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Old 10-25-2008, 08:55 PM   #1
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Default Losi XXXT Tranmission failure

Help!

I installed a Castle Creations Sidewinder 4600 in my Losi XXXT and now I am shredding transmission and drive train parts like they are putty. I am only running with 6cell NiMH batts.

Here is my drive line setup:
19t pinion
86t spur
Transmission upper gear ratio 2.19:1
Diff gear ratio 2.43:1

I just bash around the yard, and take it to local track occasionally but do not race. I have some ditches around the yard that make for big air, so i am pretty rough on it, but have only broke 1 suspension piece (a ball stud). On the drivetrain I have destroyed a spur, 2 idler gears, and a blown out slipper shaft bearing which ended up trashing all 3 gears in the transmission with the loose bearings grinding around.

I have adjust the slipper so I cannot even pull a wheelie, but the trans is still not robust enough.

Any ideas on who to save my tranny, or at least get it to last more then 2 packs? Are there metal idler gears available?

I would also appreciate feedback on your favorite online parts stores. My local shop is nitro centric, and they do not have any hop-ups for this truck.
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Old 10-25-2008, 09:37 PM   #2
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if u stay on the throttle while in the air and land with the tires spinning that fast you'll tear up the tranny. u have to go to neutral while in the air . give it a try.
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Old 10-25-2008, 09:51 PM   #3
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i dont know much about transmissions besides how to rebuild them but im sure there is some sort of mesh movement between teeth. is there? i am familiar with that transmission. too much mesh, not enough?
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Old 10-25-2008, 10:06 PM   #4
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Agree that doesn’t seem right, properly built it should handle that motor with only occasional diff maintenance. If anything I would expect problems with the diff portion first, if it’s not properly tightened. Perhaps the top shaft bearing was failing before you realized it and caused some of the idler problems? Just a guess. How do you adjust your pinion/spur gear mesh? If too tight that might have caused or contributed to the bearing problem and possibly the spur. I don’t see how the motor itself should cause a bearing problem. What was the nature of your spur failure? What is the condition of the top/slipper shaft internal gear?
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Old 10-25-2008, 10:13 PM   #5
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P.S You mention 2 different gear ratios, 2.19 and 2.43. It has to be one or the other, and they must match the gear case. Could you have mixed parts? Would screw up the gear mesh, not good.
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Old 10-25-2008, 10:18 PM   #6
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Default xxx-t tranny

i have a xxx-t mf2 and i was doing the same thing.only i run the 7700 system, i finally settled on a medium punch control seting and i race and bash with my truck. and yes you will more than likely strip gear so stock up because the xxx-t hase plastic gears. hope that helps
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Old 10-26-2008, 04:21 AM   #7
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I have a theory I've never been able to prove but seems possible. If the slipper is slipping too much it creates a lot of heat. That heat gets transfered to the top shaft via the slipper plates. Since the top shaft is also the gear at the top of the tranny that gear is getting warm too which in turn softens the plastic idle/middle gear in the transmission. In simple terms, make sure your slipper isn't too loose. Just another thing to check along with the other great suggestions above.
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Old 10-26-2008, 05:32 AM   #8
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Look at the top shaft gear. If it is worn it will cause the idler to fail fast. If any dirt has gotten in the tranny with the alum. top shaft it will wear fast. If you have landed on the rear motor mount it will crack the tranny cases I have seen a couple people have a cracked case that was not noticeable but was causeing gear failure under power.
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Old 10-26-2008, 12:20 PM   #9
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Quote:
Originally Posted by Mind_Blower View Post
I have a theory I've never been able to prove but seems possible. If the slipper is slipping too much it creates a lot of heat. That heat gets transfered to the top shaft via the slipper plates. Since the top shaft is also the gear at the top of the tranny that gear is getting warm too which in turn softens the plastic idle/middle gear in the transmission. In simple terms, make sure your slipper isn't too loose. Just another thing to check along with the other great suggestions above.
I didn't see it mentioned above.
Make sure the slipper isn't too tight, if there is no slip at all, the diff and the gears get all the stress.
Lock the slipper, adjust the diff for no slip, then adjust the slipper to slip just a little.
I know, basic but worth mentioning.
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Old 10-26-2008, 01:58 PM   #10
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Default throttle and gear mesh

I think I may be under throttle on some of my jumps. The truck noses down to much if not. What is the best way to keep correct attitude in jumps without throttle. Should i stiffen up front suspension to give more front end lift at take off?

What is the tranmission ratio for stock xxx-t? I have the 2:19 kit for slipper and idler gear, and I have the black diff gear. I have not figured out what its ratio is? Does anyone now the teeth count for the 3 gears to have matching sets?

The original problem was the blown bearing which cause wobble in the slipper shaft which caused the spur to get worn by the pinion, and the loose bearings in the tranmission damaged all 3 gears. I replaced them all, and now just have the problem with stripping idler gears. Probably a combination of on throttle landings and incorrect gear size.
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Old 10-26-2008, 02:40 PM   #11
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I think you have the wrong gear if it black. You need a LOSA3079 idler gear for the 2.43 tranny, 3036 for the diff and 9930 for the Alum top shaft. They make a steel top gear also.
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Old 10-26-2008, 05:32 PM   #12
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I regularly race a XXX-T MF2 and had ZERO trans gear problems.
I run a 7.5 orion motor/GTB with a NEU lipo.
my guess is that you lock your slipper and diff down so the only drivetrain shock is put on the gears. thats why you keep trashing the gears,
the slipper should be taking the brunt not the trans gears.
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Old 10-26-2008, 06:20 PM   #13
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is your diff tight that may be the problem, i never had problems with my protruck xxx-tcr with a 7.5gtb and lipo in 20 minute mains
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Old 10-26-2008, 10:46 PM   #14
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If you think the gear mesh inside the trans is wrong, it should be VERY obvious before you put the second case half on.
If the mesh is correct, the only thing you should need is the proper diff and slipper settings.
After the diff setting tips above, make the slipper really loose and tighten it a little at a time til the front wheels barely lift off the ground while you hold the rear wheels to the ground and punch the throttle quickly.
If you get this right you will not strip any gears.
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Old 10-27-2008, 12:40 PM   #15
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If you have a black diff gear you probably have a Sport version of the truck.. and it is a 2.56:1 ratio... black tranny case... Same gear now as the XXX-T CR.

If the tranny case is grey.. XXXT-MF2 then the ratio is a 2.43:1

The 2.19 top gear was from the XX Buggy tranny and did convert over to one of the newer trannies.. just cant remember if it was the same as the GenI or GenII...

If you have the correct gears... there really shouldn't be a gear stripping problem if all the parts are not overly worn. Tranny cases DO wear as well and need replacing periodically.

If you are on an off-road track.. this should never happen.. if you are bashing on the street and landing at full throttle and doing a lot of burnouts and speed turns... ya.. you are going to stress that off-road race truck and break gears...

The diff also needs maintenance to keep it properly lubed.. and if it cant slip because of lack of lubrication or being locked down.. it will stress the gears and break as well.

Good luck!

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