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  1. #1
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    Exclamation Broken rear diff the third time

    Hi All!
    I’m facing a serious problem about my SUMMIT’s rear differential. It was broken the third time now. I really don’t drive very aggressive or do something like bashing with it. I just installed a mid range BL system made by KD (850W). I investigated that the problem is always about the ring gear and the pinion gear inside the differential. While driving first a clicking noise appears. If I continue driving the tops of the tooth of the gears will be sheared-off.
    The first time I faced this problem it was caused by a broken bearing inside the differential housing that pivots the pinion gear. Thereby it could slip back some small tenth of a millimeter so that the gears did not mesh properly anymore. Substituting the bearings with a full metal one solved that problem for now. Anyway I had to substitute the complete differential housing because the broken bearing and the tooth parts were scattered all around the housings.

    But after repairing the differential was broken again a similar way. This time the substituted bearing is well but the ring gear was loosen from the inner differential housing (5681) because the threads were destroyed. Again the meshing between ring gear and pinion gear was out of order and the tops of the tooth of the gears were sheared-off. So I replaced all the parts again, as it were a complete new differential (including the full metal bearing).
    Not fine again! This time I stopped driving the second I realized the first small clicking noise. The noise tells me that the meshing is bad again. What could the reason be? Is the differential housing (5680) deforming itself by a power of 850W? Or is the differential carrier (5681) to weak?

    Now I think about installing the rear differential from a brushless E-REVO to my SUMMIT. It should stand the power of 2200W. Sure with this I can’t lock the rear differential anymore but an unlockable diff is worth more than an broken one. Does anybody know about a suitable differential made of metal?

    Thanks for your answers!
    Last edited by CAPITA; 12-03-2009 at 10:36 AM.

  2. #2
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    my first thought loosen the slipper clutch a little bit.it sounds like the brushless is overpowering the drivetrain and somthings gotta give.I myself have not had this problem as mine is stock.I have broken teeth off of rear spider gears.I loosend clutch a bit so far so good. somone here will have the answer.I read on here that some people were shiming the diff's. this might be the reason too mmuch power for the factory tolerances. check the revo forum i think it was a thread on there search here too
    Last edited by jamann; 12-03-2009 at 12:32 PM.
    Mountains cant stop me
    they have tried

  3. #3
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    Hi jamann,
    thanks for your advise. I already did loosening the slipper clutch sufficient. I spend more than half an hour to figure out the best settings between safety and fun. Now my setup does not allow wheelies anymore. That tells me that there is no more overpowering of the drivetrain possible.
    I wonder how the drivetrain of a brushless E-REVO braves the power od 2.2KV!?

    Thanks
    CAPITA

  4. #4
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    i would leave the diffs always unlocked...Ya i know defeats the propose of having lockable diffs ..but try that for a few runs..and also try and shim the diff it helps a lot with the gear mesh ...another option is to get some quality bearings like some acer ceramics ..you don't need the whole set of them for the whole truck just the diff bearings B/c the stock bearing's even new will have a bit of slop in them and cause the gear mesh to have a bit of gear slop....but if these tricks don't work ..go with the some e-revo diffs they have less moving parts there for stronger and less things to break
    Last edited by Notin_but_aRevo; 12-03-2009 at 02:09 PM.
    I know you wish you bought a tekin RX8

  5. #5
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    I just answered a question like this somewhere, not sure if that was you..

    The Summit and E-Revo diffs are nearly identical, outside of the locker assembly added onto the side.
    Yes, you should shim the gears closer so they are meshed together tighter.
    I've been running the Castle MMM/2200 in my Summit and have not had any issues at all with the differential since shimming it (I also replaced the pinion bearings with ceramic ones)

    Click here about shimming diffs:
    http://monster.traxxas.com/showthrea...hreadid=267016

  6. #6
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    Red face Shimming a SUMMITs diff

    Thanks again!
    Shimming seems to be a hopeful solution for my problem. I just have to get shims in Germany to proceed. I already thought about that. The thread ďHow To: Tmaxx Diff Shim ModĒ should be helpful basically. But the SUMMIT diff housings are split 90 degrees different to the shown MAXX diff housings. Hence the pinion gear is covered when the inner diff parts are mounted. So I think itís difficult to find the proper setup. How do you figure out the optimal shimming? Turning the pinion on a complete mounted diff just with your hand feels rough-running. You can feel every single tooth while turning. Is there a way to measure exactly? How do I test? I mean without destroying gearings again.

    Cheers CAPITA

  7. #7
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    Quote Originally Posted by CAPITA
    Thanks again!
    Shimming seems to be a hopeful solution for my problem. I just have to get shims in Germany to proceed. I already thought about that. The thread ďHow To: Tmaxx Diff Shim ModĒ should be helpful basically. But the SUMMIT diff housings are split 90 degrees different to the shown MAXX diff housings. Hence the pinion gear is covered when the inner diff parts are mounted. So I think itís difficult to find the proper setup. How do you figure out the optimal shimming? Turning the pinion on a complete mounted diff just with your hand feels rough-running. You can feel every single tooth while turning. Is there a way to measure exactly? How do I test? I mean without destroying gearings again.

    Cheers CAPITA
    the best way to find out what the optimal shimming is. is just to experiment since you may need more of less shimming based on your diff.....you want the gear mesh to be a close as possible without causing binding.just check for binding by spinning it will your hands after its been reassembled
    I know you wish you bought a tekin RX8

  8. #8
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    Correct.
    I shim the ring & pinion gears until I can just feel an occasional very slight bind on one or two gear teeth per revolution as I turn the gear. This slight bind will completely go away when you run it for the 1st time (you want the gears to stay as tight as possible).

    For the spider gear shims, I cut home-made shims out of that clear hard-to-open plastic packaging that electronic gadgets often come in (the ones you have to use scissors to open), and I install these shims behind the steel U-shaped thrust plates behind the spider gears. This will help the inner differential itself hold up better as well.
    Typically such packaging material is around 0.2-0.4mm thick and works well for this.
    Last edited by sfr4x4; 12-04-2009 at 08:50 PM.

  9. #9
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    shimming the rear diff/how 2 test?

    Thanks again Guys!
    Iím afraid this would have been my next question. Iím afraid I didnít understand every term quite correct. Maybe itís because my bad English.
    Since I donít have any shims jet I only can care about the inner diff parts. I never thought there would be a need to shim the spider gears. But there is, as I realized while demounting it again.
    I mounted the inner diff parts (5681) very carefully and exactly like it is shown in the drawings by TRAXXAS. Still without any shims but using the diff oil offered by TRAXXAS. Here is the next problem: The completely mounted inner differential is very hard to turn with your hands. Maybe itís also because the diff oil comes with a pretty high viscosity. But you can feel every single teeth while turning the differential outputs. Is this normal?? sfr4x4 wrote ďuntil I can just feel an occasional very slight bind on one or two gear teeth per revolution as I turn the gearĒ. Does that mean it should feel really smooth-running except some very small bugs once per revolution? My diff is really hard to turn with the hands and you can feel every single teeth. How could this be and what should it feels like? Pleas advice!!

    Cheers
    CAPITA

  10. #10
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    Hi,I did this to my T MAXX ,the internal screws came loose,I've had no problems with my summit diffs.I always slow to a "crawl" to lock diffs.My trucks standard at the mo(tried kershaw 970 but it CAUGHT FIRE),Oh well back to basics

  11. #11
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    Quote Originally Posted by CAPITA
    Thanks again Guys!
    I’m afraid this would have been my next question. I’m afraid I didn’t understand every term quite correct. Maybe it’s because my bad English.
    Since I don’t have any shims jet I only can care about the inner diff parts. I never thought there would be a need to shim the spider gears. But there is, as I realized while demounting it again.
    I mounted the inner diff parts (5681) very carefully and exactly like it is shown in the drawings by TRAXXAS. Still without any shims but using the diff oil offered by TRAXXAS. Here is the next problem: The completely mounted inner differential is very hard to turn with your hands. Maybe it’s also because the diff oil comes with a pretty high viscosity. But you can feel every single teeth while turning the differential outputs. Is this normal?? sfr4x4 wrote “until I can just feel an occasional very slight bind on one or two gear teeth per revolution as I turn the gear”. Does that mean it should feel really smooth-running except some very small bugs once per revolution? My diff is really hard to turn with the hands and you can feel every single teeth. How could this be and what should it feels like? Pleas advice!!

    Cheers
    CAPITA
    If there are no shims in it, it should turn very easily. It's likely just because of the thick oil.
    What I do is assemble the diff without the oil to test for tightness of the gears (feeling for that slight bind between the gear teeth, indicating they are as close together as they can go). Once I've found just the right amount and thickness of shims, then I fill it with the oil, and reassemble it.

    If the bind is about equal between all teeth, then that's fine, as long as it's very slight. The ring & pinion gears will normally have one or two teeth that "bump" against each other a little more than the others. Nothing to worry about as long as you can still easily turn it by hand.

    Hope that helps clarify.

  12. #12
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    Could someone please post the shim dimension ie shaft diameters.

  13. #13
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    I measured the pinion shaft as 6 mm. That would be the inner diameter. The outer diameter can be between 8 and 11 mm I think. It doesn't depend since they run between the pinion gear and the inner bearing. There is enough space. Shims use to come with 1/10 mm thickness.

    Cheers
    CAPITA

  14. #14
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    ^Thanks!! I decided not to push my luck with the Tekin onboard.
    I'm switching out the bearings as well; did you use the ceramic ones ?
    They are not supposed to be sealed I guess??

  15. #15
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    Bearings

    From my point of view it's not necessary to replace all of the bearings. The most charged bearing is the inner one that pivots the pinion gear. It has to stand a lot of axial forces.

    I thought about using an axial bearing but could not find a proper one. So I took a metal one of the same dimensions and it works fine so far. It doesnít matter if it is not sealed because itís inside the diff housing and in oil at the same time. For all outer bearings it would be useful to be sealed.
    Cheers
    CAPITA

  16. #16
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    Nice info there thanks again.

    Have you ever though of filling 20-30k oil instead of the 50k?
    I'm buying a bottle soon that's why I wonder. I crawl occasionally only, and that 50k oil seem to be very sticky!
    Stock Summit minus Tekin/2.4Ghz

  17. #17
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    Hi Guys,
    finally I did the shimming. It looks good so far. First I shimmed the pinion gear. The first test driving in our basement garage feels good. Even the slipper setup looks optimal now. No wheelies from stop, but using full throttle while moving the front wheels lift up. Lets wait and see how long it lasts this way. Actually we have lots of snow and -15įC outside. Not the best conditiones to empty 4 sets of batteries. But I will tell you the minute I've done more tests.

    Cheers
    CAPITA
    Cheers
    CAPITA

  18. #18
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    i know its an old post but i to having problems with rear diff. i think its caused by the blue rubber o- ring wearing out and causing problems with the mesh. i wish some one would make a 1/8 scale diff for the summit.

  19. #19
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    Hi Russ!
    I would like one too!
    Looks like youíre facing the same problems as me. Surely you have read the complete tread. For me it helps to do like the others advised. Especially the shimming has caused a good effect so far.
    Cheers
    CAPITA

  20. #20
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    The o-rings are seals, they don't affect the gear mesh.
    You have to move the gears closer together by putting shims behind the gears/bearings.
    Also, pack your new bearings with some automotive wheel bearing grease. They don't always have much (if any) grease in them it seems (leading to them wearing and then spitting all the little balls out).


    Quote Originally Posted by Jimmy_R
    Could someone please post the shim dimension ie shaft diameters.
    6mm.
    Last edited by sfr4x4; 03-09-2010 at 07:06 PM.

  21. #21
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    ^ Thanks ! Well I have sorted the diameters out and would share this:






    Shims goes to those pointers; this is where the bearing are seated.
    Stock Summit minus Tekin/2.4Ghz

  22. #22
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    well as i said and as you can tell, the distance from the back side of the gear and the bearing is the place that a shim would go. if i put together a dry gear assembly w/out the o ring there is allot of "slop". with it there is hardly any. if you tried to shim with the o ring its to tight. Very quickly the o-ring wears and changes the distance between the bearing and the back of the gear. all i am saying is the o-ring should not be used if you want to keep a contestant shim in the diff.

  23. #23
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    Russb442:
    That rubber is very soft; what about some "black ordinary o-rings" they might last longer?
    Would the grease escape, without those blue rings, as you indicate could be done?
    Just curious cause I'm putting mne together now.
    Stock Summit minus Tekin/2.4Ghz

  24. #24
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    Quote Originally Posted by russb442
    well as i said and as you can tell, the distance from the back side of the gear and the bearing is the place that a shim would go. if i put together a dry gear assembly w/out the o ring there is allot of "slop". with it there is hardly any. if you tried to shim with the o ring its to tight. Very quickly the o-ring wears and changes the distance between the bearing and the back of the gear. all i am saying is the o-ring should not be used if you want to keep a contestant shim in the diff.
    The O-ring is supposed to sit inside of a recess within the diff cup (same thing on the ring gear side). Maybe they weren't seated all the way into their recesses?

    FWIW, I recently switched to just packing the diff cup full of wheel bearing grease instead of silicone oil due to leakage over time. So far so good. You do lose most of your viscous limited-slip action this way though, although if you're spinning tires, you can still just lock the lockers.

  25. #25
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    Unhappy It happened again!

    Hi Folks,
    now it happened again. Yesterday while riding my new quad body I noticed that clicking noise again.
    Now I have 2 look whatís wrong. I think now I try the E-REVO diff in the back.
    Cheers
    CAPITA

  26. #26
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    Check that you didn't have a pinion bearing explode. Seems I still get this happening occasionally (if you catch it soon enough and don't keep trying to drive it, the gears will likely be OK and you won't have to replace anything more than the bearings).

  27. #27
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    Exclamation How to keep the ring gear scrwes tighten

    Yes, I checked that first, because it happens to me before. But the pinion bearing is ok. I discovered, that the screws of the ring gear became lose again. So the 3rd case in this graphic happens to me again.
    Additionally I installed one more shim on the pinion gear. That feels good so far, but while driving the 3rd set of batteries the clicking noise appears again. What now?

    Again checking the diff and discovered that the 4 screws on the ring gear became loose again. (!!!) Just after one hour of driving. How do you manage to keep the screws tighten? Using locktite should be a solution. But we are talking about a differential which is full of oil. When you mount the ring gear the excessive diff oil will leak thru the four holes. No locktite will bond here.
    Here is my idea:
    1. Mounting the (inner) diff normal using diff oil. All of the parts are oiled now.
    2. Then loosen just one screw and clean it up using a fat solvent fluid.
    3. Cleaning up the free hole in the ring gear and its close area using a fat solvent fluid.
    4. Wait until the fat solving fluid has vaporized.
    5. Reinstall the screw using lockite.
    Do this to all four screws one by one, while all other screws are tighten.
    I did so. Letís see if it survives now.
    Last edited by CAPITA; 03-26-2010 at 07:33 AM. Reason: typing error
    Cheers
    CAPITA

  28. #28
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    Are you talking about locktite threadlocker or a locktite superglue?

    I dont think the threadlocker will work on the plastic 'cup'.

    P.S. can you link the spacers/shims you use in tightening your diffs? (preferably from tower so I can get all the parts I need on one postage)

  29. #29
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    Yeah cleaning the oil out of the screw holes with some solvent might help.
    However a new diff cup might resolve the issue as well if you've had the screws in & out of it a few times already, which may have worn the holes out to where there isn't as much friction on the threads.

    Tower's site sucks hardcore trying to find shims (seems they think screws and clips are shims for some reason)

    I found these though, looks like they'd work for the pinion. Doesn't say whether they're steel or not though they look like metal
    http://www3.towerhobbies.com/cgi-bin...?&I=LXPD13&P=7

    The shims that I used behind the thrust plates inside the diff cup you'll need to make yourself though (described above).

  30. #30
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    Yeah ok cheers.

    I've just done my rear diff spider gears, so comltete diff overhaul time. Ceramic bearings as well to be sure.

    I noticed one of the screws in my diff cup seems to be stripped when I reassembled it (definatelly not me overtightening it) so I will be getting a new one (or 2 as tower only sells them as a pair).

    If I have to make some shims I might as well try make them all. I can get some brass shim material easily enough and give it a go. Just not sure how tight I can make the inner diameter. I will see.

  31. #31
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    Summit, E-Revo, E-Revo Brushless, Merv. Baja 5BSS

  32. #32
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    Red face

    That sucks!! My plan didnít work. After 2 sets off batteries the clicking noise appears again. Does anybody know an inner diff cup made of metal? Similar items made of aluminum are available for E-MAXX for a long time.
    Cheers
    CAPITA

  33. #33
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    need metal diff cup

    Now I checked the diff again. It is like I expected: The four screws became loose again and additionally one of the threads is broken.
    Until I receive spare parts I have installed an E-REVO diff (and bulkheads). But not forgotten to shim it before and replace the inner pinion bearing.
    Weekend is over now. Letís see when Iíve time to test this setup.
    Cheers
    CAPITA

  34. #34
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    Just my 2 cent here (1.96 for Canadians..) I have worked on a lot of hydraulic piston pumps which require shimming of the input shaft and if you get that wrong, damage occurs quickly. Since you have gone through three diffs, have you looked at something else pushing on one of the shafts?

    Binding in the drive shaft will push on the input shaft and drive the gears together. Binding in the axles will push on the outputs and drive the gears together. As everything heats up, lube is destroyed and wear accelerates, then you end up with a box of jewelry.

    What about misalignment of the diff carriers to the chassis? Chassis and bulkheads are cheap and if it was me I would replace everything (or make Traxxas do it) that might be a contributing factor to diff wear.

    In my experience it is always the last thing you expect or think about that causes the problem.

  35. #35
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    Quote Originally Posted by diby_2000
    Are you talking about locktite threadlocker or a locktite superglue?

    I dont think the threadlocker will work on the plastic 'cup'.

    P.S. can you link the spacers/shims you use in tightening your diffs? (preferably from tower so I can get all the parts I need on one postage)

    Threadlock will work anywhere where there is an absense of air (grease and oil can't be there either). If you want something permanent, use Loctite liquid metal or JB Weld. Once JB drys you can drill it, tap it, shave it, file it. I always carry some as it can make the difference between going home or staying out.

  36. #36
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    Try this:

    After you've blown all the oil out of the hole with some solvent, put a couple drops of CA glue down into the hole, then put the screw in and tighten it.

  37. #37
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    What about that thin tape plumberers use, to fill out the thread?
    Stock Summit minus Tekin/2.4Ghz

  38. #38
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    I have a few questions.

    1. Are you just climbing with your summit or bashing in the high speed gear?

    2. When operating in high do you keep the diffs locked?

    3. Are you using cement for your diff lube?

    4. Why haven't you just bought a whole new diff Carrier and diff housing?
    DOC ANELLO
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  39. #39
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    Hi DOC!
    Here are my answers:
    1. I hardly climb with my SUMMIT.
    2. Therefore I almost never use the diff locking function.
    3. I use the TRAXXAS diff lube.
    4. I already bought so, but the parts havenít arrived yet.

    Now I think about a solution 2 prevent the four screws from loosening a different way. In engineering there are several solutions for that problem. I only have 2 find a suitable one for an RC car.
    Cheers
    CAPITA

  40. #40
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    Hmm, I'm afraid there is no tape strong enough to stand those forces. I think about a form closure solution.
    Cheers
    CAPITA

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