Broke a Bully 2 outdrive stub on my front axle!

[SkaldidDog]

Here's my trick on screws not backing out.

Always use brand new hardware (the heads will strip eventually using this technique).
Clean new screws thoroughly with motor cleaner spray (put them in a film canister or small bottle with a short blast of spray, shake and blast dry with air hose or dump onto paper towel and air dry).
Apply Blue 246 Loctite to all male and female surfaces and assemble quickly while wet. Dip the hole end of a needle into the loctite and use it to spread the loctite around inside female threads.
Let dry overnight for damn sure locking.

Any wiggle or slop due to hardware backing out will be greatly reduced with this method. No promises if you skip any steps.

J

 

[Master Basher]

Probably will if you take Joels setup advice.

I think it's much more likely that it failed due to the violence imposed by dig with the wheels turned sharply. Have you seen how well the "constant velocity" joint functions when turned even a little bit? It's hardly constant velocity, and the awkward motion of the wheel spinning around when the steering is turned even halfway is very noticeable. All of these little toys have less than ideal dynamics at the steering joints. My ax10, my berg with stock steering hardware, my berg with sd's, both my bullies, they all have that jerky erratic motion when powered and turning at any angle.

I made the thread only to call out an item that may need further engineering attention and warn others. I will be mindful of the steering endpoints/binding issue, but I don't think that is the mode of failure in this case. I have been wrong before though.

 

[Spiitz Travsky]

I hate to keep pushing the same issue as others, but since you are claiming potentially inadequate RC4WD parts, I looked at my CVD's very carefully while installing some 8 degree parts last night. (I know that nobody is using the 8 degree stuff, but I wanted to try them out to see what the deal was with them)

The weakest point of failure is where the pin holes are located. This is where your part broke. At this point I could agree that maybe it failed because of the weakness, but more noteworthy is that weak point is exactly where the cup's outer rim will contact the shaft when turned all the way.

If I set my EPA too close to that position it would slowly wear down the weak point and fail. You can see this wear on the shaft where the cup rim makes contact at full turn.

I think these guys have it right and we need to avoid letting these parts contact each other. This means not setting it too close even because a little extra pressure can extend the turn past your EPA. On the bright side your use case is going to highlight the issue and help me and other noobs avoid this problem. I am sure the vets giving their advice knew this well and good.

Out of curiosity, can you post a picture of your axle shafts near the cup so we can see if it has those marks?

 

[Master Basher]

Yeah ill post a pick. They have nothing but dirt and grease on them. They actually have a cake of covering that would easily expose a rubbing issue...never any sign of contact which would be easily visible. Thats why I am not quick to think that epa's are an issue. Of course im sure they have made contact during a tumble before. I saw evidence of this on the cup. This was in a different location than the "weak point" though. Three distinct impressions led me to believe this. Im not poo pooing any thing related to rc4wd... these are far and away the BEST comp axle ever made...im quite happy with them...but I made the thread as a "hey take note...two months in and I broke this part...."

 

[rmdesignworks]

Another cause and affect issue is this: In the not too distant past I was having issues with cv's and the issue was breakage at the ball stub. It turned out that the breakage was heat being caused by the pin moving through the slotted sides of the ball end...with a slight tightness in one area of the slot toward the bottom of the slot (closest to the main part of the shaft) the pin was binding in one spot on one side of the ball's slot. Easing the slot with a diamond carbide rasp bit in a dremel made the pin slide in these areas much easier and rid the axle of the binding point. I noticed the issue while trying to eliminate the cause and/or affect. The wheel was lurching when the axle was supported and the steering was turned from side to side...as the wheel would reach full lock the lurching would start. I started filing or grinding the slots down upon install and the issue all but went away.

 

[Master Basher]

Another cause and affect issue is this: In the not too distant past I was having issues with cv's and the issue was breakage at the ball stub. It turned out that the breakage was heat being caused by the pin moving through the slotted sides of the ball end...with a slight tightness in one area of the slot toward the bottom of the slot (closest to the main part of the shaft) the pin was binding in one spot on one side of the ball's slot. Easing the slot with a diamond carbide rasp bit in a dremel made the pin slide in these areas much easier and rid the axle of the binding point. I noticed the issue while trying to eliminate the cause and/or affect. The wheel was lurching when the axle was supported and the steering was turned from side to side...as the wheel would reach full lock the lurching would start. I started filing or grinding the slots down upon install and the issue all but went away.

I have actually contemplated smoothing those edges. I think you just pushed me to do it.

 

[Spiitz Travsky]

Yeah ill post a pick. They have nothing but dirt and grease on them. They actually have a cake of covering that would easily expose a rubbing issue...never any sign of contact which would be easily visible. Thats why I am not quick to think that epa's are an issue. Of course im sure they have made contact during a tumble before. I saw evidence of this on the cup. This was in a different location than the "weak point" though. Three distinct impressions led me to believe this. Im not poo pooing any thing related to rc4wd... these are far and away the BEST comp axle ever made...im quite happy with them...but I made the thread as a "hey take note...two months in and I broke this part...."

I am pretty quick to think your EPA setting was the issue, but I don't think you were poo pooing RC4WD when you said "The parts are suspect". I just think you might have the wrong expectation about what the part should handle.

^it should not have broke. Period. The other hole in the cup looks stressed too. The parts are suspect. They steer more than superdaves cvds, but they are weaker too. My steering mods didnt affect it...but several tumbles over the last two months may have caused the failure.

What im saying is that I believe the design needs work to make it more robust. I would like to see bigger thread on the ends like sd's have as well. Now I know to keep spares though.

On face value maybe we should all want RC4WD parts to function as a steering stop and survive tumbles down rocks, but we also want it to steer more which means it needs a small compact joint with a wide range of motion. Is it possible you might be missing the main culprit that was mentioned in post #5?

The fragile version.

Check your steering stops/EPA etc. Any CVD cup will weaken if it doubles as the steering stop.

J

For example, your wear mark is actually considerably bigger than mine. :shock:

I have a thinner wear mark because I only rubbed the fine edge. Your entire beveled edge is contacting. That is more contact than I had before fixing my EPA. It looks as though we were indeed using our CVD's as steering stops.

Here is a stock CVD that shows the all black finish. The silver finish in our images is the wear.

I have no idea how to observe what rmdesignworks mentioned but that might be the problem as well. I just know the advice given early on in your thread seems relevant.

Count me in on any RC4WD parts that improve upon their current design because I love the Bully 2's as well. "thumbsup"

 

[rmdesignworks]

"I have no idea how to observe what rmdesignworks mentioned but that might be the problem as well. I just know the advice given early on in your thread seems relevant."

Id say you dont really "observe" it...its a feel when you move the stub shaft around at different angles as you rotate the axle shaft....just feel for the tight spot at a certain point...you can however try coloring the pin with a Sharpee then install it in the shaft and turn it and move it and then check for the coloring to be removed. All parts of the complete shaft need to be grease free when doing this though.

 

[Spiitz Travsky]

"I have no idea how to observe what rmdesignworks mentioned but that might be the problem as well. I just know the advice given early on in your thread seems relevant."

Id say you dont really "observe" it...its a feel when you move the stub shaft around at different angles as you rotate the axle shaft....just feel for the tight spot at a certain point...

I am being picky but you just described an "observation". Since you are noticing or perceiving something and registering it as being significant.

I will see if I can observe the same thing on the Bully 2's

 

[Master Basher]

Spitz, there is no more wear on that anodizing than would be expected from all the grass and hair that gets tangled around the shaft from everyday driving. I have bolts in my rear case missing anodizing and even rubbed smooth that never contact rocks at all. Metal to metal contact would make a shiny glaze, not just remove a little black anodizing. When I set my epas my tires dont touch my lower links, but at full lock not only can they touch, the rubber pushes in on the tire a significant amount.

My calipers say there is .03" more thickness to that diameter than to the side the bearing runs on, at the thinest spot

Further evidence that it is not being worn from being an endstop is that the band is wide smooth and not singularly narrow like yours. Has it made contact during a jarring fall at times? Probably many times.

Grease stays on it, grease attracts dirt and grit, the thickness of that greasy cake is sandwiched when ever the axle turns, that is the only wear you are seeing there.

 

[Master Basher]

...and the awkward motion of the wheels turning and jerking can be observed easily. Pick up the toy turn the servo and press the trigger.

 

[rmdesignworks]

Call it what you will....regardless...I'd look, feel, sense the movement of the shaft through a full range of motion to note any spot where the pin or other parts of the shaft feel tight...the amount of material needed to removed cannot in most cases be seen. Some light grit emery cloth run through the slot can remove even the tiniest burr that isn't seen but can still cause an issue. I de-burr all of my cvd's,xvd's for every application.

 

[Whiplashdjs]

MB: sounds like you cleaned all the grease off the beveled edge of the cup and the black is still there under the grease? Accurate?

Many invisible variables going on here, if it were me I'd lessen the epa's and drive the snot out of it. Err test it out

I've had 2 pair of axle shafts made in the same batch and one wears a great deal more than the other, even though there was less steering throw on that set?? Some breakage has to be expected on a highly tuned machine with use. Dig with tires cranked is really brutal on this part.

Anyone: are there some Teflon shims (washers) that could go between the hex and knuckle bearing to help keep the shaft "pulled" out and or remove some slop? Like the washers on a slash 4x4. I've used the same ones on my xr's to take up slop, seems to make e bearing last longer.

 

[rmdesignworks]

I use pinion or gear shims...0.0001"-0.0010" To pull the stub shaft tight. A piece of lexan or other poly materials can work too...a great source is the trimmings from a new body

 

[josh6575]

Some of this could be the normal action(pulsing) of a u Joint. These are truly just little U joints that allow acceleration and deceleration through its cycle. There are other kinds of joints that do not do this.

...and the awkward motion of the wheels turning and jerking can be observed easily. Pick up the toy turn the servo and press the trigger.

 

[Spiitz Travsky]

...and the awkward motion of the wheels turning and jerking can be observed easily. Pick up the toy turn the servo and press the trigger.

Damn..and I just spent all this time convincing my wife it was not a toy. She is laughing over my shoulder right now...

 

[Spiitz Travsky]

Many invisible variables going on here, if it were me I'd lessen the epa's and drive the snot out of it. Err test it out

I am working on that "test" now :twisted:

 

[Master Basher]

Here is a youtube video of the "violent" movement that occurs when just slight turning input is on the steering.

Fast - YouTube

Fast - YouTube

Here is some socket head cap screws that have rounded edges, in addition to having the anodizing rubbed off. No rocks have touched these screw heads, the top one for sure. The only explanation I can give for the anodizinng rubbed off and the roundedness is blades of grass! That is all that impinges on them, and they have been in that exact position since the first run of these axles.

What does everyone elses stuff look like?

I need to figure out how to embed a youtube video.

 

[josh6575]

The joints accelerate and decelerate through there cycle. This is just how they work. Also is why you will not find U joints propelling a front wheel drive car. Only true CVD joints keep a constant velocity through the range of steering. The joints in these crawlers are just cleverly disguised U joints.

 

[Master Basher]

The joints accelerate and decelerate through there cycle. This is just how they work. Also is why you will not find U joints propelling a front wheel drive car. Only true CVD joints keep a constant velocity through the range of steering. The joints in these crawlers are just cleverly disguised U joints.

I was simply posting to show what I think caused the failure, heavy use and this phenomenon. I have always set my epa's by going to lock, and then backing off a significant amount (5-12% of travel).

This is all taught in mechanical engineering curriculum.