I haven't actually cracked a diff case yet, even after 2 gallons of fuel, but I was inspecting my diffs for cracks and came upon something. The diff case rim around the cvd cup has been chewed up pretty badly. It appears that the set screw in the cvd cup is rubbing the case at certain times . There is a little play in the diff when I tug at the cvd, which could possible allow the set screw to hit the rim and break off small pieces at a time. This would weaken the diff case and possibly be the cause of many peoples diff cases breaking. If it hit hard enough, it could possible rip the whole section apart. I have seen pictures of peoples cases where this section has broke off.

Here are some pics;










And just for comparison, here is a good diff case rim;





Now, I'm not saying that this IS the EXACT reason why people are breaking their cases, but it's definately a possibility. I'm also not sure how to correct it. Maybe if you dremel a about 1/8 inch off the rim of the case it would keep the set screw from rubbing the case.

Jefx i think this is in line with what i said in the other 3 from 3 thred, the main chassis plate flexes up and down a lot when under brakes. if we can stop the flex it may stop the screw rubbing also. this may be why the front diff is giving the problem. i think we have to find what is causing the problem not just fixing the result. i think your hedding up the right path.

Well, i dont think my set screw is rubbing the case like that. I never got out to send this diff case to Bill today, and im not really in a hurry anyway. I'll break open the box, and inspect it, and take pics. BRB

Turns out my set screw was a little loose, I don't know how I didn't lose it like that, but I didn't.

Maybe that was the cause for the chewed up case. As you can see in the first pic, the set screw is riding right under the lip of the case. If there happened to be any dirt flying up in that area while driving, it easily could have helped in the grinding condition.

After I re-tightened the set screw, it wasn't riding as close to the case.

Could the whole problem be as simple as loose set screws?

Not with mine. I red loctite every CVD screw. Im uploading pics right now. I think some people will be shocked at how clean this diff case is. No sign of wear at all. Just the cracks.

Check this out. First pic i want to show you is that edge thats chewed up on yours. Mine is spotless. I am however glad you are wrong about that. Id be really pissed off to put aluminum cases in this, and see my case chewed up like that.


Next pic, an slightly different angle. You can see this diff case was not run long at all.


Heres a pic, where you can see the crack. This crack runs from front, near the pinion, to the back half.


Here is the crack from the inside.


Another from the inside.


I really wish i could just throw a diff case in here and run it a while. But im gonna be really annoyed if i put a plastic case in here and it breaks again. I sure wish Bill at Losi would see these.

Thermal,

One thing that could have caused the diff case to crack like that is a combination of minimalist design, an over-tightened screw, and poor gear mesh (causing backlash and hard hitting outward forces).

You could be right on the gear mesh. The gear mesh is very tight between ring and pinion. As far as over tightening those screws. Not gonna cause it. You would have to see how TINY these screws are that hold it together. Im sure at the mere thought of over tightening them, id have a stripped diff case. The cases are VERY thin. I might buy another tomorrow, and try my luck. Expect me to be a raving lunatic if i blow another front case. I really dont even wanna bother with the truck until my aluminums come in.

My over-tightened screw theory came from the diff case cracking straight through the screw hole.

With any luck, the problem is gear mesh, and can be corrected by taking your time and adjusting the back-lash when you drop it in the new case.

Well, there just simply isnt any way to change the setup. Shimming this would only make it tighter. I just put a new diff case in the truck today. I certainly hope this one lasts longer. Time to take it out and fire it up.

can the whole thing be coated in layer upon layer of CA glue maybe? I'm sure with enough coats and a thick enough layer formed that case would be indestructible. If you can use 2 part epoxy or household Goop if you want the cases to flex, I'm not sure if that would be good though.

Another though would be to coat it in PVC cement, it's thick and would probably do a good job of adding structural integrity to the thin plastic. It may not be pretty but until some stronger aluminum cases can be built it's the next best thing and keeps you running.

I just put a new diff case in today, 4 tanks later and some hard breaking, (I just could not resist testing it) it is still fine. I am racing tomorrow so that will be a good test. Tomorrow I will either be posting under "who loves the LST" or "LST piece of sh**!!"

Good to hear it man. I couldnt resist either. I put one in mine today, and went out to play. So far so good. Tomorrow i'll have more run time on it.

Just for the record. I took my diffs out to put on the aluminum diff cases. The front top diff case was visibly cracked and split. The rear top diff case was cracked in the exact same spot as the front. It was only visible from the inside and not cracked completely through yet. Glad I got the aluminum ones. Even if they aren't machined.

were you running diff oil in them or regular old grease?