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1/8 scale truggy center diff destroyed - how to prevent?

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1/8 scale truggy center diff destroyed - how to prevent?

Old 03-09-2019, 03:21 AM
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Default 1/8 scale truggy center diff destroyed - how to prevent?

I was driving my ET48 on some grass and doing wheelies and small jumps when I heard a crunch, and then saw that there was no center diff action at all.

When I opened up the diff, I saw this. If you look carefully, you will see that the cross pins holding the spider gears
are all shifted away from the grooves where they belong. The gears are no longer centered between the screw holes. As it stands, the assembly is almost welded together. I can’t get it
apart and my next step is to cut the diff case. The gears don’t look
broken though:

I was running 80k diff oil which is obviously pretty thick but nowhere near locked. What caused the pins to rip out of their grooves and what is the best way to prevent this from happening again?

The day this happened was a “light” day in terms of bashing. No flips, very small jumps, etc.
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Old 03-09-2019, 08:35 AM
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buy a new case and gear drive assembly. losi makes a diff locker that might be your best bet for bashing if you what full time 4 wd.... 7 thousand is as thick as I would go but//.. here is what IM talking about https://www.amainhobbies.com/king-he...l8-022/p157793

Last edited by chucko; 03-09-2019 at 01:24 PM. Reason: adding link to part
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Old 03-09-2019, 05:37 PM
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Im assuming you drained some of the fluid out correct? If not, thats your problem...looks like those gears melted and fused with the case!!!!
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Old 03-09-2019, 06:09 PM
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This is not common, and more than likely due to something other than parts failure. As evoking stated get a new case, and build it per the instructions. As a note DO NOT run a Locked Diff in your ET48, it will just cause something else to fail. the center diff is meant to distribute power front to rear, and a locked diff no longer distributes as needed, just straight drive. You will see higher wear, should you run it locked.

I have run the ET48 since the original up until the ET48.3 and have never come across any abnormal diff wear. If you want to be extra safe, and prevent it you can run the Aluminum Diff Cups as a precaution, and this will be avoided in the future.
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Old 03-10-2019, 08:12 AM
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How many pack cycles between the last time you serviced your diff?

Did you put grease on the rubber seals to prevent the fluid from leaking out?

This is a diff for a different brand of car but giving an example of how I use the out drive as a "skewer" by applying the seal and shim in reverse order, place a bead of grease on both sides of the rubber seal, then press/pack the seal and shim into place, then flip the out drive around to finish building the diff. You want to apply fresh grease using this method every time you service your car.

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Old 03-10-2019, 08:34 AM
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Thanks all!

- yes, I drained fluid to see what was wrong, so the pic shows a half empty diff

- in terms of age, the entire diff was brand new as of about a month ago and had maybe 15 battery packs run through it (6s 4500mah, extra long can motor - TP4050 motor).

- I did use grease and seal everything as well as I could. I assembled it per the manual and was pretty careful. The day it died, I still had plenty of resistance and was able to pull wheelies.



- Bill I like the skewer method - will see if I can get that to work next time
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Old 03-10-2019, 09:20 AM
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What is the condition of the bearings?

Not uncommon for a seized bearing to generate heat and melt plastic fairly quickly too

If you ever have a failed bearing on a hub, then you must also replace the plastic hub carrier otherwise slop will form and you will repeatedly go through bearings on the same hub.

I would also check gearing and motor temps... a hot motor can melt your center diff:
PRIMER: What gearing do I need to run for upgraded electronics in my car?
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Old 03-10-2019, 09:28 AM
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It may have been a bad diff case... You also seem to be running a lot of power, perhaps too much. Are your tires/surface very high grip?
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Old 03-10-2019, 12:31 PM
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- bearings seem ok - spinning freely

- temps are a smidge higher than I like. I have a heat gun and use it often, currently temps are 170ish with the smallest pinion I can fit (15t)

- tires are large and heavy and do have high traction:
https://www.horizonhobby.com/DYNW0041?KPID=DYNW0041&CAWELAID=320011980001424900 &CAGPSPN=pla&CAAGID=37462622311&CATCI=aud-112431678027la-531206008942&gclid=EAIaIQobChMI4N-w2qb44AIVoxx9Ch1jfQb8EAQYASABEgIso_D_BwE

- surface is grass, which is surprisingly high-traction. It would be safe to say there were plenty of landings that brought all four tires down on the grass pretty hard, resulting in stress on the entire drivetrain

- I think the diff case was ok - it was only a month or two old.

With all that said, I don’t have the space or the skills to really put the ET48 through the sort of stuff you see on YouTube, so it doesn’t seem like I am anywhere near any real edges of durability.

Oh, in case it helps, this is all for a general bashing use case. I don’t have any tracks near me.

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Old 03-10-2019, 07:51 PM
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In my opinion you need much thicker diff fluid in the center if you’re running an insane motor on 6s. You’re melting the center cup plastic because there’s too much diff action. 80k is super thin for such power. I run 1 million in the center with my TP motors on 6s.....and it’s nowhere near locked still
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Old 03-12-2019, 06:05 AM
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Originally Posted by smirkracing
- bearings seem ok - spinning freely

- temps are a smidge higher than I like. I have a heat gun and use it often, currently temps are 170ish with the smallest pinion I can fit (15t)

- tires are large and heavy and do have high traction:
https://www.horizonhobby.com/DYNW0041?KPID=DYNW0041&CAWELAID=320011980001424900 &CAGPSPN=pla&CAAGID=37462622311&CATCI=aud-112431678027la-531206008942&gclid=EAIaIQobChMI4N-w2qb44AIVoxx9Ch1jfQb8EAQYASABEgIso_D_BwE

- surface is grass, which is surprisingly high-traction. It would be safe to say there were plenty of landings that brought all four tires down on the grass pretty hard, resulting in stress on the entire drivetrain

- I think the diff case was ok - it was only a month or two old.

With all that said, I don’t have the space or the skills to really put the ET48 through the sort of stuff you see on YouTube, so it doesn’t seem like I am anywhere near any real edges of durability.

Oh, in case it helps, this is all for a general bashing use case. I don’t have any tracks near me.

Yup a combination of high traction tires and a metric assload of power, with a few 4 wheel landings will result in a borked diff.
It's impossible to tell whether the case was good or bad by look or feel, as there may be something wrong internally or on a microscopic/chemical level.

I suggest one or more of the following.
1. Try and land on 2 wheels as much as possible.
2. Reduce power, you don't really need that much.
3. Get a Slipperential.
4. You could maybe up the diff fluid as suggested above.
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Old 03-12-2019, 06:15 AM
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What sir-51d3ways said. You can also invest in a Tekno Traction drive to act like a slipper for your motor.

https://blog.teknorc.com/2018/08/31/...e-kit-is-back/



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Old 03-12-2019, 06:18 AM
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Another option to consider along the lines of that slipperential is the TEKNO Traktion Drive Kit , this will make the car accelerate more like a nitro so you can mash the throttle hard and put far less stress on the center diff, be sure to select the right size clutch bell to replace your pinion toward the bottom of the page.

*** EDIT, I see I just got ninja'd, while looking up links, ha!
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Old 03-12-2019, 10:05 AM
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Thanks for all this great advice!!

Less power is not an option. In fact this motor is my “training wheels” motor while I slowly work my way up to Overkill / Chainsaw levels (easily several thousand more watts)

My basic goals are being able to run 2 battery packs back to back without going over 175 degrees, with 6.5” tires and a top speed of about 65mph on medium length grass. I have most of the above already, except for being able to run multiple packs. Still need to grind down my motor mount so I can get below a 15t pinion (13 might be just right).

I am waiting for the m2c diff case to be in stock and then I will try that.

For now I think I will up the diff fluid to about 300k and keep increasing until the diff doesn’t overheat.

Anyway thanks for the advice - very helpful.

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Old 03-13-2019, 02:57 PM
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300k fluid in the center diff. So far so good. Excellent traction and still not an uncontrollable wheelie machine.

500k and 1m are on order for further testing. It is great that center diffs with different fluid can be swapped in 2-3 minutes. Allows comparisons within a single session.

Good advice from everyone here - thanks!

Next up is deciding what weight fluid to put in the front and rear diffs. Right now I have the stock weights. I think I will try 80k up front and 50k in the rear.
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