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Old 12-24-2008, 06:20 PM   #1
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Default xxx4 breaks rear diff

i have the vxl brushless in my xxx4g and i just keep ripping the rear pulley of the rear diff. i'm sure other ppl have had this problem. how is it being corrected? i'm about to jb weld the front and rear diffs solid cause locking just the rear would give me to much fish tail.. plz help! thanks and merry christmas!
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Old 12-24-2008, 06:33 PM   #2
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Hold up there with the JB Weld! You will do more harm than good with solid front and rear diffs. What kind of damage are you doin to the diff pulley? Meltdown between the outdrives? Then the diff is set too loose. Blowing the teeth off of the pulley? Then the slipper is too tight. Check these areas first.
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Old 12-24-2008, 06:40 PM   #3
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the pulley seperates from the bearing housing no matter how tight or loose. its only lasting maybe 5 hard pulls. i figured if i just jb welded the whole pulley and then the pully to the diff it would hold up..lol. i didn it with my drift car and it worked fine.
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Old 12-24-2008, 06:54 PM   #4
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Bearing housing? Do you mean it separates at the holes where the diff balls go? If so then your diff is too loose. The diff should be set so it has smooth diff action, but the pulley should not be able to slip between the outdrives. Also, the slipper clutch could be too tight. Remember the slipper is the shock absorber for the drivetrain. If it doesn't slip slightly the shock is transferred to the rest of the drivretrain. Chrck this out.

http://www.racers-edge.com/1_10_DIFF..._p/rce7030.htm

This tool is used to check the tightness of the diff. Slip the tool into the slots in the outdrives with one hand, then try to spin the pulley between the outdrives. When you pick up new parts for your diff rember to pick up a new diff spring. Even tho it may look ok, the excessive heat generated by the slipping can weaken it.
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Last edited by SpraydbySprague; 12-24-2008 at 07:15 PM.
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Old 12-24-2008, 10:55 PM   #5
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If you are using the original xxx4 diff nut style, be sure to change the locknut every time you rebuild it. If you reuse it, it could come loose very easy.

I have run my XXX4 with my GTB even with a 3.5bl and the diff was fine.

Are you running it on dirt or on the street?


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Old 12-25-2008, 04:13 PM   #6
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no matter how tight or loose it still breaks the pulley.. it's gettin jb welded tomorrow. i dont care anymore. broke the 4th one today and there only lasting not even a minute..
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Old 12-25-2008, 04:19 PM   #7
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No offense but if you've broken 4 of them then you're doing something wrong, find someone that has a xxx4 or has built a ball diff before and have them help you.
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Old 12-25-2008, 06:14 PM   #8
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y would it break even if it was loose?? explain that 1
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Old 12-25-2008, 06:23 PM   #9
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Quote:
y would it break even if it was loose?? explain that 1
Parts spinning against each other (diff balls against diff ring) create heat and melt out the center of the plastic pulley.

Given the details we have so far, I must ask, "Are there 12 diff balls between the 2 diff rings, sitting caged in the big white pulley holes?"
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Old 12-25-2008, 06:31 PM   #10
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missing 1 or 2
i understand the heat but its just breaking sooo fast i dont see it having a chance to heat up
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Old 12-25-2008, 06:57 PM   #11
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Quote:
Originally Posted by StampedinIT View Post
missing 1 or 2
There's your problem!
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Old 12-25-2008, 11:06 PM   #12
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Originally Posted by StampedinIT View Post
missing 1 or 2
i understand the heat but its just breaking sooo fast i dont see it having a chance to heat up
WOW. Let me guess, you ran the car with the diff loose, it heated up and came appart. Then when you went to replace the pulley and lost a couple diff balls. Then you put it back together without the balls and wonder why the pulleys keep coming apart? When the diff is missing a ball or two it puts more stress on the rest of the balls therefore the pulley is overstressed and thus it breaks. You know there is a reason that things are designed the way they are. You think the engineers over at Losi just threw all them balls in there for no reason? If your car is missing some parts, then replace them. I have been doing this hobby for almost 20 years, and only in the last 5-6 years have I got to the point where I can look at a new car and say, "This new car being designed like this is gonna cause the following problems, this needs to be done to fix the problems." I don't think that I have ever said "Hmm this diff doesn't need all them balls." The rear diff of a 4wd mod car sees alot of stress. It needs to be built exactly as it was designed. Then after you put it together correctly, you need to tighten the diff just as much as it takes to not slip. Now you need to break the diff in. Drive the car around for a couple of minutes, being careful to not accelerate to hard. After you have drove the car around for a little bit, retighten the diff. If you ever hear a barking kind of noise coming from your car stop it immediately and check to see whats wrong. Here's a little math. The material that the pulley is made out of can only take 100% of the stress it can handle. (obviously) So 100% divided by 12 balls means that at the breaking point of the pulley, each ball is seeing 8.33% of the stress. Now if we take two balls away, (like you) each ball then must take 10% of the load. Thus it doesn't take as much stress to break the pulley. This coupled with the fact that the pulleys on a XXX4 are so big, it puts more stress on the area where the balls go because the pulley has so much more leverage. So I guess what I'm saying is, put the car back together with all the parts, and build it and adjust it according to the instructions and you should be fine. Remember this is not the gear diff in your Stampede.
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Old 12-26-2008, 06:53 AM   #13
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ok.. ima go to my 2 lhs at see what they have in stock.. and yeah if it WAS my stampede diff i definatley wouldn't have any problems.. lol. i actually built that one right.
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Old 12-26-2008, 09:31 AM   #14
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dude take it to your lhs and have thrm check it you have the shims in there check it all if you lock both diffs thats bad with a drift car well thats a hole differnt anmial differnt set up check it first i run a mamba max and it screams no problems
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Old 12-26-2008, 01:23 PM   #15
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got all 12 diff balls in there and just went out and was racin it and it was all good. i really didnt think it was gonna be that bad with out a few.. learn something new everyday i guess...
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