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  1. #1
    RC Turnbuckle Jr. O.G.'s Avatar
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    Sealed differential discussion

    I started this thread to discuss the FLM sealed differential and stop cluttering up wmckay96's thread - sorry wmckay!!

    As some of you may know, I have an FLM sealed diff on order from rc-monster, and kwitty already has one and posted some sweet pics of it on a different post. (This question could be posed to Traxxas diff's that have been sealed with the gasket mod seen on this site)

    So my main question is this: how much oil should I put in the diff to make it work as it should, which is allow slipping on corners and hooking up better coming out of the corner, and on straights.

    If I completely fill it with 20,000 wt oil, will that slip more than if I 1/3 fill it with 30,000 oil?

    Any opinions/answers??
    My Black & Blue Rally is faster than your color...

  2. #2
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    You are gonna make me want to make an inch-pound gage to indicate how much resistance is built up before the wheel releases to answer this one LOL your killin me you know!

    I'll contribute with you may want much more than 20k or 30k to get enough gain, my 100k doesn't seem that tight to me at all.
    I'll say your 20k fill would give 'less' slip than your 1/3 30k additive

    Sorry too if I convoluted that post of wmckay's as that wasn't my intention it is just a hot topic for me as you might notice

    Below is an internal view of the FLM trans, gears are TRaxxas, same setup internally of the stock Traxxas unit as far as gear indexing. The FLM just offers the O ring sealed version of the Traxxas and in aluminum instead of plastic. Also note as it is difficult to see but two of the planetary gears are at the top and there are two at the bottom, these are driven off the gear that is on the output axle.
    Last edited by kwitty; 05-06-2012 at 09:00 PM.

  3. #3
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    Below is what I posted in the other thread so I think it should also go hear for 'discussion' purposes if you don't mind O.G.?


    I guess as long as the gears stay in a bath of the lube it would be fine but not as full of a benefit. If not for the sealed ability of the FLM then it wouldn't be any different than the. Traxxas unit. I can't imagine enough diff action as a benefit from only the bind up created by about two teeth meshing with the lube as the friction agent. Submersing the gears would only add greatly to the resistance created on all surfaces effected by being in the diff fluid which would account for an increase in the ability to slow down blow out to the wheel that becomes unloaded..

    Problem is this is really a poor way in the first place to accomplish a bind or locking action to solve the problem. I don't know of any automotive differentials that even begin to use the 'lube' as the device that creates the locking action we are looking for.
    GM used an advanced G-rotor pump that hydraulically created a very advanced trac system but others as we know are clutch engaged (posi) or gear engaged (locking) type or totally solid as in a spool.

    So, we needed to design a diff that is frictional plate adjustable and we just need a hollow axel that we can slide an adjusting tool into to tune the amount of friction we want it still baffles me that the best we have to work with is simply by fluid or it's tackiness ability to bind gear mesh, very crude and the wrong way to go about resolving the issue..

    Maybe a unit with a central gear with an adjustable clutch on each axel independent, you could bias the bite to the tires getting the weight transfer like in your circle track racing maybe even a internal drive gear with external clutching at the output shafts..

  4. #4
    RC Turnbuckle Jr. O.G.'s Avatar
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    Quote Originally Posted by kwitty View Post
    That is a sweet, sweet pic. I could look at it all day.

    I don't mind kwitty, post away!

    And yes, I want you to put a ft-lb gauge on your diff to give us the internal pressures. hahaha

    Well I ordered the FLM sealed diff but I thought it had a plastic external gear based on the pics and I recall someone on this site complaining about a chewed-up plastic gear ring on the outside.

    And when I saw the red-anodized diff you posted I was so glad I ordered FLM. I'm just sent an email to swami-rc asking who makes their sealed diff; maybe they'll answer, maybe not.
    My Black & Blue Rally is faster than your color...

  5. #5
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    Well here is one more for you and simply to show the Traxxas and the FLM how very similar they are.


    Look closely on the stock Traxxas and you will see the ends of the pins (4) that the gears ride on.
    Last edited by kwitty; 05-06-2012 at 09:33 PM.

  6. #6
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    Quote Originally Posted by O.G. View Post
    That is a sweet, sweet pic. I could look at it all day.

    I don't mind kwitty, post away!

    And yes, I want you to put a ft-lb gauge on your diff to give us the internal pressures. hahaha

    Well I ordered the FLM sealed diff but I thought it had a plastic external gear based on the pics and I recall someone on this site complaining about a chewed-up plastic gear ring on the outside.

    And when I saw the red-anodized diff you posted I was so glad I ordered FLM. I'm just sent an email to swami-rc asking who makes their sealed diff; maybe they'll answer, maybe not.
    On the FLM there are indexing pins that can be seen that go through the gear to lock it onto the casings so it isn't going to give under pressure!
    for those unfamiliar with the innards of there differential, there is a very small solid pin that indexes into the black gear which is the output axle gear and the other output axle gear goes on top of it and that is where the top set of planetary gears mesh into. See first pic in post for reference to this......

  7. #7
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    Another thought on your question about 1/3 filling, the entire differential spins, I may have this wrong but in this case only partially filling the unit would seem to make it out of balance as that thick lube is not going to remain at the bottom, it is going to flung by force against the the inner wall of the casing and remain there like a washing machine pins the clothes to the tub.

    The diff could act like and out of balance tire inside the trans?

  8. #8
    RC Turnbuckle Jr. O.G.'s Avatar
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    Quote Originally Posted by kwitty View Post
    Another thought on your question about 1/3 filling, the entire differential spins, I may have this wrong but in this case only partially filling the unit would seem to make it out of balance as that thick lube is not going to remain at the bottom, it is going to flung by force against the the inner wall of the casing and remain there like a washing machine pins the clothes to the tub.

    The diff could act like and out of balance tire inside the trans?
    If the oil was pushed to the outside of the differential wall, wouldn't it be even all the way around? Or do you think the gears would be in the way causing lumps of oil that would make the diff go out of balance.
    My Black & Blue Rally is faster than your color...

  9. #9
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    I have filled my other diffs 2/3 full, and they were consistent.

    I asked around at my local outdoor track. I swear everyone running the 1/8 buggies said something different. 1 thing was apparent though. Everyone's diff worked great according to them, weather it was 5/16,2/3,3/4, or completely full.


    I was looking on this site, and found this:

    roll on down to "differential"

    http://traxxas.com/pitpass/hopup/new...ng-Setup-Guide

  10. #10
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    Quote Originally Posted by rag6 View Post
    I have filled my other diffs 2/3 full, and they were consistent.

    I asked around at my local outdoor track. I swear everyone running the 1/8 buggies said something different. 1 thing was apparent though. Everyone's diff worked great according to them, weather it was 5/16,2/3,3/4, or completely full.


    I was looking on this site, and found this:

    roll on down to "differential"

    http://traxxas.com/pitpass/hopup/new...ng-Setup-Guide
    Interesting on the fill. So it sounds by this tip that 'filliing' with any lube will 'increase' the diff action. So filled with 100k may equal wetted with 300k LOL
    It still is an area of tunability that is not easy to get too and is time consuming if you do and seems to not remain constant if not attended to. We need a a better tunable diff is all there is to it.

    If you half-fill the case, then drop in the other side axle gear it probably displaces another 1/4 of the interior space so now you are 3/4 full?? LOL
    Hmmmm, the mystery continues................

  11. #11