Asuga Center diff wobble

[Atomic Skull]

My center diff and spur gear wobbles slightly in the diff bulkhead when spun by hand. However when I remove it and spin it on one bearing or the other it spins true, it only wobbles when supported by both bearings in the housing. Is this normal?

There is also a tiny bit of play in the two drive cups which I think may be what causes this. The wobble appears to go away when the motor is running faster than "extremely slow"

 

[Niekname]

Is the play in the drive cups front to back or side to side? I have a rear diff where the bore for the outdrive cups seems slightly to big so it can be slightly angled. Haven't noticed any problems there once it was seated but pretty noticeable in my hand. This could cause the diff to run slightly eccentric.

 

[Atomic Skull]

Is the play in the drive cups front to back or side to side? I have a rear diff where the bore for the outdrive cups seems slightly to big so it can be slightly angled. Haven't noticed any problems there once it was seated but pretty noticeable in my hand. This could cause the diff to run slightly eccentric.

Both, it has slight lateral and axial play between the drive cups and the diff housing. It's the opposite it runs true if I spin it while holding one of the bearings with my fingers but with both bearings seated in the bulkhead the diff housing and spur gear wobbles slightly like a top (about 0.5mm~0.8mm of wobble).

 

[SirCrashALot]

It sounds like the spur isn't sitting straight on the diff case.

 

[Atomic Skull]

It sounds like the spur isn't sitting straight on the diff case.

It runs true if I spin the diff while holding it by one bearing or the other. I also checked it with a precision machined angle and it's 90 degrees to the case. Also it's not just the gear that wobbles the diff case itself clearly wobbles.

 

[SirCrashALot]

You can also check the plastic bearing carrier inserts. They may be worn.

 

[shortround9191]

It runs true if I spin the diff while holding it by one bearing or the other. I also checked it with a precision machined angle and it's 90 degrees to the case. Also it's not just the gear that wobbles the diff case itself clearly wobbles.

With the diff in drive shafts out does it still wobble? If so pretty much only have a few things that could cause the vibration bearings or as stated the bearing support being slightly worn

 

[Atomic Skull]

With the diff in drive shafts out does it still wobble? If so pretty much only have a few things that could cause the vibration bearings or as stated the bearing support being slightly worn

Th vehicle is only a month old, also I replaced the center diff bulkhead and motor mount with the ADU 7075 aluminum versions and the wobble exists with both the original and the replacement.

With the diff in drive shafts out does it still wobble? If so pretty much only have a few things that could cause the vibration bearings or as stated the bearing support being slightly worn

Yes it doesn't matter if the driveshafts are in or out.

 

[Nelson.81]

too much play on outdrives check the shims in diff case

 

[Atomic Skull]

too much play on outdrives check the shims in diff case

That's what I was thinking. Not looking forward to draining and disassembling the whole diff ugh.

What size shims do the outdrive cups need? I assume I shim between the bearing and the diff housing so as to not to affect the gear mesh inside the differential?

 

[Nelson.81]

That's what I was thinking. Not looking forward to draining and disassembling the whole diff ugh.

What size shims do the outdrive cups need? I assume I shim between the bearing and the diff housing so as to not to affect the gear mesh inside the differential?

Get some brake cleaner just soak parts makes light work off it. Can’t remember if shims on outside but definitely inside, I’d issue with one my centre diff before but was outdrive was moving all over place not the spur but when took it apart couldn’t believe nothing was broke, I still can’t explain this but it looks like one my shims somehow replaced the o’ring . It almost looks like a washer that was made for it but there are no washers in the diffs , how it got to that size shape I don’t know, but I rebuilt diff all was good after. Corally do rebuild kits for them shims included probably lists size shims in kit, even oring looked thicker takes up bit of the slack , But yours sounds like it something different to my issue as it spur moving, could be something else but if it ok on each bearing must be something in between is my thinking , the diff the bulkhead they can wear out or even melt being plastic, replaced mine for 7075 version. Unless your motor shaft or something is bent maybe it causing it

 

[Nelson.81]

This was my issue nothing really to do with the spur gear .

https://www.facebook.com/share/v/1ATvSCDWbE/?mibextid=wwXIfr

 

[Atomic Skull]

Get some brake cleaner just soak parts makes light work off it. Can’t remember if shims on outside but definitely inside, I’d issue with one my centre diff before but was outdrive was moving all over place not the spur but when took it apart couldn’t believe nothing was broke, I still can’t explain this but it looks like one my shims somehow replaced the o’ring . It almost looks like a washer that was made for it but there are no washers in the diffs , how it got to that size shape I don’t know, but I rebuilt diff all was good after. Corally do rebuild kits for them shims included probably lists size shims in kit, even oring looked thicker takes up bit of the slack , But yours sounds like it something different to my issue as it spur moving, could be something else but if it ok on each bearing must be something in between is my thinking , the diff the bulkhead they can wear out or even melt being plastic, replaced mine for 7075 version. Unless your motor shaft or something is bent maybe it causing it

This is a brand new car about month and a half old and never more than a traction flip on grass and the bulkhead is the ADU 7075 aftermarket so no possible way for it to be wear, it also wobbles when spun freely in the bulkhead without the pinion or driveshafts engaged (though again brand new Hobbywing motor so I don't see how that could be possible either)

I've had the diff open once when I replaced the crap 10.9 grade screws with proper grade 12.9 ones and everything looked fine inside. I didn't drain it or take any gears out though. And it wobbled before I did that regardless.

I think the only possible explanation is the bearings or the play in the drive cups. It cannot be the diff housing because that and the spur gear spin true when the diff is supported by only one of the bearings.

 

[Nelson.81]

This is a brand new car about month and a half old and never more than a traction flip on grass and the bulkhead is the ADU 7075 aftermarket so no possible way for it to be wear, it also wobbles when spun freely in the bulkhead without the pinion or driveshafts engaged (though again brand new Hobbywing motor so I don't see how that could be possible either)

I've had the diff open once when I replaced the crap 10.9 grade screws with proper grade 12.9 ones and everything looked fine inside. I didn't drain it or take any gears out though. And it wobbled before I did that regardless.

I think the only possible explanation is the bearings or the play in the drive cups. It cannot be the diff housing because that and the spur gear spin true when the diff is supported by only one of the bearings.

If it not something with motor/diff mount it must be bearings or maybe a stone or something has got in there damaged the diff case or spur, if it wobbles when in place it’s not the outdrives they aren’t going to affect it. I know some people had issues with the adu motor mount having bit movement in it tolerances not tight enough and was causing a bad mesh & pinions where getting chewed up.

 

[Atomic Skull]

If it not something with motor/diff mount it must be bearings or maybe a stone or something has got in there damaged the diff case or spur, if it wobbles when in place it’s not the outdrives they aren’t going to affect it. I know some people had issues with the adu motor mount having bit movement in it tolerances not tight enough and was causing a bad mesh & pinions where getting chewed up.

I checked the diff and spur gear against a precision machined angle, everything is 90 degrees. same with the diff buklhead and motor mount I checked it against a 90 degree angle and it's all perfectly square when installed on the chassis.

The only thing left is the play in the outdrives or the bearings.

 

[shortround9191]

That’s why I asked if you ran it with driveshafts out, if it wobbles with them out it narrows down what’s wrong

 

[Jeffwazz]

Get some brake cleaner just soak parts makes light work off it. Can’t remember if shims on outside but definitely inside, I’d issue with one my centre diff before but was outdrive was moving all over place not the spur but when took it apart couldn’t believe nothing was broke, I still can’t explain this but it looks like one my shims somehow replaced the o’ring . It almost looks like a washer that was made for it but there are no washers in the diffs , how it got to that size shape I don’t know, but I rebuilt diff all was good after. Corally do rebuild kits for them shims included probably lists size shims in kit, even oring looked thicker takes up bit of the slack , But yours sounds like it something different to my issue as it spur moving, could be something else but if it ok on each bearing must be something in between is my thinking , the diff the bulkhead they can wear out or even melt being plastic, replaced mine for 7075 version. Unless your motor shaft or something is bent maybe it causing it

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Those shims and o-rings look very similar to mine!
Post in thread 'Jeffwazz's Punisher build-bash-break-fix thread.' https://www.corallyforum.com/threads/jeffwazzs-punisher-build-bash-break-fix-thread.667/post-17400
The shims are available separately from corally (bag of 10 or so), so easy and quick fix.

 

[Atomic Skull]

So I figured it out, the center aluminum housing has the screws drilled slightly off center:

When I flipped the center housing the off center rotation switched to the other end. Also the drive cups show excessive wear on one side likely due to the wobble.

I'm starting to reach the end my rope now, there have been so many things "not right" with this car and this is just the cherry on top. I feel like I got a lemon and this whole project was a mistake.

 

[Horatio]

So I figured it out, the center aluminum housing has the screws drilled slightly off center:

When I flipped the center housing the off center rotation switched to the other end. Also the drive cups show excessive wear on one side likely due to the wobble.

I'm starting to reach the end my rope now, there have been so many things "not right" with this car and this is just the cherry on top. I feel like I got a lemon and this whole project was a mistake.

I agree that with your diff looks like both the Spur and the end cap are ever so slightly off centre, meaning that the diff sandwiched in between is eccentric.

That's not great. Resulting in unmitigated vibration. Contact Corally support and politely explain that you would prefer a round diff!

If it's any consolation, it may just be a one-off thing.

Wear rate on the out drives from the centre diff is higher than anywhere else on the car (along with the input drives into the front and rear transmissions) due to sub optimal dogbone angles on centre driveline.

Making stuff better than it was is the whole point of this hobby! I would say that your exacting standards are 'significantly' higher than Corally's typical client base. Your typical basher type would probably be on their 3rd diff by now and wouldn't have spotted it.

Clearly Corally's quality assurance missed it. They really should be ISO 9001 certificated and stuff like that should never reach the customer. It's wholly unacceptable in this day and age.

 

[Jeffwazz]

I see what you mean! With the holes being slightly off, the diff planetary gears will be off axis, which in turn will push the outdrives off at a slight angle.
Looks to be a bit of duff machining of the extruded diff body. Warranty exchange perhaps?

And as a typical basher, I'll be taking a look at my centre diff