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  1. #1
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    FLM Hybrid Bulks + stock driveshafts + stock(ish) centres - what you need to know

    I thought that some people might like to know what list of parts you need if you plan to use the FLM hybrid bulks with standard or Traxxas CVD's plus FLM chassis and centre shafts.

    FLM Hybrid Bulks:
    -----------------
    FLM 18700 (kit contains front & rear combined bulk / diff housing)

    Diffs:
    -----
    HPI BUGGY DIFF

    These are now discontinued. You may be able to find some in stock still if you try different retailers. However, you can make your own by getting the following parts:

    Standard HPI diff, part number HBC8084
    Hardened gear set, HPI part number HBC8101-1
    Input pinion, HPI part number HBC8030
    Bearings, HPI part number HBC8020-1 (2 required per diff)
    Shims, 8mm diameter (a few required per diff - I needed 4 per diff)

    Diff output shafts for use with 6mm drive cups
    --------------------------------------------
    RCM diff shaft (2 required per diff)

    Input drive cup for centre shaft
    ------------------------------
    RCM 8mm drive cup (1 per diff) - comes with 2 x 5mm grub screw


    Using the above parts, I was able to install on a 3905 EMaxx with the following specification:

    - 3905 Emaxx
    - FLM V2 chassis
    - FLM centre shafts
    - Traxxas steel CVD's
    - MM2200 on 6S

    THe above setup is supposed to be pretty bullet proof. As I got through 3 x stock diffs in 3 weeks, the most recent of which lasted less than 5 minutes, time will tell if the above expense is worth it or not. All I can say is that the parts look pretty beefy so keeping my fingers crossed.

    The link to an on-line retailer has been removed. Please review Rule 11 of the Traxxas On-Line Community Rules, which prohibits the posting of links to on-line retailers.
    Last edited by cooleocool; 09-13-2011 at 05:48 AM. Reason: Old post brought into compliance with Rule 11 due to it being linked to in a new thread.
    EMaxx MM2200-6S,Rustler VXL,Twin Detonator,L/Box

  2. #2
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    I just did the same setup on my T-maxx 4908 earlier this summer. I wasn't happy about the way the front center shaft fits. It seems to be too long.

  3. #3
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    Can anyone comment on the above setup? Looks like this was posted over a year ago and i was wondering how well it lasted?

  4. #4
    RC Turnbuckle Jr.
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    It'll last forever pretty much- I've been using 1/8 UE diffs for over 3 years with no signs of wear; all thats needed is the occasional fluid change and check bearings for smoothness- barring a default or some catastrophic incident the gears will not wear down or break with years of use.
    Keeping the Mods busy is my specialty...

  5. #5
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    Been running for over 1 year with this setup. During this time, it has only been run on 6S, and run HARD. I've had 2 catastrophic failures (nothing to do with the diffs) when i) the gearbox shredded causing instant lockup at over 40mph. This obviously caused massive stress to front diff when all weight and forces were suddenly applied when the car tried to from 40-0 mph in an instance; ii) when the CC2200 seized, again causing instant lock up.

    During recent routine maintenance, stripped it down. Not a single wear mark anywhere on front or rear diff.
    EMaxx MM2200-6S,Rustler VXL,Twin Detonator,L/Box

  6. #6
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    What would i need to change my pinion and spur to after installing the parts above to keep the stock gearing? I was pretty happy with stock gearing on a 6S.

    Where did you buy the shims and what thickness where they?

    Thanks.

  7. #7
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    Can't remember what the shim were, but any 8mm ones will do. Not sure about keeping it at stock gearing (easy to work out if you use the speed calculator web page). I use 24/65 on mine, running on grass. Remember that the above mentioned diffs have a much lower gearing than stock so you need to gear up to compensate.
    EMaxx MM2200-6S,Rustler VXL,Twin Detonator,L/Box

  8. #8
    RC Turnbuckle Jr.
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    As a rough rule, gear up by a couple teeth on the pinion to get the same gearing as with the stock diffs- best to use BrianG's calculator to work out the exact ratios needed, just select the 43/13 diff option and enter the rest of the items like normal ( see the faq for a link ).
    Keeping the Mods busy is my specialty...

  9. #9
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    Been running pretty much that set-up for a while now on 4S, no problem what so ever.
    KD 700-HO 3905 - FLM E-Maxx MMM - ERBE - Slash 4x4

  10. #10
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    That HPI diff has been discontinued.

    I really don't understand that Calculator at all. I don't know the first 3 questions on a stock BL 3908 e-maxx.
    Last edited by RC Nut; 11-26-2010 at 08:43 AM.

  11. #11
    RC Turnbuckle Jr.
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    You dont need to- they are all there in the drop down list, you just have to read the words and select the correct options; I'll make it easy for you:

    1st option is traxxas emaxx ( who'd have thought it... ) 2.85:1
    2nd option is traxxas emaxx 1 speed or 2speed 2nd gear ( since thats what comes as standard, locked into 2nd gear; the 2spd kit gives you first gear )
    3rd option you dont have to touch- see the little blue question marks? they explain what each option is for/ does.


    Differential Ratio: 2.8461538461538463
    Transmission Ratio: 1.8333333333333335
    Other Ratio: 1
    Spur Tooth Count: 68
    Pinion Tooth Count: 24
    Total Voltage: 14.80
    Motor KV: 2200
    Tire Diameter (inches): 5.9
    Tire Ballooning (inches): 0
    Motor Current Draw: 0
    Motor Coil Resistance: 0.006
    Spur/Pinion Ratio: 2.83 : 1
    Total Ratio: 14.78419 : 1
    Tire Circumference (inches): 18.54 inches (470.8 mm)
    Rollout: 1.25:1
    Total Motor Speed: 32560 RPM
    Vehicle Speed: 38.66 mph (62.1 km/h)
    Effective KV Value: 2200
    KT constant: 0.61 oz-in/A

    Anyway, to get the same 39mph with the 43:13 diff ( misc 1/8 buggy option ):

    Differential Ratio: 3.3076923076923075
    Transmission Ratio: 1.8333333333333335
    Other Ratio: 1
    Spur Tooth Count: 62
    Pinion Tooth Count: 25
    Total Voltage: 14.80
    Motor KV: 2200
    Tire Diameter (inches): 5.9
    Tire Ballooning (inches): 0
    Motor Current Draw: 0
    Motor Coil Resistance: 0.006
    Spur/Pinion Ratio: 2.48 : 1
    Total Ratio: 15.03897 : 1
    Tire Circumference (inches): 18.54 inches (470.8 mm)
    Rollout: 1.23:1
    Total Motor Speed: 32560 RPM
    Vehicle Speed: 38 mph (61.04 km/h)
    Effective KV Value: 2200
    KT constant: 0.61 oz-in/A
    62/25 gearing, vs 68/24; nice and easy- now you know how to use the calculator you shouldnt have any issues working out optimum gearing for any given setup ( motor kv/voltage/cellcount/tire diameter etc alterations ).
    Keeping the Mods busy is my specialty...

  12. #12
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    I was confused about the 1st and second gear but thanks for your help

    What about the HPI diff, i get more than one result with part # HBC8084....There seems to be two diffs using that number one says hardened and the other doesn't say and it appears to be discontinued. Only places i found it where not in the US.

  13. #13
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    Oh yeah, its been discontinued for a while- I think that was/is the Hotbodies lightning diff- came in regular & hardened steel ( not sure which one I have to be honest, but its not worm at all so no worries ). As a substitute you have a few options:


    The insides of those should fit perfectly, or this is a complete list of parts to add to the hybrid bulks to complete them:

    1) Hot Bodies Differential Lightning Stadium = complete truggy diff
    2) Hot-Bodies 43T Lightning Buggy Series buggy ring gear ( swap for the stock one on the complete diff )
    3) Hot Hodies 13T Bevel Gear Lightning Buggy Series pinion gear
    4) XRAY 8x10x02mm Washer shims- 1 or 2 behind the head of the pinion usually is fine to set the mesh, but you will have to check yourself by feeling
    5) ProTek 8x16x5mm dual sealed speed 1 8 wheel bearings - 2 for each diff cup, 2 for the pinion gear
    6) RCM diff shaft x4- if you want to use traxxas driveshafts or cvds and drivecups
    7) diff fluid- 7k front & 5k rear is generic goodness, or 5k/3k- very much personal taste so cant recommend a brand or specific weights.
    8) RCM revo coupler (v2) if you want to usae stock center driveshafts
    9) RCM 8mm drive cup if you prefer center dogbones- dogbone length & where to get them from is tricky, many people use items sourced from other models/ manufacturers ( FLM 3905 chassis comes with bones ).

    The link to an on-line retailer has been removed. Please review Rule 11 of the Traxxas On-Line Community Rules, which prohibits the posting of links to on-line retailers.
    Last edited by cooleocool; 09-13-2011 at 05:42 AM. Reason: Old post brought into compliance with Rule 11 due to it being linked to in a new thread.
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  14. #14
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    Those HPI diffs are still available from Wheel Spin Models in the UK.

    The link to an on-line retailer has been removed. Please review Rule 11 of the Traxxas On-Line Community Rules, which prohibits the posting of links to on-line retailers.
    Last edited by cooleocool; 09-13-2011 at 05:41 AM. Reason: Old post brought into compliance with Rule 11 due to it being linked to in a new thread.
    EMaxx MM2200-6S,Rustler VXL,Twin Detonator,L/Box

  15. #15
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    Quote Originally Posted by tmaxxnutter View Post
    Those HPI diffs are still available from...
    There in the UK as i said above, i don't see any in stock in the US. I guess if i want them bad enough i can order them anyway.

    Does anyone else sell thouse parts besides RC Monster? They do not have enough of the 1/8 output shaft.
    Last edited by cooleocool; 09-13-2011 at 05:42 AM. Reason: modfied quote

  16. #16
    RC Turnbuckle Jr.
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    Quote Originally Posted by dtnel View Post
    So will these work on the 3908 with the stock chassis ?
    Yes, they will work on any maxx based truck.

    I see THe original post talks about the flm chassis and center shafts ?
    Thats because he had an FLM chassis when he did the upgrade- the only thing different between the flm and the stock 3906 chassis is the length, so you would have to source your own center-shafts. Truthfully though, the stock 3906 is a turd, you'd be better off upgrading the chassis to better handle the power of BL,- cant imagine putting such nice diffs & powerplant onto the crusty old chassis...

    Would I have to upgrade from the 3908 driveshafts and since these are 1/8th diffs do they have aluminum bulkheads for say made by gh so I can not have to change out my other aluminum stuff ?
    You dont have to use alloy bulks if you go the UE route ( see: above insults about 3906 in stock form ), FLM hybrids obviously replace whatever bulks you have now anyway. There is no upgrade 'from' 3908 driveshafts since those are the best traxxas make currently ( ignoring summit shafts and cvds ). If you try to use the old 3906 driveshafts though they will twist like pretzels under BL power; cant imagine anyone wanting to use UE/ FLM hybrids with brushed motors though. What exactly does your truck look like now and what upgrades does it have?

    This will be a slow gradual switchover as $$ is available so I would have to stay with the stock diffs till I get all the parts to make the diff and the bulks to hold the diff for the emaxx. THE only reason I'm considering this is a lot of people say the stock diffs don't last and I don't want to have to replace them over and over. I don't mind making them so long aa I can use them. DO they make a plastic bulkhead by chance so I can get THE diffs and make them and run them till I can afford the aluminum ? I'M thinking not but it never hurts to ask.
    Like I said, if you go the UE Ultralite diff route you can use whatever bulks you want; if you go the FLM hybrid route then your current bulks get replaced by the hybrid bulks- there is no plastic hybrid bulk option; its all or nothing...

    If you run brushed motors and dont intend to upgrade to BL any time soon, you are better off sticking with 3903/05/08 spec diffs as they will be fine, just shim them according to the how-tos posted on my website ( see: useful links page ). If you currently run BL or are intending to upgrade in the near future, then you are best off upgrading to 1/8 diffs; driveshafts, knuckles and turnbuckles could/should be upgraded at the same time to new emaxx spec parts ( unless you have beefy 3906 spec upgraded parts already ).
    Last edited by cooleocool; 09-13-2011 at 05:46 AM.
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  17. #17
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    I dont keep track of what trucks everyone has- if you dont say what truck you are talking about then I end up having to guess & sometimes get it wrong, so its always best to be specific.

    Since we talking about your 3908 then thats alright- any bulks does really mean any bulks you like that will fit the maxx chassis; GH included They will work just fine with the UE diffs ( I use FLM, its all good ) with no fitment issues. As for the rest of the driveline, if you have the stock plastic center shafts then you will want/need to use these:

    RCM diff shaft

    on the diffs, that way you can keep the stock center shafts and wont have issues finding custom shafts ( it replaces the plastic yolk that fits to the regular diff input shaft ). As far as the output shafts go on the diffs, you can make your own if RC-M doesnt have enough in stock:

    Traxxas p/n 5454

    just cut the threaded part off and hay-presto- not identical as the RC-M ones have grooves for the o-rings, but they will work just fine too.

    The link to an on-line retailer has been removed. Please review Rule 11 of the Traxxas On-Line Community Rules, which prohibits the posting of links to on-line retailers.
    Last edited by cooleocool; 09-13-2011 at 05:45 AM. Reason: Old post brought into compliance with Rule 11 due to it being linked to in a new thread.
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  18. #18
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    To be clear. The FLM 1/8th bulks are just that - they are complete replacement bulks so you can put 1/8 diffs in them. Therefore you cannot use GH bulks as well. GH bulks take stock diff assemblies (I assume), and FLM 1/8 bulks take well, 1/8 diffs. Take a look at the picture on the FLM site and you will see what you get for the money.
    EMaxx MM2200-6S,Rustler VXL,Twin Detonator,L/Box

  19. #19
    RC Turnbuckle Jr.
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    You're falling to bits man...

    Metal diff cases will hold up better due to reduced flex, but if you arent gentle with the throttle and brakes the spider gears in the diff cup can still strip teeth, same too with the ring & pinion.

    A much cheaper 1/8 upgrade route is to install some LST2 diffs between your garc bulks:



    All you need to do there is cut some pvc pipe to size to remove the slop, then install the output shafts if you need to ( not sure if the stock output cups are long enough so work with traxxas or mip cvds ) and the input cup/ coupler.

    Its never gonna be cheap though no matter what, so if money is tight you may have to sacrifice one of the other trucks to pay for upgrades on the other..

    The link to an on-line retailer has been removed. Please review Rule 11 of the Traxxas On-Line Community Rules, which prohibits the posting of links to on-line retailers.
    Last edited by cooleocool; 09-13-2011 at 05:46 AM. Reason: Old post brought into compliance with Rule 11 due to it being linked to in a new thread.
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  20. #20
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    Dumb question here.

    What is the Hardened gear set, HPI part number HBC8101-1 needed for? On FLM website it only list two parts needed (ot Bodies diff part #s. Diff c8084-1 and Pinion c8030)

  21. #21
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    When I tried to buy the listed parts, I was told that HBC8101-1 was discontinued. However, I was advised to buy the standard diff mentioned, and then hardened gears. Together, these make the diff back into the same item as HBC8101-1.
    EMaxx MM2200-6S,Rustler VXL,Twin Detonator,L/Box

  22. #22
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    Read post #5
    EMaxx MM2200-6S,Rustler VXL,Twin Detonator,L/Box

  23. #23
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    armyofdarkness, whats the part numbers for the ring and pinion gears you describe in your thread #13

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