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  1. #1
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    Aluminum diff cups that work without modding

    Lost in one of the rebuild threads discussing the LST2 diff mod I had stated I was on a quest to try aluminum diff cups and beefing up the bulkheads first.

    Problem is finding a diff cup that will actually work without having to grind down the cross support for the spider gears. Ive seen several HR cups where folks ground down the cross support to get it in ( I ordered some of those too but retunred them) and just to let everyone know I odered up a pair of RDlogics and guess what, they use the same cnc program and got it wrong too in the same aspect.

    While I was building the diffs for my over powered slash 4x4 I used FLM cups and the ERBE internals with the exception of the ouput gears and shafts. I was mistaken when I said that the shafts were a different diameter (thats right, I was wrong so if you are gonna bloat now is the time to do it becasue it doesnt happen often! LOL). They are in fact the same diameter with the only difference being the machining on the end where the shafts connect. All else is identical. So I just finished building two diffs using FLM cups for a slash 4x4 as you never see the cups listed for the ERBE with the exception of the modified version with a different ring and pinion gear and they are never in stock anywhere. The cups fit perfectly and shimmed great.

    So if you are having a hard time finding aluminum diff cups that actually work and need no grinding of the cross support look up FLM diff cups for slash 4x4.

    Whooda Thunk?

  2. #2
    RC Turnbuckle Jr.
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    I don't think 5 minutes of grinding on the I Beam is too much to ask!
    But glad it worked for you. How much are those cups?

  3. #3
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    Seems like the HR cups with the Stainless plate are unavailable, are they discontinued?

  4. #4
    RC Turnbuckle Jr. 87 GN's Avatar
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    with an air grinder or even a dremel you can knock it down in no time....
    Would you go flip my truck back over??

  5. #5
    RC Turnbuckle Jr.
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    you do have to be careful though grind a little too much on one side and you will throw off the spider gear alignment

  6. #6
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    With an FLM cup you dont have to knock down anything and no worries about over grinding.
    I picked up the FLM cups for $15.99 ea, less than the HR cups and better machining IMO.

  7. #7
    RC Turnbuckle Jr. 87 GN's Avatar
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    FLM does make some fine products........
    Would you go flip my truck back over??

  8. #8
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    do that flm's also use the side supports for the shaft the spider gears ride on?

  9. #9
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    Quote Originally Posted by JustinThyme View Post
    Ive seen several HR cups where folks ground down the cross support to get it in
    If only those guys took the time to read the instructions... From the HR website...

    The metal "bow-tie" shaped piece in the TRA5382X will not fit in this unit. Since the entire unit is metal, this piece is redundant. All the other parts fit perfectly.
    200, 202, 420, humor 404, 301 to rc10talk, 410.

  10. #10
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    Quote Originally Posted by danielhr77 View Post
    If only those guys took the time to read the instructions... From the HR website...
    I read that mate...I wanted to put it in anyway. The tie rod that held the spider gears in place side wall support looked a bit flimsy for my liking and adding the I -bar looked like it would add added support to holding the spider gears in place...that's just my opinion.

    There was nothing to it grinding the I-bar down to fit .
    Last edited by craig.mitch316; 01-03-2013 at 03:54 PM. Reason: spelling
    Rock n Rolla !

  11. #11
    RC Turnbuckle Jr.
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    pretty sure we all read it ! and know a great mod when we see it!

  12. #12
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    Quote Originally Posted by danielhr77 View Post
    If only those guys took the time to read the instructions... From the HR website...
    Problem is redundancy is a matter of opinion on the part of HR and when shopping for the HR cups no one goes to the HR wesite as they dont sell anything there and have no customer support. When you buy somthing that is advertised to work then it should work. The couldnt even get the nomenclature right. "bowtie shaped piece" or correctly referenced as "carrier support I bar" keeps the carrier pin from flexing under heavy load at high RPMs. Metal housing has nothing to do with this aspect.

    After the seeing the cups and also ordering a set of aluminum knuckles that are not machined correctly to where you cant get the pin in the 17mm adaptor (even the HR adaptor wont fit) without grinding down the inside surface of the adaptor and the bearings fall right out I have come to the conclusion that HR has a severe case of cranial rectal inversion. The fact that they dont have a solid customer support speaks volumes. There is no number to call and you have to dig deep to find an email address that they dont respond to.

    So back to the point of the thread. If you want aluminum diff cups that work and the parts fit perfectly the FLM cups #FLM26030 for a slash 4x4 are a perfect match and can be bought HERE


    Quote Originally Posted by hottrodd1090 View Post
    do that flm's also use the side supports for the shaft the spider gears ride on?
    No, none of them do. They do have a different machining than the HR cups with a broader surface and they come with a different pin. It would be nice to for a company to machine an aluminum cup just like the stockers
    Last edited by JustinThyme; 01-04-2013 at 08:53 AM.

  13. #13
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    yes it would be really nice.most of them say "stock replacement cup" to me that means every part fits inside that cup.i would think the side braces are there for a reason and give support the the spider gear shaft.i dont mind grinding a little off the i bar but would also like the side supports to be able to be installed.

  14. #14
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    I dont think the side supports are as crucial as the carrier support. It would be nice for them to fit but I believe the reason they are there in the stock cup is I dont think a slot in plastic would hold up for very long holding the carrier pin. If you get the FLM cups I mentioned no grinding on the carrier support I bar is necessary. Ive looked at pretty much every after market cup there is and none of them allow for installing the side supports.

  15. #15
    RC Turnbuckle Jr.
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    Without a stronger ring and pinion and stronger spider gears any diff cup only helps so far. Any with hard bashing the flm cups wont make a difference

  16. #16
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    Quote Originally Posted by 50togo View Post
    Without a stronger ring and pinion and stronger spider gears any diff cup only helps so far. Any with hard bashing the flm cups wont make a difference
    So with that in mind should we all chuck out ERBEs in the trash?

    There is a distinct difference between hard bashing and plain out trashing.

  17. #17
    RC Turnbuckle Jr.
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    Just saying there should be stronger ring and pinion and spider gears from the factory. Diff cups wont solve the problem

  18. #18
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    Agreed they should be made with more and better gears but thats what we have to work with without putting differentials in from a Ford F650 4x4.

    Ive been watching the LST2 diff mods and they have issues of their own, not in the diffs but in the bulkhead mounting leaving too little material on a major support of the truck and its drive train.

    Ive only trashed one diff and it wasnt the gears that caused it. I caught it before it turned into noodles inside the outer cup. The failure point was the plastic inner cup against the bearing. Had it happened in a fashion where it just blew apart I would never have caught it. One more high speed pass and that would have been all she wrote.

    IMO most diff failures are caused by poor driving habits.....ie running 6s and landing a 10 ft jump on power.

    My only point to this thread was trying to find a viable alternative to the LST2 mod. I run mine pretty hard but I dont do 6s, 4s most of the time and ocasionally 5s for speed runs. 6s is going to break things unless you are running a Baja with a brushless kit. After running 5s and barely being able to top it out before I ran out of radio my personal thoughts were....whats the point of 6s?

    I did a major overhual over the last couple of days and spent a good bit of time eyeballing the diffs and how they are mounted. From an engineering point of view the design is flawed in the most fundamental of ways in the mounting of the diff in the bulkhead. For the current design aluminum would be a better material. Nylon or plastic could work but it would take closing it in all around, heavier casted cross supports and more hardware clamping the bulkhead tight around the diffs outer housing.

    ATM whats on my mind is a metal clip on the bottom to keep it from spreading.


    Necessity is the mother of invention.

  19. #19
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    OK, so we have now established that FLM cups > stock cups, and fit without any mods. What about the gears? Who sells grears that also fit without any modifications but are stronger than stock ones?

  20. #20
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    I agree with what most of JustinThyme says about the bulk head and diff housing design. I posted a thread about how i think the housing should be built into the bulk head. I was thinking more about it and if you use a big enough diff, you wouldnt even need a outer diff housing and could use the bulkheads themselves to mount the diff in it.

    I had my last E-revo for around 3 years and only busted 1 diff. I dont jump off of 10 foot high ramps or do back flips but i do run 6s and i believe the diff going out on me was my own fault. When i installed the center cvd shafts, i didnt shim and there was ALOT of play on them stubs.

    Iv seen a few lst diff mods go bad on here too and i think peeps might be shimming there diffs wrong.
    E-Revo MMM-2200 6s

  21. #21
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    Quote Originally Posted by ignis View Post
    OK, so we have now established that FLM cups > stock cups, and fit without any mods. What about the gears? Who sells grears that also fit without any modifications but are stronger than stock ones?
    I just installed a ring gear made by GPM. It is a direct replacement and no mods needed. GPM sells a whole diff gear replacement pack but i only have the ring gear right now. iv only tested my revo once (we have alot of snow on the ground). I havent driven it hard yet but ill post updates on it as time passes.
    E-Revo MMM-2200 6s

  22. #22
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    wow lots of good info.i have to agree with 6s breaks alot of stuff and i am sure it has alot to do with the way i drive.i did the lst2 diff mod on one of my erevo's and the only bad thing so far is i broke an outer case on a bad landing.but eer since i bought some 4s batteries and using them in the other erevo i built i have not torn up almost anything.none of it has been to do with a diff.i am the type of person that likes to lets say buy parts that fit right in and not do alot of modding since i have two grandsons i let drive these things sometimes.

  23. #23
    RC Turnbuckle Jr.
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    The only other stronger ring and pinion is the discontinued robertson racing 8090 that can be found on the rare occasions
    But I have broken even those. Without thrashing!

  24. #24
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    50 you break everything! LOL
    In the chance we should ever meet for a bashing session remind me to never let you near my radio or truck!

  25. #25
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    Ain't like that! But do I push the limits? Sure. Should the diffs be stronger from the factory absolutely
    I went through the same thing with my two mervs. Had to shim the diffs aluminum cups and aluminum bulkheads to run 3 cell. When advertised to be able to run on 3's
    Last edited by 50togo; 01-06-2013 at 06:45 PM.

  26. #26
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    Ive shim everything from the get go in every build I do. Steering linkage, hex adaptors, diffs inside and out, on these cups I put a .01 shim on the ends of the carrier pin, tight fit but it keeps the spider gears away from the wall of the cup, A arms, all pivot joints and shock mounts well basically any conection that moves and has slop.

    Im pretty much done with the street ERBE for now. Did a shake down this afternoon, it was not so bad here today at 47F. Yeah I know that makes you SoCal folks shiver but it was a heat wave for us seeing how our highs have been right at the freezing point for some time.

    Ran out two sets of packs on 5s, scared the crap out of my neigbor down the street when I cut in in his yard while he was cleaning up. His kids got a good laugh though! Didnt break anything, Its all nice and tight and went through checking torque on everything. Set up stations are worth their weight in gold! I tuned it out and had zero steering correction on the radio. The only thing two things I havent settled on are steering knuckles and A arms although everything thats in it now is new. Have stock arms and ingtegy (bought the whole set brand new for $20) steering knuckle with the oversized bearing. They seem to be holding up so far but Im sick of blue! Its bad enough with the CVD boots that already make me want to change out cvds to something else. Other than those two items everything else is either black, red, or stainless. Put the faux carbon fiber wing on too. Now just have to get busy painting the slipstream for it so the stock red is on for now. For the A arms Im thinking RPM lowers and aluminum uppers as soon as I can find some decent uppers. Ive already got the RPM everything on the off road. Im not posting up pics until Im done so you guys dont laugh at the blue knuckles amidst the sea of red and black. Especially red rods and links connected to a blue knuckle with a red 17mm hex poking out the front!

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