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Old 04-18-2012, 04:57 PM   #1
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Default Rebuilding my BK2 tranny - Been a while

Hey guys,

Last time I ran my XXX BK2, was back when I lived in Nor-Cal (now I live in Atlanta), which was Fall of '04, and was running in 2wd Pro Mod club races every week/every other week.

Wow.. A LOT has changed since then, to say the very least!

Brushless and LiPo setups have become the primary 'weapon of choice'. Brushed setups nowadays, seem to only be for Club-Spec/Stock-Spec classes (and Rock Crawlers, lol). Now, it appears that ROAR has actually opened up to Brushless for those guys - Provided it's a 'ROAR-approved' Motor, etc.

Dang and even the Radios/Receivers/Servos have changed totally...

Not that any of these changes/progressions to new tech, is bad in anyway whatsoever! In fact, I am ALL FOR IT!! I just have LOTS to catch up on, and a ton of new self-education, I've gotta get cracking on!


Okay, now onto my question.. Just had to get that out in the open is all haha


I'm planning to rebuild my BK2 tranny (GenII) [grey], and I noticed that when the CR-variants came to fruition, it seems to me that Losi brought back the original [black] XXX tranny/internals - Correct?

Well, now with the advent of the new '22' platform cars, and shoot, even on the CR's.. And with the typical shared parts/part no.'s between cars/etc. that Losi and all other MFR's do, I've noticed there are some revised parts either implementing the original part no.'s, or with new part no.'s, altogether.


My main question, is for the BK2 with the grey GenII tranny/diff... The part numbers (in question) of the original/stock and 'newer' counterpart components are:

BK2 (GenII)
*A2933* - Differential Screw, Hardware, and Seal (It's the nut/carrier that I want to 'upgrade')
^A3099^ - Full Thrust Bearing Set (individual balls/washers)

Newer 'Counterpart' Components
A2908 - Monster Differential Square Spring/Screw Set
A2909 - Monster Differential Adjusting Screw, Hardware
A2910 - Monster Differential Adjusting Screw Set (Sport)
*A2911* - One Piece Differential Nut/Carrier
*R2948* - TLR Aluminum Differential Nut Holder (22)
^A3018^ - Heavy-Duty Thrust Bearing Set (pre-assembled/set thrust bearing washer/balls)
^A3098^ - Molded Differential Thrust Bearing

NOTE: Please observe the *asterisk* and ^caret^ designations used above and their corresponding 'counterparts' between the two lists.


I'm not quite sure of the fitment/interchangeability.. Primarily, because I know that 95% of the internals of the GenI and GenII tranny's are totally different. So I just want to make sure that these specific parts in question, are the correct/matching ID and OD (inner and outer diameter), so I can sort of 'upgrade' my BK2 tranny to some of these newer parts, that the awesome TLR team drivers have helped develop, as better/faster/stronger revisions, to already great parts.. (no Daft Punk pun, intended.. lol)


My main goal is to have a little cross-compatibility 'crash parts' excel sheet that I'll have in my DropBox folder, that if I'm somewhere at a track somewhere that has some of the above 'counterpart' components. I'd know that 'Part ABC123' can be replaced by 'Part XYZ321', if they didn't happen to have the EXACT part no. replacement in-stock, that a similar/same component found in a different part no. can be used instead.

Oh and of course, I'll spread the wealth and post up my cross-compatibility 'crash parts' spreadsheet for you guys to use yourself, or add onto!



Thanks for your help in advance! Look forward to getting back into the swing of things!!

PS, this is also my first post on the forum.. Haha, so pardon my formality, as I'm an Industrial Designer/Mechanical Engineer - I'm a little OCD.


Thanks!!
Weavty1
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Old 04-18-2012, 09:09 PM   #2
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It's been a long time since I ran XXX's, but if my memory serves correctly-

The only things that interchange between Gen I and II are the diff balls, thrust assy, bearings, idler shaft, slipper plates/pads/spur and diff nut itself (not the diff bolt, one is longer than the other). Maybe the rings but I'm not sure, at some point they removed the "D" shape and put in copper shims, I think when the XXXCR came out, so the outdrives and rings go together. The monster diff is a variant of the Gen I trans diff and everything interchanges with the Gen I as such.
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Old 04-19-2012, 06:35 AM   #3
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That's about right. The diff rings work too, the "cr" rings have copper backing shims that make it smoother/less prone to slip.

FWIW, the Bk2 can still be quite competitive. Apply the Matt Chambers standard setup from the TLR site for the xxx-cr. At the end of that car's run they were using rear end parts that were a lot closer to the Bk2 configuration than the cr. I'm still using the older cars, they do not hold me back at all.
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