vasco

My friend have a SC 8.2 (mamba monster 2, 5s battery) and after changing oil
in all 3 differentials he started to get direct problems with the rear one.

Everything seemed right after putting it together.
Wheels acted the right way, turn one wheel, other go opposite way.

But after short first run he noticed it didn't act right on rear wheels.

Took it apart, gears were damaged.
Old gears, so he replaced every gear to new ones. All seemed right, easy to turn, wheels goes opposite way.

Made a new test run and same again, if he turns one tire the other goes the same direction.
Haven't taken it apart to inspect the new gears yet.

He speculates that the car got too much power.

But i drive almsot the same setup with 6s. And so do many others also so I'm skeptic thinking that
he is doing something wrong when he installs the rear diff.

Any suggestions? What would you check/do?

phmaximus

A lot does come down to driving style, punch setting and slipper settings... Well in fact there can be a lot of contrubiting factors or just one.

there could be a very real possibility that there was a issue with rebuilding it it's hard to say with out seeing it.

frist thing is what oils was he running and what did he swap to and why?
next, what gears failed?? Was it the pinion and crown gears or the planet gears?

vasco

* He didn't drive long before it happen. 3-5minutes. No extreme acceleration or such.
* Punch setting and slipper settings - don't know what this is.
* I think his is a rebuild one from nitro. Looks little lower than my new one.

* Before: 6,000 in every diff.
- changing to: 5,000 front, 60,000 middle, 10,000 rear. Team Associated oil.
- He bought an used car and waned to prepare it to match my new one with same but 50,000 middle.

* All spider gears were damaged, outer side of gears, probably sun gear also.
He replaced them all to factory new. All seemed correct. Drove, and now the same. Hard to turn tire and both turns the same direction.

1QwkSport2.5r

There could be too much play in the gears which would require shimming to tighten up. In addition, make sure the bearings are tight. If they're loose they can throw the gear geometry off causing wear or breakage. These items are probably not going to fix the extreme situation you (the OP) have going on but may help? Something is really amiss to cause such catastrophic damage so quickly. I don't think the oil has anything to do with it. Something is faulty with the parts or the assembly.


Below is a link that details shimming diffs. It's a Losi forum and about the LST2 diffs, but the pictures and information could be extrapolated to other models.

http://losiforums.net/showthread.php?t=113

EXT2Rob

My Feedback: (1)

Punch refers to an ESC setting than has several "steps" you can set. Full punch gives you all the power the motor can deliver right off the bat. Dialing it back to a lower setting limits the amount of power the motor puts out in the initial seconds of acceleration, ostensibly to limit wheel slip. The slipper setting refers to the slipper clutch on the spur gear. The tighter you set it, the less slip it has. Loosen the set nut, and it allows the clutch to slip. Finding the right setting can be tricky. Generally, it is there to allow a little bit a slip in the drivetrain when landing jumps or running on bumpy tracks, so that the strain is not transferred to the gears.

But then you mention that you guys have CENTER diffs. You may not even have a slipper clutch. My Ofna (HoBao) Hyper TT doesn't have a slipper.

Curious that it only seems to be the REAR diff you're having a problem with. Is it possible that there are some shims missing from that diff that the others have? A thin washer is sometimes used behind each planetary gear that moves them toward the center of the diff, and effectively "tightens" the gear mesh. If the diff gears are not meshing properly, and you're running on a high-traction surface with a high power motor, those diff gears can get munched in a hurry. Same thing happens if the diff screws in the diff case get loose. THAT could be your problem. Check the diff screws, and use thread lock if needed.

phmaximus

ok by the sounds he shattered the planarity gear set... changing to a thicker oil wouldn't of caused that. if anything it would of slowed down the diffraction reducing temps. even over filling the diff would or just caused a leak.

possible causes.
screws camp loose (most likely.... people forget thread locker)
under filled diff (unlikely)
excessive play and backlash in the diff assembly
excessive play and backlash in the diff carrier
to much power (unlikely)
bearing failure

Id recommend taking the diff completely apart and inspecting everything.
Shafts, are they worn or bent
diff carrier, check the keyway for where the shafts sit to the shafts fit nice and snug... and check screw holes
planetary gear set, sounds exploded so replace and shim as per manual/instruction
Pinion/crown gears. check wear pattern, check for pitting and any general damage to the gears... shim as per manual/instructions
bearings, check bearings. clean and re-oil as necessary
Diff cups, check or elongated pin holes, inspect cups and check pins
complete diff assembly, check to see if it rotates true with in the housing.
screws. inspect and use a thread locker

supertib

60K in the center is the issue.... your locking the center up and tearing up the rear end......... lighten that center back to a more normal number like 10K...