Rear dif blues

[Notorious J]

I'm done. 3 out of the 4 last runs ending with the rear dif getting smoked. This time out it was after only 4 or 5 jumps, which was mild in comparison to what I e done in the past. This was the second run with all new gears inside the Arrma aluminum dif cup. WTF is going on! Maybe a 40k mix of fluid so nothing out of the ordinary and I just had the truck apart from the center back for repairs, so everything was buttoned up nicely. The term "throw in the towel" crossed my mind when the truck started spinning in one direction. I've been bashing and jumping since November last year, and this rear dif problem started in late July so my driving style can't be the cause. Something else is amiss. Maybe a ghost in the machine? Heeeeellllllpppppp me pleeeeeeeeaaaasse!

 

[zerocool135]

If you don't have aluminum cases you could try checking for cracks that might be letting the mesh go bad. I haven't had or bashed my kraton long or hard enough to have that happen to me so good luck finding the cause.

 

[jondilly1974]

Wish I could offer some guidance but I haven’t even ran my 6S yet. Still going thru it piece by piece to get it right.

 

[Notorious J]

As expected, it was the larger sun/planetary gear on the cup side (bottom of the cup) broken into four pieces. I am putting a new one in but I removed one shim from each of the satellite gears. If it keeps going like this, I'll have to buy and replace that gear after every bash.

 

[bicketybam]

Stop shimming the inside, whether you think it's right or not. What's the worse that can happen other than me being right?

 

[slick2500]

As expected, it was the larger sun/planetary gear on the cup side (bottom of the cup) broken into four pieces. I am putting a new one in but I removed one shim from each of the satellite gears. If it keeps going like this, I'll have to buy and replace that gear after every bash.

Another member kept having an issue with his exploding too. I don't remember his name off the top of my head, he was the veteran guy that always argued with @bicketybam, and I don't know if he ever found a solution.

 

[jondilly1974]

Lol I thought it was YOU that argued with Ed ??????

 

[Lazy Bushman]

As @bicketybam says, review your shimming. I don't add any extra shims to my diffs when I rebuild them and have always left the rear diff at stock fluid weight although I up the the centre and front. I'm probably in the minority in that area I'm guessing. My logic is, and I could be wrong, is that the lighter fluid will help be a little more forgiving if I happen to land under throttle.....when I say it out loud it doesn't make quite as much sense but I'm happy to be living in ignorance for now and I haven't busted a diff yet

 

[slick2500]

Lol I thought it was YOU that argued with Ed ??????

No we just like to give each other a hard time.

 

[Outcastblxnut]

Hot racing bulk head and stock diff case shimed been working for me.

 

[Lazy Bushman]

Hot racing bulk head and stock diff case shimed been working for me.

Do you run a Tbone bumper with this diff casing?

 

[Outcastblxnut]

Nope rpm with hot racing hinge pin holders

 

[Yonic]

could it be that you went up on the center diff oil in July?

 

[Notorious J]

could it be that you went up on the center diff oil in July?

I went up back in winter almost right after I got the truck. The problem started a little over a month ago.

 

[olds97_lss]

I cooked my rear diff this weekend after 1.25 packs of run time. I had just removed it and replaced it with all new internals as well as the arrma alloy diff case. I also shimmed it the best I could for the ring/pinion.

I haven't taken it apart yet, but I'm 99% sure it's the ring/pinion again for me.

Last time a blown bearing took it out. So this time, when I first heard what I thought was a skip, I stopped, wiggled the input and diff to see if anything was loose and the bearings will still 100%. So I either have a crack in the case I'm not seeing, got a bad ring/pinion or I need to drop my punch down from 8. I had it at 5 or 6 when I started 6S, but it would hesitate bad and unpredictably up the face of jumps which caused a lot of bad landings.

 

[LibertyMKiii]

It might be worth the $9 to put in a new diff housing just to be sure some extra slop isn't coming from there...
When in doubt start fresh!

 

[Notorious J]

I cooked my rear diff this weekend after 1.25 packs of run time. I had just removed it and replaced it with all new internals as well as the arrma alloy diff case. I also shimmed it the best I could for the ring/pinion.

I haven't taken it apart yet, but I'm 99% sure it's the ring/pinion again for me.

Last time a blown bearing took it out. So this time, when I first heard what I thought was a skip, I stopped, wiggled the input and diff to see if anything was loose and the bearings will still 100%. So I either have a crack in the case I'm not seeing, got a bad ring/pinion or I need to drop my punch down from 8. I had it at 5 or 6 when I started 6S, but it would hesitate bad and unpredictably up the face of jumps which caused a lot of bad landings.

It might be worth the $9 to put in a new diff housing just to be sure some extra slop isn't coming from there...
When in doubt start fresh!

Sorry to hear that you had the same thing happen @olds97_lss. Not sure where the tolerances have changed, but definitely been an issue of late that I didn't have for the first six months of running. @LibertyMKiii, I have recently rebuilt the whole rear end with new case, cup, pinion and gears. I have narrowed down that the damage occurs more when bashing in the dirt and grass, as the skate parks I visited recently, didn't cause the same issue. First it was chipping the large crown gear on the outside of the cup, then I started cracking the larger planetary/sun gear on the inside of the cup. I did remove two shims at the recommendation of @bicketybam, but haven't had a chance to run on the dirt and grass since I did. I definitely don't want to go all aluminum because of the weight, so I'm sticking with the plastic gear box for now. Time will tell I guess.