I'm in the process of changing out the swing bearing due to excessive wear on my Bobcat 328d. I'm concerned about the wear of the swing gear that engages the slew ring. Will the worn gear damage the new ring? Replacement of the slew ring is quite a process in itself (parts cost and labor) but changing out that gear looks to be a hell of a job as well. I don't have a press that the job may require. Here are a few pictures. Any advice would bewelcome and much appreciated. Also, the old slew ring has very even wear except for one area where the gear teeth are worn excessively. What would cause uneven wear on just a few teeth? About 3 or 4 of the 96 teeth are worn more than the rest.
With that much wear I would replace it
Good day Swing ring bearing wear are known to make excessive loads on the transmission final drive, having invested in a replacement ring we would recommend you rebuild the transmission take a careful look at the support bearings while you have it split down. Kind regards Uffex
Yes, yes, & yes. I cannot imagine why, after investing so much time & effort to split the machine to replace the ring gear & bearing, to do "half a job" and not replace the swing pinion. I endorse what Uffex said above, while you're in the swing transmission changing the pinion rebuild it also with new bearings, seals, etc, as required. The fact that only a few of the teeth are more heavily worn that the rest suggests that something could be out of whack in the swing transmission. A bent pinion shaft maybe..? Only disassembly will tell.
With the amount of labour already invested I'd replace the swing pinion. Especially with that kind of wear.
I figured as much... The slew ring is around $1900.00 for an aftermarket part. The shaft, bearings and seals are around $1000.00 from Bobcat with the shaft itself around $700. Would a shaft like this be available aftermarket? I'm not to sure where to look. Thanks for everyone's opinion.
May be worth a call https://www.texasfinaldrive.com
Can you figure out the position of the house when the pinion is engaged in those worn-out teeth? I might venture a guess if the machine was trailered a lot, and loaded the same direction every time that could explain the wear? Also, I could imagine quite few probable operations where you would be working straight in line, and not swinging, just tracking ahead or back.
Shimmy, that might explain how it got damaged in the first place but consider this ........ Call me anal (because I counted them) but it appears to me as though the ring gear has about 86 teeth give or take, the pionion appears to have 12. So if those numbers are correct the pinion rotates 7.17 times or thereabout for every complete rotation of the house. So if the house were to rotate more than 360 degrees at one time which it will at various points in the life of the machine the same tooth on the pinion would not be engaging on the same tooth on the ring gear the 2nd and subsequent times around. It would be off by a couple of teeth. I would expect that there ought to be ring gear tooth wear in more than one spot.
^What everyone else said.
Looks like it did not have a lot of grease packed in the turn table
You enjoyed typing this post, didn't you? No worries, I had a thought and didn't think it through. However, after I have, I'm going to have to disagree with you (I WISH there was still a :stirpot emoji). While every complete rotation of the house puts a different tooth on the pinion on a different tooth on the slewing gear, the slewing gear is fastened directly to the undercarriage. If you're always digging over the idlers, then won't the pinion always be engaged with the same few teeth on the slewing gear??
Under those circumstances, I agree 100%. But if the house rotates 360 degrees it will be a different tooth on the pinion engaging with that same tooth on the ring gear, and yes I agree with you that particular location on the ring gear should show greater signs of wear than the rest of the teeth. But it still doesn't explain to me though why there is unequal wear on the pinion teeth..? The only thing I can think of right off the top of my head is a bent pinion shaft.
What I see are soft gears. How many hours are on the machine? Why is the slewing bearing being changed? I've changed out a few ring and pinion gears on excavators and never seen the gears worn like that. Maybe seen it on a couple of old line cranes with tens of thousands of hours and those used hook rollers instead of a swing bearing. That machine probably doesn't weigh more than 7,000 in total so I have to wonder about the quality of the parts from the manufacturer. I would have to say depending on the hours on the machine that yes that is excessive wear.
The pinion teeth seem to be worn evenly, it's uneven wear on the slew ring gear(and only in one spot). There are 13 pinion gear teeth and 96 ring gear teeth.
That being said, the position of the machine while the gears were wearing against each other would have been "digging over the idlers" and the machine, when trailered, would have been with the digging arm over the final drives. The bobcat service manual says there is a "soft zone" on the inner race. I guess the soft area on the race would also mean a soft zone on the toothed inner gear as well. The machine has 3,600 hours on it and was previously owned by the public works department in Kingsland, Georgia. It's a 2003 model year.
That amount of wear for those indicated hours is totally excessive and doesn't bode well for that line of machines.
i misunderstood the OP. I thought that he was complaining of unequal wear on the ring gear AND the pinion. My bad. In that case could the fact that you’re replacing the swing bearing “due to wear” indicate, like Dave Neubert mentions above, a lack of grease..? If failure to lubricate frequently was the reason the swing bearing wore out then what’s the chances nobody ever repacked the ring gear cavity with grease..? To the OP. Had you done any cleaning of accumulated grease on the ring gear & pinion before you took those photos..?
Is there any grit in the grease? Maybe from being buried up to its eyeballs in mud at some point? I think I would have taken the hydraulic swivel out as a unit instead of splitting it. I would think it will need a reseal now, if it didn’t before.
^^^^^^ Wot he said ......... a combination of swimming the machine + lack of grease will easily take a swing bearing out, and the resulting grinding compound will take teeth off the pinion & ring gear.
I know I have never put the thing in mud or water more than a couple of inches deep. There was no indication that it had been before either(not a lot of crud or dirt buildup in the belly pan or otherwise) but of course I don't know how it was treated before me. The swivel joint seal was leaking from the main seal in the top and the wiper seal was trashed as well. That's actually what started me down the long road of repair. I just brought it home from a job where it was used for about 8 months and while I had some downtime between jobs and the holidays I figured I would eliminate the hydualic oil drip from the underbelly. A leads to B leads to C... I knew the swing gear was sloppy so since it was in my shop and the swivel was already out I thought why not. The swivel and slew ring are bad enough for me cost wise... But the extra $1000.00 for the pinion shaft rebuild stings even worse. Oh well, I've made it this far and getting it split apart and cleaned up was the hard part (hopefully) The gears was cleaned before I photographed it. The grease coming off of it didn't seem odd. Just like regular old brown gease. No metallic particles and the seal on the ring seemed in good shape. Overall the machine seems excessively rusty which makes me wonder what the public works guys were doing with it in the years before I owned it.
Also, I don't think there is a way to pack the ring gear cavity on this machine. It seems sealed up from above and below. There is a grease line that goes to where the pinion gear would be running by but the grease line doesn't put grease directly on the pinion. All that said, I wonder what the appropriate was to grease the pinion would be? Pump grease into the fitting while spinning the machine or just pump a gob in @90 degree increments. How often would greasing be needed? Once a day?
If the grease was brown that sounds "old" to me, although without seeing the actual condition it's difficult to really tell just by a description of the colour. From your photo there is only one grease point (LH) for the swing pinion and one (Center) for the swing bearing. Larger machines tend to have a cover that can be opened to give access to the pinion/ring gear cavity. The grease lines from those two fittings in your photo - IMO one should should go to a point where it literally "squirts" grease into the contact area between the swing pinion and the teeth of the ring gear - that's why it's important when greasing to swing the machine the correct way (clock or anti-clock) after applying grease so that the grease is squashed into the ring gear teeth and not flung off the pinion. The other grease line should go into the swing bearing itself. Greasing frequency and quantity of grease to apply would be determined pretty much by what the machine operation/maintenance manual recommends. Personally I would say that it would be difficult to over-grease the swing pinion/ring gear because any excess would simply work its way inwards eventually fall down the hole in the centre of the machine. Over-greasing the slewing bearing would be a definite possibility. Unless you removed it I don't see any type of "tray" to hold the grease into the ring gear cavity. The Cat equivalent of your Bobcat 328D would I guess be a 302.5, which co-incidentally also has two grease points marked just like your Bobcat. Here's what the Cat manual says for the 302.5 swing pinion & swing bearing lubrication......... Frequency - Every 50 service hours or 1 week. Apply grease to the fitting for the swing gear pinion and to the fitting for the swing bearing. Rotate the upper structure 90° in a clockwise direction. (your Bobcat may be different rotation depending where the end of the grease line comes out) Repeat Steps 1 and 2 until the upper structure has rotated 360°.
Where you have the rags sitting in the photo of the ring gear is called the tub. The should be filled with grease to cover the about the bottom 30% or the pinion gear. As the gear turns and the house rotates grease is pushed up into the mating ring and pinion gears. One of the things that happens over time is that the grease turns hard and forms a channel and doesn't flow into the mating gears any longer and you get vibration when the house turns. I've been on many machines that had dry ring and pinions. Your machine should have a plate on the base plate of the house than when removed gives access to the grease in the tub. I haven't done an inspection on a Bobcat in awhile so can't tell you the specifics of where the plate is exactly but on most excavators it is under the boom foot. The small Cat excavators don't all have the pinion tub so they have to be greased on a continuing time frame. On those machines with a tub it's generally a long time frame, six month to a year. All the ring and pinion gears for slewing bearings and swing reductions that I have seen have been case and flame hardened. The damage seen in your photos is consistent with what you would see on a road grader ring gear and pinion. Grader ring and pinions are not hardened. I've changed many swing bearings and rebuild nearly as many swing gear boxes and not seen that type of wear. The normal failure mode in swing bearings is in the bearing and not the gears. When a bearing fails it moves up and down. My opinion in your case is that the ring and pinion gears were not hardened from the factory. Whether that is a concous design to lessen the expense of the machine or it was a failure on the part of the supplier, it is still a failure on the part of the manufacturer. As far as the swivel goes, I would remove both halves from the machine and repack it, then reinstall it when the house is reinstalled on the carbody.
The help given here is appreciated very highly by myself. The knowledge base here is so helpful when mechanic-ing is not your every day job. Again I appreciate it.
What John refers to as the "tub" is item #3 on the illustration below, taken from a Cat 302.5. I referred to it as a "tray". Either way it's designed to contained the grease around the ring gear/pinion and I am somewhat surprised that your machine does not appear to have one, unless you removed it while doing the cleanup.
Mine does have the tray. It has 4 holes in the bottom of it that are about 3/4" (to drain water maybe?) Should the tray be packed full of grease upon reassembly? The only access to it when the machine is all put together is reaching up from the bottom of the undercarriage
As John said, the tub normally needs to be filled grease with grease to about 30% of the height of the pinion. It would be better to do this using a suitable shovel & a bucket before assembling the upper frame onto the undercarriage frame. It will certainly be a sight quicker than trying to pump it in a tube at a time through that single fitting.........!!