E Revo Center Diff questions and Opinions
 

Hi Guys,

Well I've trashed my second diff in my E Revo so far.

The first was the stock rear diff. It sheared a tooth off the pinion, then began chewing it up.

I upgraded with RCM V2 diffs using 13/43 gears. Everything shimmed perfectly. For output shafts, Ofna Mutilator cups were used. These took the place of the inner cups for the Traxxas CVD's. Also installed.

The front diff pinion bearing on the RCM diff is gone this time.

I also see the rear center drive shaft is about to shear off the Rear U-joint.

My current setup is:

MMM ESC
Medusa 36-70-2000kv geared 22/40 (46mph with the 13/43 diffs)
4S Lipo.

I do like to run a tight slipper. It is usually screwed all the way in, then backed off about 1 turn.

I know the Traxxas center diff will lessen the shocks to the drivetrain, but it will also change how the truck drives. Front Tire ballooning on acceleration, difference in braking, and other things I'm sure.

Should I get the center diff? Please tell me about your opinions and experiences.

I'm really tired off rebuilding/replacing diffs, but I want my truck to haul butt.

I'm putting together a parts list. Should the Traxxas Center Diff be part of this rebuild?

Thanks

If you mostly bash, don't even consider the Traxxas CD. They leak and are weak.
If you ultimitely decide you want a CD either look for a premade 1/8 scale used one or build your own.
Check out "Mistercrash" erevo build thread,he's posted pics and details on a CD build.

I like my center diff, if you tape your tires you won't have as much ballooning, almost not noticeable at all. I don't know how it affects braking, but it's nice keeping the front tires down, but with a loose slipper, you may not have that issue anyways.

I have ran a CD from the start and never had an issue with a diff, since March anyways.

I say get one, try it out! For the price, it's worth a shot!!!

I'm currently debating if I'm going to make one of those hybrid center diffs. The hardest part is grinding all the teeth from the Thunder Tiger spur and drilling/tapping the hardened steel. After that it's basic assembly.

I'm wondering what is the reason you need to use the TT spur and modify it? Seems like it might be easier to make your own out of alum. since the hardened steel is so much tougher to work with. All you need is a circle of alum with the correct diameter, then drill/tap the four mounting holes and drill a hole through the center for the shaft to go through.

I would say it's a bit more complicated than that. You need a small round groove on the inside of the cap for the O ring to fit in nice and snug so the lube won't leak around the output shaft. A lip around the edge of the cap that fits over the diff case to center it. The hole for the output shaft has to protrude by 6 or 7 mm so the shaft turn straight and true and doesn't wobble all over. The aluminum cap you speak of would have to be quite a bit thick if you want to screw into it to hold the output gear in place. The modified spur gear or ring gear is not that thick but it is so hard that even though there's only 4 or 5 threads to screw in, you can torque those screws very hard and the threads won't strip, the threads on the screws will strip first even if you're using 12-9 screws. CowbyRay made his cap out of aluminum but they were done right and there was some extensive machining involved. It was more than just a flat piece of round stock.

Well, so much for that idea. I have a drill press, but don't know how I'd grind down all the teeth on the TT spur since it's so hard, but I'll have to figure something out.

mistercrash: Do you have to use the TT center diff or will most common center diffs work? Is there any reason the TT diff was chosen in particular?

I went to the store and got a long 6 mm bolt with a lock nut and a couple washers. I put the bolt in the 6 mm hole of the gear for the output shaft and secured the whole thing with the washers and nut. Then I chucked the assembly in the drill press and made it turn fast. I put an angle grinder to the gear and started grinding away at the teeth. A lot of sparks and a lot of noise but it worked.

The reason I ask if you have to use the TT diff is because I'm going to be putting the RCM Slipperential in my Caster truggy so I'll have the stock Caster center diff already that I'd like to use instead of buying the TT one.

EDIT: I decided I wanted to make things easier on myself so I ordered the Thunder Tiger parts. Maybe the Caster diff will work, but I'm going to have a hard enough time following the directions with all the correct parts, let alone trying to modify it for different parts. I might be PM'ing with some questions once I start the build if that's alright with you mistercrash.

For anyone else interested in building the hybrid center diff: Total cost shipped for all parts came to about $50 (I ordered two of the plastic Revo gears in case I mess one up or shred it while driving). You'd expect to pay close to that for any other decent buggy/truggy diff so it's not too expensive IMO.

traxxas CD sucks balls

:lol:

Other kinds of diffs work to make a CD out of them. I used a Thunder Tiger diff, I used an Ofna Hyper 7 diff following scjrss instructions and I am presently running a CD made of a Losi LST2 diff.

Isn't that a good thing ?

I used a bench grinder to cut the teeth off of the hyper 7 diff's ring gear, I just cooled it with water after it started to get hot, also the revo plasic gears won't work, the teeth count is incorrect, you need the gear from the traxxas CD or mod the original lower gear like Mc did. Don't forget the (1) 8X12 bearing for the one end also.

I ordered 2 of the plastic Traxxas gears that mistercrash listed (Traxxas Output Gear 33T: TRA3984X) I believe they are from the Traxxas CD. Going to get the bearing also.

EDIT: Where did you guys find the 8x12x5 bearing? I can only find 8x12x3.5, which probably would work? mistercrash are you sure it's 8x12x5?

The gear you ordered is for use in a 3.3 revo tranny, you need the gear from the traxxas CD or use the original one and mod it for use with the Erevo trans. Also look on avid rc, and the bearing you find is the 8x12x3.5, and it will work just fine. Thats what I used and it works great.

So Can the Traxxas Center Diff hold up to the power of the Castle 2200kv Motor on 6S?

I'll have to ask mistercrash. I ordered the exact part number he gave in his build thread.

EDIT: I'm almost positive it's the right gear (TRA3984X) but you just need to modify it quite a bit. The other gears can be used, probably with less or no mods even, but I'm following mistercrash's instructions exactly. There might be a reason he chose that gear instead of the other CD gear. Waiting to see what he says.

SC, I'm pretty sure it wont work, because Mc received all the info from me, considering I designed and built the first one. the reason it won't work is the teeth count s incorrect. So I'm just saying this is all. But you can wait for MC....

TRA3984X is the output gear that comes stock on the Forward Only Shaft in the ERevo's tranny. It has 33 teeth on it just like the output gear of the Traxxas CD. I used that gear because the output gear on the Traxxas CD is not sold separately. I found it was a lot of money to buy the whole Traxxas CD just to use the output gear so I modified the output gear TRA3984X instead. I am also working on fitting a different gear from Traxxas that has the same tooth count and that is inexpensive and may require less modifications.

OK good, just needed to make sure I had the right one. Be sure to let us know how that new gear works out.

Sorry for my miss understanding... let us know how it all works, also SC, sorry if I came off harsh......but sometimes it appears to me that when I put input into the discussion about this CD, it's like im treated like I dont the what the heck im talking about and that everyone is waiting for Mc to respond....

No big deal at all. I just needed to be absolutely sure before I sent back the gears I bought and ordered different ones.

Thanks man for understanding.....hope it works...... if you need any more info, ie bolt pattern, ect.. shaft length...go ahead and ask...

no cause i have one:whistle:
500k oil feels like it's empty!! the E-revo diffs in front/rear are able to be put up with, still 500k in the front diff is what's needed (5k in rear lol)

when i get hold of one i'm going with the hyper 7 diff mod.

Actually I think I'll ask mistercrash.... oops sorry... :lol:

All joking aside I'll definitely have some questions once all the parts show up and I start the build. Thanks for the help so far.

OK, I don't mean to be rude guys, but...........

9 Posts later and I'm going to ask again.

"So Can the Traxxas Center Diff hold up to the power of the Castle 2200kv Motor on 6S?"

The gears are small just the the regular diff, set the slipper to your tatse and it'll last a while. You wanna use 6s with 1/10 scale diff,it's gonna give sooner or later ?
I was using one with nitro for a few months befor I decided to convert it, I checked the CD and gears were ok, but leaked dry. Leaking is problematic with the silicone gasket design. Sorry I can't be of more help..

How dare you ask us not to hijack your thread!!!!!!

Go for a hybrid CD if you are going to use one. From what I've read the Traxxas CD will unload way too much to the front, especially since you'll be running 2200kv on 6s. The hybrid CD will handle the power much better. The Traxxas CD may be able to handle the power you're going to give it, but I think you'll have a hard time getting it to function how you want.

Thanks Bondo. I appreciate it.

I just want to get this "pick list" of parts together.

My setup is going to use 4S actually.

A MMM ESC and a 36-70-2000kv Medusa. I may upgrade to a larger motor later. But first I have to get this setup to be reliable.

I'm not sure If I will like the handling changes the center diff brings, since I mainly bash. I may give it a try though. :yes:

PS.....I've been running the 1/8th scale RCM diffs. Kinda disappointed they didn't hold up longer

:lol::slap:

I take it that it comes with oil that is waaay too thin?

What do you suggest the diff be filled with? I could fill it with bearing grease or something really heavy. LOL

This might also help with the leaking problem.

My TRX CD in my nitro powered 3.3 Revo w/500,000 wt still diff out.

If you bash,considering staying with the tranny as is.

Murphy's Law- "If It Aint Broke, Don't Fix It ?

I have said it before and I'll say it again, sjcrss is the one that came up with this idea of an 8th scale CD that can be done without the help of a machinist. All questions and PMs should be directed to him :mdr: Whatever I come up with using a different gear will be derived from HIS original ideas so even questions about that CD should be directed to scjrss :lol:

It comes filled with 500k, and people still say that's way too thin. The problem is it only has 2 spider gears instead of 4 like in normal 1/8 diffs. Less gears means less ability for the viscous oil to apply resistance.

People have tried all kinds of diff lock greases and thick stuff in it. I'm not sure how successful they've been though. It sounds like 1/8 hybrid is the way to go if you want a CD. I'm only speaking from what I've read, but once I build mine I'll let you know how it works.

Thanks MC

Not to argue w/you Jason but the CD comes w/100K, I had to buy 500K to refill mine and it was much thicker than the stock fluid.

Is 500K about the thickest fluid you can go with?

Trying to start $h1t with me huh? That's it, I'm coming back down there to have some words with you.

Bondo is right it's 100k. But someone should tell Impakt RC:

http://www.impaktrc.com/product_info...oducts_id=3469

I think 500k is pretty close to max as far as silicone oil. I know there are several "diff lock" products on the market, but I think they are more like greases/pastes/putty.

EDIT: According to some other forum posts I just read there is 750k and 1M weight silicone oil, but it's kind of tough to find.

Bring it Kid ! :whistle::lol:
When we get done scraping we'll hit the track !
Did you get my email w/the news I got a buggy finially ?

really?
ok then in that case i'm gonna put this kyosho 500k to replace the std oil in the revo center diff and see if that makes it any better...