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Old 05-01-2008, 09:42 PM   #1
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Default Losi XXX-T Differential solution?

Hello all, a bit ago I bought a novak gtb with a 5.5 velociti motor. So anyway, as soon as I mounted it all in the car, the differential slipped immediately. So I tried to tighten it a bit, and it would still slip on occasion, which gives off an extremely loud and annoying noise. I have broken about 4 of the differential screw nuts that are made of the weakest aluminum I have ever seen by the way, so that prevents from torquing it down very much.

So I am just curious if there is an after market differential that will fit into this with minimal problems. This ball differential just doesn't cut it with this kind of motor. I have rebuilt the differential numerous times. I see that the new Losi desert truck is going to have a planetary differential, which seems nice, but is unavailable since it is so new.

So are there any after market differentials out there that work well? Thanks.
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Old 05-02-2008, 01:11 AM   #2
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Maybe you are tightening the diff too much if you're ripping the diff nut. It can't be bottomed out, or it binds, that will cause problems. Be careful to not even bottom it out very hard when first tightening. It needs to be at least 1/8 of a turn away from any hint of bottoming out. Needs to be riding against the spring. If you have the version with the cupped washers they tend to lose their spring action. If so try the Monster diff screw set with a coil spring, it holds up better. And how tight is your slipper? It needs to be loose enough to slip before the diff. Some guys claim that overgreasing the diff balls/rings will cause issues, don't know myself.

Don't know about a gear diff, other than the new desert truck you mentioned.
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Old 05-02-2008, 07:07 AM   #3
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Like Dave said, you may need to loosen your slipper. I had to rebuild my xxxt CR's diffs a couple of times, and the last time I used less grease on the balls and loosen the slipper. I have had no problems with it since, and I was running a MM5700 in it for part of the time.
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Old 05-02-2008, 06:15 PM   #4
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Well that isn't the problem. I have messed with this differential in every possible way for the last 4 months.

I was just curious if anyone knew of some maybe aftermarket bolts or differential screws that were much stronger. Or possibly a whole differential that doesn't use balls that will fit into the xxx-t. Thanks.
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Old 05-02-2008, 08:04 PM   #5
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personally I'm waiting to see if the gear diff for the desert-t fits the xxxt. I am running a 3 star brushless and a 7.5 in my kids' xxxts with no diff slipping. I have them locked down pretty tight too. I wonder if there is something more going on that is not obvious.
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Old 05-02-2008, 08:35 PM   #6
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Is this the XXXT or MF2?

are you using the HD thrust bearing?
if you upgraded to the HD thurst bearing, you may not be getting your diff tight enough, you may need to add a 1 or 2 washers to each side side of the thurst bearing. usally one on each side will do, and this will get you back into the adjustment range , without over tightning
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Old 05-03-2008, 07:06 AM   #7
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The Speed-T has a locked diff, but I would guess it wont turn for poop.
Are you racing or bashing, if racing, you will probably want to stick with a ball diff. There are tons of people running that motor on all kinds of ball-diffs, with no problems.

When you said you rebuilt the diff, did you replace the rings, balls, thrust bearing? The rings get grooves,the balls can get flat spots
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Old 05-03-2008, 07:14 AM   #8
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The stock differential can handle your motor. Most likely there is something wrong in the assembly. Once you build the differential according to the instructions the break in process is very important. The differential should never slip. Loosen your slipper clutch so that it slips before the differential. It makes a different noise. You should never have to tighten the diff that it strips the nut. I've never done that before. Tighten the diff in very small increments. To check if it's tight, lock your slipper clutch by tightening it all the way. Hold the left rear tire and the spur gear securely and try to turn the right tire. If you can spin it, it's too loose. Tighten in small increments until you can't turn the right tire. As soon as you hit that point, you shouldn't have to tighten the diff further. You may have to re check it and repeat that process after you run it a time or two. Don't forget to loosen the slipper clutch back up. To check that hold the rear tires on the ground. Give the car throttle. The slipper will just slip as it sits there if it's too loose. Tighten the slipper in small increments until the front end of the car starts to lift when you apply the throttle. As soon as you can get the front tires to lift off the table, you're done. You should be ok after that.
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Old 05-03-2008, 09:51 AM   #9
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Great info Chris. I'm building the XXXT and the instructions don't give squat on adjusting the slipper. Just "loosen it 4 turns after adjusting the diff". For a newbie like myself with no experience, doesn't do me much good.

thanks.
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Old 05-03-2008, 09:56 AM   #10
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If your diff has been slipping excessively you will need to replace some parts. You will likely need new diff rings and diff balls. If the diff balls wear they become non-uniform in size. This will make it impossible to find a stable adjustment. It'll cost you about $15 to get these parts but it's worth it. Also, when you re-build, use as little clear grease on the diff balls as you can. Just a tiny dab on each ball.
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Old 05-03-2008, 10:26 AM   #11
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Quote:
Originally Posted by cantari View Post
Well that isn't the problem. I have messed with this differential in every possible way for the last 4 months.

I was just curious if anyone knew of some maybe aftermarket bolts or differential screws that were much stronger. Or possibly a whole differential that doesn't use balls that will fit into the xxx-t. Thanks.
What the above posts are saying is excellent advice. Get the slipper and diff adjusted and built right and it will hold up. Overtightening the diff is not the answer.
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Old 05-03-2008, 12:22 PM   #12
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+1

I had a 7700 in my MF2 and I ran it around a LOT with no diff problems whatsoever.

If you're killing anything, it should be the slipper, not the diff. I went through a few slipper pads and spurs (and washers...and covers...and...LOL...) before I got the hang of adjusting it. In fact, I never even rebuilt the diff once. It was really smooth the whole time and I ran it really hard.

Awesome truck.
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Old 05-03-2008, 02:26 PM   #13
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Are you certain you didn't miss one of the bearings in the diff? If you leave one of them out, you cannot tighten the diff properly. If you tore up aluminum diff nuts with the bolt, you were way to tight. The diff should be almost locked without that much pressure on bolt.
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