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  1. #1
    RC Turnbuckle Jr.
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    Exclamation Aluminum Differential Cups: A "sort of" Review...

    Ok, everyone knows that running aluminum diff cups (inner diff housings) increases drive-train strength and durability, but deciding which ones to run is a little tricky with all of the options that are available. Well, since I am building new diffs for my project Revo, I decided to get a set...and while looking at all of the cups available, I noticed a few differences that make or break each one.

    As we all know, aluminum does not make a very good wear surface, so it is not a good idea to have a harder material (such as steel) constantly rubbing against it, because the harder material will quickly wear away the softer material...which causes lots of slop, and will eventually lead to catastrophic failure. During my search for aluminum diff cups, I came across some bad ones, some good ones, and some extremely good ones...here is what I found.

    I will start with the worst ones and work my way to the best ones, rating them 1 through 10 (10 being the best)...


    [1] This is the Golden Horizons aluminum diff-cup; It is made of billet 6061 aluminum, and has the steel output shaft riding directly against the aluminum cup. To make it even worse, the ring-gear mounting holes go all the way through the cup, making it more likely to leak diff oil.
    -Rating: 1



    [2] This is the RD Logics aluminum diff-cup; It is also made of billet 6061 aluminum, and also has the steel output shaft riding directly against the aluminum cup. It's not as bad as the GH cup, but it's still pretty bad.
    -Rating: 3



    [3] This is the Team Integy aluminum diff-cup; It is made out of cast 7075 aluminum, which is a lot harder and more durable than 6061, but the steel output shaft is much harder than even 7075 aluminum, and the cup will still wear out very quickly. Cast aluminum is junk, even if it's 7075 cast aluminum.
    -Rating: 4



    [4] This is the Nova RC Products aluminum diff-cup; It is made out of billet 7075 aluminum, but like the Integy cup, it has the steel output shaft riding directly against the aluminum cup. Billet 7075 aluminum is the best aluminum you can buy, but it still can't hold up to steel constantly rubbing against it.
    -Rating: 6



    [5] This is the RC BEST aluminum diff-cup; It is made out of billet 7075 aluminum, and has a billet brass insert for the steel output shaft to ride against. Brass is a very hard material, much harder than even 7075 aluminum, and has excellent wear properties that are very similar to steel...and it even has a very good lubrication quality, that allows the steel output shaft to ride against it with almost no friction at all. This is a very good design, but not quite the best.
    -Rating: 9


    [6] This is the Hot Racing aluminum diff-cup; It is a 2-piece design, and is made out of billet 6061 aluminum and G-410 stainless-steel! The main cup is made out of lightweight 6061 aluminum, but the outdrive plate where the steel output shaft rides is made out of ultra-hard (but still lightweight) G-410 stainless-steel. The 6061 aluminum and G-410 SS 2-piece cup is the same weight as a 1-piece cup made out of 7075 aluminum, so weight is not an issue. This is the ultimate diff-cup, with virtually no wear at all! This, my friends, is a perfect 10...and is what I am going to run in my BL Revo!
    -Rating: 10
    Project: BL Revo Race Quad & BL G-Maxx G3R CF Revo

  2. #2
    RC Racer
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    is there something wrong with the stock ones?
    mean: I can't recall any broken or bent diff cups here in the forum.

    I'd personaly prefer steel against brass to steel against steel unless there is dome decent lubrication. e.g. an oil-pump

    steel vs. steel tends to roughen each others surface.
    brass doesn't do that. as you said, it 'lubricates'
    however... even the brass wears with time, so it should be replacable.

    a ball bearing would be perfect

    one should keep an other thing in mind:
    the cups are supposed to keep the oil in.
    so the x-ring should have a perfekt seat but this has to be tested and cannot be determined by comparing the specs.


    btw.. has anyone seen limited slip or torsen-like diffs?
    my Baja 5B has an LSD and it is the best rc-diff I've ever seen.
    maybe I'll send some suggestions to traxxas how to turn their standard diffs into LSDs. it's rather easy

    however.. good work Revoš
    if I break a diff cup I hope I'll find this thread again
    E-Revo,700HO/Novak5.5,5Ah LiPos
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  3. #3
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    New Era Racing makes a diff cup the same as the Hot racing one. I run New era alum cups front and rear and love them.
    What shall I put here?

  4. #4
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    doesn't the output shaft ride on bearings and not directly against the housing?? not to detract from the point of this post, but the housing itself wont see any "rubbing" from the output shaft. Rather it will feel a load from the bearings surface area (or bearing area oddly enough), and the harder materials will more adequately support the load that the bearing will cause on the housing during heavy acceleration. This helps prevent the dreaded flex that allows the gears to spread enough to slip and eventually shear/round the teeth off the ring gear. At any rate the larger modulus or elasticity of the steel (28,000-30,000 ksi) is far greater than that of AL (10,000-11,400 ksi) and Brass (14,000-16,000 ksi), and will therefore have less flex for a given load.

  5. #5
    RC Turnbuckle Jr.
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    No, there is nothing wrong with the stock diff-cups, I just like to replace them with aluminum cups in high-power applications such as 6S BL Revos.

    Technically, the stock Revo diffs are limited-slip diffs, that's what the oil is in there for...and all the replacement cups I listed have new seals to keep the oil in, I just don't like that GH design with the screw holes going all the way through the diffs, and think they might invite a leak.

    And yes, a bearing for the output shafts would be great, but that would require lots of machine work in the ring-gear and the diff-cup, which would raise the production costs substantially.
    Project: BL Revo Race Quad & BL G-Maxx G3R CF Revo

  6. #6
    Marshal carraig042's Avatar
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    The nova cup for sure uses bearings for the output shafts. The aluminum ones work just like the stock plastic ones.. I may not quite get what you are saying though.

    -Brett
    4wd Sportmaxx 3.3
    E-Revo - Mamba Monster - Neu 4s

  7. #7
    RC Turnbuckle Jr.
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    Quote Originally Posted by shizzon
    doesn't the output shaft ride on bearings and not directly against the housing?
    No, the output shafts spin inside the diff-cup, take a diff and twist the output shafts in different directions...the cup stays still while the output shafts turn inside the cups. This is where we get the "diff action". If the diff were locked, or there had 100% equal traction to both tires, the diff-cup and output shafts spin as one unit, but if there is diff action, the output shafts spin inside the diff-cup.

    But, the output shafts do ride on bearings in the outter diff cases, just not in the diff-cup.
    Project: BL Revo Race Quad & BL G-Maxx G3R CF Revo

  8. #8
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    Quote Originally Posted by carraig042
    The nova cup for sure uses bearings for the output shafts. The aluminum ones work just like the stock plastic ones.. I may not quite get what you are saying though.

    -Brett
    No, there are no bearings in the diff-cup or ring-gear where the output shafts come through them...there are bearings that the output shafts go through the outter diff cases, though, and that's what you are thinking about.
    Project: BL Revo Race Quad & BL G-Maxx G3R CF Revo

  9. #9
    Marshal carraig042's Avatar
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    Quote Originally Posted by Revoš
    No, there are no bearings in the diff-cup or ring-gear where the output shafts come through them...there are bearings that the output shafts go through the outter diff cases, though, and that's what you are thinking about.
    Ah, yes, I see now. Yeah, I was trying to think of when I installed these in my Maxx.

    -Brett
    4wd Sportmaxx 3.3
    E-Revo - Mamba Monster - Neu 4s

  10. #10
    RC Racer
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    Revoš, there is quite a difference between an LSD and a viscous-diff like the revo has.

    look at:
    http://www.hpieurope.com/manuals/pdf/10611.pdf
    Page 29

    you will notice, that the torque is not transered to the spider gears via their shafts. these are just here to guide the spider gears.

    the torque is transfered by the washer (87474).
    the effekt is simple:
    as acceleration torque increases, the diff lock increases as well.
    while turning without acceleration, the diff is open to allow maximum sidebite.

    the revo diffs can't lock under heavy acceleration like the LSD does.
    they are mutch better than open diffs as they apply a little bit of locking while turning and a little bit more if one wheel spins free but they can never transfer so much torque to the wheel with traction like the LSD does if one wheel has no traction.

    LSDs lock by mechanical friction, viscous-diffs lock by fluid dynamics and friction or in case of the erevo, just by fluid friction (there is just no room for fluid dynamics. the Baja diff is about the size of a mans fist).
    E-Revo,700HO/Novak5.5,5Ah LiPos
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  11. #11
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    Yes, I know...I am hugely into both hardcore 1:1 off-road rock-crawling and hardcore 1:1 performance/race cars, so I fully understand the differences between the types of diffs available...such as; gear-type LSDs, clutch-type LSDs, automatic full-lockers, selectable lockers (air, electric, cable), spools, and open differentials.

    I was simply saying that the diff action of an open diff can be adjusted and controlled via different viscosity diff-oils, so they can, in effect, act like limited-slip diffs...that's all. When you can change the amount of diff-action in a diff by simply changing the viscosity of the diff-oil, from full-open with no oil to almost full-lock with insanely heavy diff-oil, you are literally limiting the diff-action "slip" of the diff, which makes it a limited-slip diff...technically.
    Last edited by Revoš; 02-25-2009 at 04:05 AM.
    Project: BL Revo Race Quad & BL G-Maxx G3R CF Revo

  12. #12
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    Great review and very informative comments.

    A couple of things I've learned the hard way. My e-revo (purchased July 2008) came with the same differential carrier cup as the 3905 e-maxx (part numbers: 5382x, 5379x, 5380, 5117, and 3978).

    I rebuilt the e-revo differentials with the traxxas cup for the e-revo (part 5381) in this link and ended up with shreaded plastic inside the carrier cup. In order to keep from shreading plastic, the ERBE really should have the e-maxx cup shown on the second page of the link above. The stock e-revo carrier cup and inside parts are the same as the e-maxx in the link. The only difference between the e-revo and e-maxx differentials is the outer housing.

    The "x" designation is the hardened version of the predecessor gears and the 3978 carrier allows for the side plates to the spider gears with the 5382X I-bar (based on my conversation with a Traxxas rep a couple of days ago).

    It doesn't seem like any of the aluminum cups have room for the side plates for the spider gear and would cause wear to the walls where the spider gear shaft makes contact.

    Here is what I learned the hard way:

    The screws used to fasten the carrier cup gear top stripped the plastic carrier, so the plastic carrier is now useless. It doesn't seem like that would be a problem with the aluminum cups.

    One question, does the spider gears carrier shaft (holding the I-bar and side plates on the second page of the link above) dig into the aluminum carriers such that it results in a little bit of slop?

    Not sure if that question can be answered, but just a concern.

  13. #13
    RC Turnbuckle Jr.
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    Aluminum cups are milled in such a way as to limit the "slop" to almost none, and will work very nicely for upgrading your diff, making it stronger and more durable...plus, you don't have to worry about stripping plastic screw holes.

    On a side-note, you really shouldn't have been torquing down on the ring-gear bolts hard enough to strip the plastic diff-cup...heh! Just snugging them up and then adding one more ź turn is all that they need.
    Project: BL Revo Race Quad & BL G-Maxx G3R CF Revo

  14. #14
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    OK, sorry to bring back this thread, but after replacing/repairing/rebuilding the stock differentials too many times, it is time for me to upgrade to an aluminum cup.

    A couple of questions please:

    1) What is the weight/viscosity of the diff fluid used in the aluminum cups as compared to stock plastic cups (go lighter, the same)?

    2) Now for the dumb question, how do you fill the cup if both ends are open without spilling diff fluid (or does the cup even need to be filled)?



    It seems that putting the cup inside half of the housing might help anchor the bottom and cup enough to put the bolts on one side, then rotate for the other side.

  15. #15
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    Yes, you use the same weight diff-oil you used in your plastic cups...

    To fill them, just hand assemble the diff with all of the internal gears installed except the large spider-gear that goes through the spur, holding the stainless-steel end-cap as tight to the aluminum cup as you can...fill the cup, then with the large spider installed into the spur-gear, install the spur-gear onto the cup and tighten slowly. Keep one screw slightly loose so the excess oil can bleed out as the spur-gear tightens against the cup. Once three of the screws are almost all the way tight, install the 4th screw, and tighten all 4 down fully.

    Don't forget to use all of the seals that are included, there are four...two small ones that the diff outputs go through (inside the cup) and two large ones that go between the spur-gear and the cup and the end-cap and the cup.
    Last edited by Revoš; 04-01-2009 at 03:40 PM.
    Project: BL Revo Race Quad & BL G-Maxx G3R CF Revo

  16. #16
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    Though pretty, these are not needed even in a 6s setup.. rebuild your diff's a couple times a year or more often if you drive in crap or submerged and you won't have any issues w/ stock. Rebuild kits are cheap and for the cost of a set of those aluminum ones above you can have 4 or 5 new replacements off ebay when people are parting their trucks... You can buy emaxx 3905 or either emaxx diffs just keep in mind the emaxx housing is different so you will need to swap out the innards w/ your current housing if you buy those.

    Sorry had to be said... this money would be better spent on many other things. Good information though.

  17. #17
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    Hi - thread back from the dead....

    I just bought the hot racing diff case and have 2 questions

    1 - there are two seals included in the set, do you use one on "each side" (and them one of them with the stock seal)?

    2 - do you still shim the diff ref other threads in here... Anyone who have done this and can share how many shims they placed where when you did this? If not - how thight should you shim with Alu case?

    E
    The ERBE viking will never walk alone

  18. #18
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    A word of advice... just throw the hot racing diff in the trash can.

    The RC Best seems to be far superior for one reason. The screws don't go all the way through the cup like the HR diff. I have run the HR diff's and both the front and rear completely broke in half. I don't know if it was due to leaking of silicone through the screw holes or weakness of the aluminum but this is deffinately not a 10. It's possible that the aluminum was cast or billet and that's why it broke. Either way.... the stock e-maxx reinforced cup has held up to more than the HR ever did.

    I've just gone back to replacing the plastic e-maxx reinforced cup whenever it gives. If i ever do get tired of the plastic i will go for the RC Best off of ebay.
    Last edited by anr2442; 02-17-2011 at 01:37 PM.

  19. #19
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    Quote Originally Posted by qorron View Post
    is there something wrong with the stock ones?
    mean: I can't recall any broken or bent diff cups here in the forum.
    Broke mine last week with only 4S.

  20. #20
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    I put Hot Racing cups in my E-Revo at the end of the summer. Havn't used them much yet, but we will see how they hold up this summer, whenever It decides to arrive here.
    Using while stupid may cause serious injury.

  21. #21
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    Huge Power!

    so I have so problems that I caused by adding a lot of power and torque. pics show only 1 run on new everything you see.

    This is the reason and I hope HR is the fix! broke gears and chewed up the housing and the bolts!
    I run RC4WD Baja tires on HPI baja rims. I need to stay off the street with these large tires! The motor has no problem. It's everything else.

    What your looking at is 6 cell lipos turning a 4577 can 1600kv and will handle 3600 watts. The slipper is new and is a Robinson Racing 65T Gen3.
    More broken parts!
    Last edited by reallytwissted; 06-07-2012 at 06:51 PM.

  22. #22
    Marshal ksb51rl's Avatar
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    Where is the I-bar brace (diff carrier support) that is supposed to be in the brushless diff?

    Alt-248 on the number pad = °

  23. #23
    RC Turnbuckle Jr. Snook Man's Avatar
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    I also don’t see the spider pin cup supports.


    The stock diff cup doesn’t stand much of a chance without both the I Beam and the side supports.
    No slipper/tall gearing/power = broken parts.

  24. #24
    RC Turnbuckle Jr. jamann's Avatar
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    Quote Originally Posted by Snook Man View Post
    I also don’t see the spider pin cup supports.


    The stock diff cup doesn’t stand much of a chance without both the I Beam and the side supports.
    And maybe shimming as well.
    6s ...Theplastic Cup it's going to get unhappy
    With that kind of power


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  25. #25
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    Does RC best have a web site?

  26. #26
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    I'll try it as well. I'll pic up a few of them as I have built two 1/5 scale revos with stupid horse power!

  27. #27
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    I bought 4 of everything. I hope it last a while!

  28. #28
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    So I got some of the parts in and heres what it looks like.


    I did some grinding to get the parts to fit. here is a picture of that work.

    If this doesn't work I'm at a loss.

  29. #29
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    Has anyone had issues with running The HR diffs cups With XO-1 Diffs in a Slash 4X4

  30. #30
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    Problems with the Hot Racing Diff Cups

    There are two different Diff cups offered for the revo trucks through Hot Racing. I have the RVO11C01, I can honestly say now that I would not purchase this cup. As of now I still have been unable to get this cup to stop slipping with the internal gears, the internal gears are also new and came from gpm racing. This is after shimming with 7+ shims, almost a 6mm difference in space, and testing it before reassembling the entire front chassis once again.

    I have purchased the RVO11X06 in the hopes that it is machined to be a more correct fit with the pinions and gears. If this does not work, I will be going back to the stock plastic cup.

  31. #31
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    any tips on where to find the HR diff cup to fit the slash 4x4? PN?

  32. #32
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    I got mine off of ebay.

  33. #33
    RC Turnbuckle Jr. humayrayakongkinaon's Avatar
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    Quote Originally Posted by reallytwissted View Post
    I got mine off of ebay.
    you got the old design, newer ones fits the I bar without a problem.
    http://www.ebay.com/itm/Hot-Racing-T...item2c7d6311cb
    | Rally GT8 Powered By CC | 360mm XO-1 GT |

  34. #34
    RC Turnbuckle Jr. humayrayakongkinaon's Avatar
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    Quote Originally Posted by JCsCustom View Post
    Has anyone had issues with running The HR diffs cups With XO-1 Diffs in a Slash 4X4
    guys from slash section upgrading their diff cup to aluminum and ended back to stock or XO diffs. aluminum wear out and start leaking thru the output shaft.
    | Rally GT8 Powered By CC | 360mm XO-1 GT |

  35. #35
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    Quote Originally Posted by humayrayakongkinaon View Post
    guys from slash section upgrading their diff cup to aluminum and ended back to stock or XO diffs. aluminum wear out and start leaking thru the output shaft.
    This is the problem I have on ALL my 4 traxxas and I don't know how to deal with. I kept breaking the stock diff so I upgraded to the newer HR aluminum diff but after 2 run, the aluminum where the output shaft is already wearing and the oil leaking thru. Only 2 run! The HR's first design with a 2 part design (RVO1011CS06) could have solved this issue but it is discontinued and I can't find any similar diff cup. I went through all brand (FLM, Rc best, Nova, etc) all are 100% aluminum and will have this same issue...
    I just can't find any good differential! Can you guys help me?
    ... for the fun of excess!

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