Swing Gear Wear Excessive?

PRDiesel · Dec 12, 2018

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.

Dave Neubert · Dec 12, 2018

With that much wear I would replace it

uffex · Dec 12, 2018

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

Nige · Dec 12, 2018

PRDiesel said:
I'm concerned about the wear of the swing gear that engages the slew ring. Will the worn gear damage the new ring?

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.

92U 3406 · Dec 12, 2018

With the amount of labour already invested I'd replace the swing pinion. Especially with that kind of wear.

PRDiesel · Dec 12, 2018

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.

uffex · Dec 12, 2018

May be worth a call

https://www.texasfinaldrive.com

Shimmy1 · Dec 12, 2018

PRDiesel said:
View attachment 189270

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.

Nige · Dec 13, 2018

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.

Vetech63 · Dec 13, 2018

^What everyone else said.

Dave Neubert · Dec 13, 2018

Looks like it did not have a lot of grease packed in the turn table

Shimmy1 · Dec 13, 2018

Nige said:
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.

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??

Nige · Dec 13, 2018

Shimmy1 said:
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.

John C. · Dec 13, 2018

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.

PRDiesel · Dec 13, 2018

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.

PRDiesel · Dec 13, 2018

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.

John C. · Dec 13, 2018

That amount of wear for those indicated hours is totally excessive and doesn't bode well for that line of machines.

Nige · Dec 14, 2018

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..?

brianbulldozer · Dec 14, 2018

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.

Nige · Dec 14, 2018

^^^^^^ 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.

Swing Gear Wear Excessive?

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