Bushings instead of bearings for diff pinions

[fyrstormer]

After a year of unkind treatment, the diff pinion bearings in my Wraith were pretty much shot. So I replaced the outer bearings with new bearings, and the inner bearings with bushings. First I tried LockedUpRC's Black Ice bushings, and then Traxxas oilite bushings, but in both cases I saw a significant amount of slop develop in a short amount of time. I've shimmed the diff pinion propshafts so they can't slide in and out of the diff case, so the pinion is held flat against the face of the bushing as tightly as possible without binding, so I'm not sure what else I might be doing wrong. Suggestions?

Is the concept of using bushings, because they can resist the diff-pinion trying to push out the back of the diff case, fundamentally flawed? I've seen some people using thrust-bearings in the inner bearing slot, but they aren't any better at supporting sideways loads than a worn-out bushing is, and anyway most of the wear I see is wear in the thru-hole, not wear on the face of the bushing. So is there really any solution other than buying an aftermarket axle that holds larger bearings? That's an expense I'd rather not incur right now.

[binaryterror]

It's simple, the Bushings were supposed to wear and prevent the ball bearings breaking and spilling the small ball bearings into the gear area and taking out the gears, yes even HD ones. They are a wear item and you will replace them. Band-aid fix.

For the AR60/Wraith housing there are 2 valid solutions. Dlux housings with the bigger bearing inside, or the thrust bearing inside. Of course recently SSD and VP released bigger bearing housings as well.

Dlux modded hougins works on the fact that technically the stock bearings are too small to handle power. Using a bigger bearing means bigger ball bearings inside and more able to take forces without breaking.

The Thrust bearing method works on using the outer stock size to handle the rotational loads, but the inner thrust bearing handles the outward load the pinion is having. Remember the ring gear is trying to push the pinion gear out, that's its goal.

Also switching to the 43/13 gears has made the mesh better and seems to help both options even more.

[Highmark]

Originally Posted by binaryterror

It's simple, the Bushings were supposed to wear and prevent the ball bearings breaking and spilling the small ball bearings into the gear area and taking out the gears, yes even HD ones. They are a wear item and you will replace them. Band-aid fix.

For the AR60/Wraith housing there are 2 valid solutions. Dlux housings with the bigger bearing inside, or the thrust bearing inside. Of course recently SSD and VP released bigger bearing housings as well.

Dlux modded hougins works on the fact that technically the stock bearings are too small to handle power. Using a bigger bearing means bigger ball bearings inside and more able to take forces without breaking.

The Thrust bearing method works on using the outer stock size to handle the rotational loads, but the inner thrust bearing handles the outward load the pinion is having. Remember the ring gear is trying to push the pinion gear out, that's its goal.

Also switching to the 43/13 gears has made the mesh better and seems to help both options even more.

Well said.

IMO the bushings were a neat idea but now there are better options.

[altd896]

Binaryterror summed it up right there.

The bushing has to wear, if it doesn't your chewing out the pinion shaft. The bushing will be a consumable & regular replacement item.
What they won't do is fail without warning like the stock sized bearings seem prone to & taking out a gear set in the process.

A Dlux modded housing is brand new & less $ than a replacement gear set, that's a bargain in my mind, I just wish I'd had the brains to order 2 when I ordered trusses & stuff via UCFab for my 2.2 U4RC rig. (wheres the face slap smilie)

[fyrstormer]

I didn't realize there were stock axles modded to hold larger bearings. Yeah, that seems like a better solution, though it still doesn't address the fact that radial bearings aren't designed to support thrust loads, such as those generated by sudden shock to a right-angle gearset.

I guess I must've gotten lucky. After a year of running through water and "flying dismounts" off rocks that had no good path to drive down properly, all I noticed was the diff pinion bearings were loose and wobbly. I didn't realize spontaneous disintegration was even an issue people were having.

[fyrstormer]

Anyway, I was talking to LockedUpRC a while back, and they seemed inclined to try making a run of stainless-steel bushings. Stainless steel self-polishes and is softer than the hardened steel used for the diff pinions, but it's much harder than Oilite, so if LockedUpRC actually makes them, they should last a lot longer *and* support thrust loading that the inner diff pinion bearing has to deal with.

[binaryterror]

Originally Posted by fyrstormer

Anyway, I was talking to LockedUpRC a while back, and they seemed inclined to try making a run of stainless-steel bushings. Stainless steel self-polishes and is softer than the hardened steel used for the diff pinions, but it's much harder than Oilite, so if LockedUpRC actually makes them, they should last a lot longer

And still be a wear point and offer no better wear since Oilite, while softer has an oily compound that prevents friction and galling as best it can for being a bushing. Friction and galling (or resistance to it) is the cause of the bushing wearing, keep in mind harder materials can still gall easily. Steel and Stainless rubbing in the same way will generate far more heat. And once you research the cost of a viable Stainless, which no one uses it for - so good luck finding an Stainless alloy rated for the bushing needs, you'll realize the Dlux or thrust bearing options are cheaper.

*and* support thrust loading that the inner diff pinion bearing has to deal with.

But will not support thrust loads like a thrust bearing at all. This will causing wear on the inside surface which will cause your gear mesh to be off.

$20 for a Dlux housing (with large bearing) and $35 for the Axial HD 43/13 gears and you never have to worry again. My Yeti has tons of time on this set up, no failures on 3S and the RTR motor which is quite fast on 3S.

Or the $3 Thrust bearing and $35 for the HD 43/13...

Neither option is going to break the bank if you are looking for cheap. Of course if you want even better the SSD axle and NEW VP housing, but those will be a few pennies more.

I explained working answers, if you choose to waste time with a bushing material that isn't used as a bushing material in the metal world go ahead, but you are just wasting time and money.

[P.A.Myers]

What about a torrington?

[fyrstormer]

Originally Posted by binaryterror

And still be a wear point and offer no better wear since Oilite, while softer has an oily compound that prevents friction and galling as best it can for being a bushing. Friction and galling (or resistance to it) is the cause of the bushing wearing, keep in mind harder materials can still gall easily. Steel and Stainless rubbing in the same way will generate far more heat. And once you research the cost of a viable Stainless, which no one uses it for - so good luck finding an Stainless alloy rated for the bushing needs, you'll realize the Dlux or thrust bearing options are cheaper.

Oilite is sintered with (relatively) large gaps between the metal fragments, so it doesn't just wear-down, it also crushes under load. Anyway, a little thick oil on a stainless bushing should work fine for minimizing wear.

Originally Posted by binaryterror

But will not support thrust loads like a thrust bearing at all. This will causing wear on the inside surface which will cause your gear mesh to be off.

While this is true, a thrust bearing can't support radial loads, and a radial bearing can't support thrust loads, so a sufficiently hard bushing may still be the best compromise. The inner bearing *must* be able to support radial loads, because that's most of the loading it will be burdened with. (I realize the modified axles that use larger radial bearings can withstand the thrust-loading without failure for longer, but radial bearings *still* aren't supposed to support thrust-loading.)

Originally Posted by binaryterror

$20 for a Dlux housing (with large bearing) and $35 for the Axial HD 43/13 gears and you never have to worry again. My Yeti has tons of time on this set up, no failures on 3S and the RTR motor which is quite fast on 3S.

Don't worry, I *am* considering it. But I'm still intrigued by the possibility of using bushings because they can support loads on more than one axis at a time.

Originally Posted by binaryterror

I explained working answers, if you choose to waste time with a bushing material that isn't used as a bushing material in the metal world go ahead, but you are just wasting time and money.

Stainless steel is definitely used as a bushing material. I discovered this by searching for "stainless steel bushings" and got lots of results. They just don't make any in a convenient 5x11x4 size.

[binaryterror]

Originally Posted by fyrstormer

While this is true, a thrust bearing can't support radial loads, and a radial bearing can't support thrust loads, so a sufficiently hard bushing may still be the best compromise. The inner bearing *must* be able to support radial loads, because that's most of the loading it will be burdened with.

If you seek radial and axial loads, the combination of Thrust and Roller ball would be both wouldn't it?

And actually the inner bearing is getting Thrust loads, from the pinion trying to be pushed away from the ring gear, into the bearing itself. The radial bearing is the outside one, and handles the radial action of the pinion as it spins.

Stainless steel is definitely used as a bushing material. I discovered this by searching for "stainless steel bushings" and got lots of results. They just don't make any in a convenient 5x11x4 size.

Show me one link, where it is used as a bushing in radial and axial loads with a rotating shaft. Most SS bushings are to change size, another term used as bushing. SS is a very easy to gall material, galling is bad when it comes to being a bushing material for the bushings we need.

[fyrstormer]

Yes, I understand that the outer bearing supports radial loads. But the inner bearing needs to be able to support radial *and* thrust loads. The only ball-bearing that could do that is a ball-bearing with 45° races, and I have no idea where to find something like that in a 5x11 or 5x14 size. Hence my interest in bushings in the first place.

I have never seen stainless steel gall when lubricated.

[Ditchrat]

Originally Posted by fyrstormer

Anyway, I was talking to LockedUpRC a while back, and they seemed inclined to try making a run of stainless-steel bushings. Stainless steel self-polishes and is softer than the hardened steel used for the diff pinions, but it's much harder than Oilite, so if LockedUpRC actually makes them, they should last a lot longer *and* support thrust loading that the inner diff pinion bearing has to deal with.

Bearings and bushings are designed to be sacrificial, as pointed out earlier. In a different life I was a commercial washer and dryer mechanic and had to replace several hardened steel rollers because cotton belts literally cut them in half.

Bushing material is simple a choice between replacement frequencies. Softer require more frequent replacement of the bushing and less frequent replacement of the shaft. As the bushing material gets harder the frequency inverts.

Bearings are the same except it is the balls and the race getting the wear.

With bearings the fit on the shaft and the housing are important. Once you get wear at either of those locations you will wipe out the bearings faster. Bearing should be press fit optimally or locked in place with adhesive to stop lateral torsion, which eats bearings.

You might try Bocas bearings, they have almost every bearing known to man. They as have lots of information to learn about different types of bearings.

Either way, bushings or bearing, proper lubrication is important to keep heat down. Almost all materials get softer and wear faster as they increase in temperatures.

An after thought is bushings should not ride directly on a shaft. Ideally they should ride on a micro film of lubricant.

[JesterSpec]

I've been running a ceramic hybrid in my yeti for a few months with great results after blowing out 1 stock and 1 fast eddy pinion bearing.

5x11x4,SMR115C-2YS NB2,Metric, Radial Bearings

[fyrstormer]

I always upgrade to Boca's ceramic bearings when the stock bearings fail, or after a year of use. My Wraith is actually overdue for a complete bearing replacement, but I keep spending money on other stuff. Good to know the Boca bearings are serving you well in the AR60 axles, that makes me feel a little better about going with that option.

I see the Dlux-modded AR60s have the inner bearings pre-installed. Does anyone know if they are Boca ceramic bearings, or just some generic bearings that happen to have yellow seals?

[JesterSpec]

Boca has a line that is not a hybrid that still uses the yellow seals. Probably that one, I can't see him putting $20+ in bearings into the housing.

[fyrstormer]

Bah. Oh well, it's not like upgrading to ceramic bearings is going to be significantly cheaper just by not having to buy two more bearings.

I just replaced the axle housings on my Wraith, too. I really wish I'd known there were modded stock axles available, and the reason why they existed, back when I went through the trouble to do that.

[binaryterror]

Ceramic bearings are horrible in thrust situations. They should never be used in areas of any thrust load if you want longevity.

Also, Avid's from my years of racing have outlasted anything Boca makes. Also way cheaper.

[JesterSpec]

Originally Posted by binaryterror

Ceramic bearings are horrible in thrust situations. They should never be used in areas of any thrust load if you want longevity.

Also, Avid's from my years of racing have outlasted anything Boca makes. Also way cheaper.

I have to say that you are way off base on most of your statements, and I have listened to it for as long as I can.

Being in the aerospace bearing R/D and design I'm pretty sure I know my stuff.

Thrust bearings in this application are only partially correct, you really need an angular contact bearing, and they don't make them that small.

The only way a thrust bearing will hold up is if you preload it heavy enough to withstand the radial load being placed on it. You are correct in saying there is a thrust load in that location, but there is also a radial load, and thrust bearings WILL NOT HOLD a radial load.

I have analyzed the bearings I have destroyed from the rear diff, and found that it is actually ball failure that is the primary culprit. The dynamic load of the tiny bearings is just too much. Your not seeing that failure with the larger bearing due to the dynamic load capacity of those being greater due to the ball size. The only way to keep the OEM size bearing from killing its self is to insert ceramic balls. Ceramic balls are basically indestructible, and are great in dirty conditions.

I respect your opinion on most things, but this misinformation must stop. A thrust bearing in this application is 100% incorrect, you'll find your housing will get worn down from the race pushing against it when a radial load is added.

The only time a ceramic hybrid is a bad idea is when there is a very heavy static load on the parts, this will cause false brinelling on the bearing races, and self destruct the races, the balls will remain intact.


Take a ceramic ball, place it on a piece of steel, and beat it with a hammer, you'll either dent the steel plate, or dent the hammer, but you woln't break the ball.



BTW Avid and Boca both buy from the same manufacturer.

[binaryterror]

Originally Posted by JesterSpec

Thrust bearings in this application are only partially correct, you really need an angular contact bearing, and they don't make them that small.

The only way a thrust bearing will hold up is if you preload it heavy enough to withstand the radial load being placed on it. You are correct in saying there is a thrust load in that location, but there is also a radial load, and thrust bearings WILL NOT HOLD a radial load.

I never said to replace both bearings with thrust...nor should that be done for the reasons you have posted. I'm recommending both bearing types to be used in combination to handle both of the the forces present.

I have run this and never had any issue in a AR60 VP housing. This same housing used to blow out the inner including a ceramic bearing when they were both typical roller bearings. I, like many others on here have posted, found positive proof this combination method works in greatly extending the life and protecting the gears from failure.

Also the Thrust is .5mm thicker, to add the preload needed to keep it running, and help properly shim the gear mesh.

The only way to keep the OEM size bearing from killing its self is to insert ceramic balls. Ceramic balls are basically indestructible, and are great in dirty conditions.

I did change to Avid Ceramic bearings, before going to the combination with a thrust because in theory it shouldn't work as well as Ceramic. They might have lasted slightly longer than their steel counterpart as I didn't really stop watch each, but not nearly as long as the Thrust/Roller ball combination has lasted and continues to last.

VP housings (Class 3 Wraith):
Steel failures: 3
Ceramic Failure: 1
Thrust/Steel failure: 0 (this one has more time on it than all 3 of the above combined)

Plastic DLUX Big Bearing modded Housing (Yeti):
Steel Failures: 0

Take a ceramic ball, place it on a piece of steel, and beat it with a hammer, you'll either dent the steel plate, or dent the hammer, but you woln't break the ball.

I don't disagree with the actual hardness of the ball itself. I do disagree that this helps, the harder Ceramic ball inside the same metal or usually plastic cage race has an even easier chance of breaking because the harder balls are stronger than the cage and race is. Once the race lets go, the shields eventually fail spilling now even harder balls into the gears causing even more damage. From my experience, catastrophic gear loss.

BTW Avid and Boca both buy from the same manufacturer.

Interesting people still overpay for the Boca options then.

I'm glad you know more due to your background, but I know enough engineers to know sometimes theory doesn't pan out perfectly in the real life applications. I have time on each method and solutions, that's all the proof I need and it's cost me a lot replacing gears. Books and theories on how things work do not over ride physical proof I have received.

And I don't disagree with you on Angular contact bearing being the answer, just not being an option.