Diff cases wiggling inside bulkheads on Summit

[fyrstormer]

The axles on my Summit started squeaking, and while I was finagling them so I could oil the CVD joints I noticed the outdrives were able to wiggle back and forth. I removed the axles from the outdrives, and it appears the diff assembly is solid, but the entire assembly is able to wiggle inside the bulkhead. This is more noticeable on the rear diff than the front diff, which makes me wonder if something is wearing out or coming loose.

Normally I'd just dig in and see what the problem is, but the Summit's bulkheads are so complicated I'd rather not take them apart unless I know for sure that 1) This is actually a problem, and 2) How to fix it.

Help?

Nevermind, answered my own question. The diff is fine, but it's been wiggling inside the bulkhead for so long it's started to wear down the plastic inside the bulkhead. Looks like I'll be buying a hot-glue gun today.

That's never gonna move again.

[BlackIce05]

Glad you have this up, even if you answered your own question. I happen to have my summit in pieces right now since I destroyed the rear diff. Looks like I could do the same thing to keep it from working loose in the future. Thanks for the idea.

[fyrstormer]

I think the idea came from the Traxxas forum, but you're welcome that I reposted it. ;)

For the record, I bought a dual-temperature hot-glue gun, set it on the high setting, and put several dabs of glue in various places under the diff before inserting the diff into the bulkhead. There was no way to show the glue under the diff, though, so all you get is a picture of the glue on top of the diff.

What did you do to destroy the diff? Mine felt pristine after months of use; as long as I had the bulkhead off, I pulled the diff out of its case and examined it, and couldn't find any roughness in its operation.

[BlackIce05]

I'm fairly new to the hobby so I'm guessing it was a combination of user error and a lot of torque, but I have read about people having issues with the summit diffs. Basically, every gear inside the diff cup was missing over half it's teeth, the metal block between the spider gears was broken in half, and the plastic diff cup had rotated on the ring gear which pulled the screws out the side of the cup. Oh and the cup itself also has a big crack down the side.

[fyrstormer]

Yeah, that definitely sounds like too much torque. Are you still running the stock motor? Is your slipper clutch set so it can actually slip?

[BlackIce05]

nowhere near the stock motor, I have a Tekin 2250kv on it, and yes slipper can slip when it needs to. I figure it was mainly the bigger motor and bigger than stock tires. I put a set of mudslingers on it.

[fyrstormer]

Yeah, that's probably why. Especially in low gear, where the amount of force the slipper clutch can transmit is multiplied by the lower gear ratio.

[BlackIce05]

Yep, put that stuff on fully expecting to break a few things, and I was not disappointed, but it sure is fun to watch that thing go.

[fyrstormer]

Perhaps you should consider an E-Revo with long-travel rocker arms? There's less stuff to break on that vehicle.

[BlackIce05]

I did, thought real hard about it, but wanted the 2 speed tranny and locking diffs from the summit. I think once I put the aluminum diff cups in. I should be in good shape. About the only time I break much on it now is if I wreck it. Don't get me wrong, I'm not complaining about breaking stuff, it's bound to happen with that motor and me learning.

[twissted]

The trick if your looking to beef up your drivetrain is to use Losi LST diffs. you have to use a dremel to make them fit but they fit. I use Silly puddy to lock the gears up.
Glueing in your diff is only going to cause problems when you need to work on the diffs later on. If you need to shim the diff hot glue would be a good trick if you oiled the diff case and set it in the hot glue so that it didn't move but able to be removed when needed.

[twissted]

I went even farther and built the ULTIMATE rc buggy using the best of whats out there and came up with the Summit tranny, Losi LST2 chassis stretched 4'' using carbon fiber chassis plates top and bottom with 1/5 bead lock wheels mounted to RC4WD 40 series tires. Now it's easy to work on crawles great and doesn't break all the time. The best part is it looks great using the Yeti XL cage and body panels.

[BlackIce05]

I looked at other diffs a little, but haven't seen any that lock and unlock like the summit diffs. Granted you can lock it with the puddy, but the locking and unlocking diffs were half the reason I chose the summit over the E-Revo.

[twissted]

I added a pair of hitec 7954 servos to get 800oz plus of torque so that turning isn't a problem.

[fyrstormer]

Originally Posted by BlackIce05

I looked at other diffs a little, but haven't seen any that lock and unlock like the summit diffs. Granted you can lock it with the puddy, but the locking and unlocking diffs were half the reason I chose the summit over the E-Revo.

Exactly. A Summit without locking diffs is just a pointlessly over-expensive E-Revo with lifted suspension.

I'm running the stock brushed motor, which I may upgrade to a DeWalt motor in the future, but for now the stock motor is hanging in there like a champ. Either way I'm not putting tons of power through the diffs, I still have the plastic axles to act as sacrificial parts to prevent over-torquing the diffs and breaking the internal gears, and the diffs are stuffed with grease instead of silicone, so the gears are actually properly lubricated. (silicone is not optimal for metal-on-metal contact, but it's used in RC diffs anyway because it can be made thick enough and sticky enough to provide limited-slip action.) I don't need limited-slip diffs in my Summit, because I can just lock the diffs when necessary, and that eliminates any need for me to run inferior lubricants inside the diffs.

In other words, I don't foresee needing to service the diffs any time soon, and if I can't get the diffs apart, I can always just buy whole new diffs and new bulkheads to go with them. Might not be a bad idea either, since I could see some wear and enlargement of the spots inside the original bulkheads where the diffs are supposed to anchor themselves.

[fyrstormer]

Originally Posted by twissted

I added a pair of hitec 7954 servos to get 800oz plus of torque so that turning isn't a problem.

What kind of steering mechanism are you using that can handle that much torque? I know for damn sure the stock Summit/Revo steering mechanism won't transmit that much torque, the servo-saver unlocks way before that.

[twissted]

Awe now your asking the right qustions. I Have a custom build that uses the Summit Transmission and a stretched 4 inch LST chassis that uses duel servos also. I uses a single servo in my stretched Summit that 480 oz. of torque that is a HV Hitec also.

[twissted]

As for locking diffs I use the lock mode 98% of the time with the summit diff that use the LEM diff cups. It is a waist. The tranny is what I really like.

[fyrstormer]

I definitely lock and unlock my diffs more than you do. For me, the remote diff lockers are much more valuable. I have my Wraith for hardcore crawling.

[BlackIce05]

I would estimate I run mine unlocked 80% of the time and only lock them when I need to, but would hate to lose that option. I changed mine to a single futaba 425 oz servo and love that so much better than stock, I can't even imagine how the 2 400's do.