What am I doing wrong? (XXL Diff question)
 

Since I've owned my XXL (roughly two years), I've had more than my fair share of diff issues. Usually, the rear diff blowing up. I just upgraded to TiNi diff ring/pinions, with Hot Racing aluminum diffs, and just yesterday, again, I blew up a rear diff.

I haven't disassembled the diff yet, but I can tell it's pooched. Lift the rear tires, turn one, and the other one locks up, diff goes "crunch crunch crunch" -- You know what I'm talking about...

So, here's my question... I know the diffs are shimmed well, with little to no play. I've tried many different diff fluids (from grease - 50K) and had issues with them all... I'm starting to think my slipper is too tight? I mean, if I hammer the gas, I'll wheelie all day (4S, 25C LiPo, MMM 2200kV), so I know the slipper is tight, but is it TOO tight???

I've noticed that when I land a jump (from one foot, and higher), if my rear wheels touch down first, I can hear a bit of a "crunch" or "grind" noise come from the rear end. I can only assume that this is my rear diff binding up under the load, but am I the only XXL owner that has this problem? I've heard of guys running stock diffs, NO problems, and me, I seem to go through one every couple batteries... Help a guy out! :)

First I would leave the stock diff housing, they are better than the hot racing diff casing. I ran in to some diff problems with my MMM 2200 on 5s with trenchers, but I have them pretty much figured out.
Do you have the high torque/friction slipper pads?
Is it the bevel and spider gear or the ring and pinion that keep stripping?
Are you on the throttle when you land?

I did put a shim or two under the pins in the diff, and my slipper is pretty loose.

I was wondering about on throttle landings, too.

Another thing you might want to try is getting the castle link software and increasing the punch control settings. That can help reduce some of the stress.

I have mine set to 50%, I can still wheelie on demand on 4s in my Revo.

Ring and pinion, or spider gear issues?

Definately do your best to not land on the throttle. Brushless has a lot of torque and it is hard for the diff to stand up to an on throttle landing.

If your ring and pinion gears are stripping, try shimming them if you arent.

Loosening the slipper would definately help, but then if you get it too loose you have lost your acceleration and wheelies and will be burning slipper pads.

This is the best LST diff rebuild thread ever.

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

Run 15,000 fluid and HPI hardened pins under the sun gears, HD cups, HD oudrives. Follow the rebuild thread and your issues will clear up. I run my slipper really tight and with that set-up I rarely break diffs anymore. i also run my Punch controll at %80 with the castle 1800 KV.

I've used the XXL diff casings, as well as the HR aluminum casings. I've had issues with both... I do not use the high friction slipper pads, just the stockers. I've had issues with the pinion gear wearing, as well as the bevel, and spider gears.


I followed this rebuild thread last year when I went through my diff-rebuild phase. Followed to a "T", and I'm still having some issues. As I said before, I notice a "crunching" or "grinding" sound when the back tires land off a jump.

Pick up the high friction slipper pads, you have to run the stock ones so tight you basically don't have a slipper.
Also, check your cvds, mine started to crunch and it was because they were breaking.
I've been using 5k diff oil with out a problem.

Sounds to me like your slipper is too tight.

Agree. Loosen the slipper up a bit. It isn't supposed to be locked. Otherwise, turn the punch control down on the ESC and don't land a jump under throttle.

I finally grenaded my XXL's rear diff after tons of running. I did tighten the slipper too tight so that's on me.

The diff may be too tight, but if you hear a crunch when landing. Its probably because you still into the throttle. the diffs wont last long under that brushless torque doing that. I went thru 2 nitro engines....worn out! and never took out a diff. Still have that bugger , just does use it anymore. But I almost never came down on the gas. I may be into it within milliseconds of hitting the ground, but with the wheel speed these things get to, to do it under power is extreme shock to the gears in that diff.

I'll definitely try loosening up the slipper some... I've had these diff issues when the rig was nitro (95% of the time I've owned it) so I have a feeling it's not just BL related...

If the issue persists, I'll look into the High Friction slipper pads, but at this point, I'm leaning towards the slipper being the problem...

So another question... When correcting the truck in the air (assuming I'm nosing down, hard...) I'll have to stomp the throttle to pick the nose up. I definitely don't land with the gas hammered, but I'll let off the throttle just before the tires touch down. Is this cool? Or is this adding to my problem? Should I be letting off the throttle MUCH earlier than juuuust before my tires touch down?

Does it tend to come down nose heavy? Sounds like a weight distribution issue. Never ran mine brushless. But as Nitro it always wanted to land level, or if I hit a jump on the throttle it would be nose high. It was easy to do back flips. If it always comes down nose first, I'd see about moving batteries back if possible. I would typically let off the gas as I hit the jump. If your having to stay into the gas to keep the nose up, its a weight thing or maybe try stiffer front springs. But yeah, landing with the wheels spinning real fast is not good on diffs.