is to be expected even from a good BGB or is a sign of a needle bearing going bad?

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RayS

Side play on the input shaft is more than likely just the play between the bearings and the race of the needle bearing.

I have rebuild a bunch of these and that is good. I have rebuilt with all new bearings and shafts and backlash on the gears is 1/16" to 3/32" with all new parts.

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Gordan

Thanks, Ray, that's reassuring!

How is the input shaft held in place, anyway? I have stared at the parts diagram until crosseyed and I still can't figure out what would hold it (and the bearings) fixed in the housing.

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Gordan

Would that be parts W-V-U on the diagram? So... both bearings go on the shaft and the shaft gets inserted into the housing from inside, and then that little square holds the whole thing tight to the housing by pushing on the ball bearing T? It still doesn't seem like this offers much strength in the axial direction of the shaft but maybe the driving gear provides that against the driven gear?

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humphrey

Part c is what actual keeps the input shaft from backing out. It phisically occupies the escape route of the shaft from the backside, while the bolt and washer hold the bevel gear to the input shaft which keeps it from creeping forward.

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RayS

Part U holds the input shaft and bearing in place. It also keeps it from hitting part C. The driven shaft. You can remove the driven shaft and if you do not remove part U, the input shaft is not going any where.

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PhanDad

I'll add my 2 cents. It's been a while since I've been inside a BGB and I hope I remember correctly.

First, Ray is correct, if you don't take part U off, the shaft doesn't move. The "key" is the retaining ring that no one has mentioned.

How it works:

The retaining ring, part S, snaps into a groove on the input shaft. The shaft is inserted into the ball bearing; the key is placed into the shaft and the driver bevel gear is then bolted to the shaft with parts AA and Z. The distance from the retaining ring groove to the end of the shaft is less than the depth of the gear; so at this point the inner race of the bearing is sandwiched in compression between the retaining ring and bevel gear.

Now the shaft/gear assembly is inserted (from the inside) into the outside needle bearing which is held in place by an interference fit between the outside side of the needle bearing the the BGB case. Parts U, V, and W are then installed which holds the outer race of the ball bearing against the case and therefore the shaft/gear in axial alignment.

The above parts schematic is an older BGB; the newer ones have some additional washers but the principle is the same.

Hopefully what I wrote makes sense. In a post several years ago I explained how the cross shaft is held in place. If any one's interested, a search may find it.

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Gordan

Thanks, all! Yes, I think I'm getting it finally. It just doesn't seem to be designed to endure much axial force due to driveshaft vibration. But they seem to last unless abused, so...

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1meanZ
quote:Originally posted by RayS

Side play on the input shaft is more than likely just the play between the bearings and the race of the needle bearing. I have rebuild a bunch of these and that is good. I have rebuilt with all new bearings and shafts and backlash on the gears is 1/16" to 3/32" with all new parts.


id="quote">
id="quote">I know I'm digging up an old thread here but Ray, can you tell me how and where that dimension you listed is measured? My BGB had some backlash, but not much more than a click when I built it. The way I'm used to measuring backlash is with a dial indicator on a gear tooth. I didnt use a dial indicator when I built my box, but I'd guess it had about .010" of backlash or so. Now that the tractor is assembled and working, I noticed today that I've got what seems like a lot of backlash. The box is not noisy, and I changed the fluid and ran a magnet through it and didn't get ANY metal out of it so I'm assuming the 'box is healthy, I'm just wondering if I didnt put enough shim in it and now that things have settled in I've got more backlash than I had originally. I also understand that 3/32 of rotation of the driven shaft doesnt look like much on the shaft surface, but trig that out over the OD of the cone clutch and it seems like a ton. So thats a long winded way to ask my original question, but I just need to know where you're measuring. If I need to pull my machine back down and add some shim to tighten things up, now is the time before I start running a tiller etc. this spring...

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RayS

The shims control side to side movement on the cross shaft. The shims go between the seal and side plate. If not enough shims the bearing will move side to side or lateral causing the whole driven shaft to move side to side.

The 1/16" to 3/32" is rotational at the cone clutch that I am talking about. Shims won`t remove that unless you are shimming the keyway(which I wouldn`t do). Keyway wear in the shaft, gear and just plain wear in the gear teeth cause backlash issues. But now that I think of it you can get some rotation play if they are not meshed properly with the side plate and seal shimmed correctly (worn out of spec. gears). The book says to shim between the side plate and the seal. It also says to shim the seal to it is flush with the side plate. If the gear teeth are worn as well you are not going to shim that out. Some say you can shim between the case and the gear. The book doesn`t mention that. I would assume since it isn`t mention that they would want the gears replaced.

These gear boxes are not as weak as some would say they are. I have had tractors (B10 Allis) which are 40 years old that were pm`ed or maintained as they are suppose to be and were as good as new. One thing they could have done to make these shafts and gears to last longer would have been to use two keyways 180 degrees apart.

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1meanZ

Ray, we're talking about the same thing. I'm talking about rotational movement at the cone clutch while holding the input shaft still. Unless I misunderstood the function of the shims, I thought the purpose of the shims between the seal and side plate was to push the seal/bearing/driven gear over towards the drive gear to reduce backlash. Conversely, if you left all the shims out, the seal/bearing/driven gear would move away from the drive gear allowing more backlash. When I built the BGB I tapped the bearing in and out to adjust backlash. Once I got backlash where I wanted it, I measured the depth of the seal below the BGB surface and selected a shim thickness based on that measurement to keep the seal in that spot once assembled. Now that the tractor is assembled it seems there is more backlash in the gears than I remember it having when I assembled it. Hence why I asked where you are measuring the 1/16-3/32 from. Are you measuring it from the OD of the cone clutch drum or are you measuring it at the shaft OD on the BGB?

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RayS

At the outer diameter of the cone clutch. Under my profile in cool links is the repair manual for the large frame tractors. The shims have to be flush with the side plate or BGB case. If not the seal, bearing and shaft will move side to side. Yes, that would set back lash. A worn out retainer ring on the shaft will affect back lash.

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1meanZ

Well I measured at the OD of the cone clutch and I'm exactly at 1/8. More than the spec but not sure it's worth splitting the tractor over. What would you do?

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RayS

I wouldn`t mess with it. That is only .032 difference. My numbers were on all brand new parts. Not used parts and there is nothing written in the repair manual on what I came up with. Simply what I have observed in the ones that I have rebuilt with all new parts.

If you had a 1/2". Then there would be an issue somewhere.

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donmoore1904

I'm glad to hear the end result of this conversation - my "spare" BGB off a 3410 had 1/8" at the outer diameter. My tractor was suffering from old age and had about 1/4" - more than I was happy with, and since I was rebuilding the transmission (which had its own slop) I swapped out the key parts of the 3410 BWB. When I was done I was very happy with the result, including the 1/8" at the BGB. After 4-5 years of use with using wheel weights not previously used (I mow on steep slopes + winter plowing), I have play back but not as bad as original. Haven't looked, but my guess is it is the axle. Hoping it isn't the BGB, but the axle/tranny is no picnic either. It is amazing that the BGB is as sturdy as it is - wish the rear axle was as well.

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RayS
quote:Originally posted by donmoore1904

I'm glad to hear the end result of this conversation - my "spare" BGB off a 3410 had 1/8" at the outer diameter. My tractor was suffering from old age and had about 1/4" - more than I was happy with, and since I was rebuilding the transmission (which had its own slop) I swapped out the key parts of the 3410 BWB. When I was done I was very happy with the result, including the 1/8" at the BGB. After 4-5 years of use with using wheel weights not previously used (I mow on steep slopes + winter plowing), I have play back but not as bad as original. Haven't looked, but my guess is it is the axle. Hoping it isn't the BGB, but the axle/tranny is no picnic either. It is amazing that the BGB is as sturdy as it is - wish the rear axle was as well.


id="quote">
id="quote">The axle seem pretty sturdy to me. We are talking about 40 year old tractors. MTD`s are usually melted down into new Toyotas or whatever by then.

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donmoore1904

Ray, I am referring to the outboard keyway failure mode of the axle tube, which appears to be a common failure and weak point. I am little more than a novice - am I wrong?

Both my 7010 and 3410 axles had splits at the keyways, which I believe created a fair amount of "slop" in the drive train. I rebuilt the runner (7010) with a new axle 4-5 years ago, it was tight, and as of a year ago I noticed I am back to about 50% of the original overall play. I haven't hit anything with my plow and I let the clutch out easy - try not to abuse it. I'll admit, I should look more closely to see if it is actually the axle. I am going based on my memory of how thin the tube is and seeing those cracks.

I am not a mech-engr, but to my mind, the axle tube wall could have been made thicker, resulting in greater reliability. I could be way off base with my conjecture, with two failed tubes from a lifetime of use, and wrongly assuming the new one has failed.

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