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  1. #1
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    Angry Drivetrain is blocking - I can't find the reason!

    Hey,

    first - sorry for my unperfect english i try to explain my problem as detailed as possible:

    I own two Slash 4x4. One of them is driving me crazy, the drivetrain is blocking somewhere, but I can't find where...

    As soon as I attach the rear to the chassis, the rear starts to block quite heavy. I thought something with the diff maybe wrong, so i replaced ALL parts of the rear diff, except the spider gears.

    Unfortunately, the problem persists. It sounds like the spur gear is grinding somewhere, but JUST then when the chassis is attached. If I attach the working rear end of my 2nd Slash, it rolls just fine, nothing is grinding. I can't see any difference between the 2 rear ends...

    I make a video now, i think this describes it a little bit better.

    Thanks in advance..
    Lybs, frustrated german Slash owner

  2. #2
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    Hi, Lybs! Welcome to the forum.

    Since you seem to be an experienced Slash 4x4 owner, and probably know most of the tips and tricks with it, I can really understand your frustration.

    Have you changed something on the slipper clutch assembly lately? Maybe installed the spur gear backwards? I know the problem then should persist with both rear ends, but one can never be absolutely sure...
    Have you checked that there isn't any grit inside the hole in the pinion gear where the slipper shaft goes into? If the hole is partially blocked, the slipper assembly will be pushed forward when the rear end is attached.

  3. #3
    RC Turnbuckle Jr. El Sob's Avatar
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    Welcome to the forum and the addiction! You are among a group of people who share the love of the Traxxas Slash 4x4! If you have any questions please feel free to ask. Remember we are here to help!

    Let me throw this at you. Sometimes if I don't line up my rear bulkhead up perfectly it will go together but the slipper shaft won't be properly engaged. It causes a huge amount of drag. Pull the motor off and it hardly rolls. Try to eyeball the two very good and get them together perfectly.
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  4. #4
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    Hey, thanks for the fast support!

    Here you can here what it sounds like: http://youtu.be/Jb5LrblxBRY

    I have made no changes on the slipper clutch - i tried it with a new slipper clutch too - same problem. The spur gear is correctly mounted.
    The pinion gear hole is clean, ive checked, reassembled and cleaned the complete differential several times now

    The interesting thing is: If i push the slipper (a little bit, not with high pressure) in the pinion gear hole, it starts to make the same noise as you hear in the video. But my other differential does the same, but it works flawlessly. I don't know why, but I think something is pushing the slipper shaft too wide in the pinion hole at the defective Slash..

    The bulkhead is lined up correctly, too

    Thankyou guys! Hope to get this fixed.. the Slash is idleing for 2 weeks here now

  5. #5
    RC Turnbuckle Jr. Jezza's Avatar
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    Welcome to the forum and this great hobby of ours.

    Is it possible that the rear bulk of your 4x4 slash is too tight, I noticed that if the shock tyres and the bulk have been tightened too hard, nothing moves at all or everything in the diff just binds up.

    I cannot figure out how would you try to fit the rear of your 2wd slash to the 4x4 , when they are totally different plattforms. The 4x4 uses a diff in the rear, the 2wd uses the transmission at the rear, which has the diff in it.
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  6. #6
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    Hey Jeeza,

    thanks for the rear bulk tip. I did not try anything at this part yet.. I take a look now.
    edit: even if i fully remove the screws, the sound / struggling is exactly the same... ;(

    I got two Slash 4x4 :-)
    Last edited by lybs2k; 06-11-2015 at 07:01 AM.

  7. #7
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    A few pics, maybe they can help in any way...

    Working Slash 4x4 Rear End
    http://www.pic-upload.de/view-273295..._0816.jpg.html
    Defective Slash 4x4 Rear End
    http://www.pic-upload.de/view-273295..._0814.jpg.html

  8. #8
    RC Turnbuckle Jr. Jezza's Avatar
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    Quote Originally Posted by lybs2k View Post
    Hey Jeeza,

    thanks for the rear bulk tip. I did not try anything at this part yet.. I take a look now.
    edit: even if i fully remove the screws, the sound / struggling is exactly the same... ;(

    I got two Slash 4x4 :-)
    Just realised you mentione 2nd slash 4x4...lol. Yup check the shock tower and bulkheads if you have tightened them to hard.

    Just curious, is your bearing shot over there and also you have a crack on the left screw, maybe , its not hlding the whole bulk as it is suppose to while running causing some slop and possible the diffs will noty be alligned properly....

    If it is craked too, you will end up tightening the bulk too hard to compensate , and that causes a huge bind on the outer diff gear and centre.
    Last edited by Jezza; 06-11-2015 at 07:07 AM.
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  9. #9
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    I just noticed the same as Jezza! Check it out, and maybe get a new diff housing.

  10. #10
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    It looks like it's missing a metal tab, but that is maybe the camera angle...

  11. #11
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    Alright... i didn't notice the crack on the left side, anyway, this is a "new" diff housing, the problem has been there too with the old one.. i renewed all parts of the diff, except the spider gears. Maybe i should change them too? There are not many options left..

    The bearing has a scratch, yes, but till now it's working hehe, i'm gonna change it..

    Snorkel, which metal tab do you mean? Inside of the Diff-Housing?


    Edited for language abuse. If you see a starred out word in your post, you must edit it out to avoid earning warning points.
    Last edited by cooleocool; 06-11-2015 at 08:55 AM.

  12. #12
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    You see it when looking through the bearing. Its the pinon you connect to the bearing (ring gear)
    Last edited by Snorkel; 06-11-2015 at 08:02 AM.

  13. #13
    RC Turnbuckle Jr. Jezza's Avatar
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    Quote Originally Posted by Snorkel View Post
    It looks like it's missing a metal tab, but that is maybe the camera angle...
    Its the rear diff so he will not have the same as the front, he has the 6879 out gear inside.

    Here are the diagrams I use for diff refferences

    https://traxxas.com/sites/default/fi...-ML-121120.pdf
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  14. #14
    RC Turnbuckle Jr.
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    I think the problem is that crack, not making it sit right and that blue silicone, again not letting it sit right.

    Part #6880 would probably fix it. And put it together without the silicone.


  15. #15
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    Hey everyone,

    thanks for all your replies. I think I found the reason.. I try to explain.

    I used larger screws in the Shock Tower (there, where it has cracked) on both sides, so the screws push the chassis just about 1mm more away. The problem is 100% fixed, the drivetrain runs totally smooth this way.

    What part could be causing this? I can leave it this way.. or fix it the right way (i prefer the last method )
    The only thing i could imagine, is the rear bulkhead..

  16. #16
    RC Turnbuckle Jr. El Sob's Avatar
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    The noise could very well be the ring gear rubbing the differential housing. Snorkel, I see what you are talking about. There seems to be missing a part in the center. Looking at some of my Flickr pics, it is part #Tra6879. That part is how you align the slipper clutch with the rear bulkhead. It is also the pinion in the rear differential. OP, you may want to replace that part. I have broken a few Tra6879's and the sound is similar.
    Last edited by El Sob; 06-12-2015 at 07:53 AM.
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  17. #17
    RC Turnbuckle Jr. El Sob's Avatar
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    Please let us know what you find when you disassemble the differential housing so we can continue to assist you
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