Was doing some diff maintenance to my xxl HD diffs and was just checking slop between the diff outdrives and where they enter the housing..not on the crown side but the other..
I noticed a bit of slop but looking closely I could see that the housing nib where the outdrive enters, was coming away from the housing itself..a bit more wiggling later the whole thing pops off..and I'm like WTF????
So I tried another diff HD housing and it also popped out ..I took out one of my older lst non HD diffs and they seem to be all one piece with little to no slop
Which begs the question, why did the HD diff while fixing one problem, cause another??
Weird thing is, I can't get the bloody thing back to sit back into the housing the way it should!!
Does anyone know any more?? Just when you think you know it all!

Can you post a picture? I've never had a HD diff so I'm not familiar.

BTW I assume you're talking about the diff cup?

Yeah I'll take a pic today and post it..I would have never thought it would come apart like it did..and the weird thing is, it didn't break off but it popped off and it's as if the bit that popped off is replaceable and I know it ain't..it's the nib where the bearing sits over on the diff cup
Zoom in on the pic and you'll see exactly what I'm talking about
http://www.amainhobbies.com/product_...ferential-Case

The HD diff adds the inserts, instead of the shims behind the planetary gears..
Apparently the cross pin use to "engrave" the inside cup so hence they came up with the insert design..if you have a look at one of loosemans lst2 diff rebuild you'll see it there..it's a great read

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

Here ya go!

So is the diff cup still plastic? with a steel nib around the outdrive? At a rough guess - your diffs are getting hot enough to affect the plastic integrity. Now you have a temp gun, run your muggy and when you measure the electronic's temps also measure the centre diff temperature. The centre will be working the hardest but the front/rear are inside casings, meaning they cannot dissapate heat as well.

I don't remember if these HD diffs were available when I bought diff upgrades. I ended up with nova rc diff cups front and rear with a slipperential centre. There still rockin' (mind you I don't run it much nowadays)

This is for my xxl, not the muggy which is running the 1717 and very cool..
But the nib didnt melt or break off, it popped off as if its a serviceable/replaceable part..there is no damage done to the case, it hasnt simply snapped off as a result of excess stress/heat etc.
Ill take a photo after work and show you..
Its a b*tch to put back in too..im gonna have to get creative
Pink..the HD diff cups have been around for donkeys years..get with the times

My point about the diff temps is you would be surprised how hot they get. I've had the diff be the hottest part on the car. The esc has a fan, the motor and battery have a much greater mass and surface area for dissapating heat.

The metal bearing support on the diff cup obviously shouldn't come out. Looking at my spare HD and non HD diff cups, it looks like the diff cup was molded around the metal bearing support. I think your best bet to getting it back in is to use a vise to press them back together.

I think new diff cups are in order. If you manage to press them back together like OD suggested it will not have the same strength as a new cup. The mear act of popping out and pressing back in will stretch and/or deform the hole it sits in and will likely pop out again only easier. The diff casing is probably what's keeping the diff together in the car but only to a certain degree. That would explain the diff's skipping under load but 'appear' to be fine when inspected.

I'm already awaiting new diff cups anyway as the diffs were way overdue for an overhaulin..
OD see if you can hit the bearing support with something heavy like a hammer and see if it pops out..I'd tend to agree with you if it was for one housing..but for both?? And as I say, there's no tears or damage, to me it looks as if it's a part that can be replaced which it can't which defeats the purpose of having this part seperate so cleanly off the main diff cup..
Standby, pics will be up shortly

Your asking OD to wreck a perfectly good diff cup?

If the metal part has heated the plastic enough (and periodically) it will make the plastic slightly more brittle and it will lose it's adhesion. Even pressure, spiders inside and bearing outside keeping it central will stop any tears or deformations.

ok well i found a spare lst cup off my old losi 8T (same HD diff cup) and after a few knocks it didnt pop..
guess i got unlucky with 2 of them and no wonder ive got one crown and pinion with skipped teeth!! guess from now on, i will be replacing the cups as well the HD cups should have been more stronger than this..NOT HAPPY!

I would say it has definitely worn/melted. The one on the right looks out of shape. The bearing that was on that side, is it still good?

Id say youre 100% right..
Bearings were only recently swapped over so theyre all still good.

Just remember these are super high power machines for what they are (particularly yours). Those little gears and plastic diff cup are dealing with +3HP. Think how many race cars have their engine built from the best available materials and is made only to last one race.

Very true..i think also that the heavy wheels of the xxl dont help things either..they way a tonne which puts alotta strain on just about every part of the diff..will definately be doing more diff maintenance more often...providing parts dont dry up by then