Why did my diff self destruct - again!

[RC944]

ok so im bashing the b3 after having rebuilt the diff as per intstructions and slowly but surely the car starts losing speed and finally all i hear is the clutch slipping but no drive transferred to the wheels.... fearing the worst i open the tranny case to find (for the second time) that the diff gear with the bearings has killed itself - what was once a single plastic gear has now become two pieces with the plastic on the inners side of the bearings separating itself into a separate piece of plastic that spins freely from the geared part on the outside with the bearings acting as the roller! given that this is the second time it has happened and each time i need to wait 2 week to get a new diff gear im hoping someone can point me in the right direction! to my mind there could be a few causes:

- overtightening of the diff washers via the diff bolt
- left outdrive and right outdrive wrong way around in tranny case
- problem with the left outdrive hub that has diff spring to maintain correct tension with the diff bolt
- anything else?

im convinced that i have re-assembled the diff correctly but am really struggling to find a cause!

[Chrislong]

Does it look melted? if it does, then it is heat through it slipping. Perhaps it was in back to front, and so backed off (loosened) and thats when the heat was generated.

If its not melted, and your sure it was built right, I can't help you.

[peetbee]

Did you rebuild it with a new bolt and captive nut?
What side of the car did you have the head of the bolt?

Once it's built and installed - tighten the slipper clutch right up and give the car a try, if you hear the diff slip, tighten it slightly and try again. (small adjustments)

Once you are happy the diff isn't slipping, loosen the slipper clutch back off so that you hear it slip the first foot on full throttle starts.

[RC944]

actually yes it looks like its melted! and i would say that i backed it off too much. i backed off the bolt until it did not feel gritty even though i cleansed everything and the balls are in good order and the washers polished with fine wet and dry...

[RC944]

Originally Posted by peetbee

Did you rebuild it with a new bolt and captive nut?
What side of the car did you have the head of the bolt?

Once it's built and installed - tighten the slipper clutch right up and give the car a try, if you hear the diff slip, tighten it slightly and try again. (small adjustments)

Once you are happy the diff isn't slipping, loosen the slipper clutch back off so that you hear it slip the first foot on full throttle starts.

pete i used the old captive nut and bolt

head of the bolt on the right side of the car - the same side with the drive shaft coming out. if i recall correctly this is what is stated in the manual?

once i get the new parts ill try the above for the final adjustments

[peetbee]

Yes, the bolt head should be on the same side as the slipper clutch.

I'd get hold of a new nut at least, just in case the old one isn't holding the bolt properly.
Have you got the right greases for thrust race and diff?
Sounds like it may have been too loose then, it can feel a bit gritty and too tight when it's outside the car.
Good luck

[Col]

1. It's a B3, so it's an older design and maybe not as upto taking modern stuff?
2. What motor and batteries are in it?
3. What surface is it running on? Anything but the shortest grass will cause massive wear and resistance...

[bigred5765]

and if u like doing donut wheel spins this will tend to kill any diff,

[Gaz_Stanton]

Originally Posted by RC944

slowly but surely the car starts losing speed and finally all i hear is the clutch slipping but no drive transferred to the wheels....

B3 stealth gearbox should be robust enough if setup properly.

Sounds like it has worked loose (possibly caused by being installed with bolt in wrong direction), slipped and then the heat generated by the continued use whilst slipping has melted the gear.

Never run with the diff slipping as it will cause damage.

Build up as per instructions (may need new diff plates and thrust race now) then test it is not slipping. Do this by locking up the slipper clutch fully and then trying the car on a grippy surface. There should be no slipping whatsover and the front wheels should lift. If there is any slippage at this point then the diff is too loose. (and you will hear a 'bark' noise)
Tighten and repeat until correct.
Once you're sure the diff is not slipping then back the slipper off until you can hear it slipping for a few feet. (will be a different pitch noise to the diff slipping. Learning to distinguish between these sounds would be useful )

[RC944]

cheers all

i can confirm that the car was running on short but wet grass and was spinning around quite a bit - i cant see that helping at all!

parts are on order so ill report findings in a couple of weeks!

[RC944]

Originally Posted by Col

1. It's a B3, so it's an older design and maybe not as upto taking modern stuff?
2. What motor and batteries are in it?
3. What surface is it running on? Anything but the shortest grass will cause massive wear and resistance...

ive known others to run modern electrics on the b3 stealth with no issues but for info i have a lrp sphere comp, vector x11 10.5t and 2s 40c lip trakpower and bionic lipos...

i think the likely cause is that a loose diff has allowed heat to melt the diff gear esp as i was running on wet grass and spinning like a mother...

[Chrislong]

Cleaned the plates with wet n dry? That'd make the diff action rough. You don't want to be doing that.... years gone by I used to polish up diff plates on a flat tile with a cutting compound for hours... sad I know.

If you hear a 'bark' rather than a 'squeel' thats the diff slipping slightly (if it slips lots it'll just squeel though). If it squeels, thats the slipper clutch and that is okay. If any doubt, take gear cover off, hold a wheel and thumb on spur - turn the other wheel so something has to slip - the slipper nut should always turn otherwise its the diff slipping.

Any doubts, take it to a shop or a club and get a second opinion.. its far easier to diagnose & solve hands-on, rather than like this on a forum

[bigred5765]

you only need to ruff up and polish the plates really if your using ceramic diff balls

[RC944]

i thought giving them a rub with 2000 grade would help remove any surface contaminants but i guess that may not have been needed!

[RC944]

just one thing; when i hold both the left and right outdrive hubs together following assembly of the diff gear, bearings and hubs, etc, should i not be able to hold one side and the other should rotate smoothly with no gritty feeling?

when i re-assembled them i did so following the instructions which was to turn the bolt so that the captive would reach max with the spring underneath and then to back off 1/8 of a turn. when i did this it still felt gritty so then i backed off more

what i have no idea of is what a normally adjusted one should feel like when adjusted properly. if a bit of a gritty feeling is normal then it sounds like i kept it too loose. if there should be no grittyness at all then chances are i could have wear in the washers, bearings or some dirt in the diff gear where the bearings are...

[Chrislong]

Grit is not uncommon, but not ideal especially in a new diff. Loosening it more is not the right thing to do though!

Gritty feeling usually comes from the thrust race, id defo replace this every rebuild at the minimum. Turn the diff plates over, and regrease everything.

To clean, I strip down, motorspray everything then individually wipe everything with kitchen roll. Then regrease (AE Stealth Lube, and AE Black grease are best), and re assemble as per the destructions. If its been a while since the last rebuild (it usually is because the diffs are so good) - Renew the thrust race, diff plates, diff balls and lucking nut... infact, when I was running an X-6 I used to just buy complete diffs, as outdrives would wear and replacing those got expensive, may aswell buy the complete diff.