Official Erevo 1/8 scale center diff thread
 

Well , I decided to collect some of the info from MC, and my self and anyone else who has contributed to this CD, so it would be easy to find for everyone, I'll be copying & pasting in the info....
The birth of the 8th scale Revo CD - <!-- status icon and date --> <!-- status icon and date --> 08.31.2009, 10:30 PM <!-- / status icon and date --> <hr> (Mistercrash)
<!-- message --> I experimented with a few options and ideas posted on the net about these diffs.
Two of them I found to be very interesting, a third one was made by a guy in France but it was almost a carbon copy of someone else's. The very first was made by CowboyRay some years ago for the nitro Revo 2.5. This was before Traxxas even came out with their own CD for the Revo. It was made with a Thunder Tiger S3 center differential, the TT spur gear was replace with a machined aluminum cap on which a custom plastic gear was secured with 4 M3 screws. I got my hand on a well used CowboyRay diff and inspected it carefully. The diff is smooth and the cap is very well machined, a thing of beauty. I noticed quite a bit of slop on the output shaft that went through the aluminum cap. Might be that a stronger and harder metal is needed there as the aluminum of the cap wore out and allowed the output shaft to wobble a bit too much for my taste.
The other one was made by scjrss and with his coaching; I made three of his CDs. He came up with a clever solution to secure the Traxxas CD output gear to an Ofna Hyper 7 CD spur gear. The Hyper 7 spur gear had its teeth grinded off to transform it into a cap and 4 holes were drilled and tapped in it matching the holes of the Traxxas CD output gear. The Traxxas output gear could then be secured to the Hyper 7 spur gear (cap) with 4 M3 screws of the right length. A brilliant idea and it works. But the part I did not like is threading the 4 holes in the Hyper 7 spur gear. It’s hardened steel that is probably as hard as the steel from the tap. It can be done but really, it’s a PITA. I noticed some seepage of diff lube using those CDs. It seeps from between the threads made in the spur gear and the screws. Not a lot but enough to annoy me.
Then there’s this guy that came up with a different way. I would like so much to remember where I saw the thread, I have searched and searched and can’t find it or remember where I saw it. If you know about it, please post his name here as this is HIS idea. He made four holes in the 8th scale CD spur gear and counter sunk from the inside. That way he was able to secure four aluminum inner threaded posts with M3 flathead screws and with some minor modifications, the Traxxas output gear could slide on the posts and secured to the posts with M3 screws. This post idea is the base of the CD I did last. I used a Losi LST XXL diff, just a regular diff, not a center diff. And instead of using four posts I used two. For the output gear, I used a different Traxxas gear since the Traxxas CD output gear is not sold separately. Once I was done with this last CD from a Losi diff, I decided to take the time to fit this new Traxxas gear to the CowboyRay CD and the sjcrss CD.
It is good to be as precise as possible when modifying the parts to make these CDs, but it doesn’t have to be down to a thousandth of an inch, you’ll see from the pics that the parts I modified are not perfect. It doesn’t matter because the thing works anyway. We are not touching any internal components of the diff and as long as the output gear is centered on the diff, all is fine.

So lets begin with the Losi CD, first you need a few parts, here is where I found the parts I needed. I give you the links to where I got the parts but you might have other sources to get parts from.

The Losi LST XXL diff, I found and bought it on ebay, I am posting a link but it might not work for a long time, just do a search on ebay for ‘’Losi LST XXL diff’’ and a lot will pop up.

http://cgi.ebay.com/NEW-LOSI-LST-XXL...d=p3286.c0.m14

The output shafts, made from the Traxxas 3.3 Revo CD output shafts. Part numbers TRA5415 and TRA5416. The shaft measurements can be seen on the pic.

http://www.amainhobbies.com/product_...put-Shaft-Revo
http://www.amainhobbies.com/product_...t-Gear-Revo-33

The Traxxas gear, part number TRA3985X. I think they were output gears for the old E-Maxx tranny.

http://www.amainhobbies.com/product_...r-33T-2-E-Maxx

For the aluminum posts, I had a few inner threaded aluminum posts and all I had to do was cut them to the length I needed. To find posts, just search on Tower Hobbies or A Main for ‘’post’’ and a lot of inner threaded aluminum posts will come up for servo trays, steering bellcranks etc. Just find the ones that would be easy for you to cut to the right length. I found these from Axial and I think they would work without any modification to them.

http://www.amainhobbies.com/product_...mm-Post-Grey-2

Two 8X12X3.5 mm bearings

http://www.amainhobbies.com/product_...all-Bearings-2

8x10 mm shims and 6x8 mm shims to center the CD perfectly in the tranny.

http://www.amainhobbies.com/product_...mm-shim-kit-10
http://www.amainhobbies.com/product_...6x8mm-Shim-Set

1.5 mm thick carbon fiber. Aluminum or other kinds of metal can be used also. Even a simple washer of the right size.

http://www.fullforcerc.com/Carbon.htm

Four M3x6 mm flathead hex socket screws. No link here as I am sure everyone has a place to get them, hardware store, LHS or online.

Here’s a link to some carbide bits that will help tremendously in drilling and counter sinking the holes in the ring gear

Drill bit
http://www.usacarbide.com/catalog/pr...ducts_id=17778

Counter sink bit
http://www.usacarbide.com/catalog/pr...ducts_id=17916

(Mistercrash)
I started by modifying the Traxxas TRA5415 and TRA5416 Traxxas output shafts. You cut the gear part off and have to drill a 2.6 mm hole for the spider gear pin. The tricky part is having the hole perfectly centered in the shaft.

http://i177.photobucket.com/albums/w...16_shafts1.jpg

Here are two of the TRA3985X Traxxas output gears, you see them with the flat side of the spokes up. The left one is stock and the right one has been drilled in two holes with a 6 mm bit. If you use the Axial posts I linked above, the holes will have to be 7 mm or 9/32 inch. There are two of the gear’s spokes that are thicker than the rest. The holes have to be drilled next to those thick spokes and which side of the spoke you drill is also important. I drilled according to the rotation of the gear inside the tranny, I wanted the forces exerted to the gear to be transferred to the posts from those thick spokes. The center hole has a little ridge that was cut off to allow the 8X12X3.5 bearing to sit a little deeper in the gear.

http://i177.photobucket.com/albums/w...f/th_mccd1.jpg

The two inner threaded aluminum posts that will be screwed to the diff cap. The length on the posts is about half a millimeter less than the thickness of the Traxxas TRA3985X output gear.

http://i177.photobucket.com/albums/w...f/th_mccd4.jpg


Now to start modifying the ring gear. I make the holes and I counter sink them first. To make sure that the holes were in the correct position, I used the Traxxas output gear and aluminum posts as a template. I slipped the two posts in the holes I made in the output gear and the 8X12X3.5 bearing in the center hole. The bearing is there just to center the gear perfectly on the ring gear. An 8X12 bushing would work also but I couldn’t find one.
I take the Traxxas output gear with the posts and bearing and I slip it on the ring gear, I rotate it to center the posts between the screw holes of the ring gear the best I can and with a 2.3 mm drill bit chucked in the drill press, I go through the posts and make contact with the ring gear. The 2.3 mm bit will not touch or damage the threads in the posts, this is just to make a couple marks on the ring gear to show me exactly where to drill the 3 mm holes with the carbide bit. I take off the Traxxas output gear and then I can make the holes and counter sink them.

http://i177.photobucket.com/albums/w...f/th_mccd2.jpg

Then I take a 6 mm threaded rod I have and with two nuts and two washers, I secure the ring gear to the threaded rod. I can then chuck the rod in my drill press and with an angle grinder, I grind off the teeth until the gear is left with a half millimeter lip that will fit over the diff case.

http://i177.photobucket.com/albums/w...f/th_mccd6.jpg http://i177.photobucket.com/albums/w...f/th_mccd8.jpg

This step is optional; I chuck the threaded rod in a power drill and with a belt sander, I can clean up the marks left by the grinder.

Here’s the finished ring gear from both sides, now transformed into a cap. You can see the counter sink holes on the inside of the cap.

http://i177.photobucket.com/albums/w...f/th_mccd9.jpg http://i177.photobucket.com/albums/w.../th_mccd10.jpg

We’re ready to assemble the center diff. I start with securing the posts on the ring gear with the M3X6 mm flathead screws. I put blue Locktite on the threads.

http://i177.photobucket.com/albums/w.../th_mccd11.jpg http://i177.photobucket.com/albums/w.../th_mccd12.jpg

(Mistercrash)
Then I put the 8X12X3.5 bearing on the cap. Here you can see a shim underneath the bearing, you can do without it. I had the shim so I used it, it just positions the bearing in the middle of the output gear.

http://i177.photobucket.com/albums/w.../th_mccd13.jpg

I assemble the diff with my choice of diff lube. I like to run 100k for a stiff diff. On 4S, this lube is thick enough to allow some wheelies but unloading to the front is minimal. 50k will give you a looser diff with more unloading to the front but on 4S wheelies are practically inexistent.

http://i177.photobucket.com/albums/w.../th_mccd14.jpg

I slip on the Traxxas output gear over the posts and bearing.

http://i177.photobucket.com/albums/w.../th_mccd15.jpg

Now for the carbon fiber disk to hold the gear in place with two M3X6 mm flathead screws.

http://i177.photobucket.com/albums/w...f/th_mccd5.jpg http://i177.photobucket.com/albums/w.../th_mccd16.jpg

The last part is one of the plastic spacers that come with the stock output gear and shaft of the ERBE. I sanded it down to the right length and it serves as a spacer so the CD can butt against the bearing in the tranny case.

http://i177.photobucket.com/albums/w.../th_mccd17.jpg

I slipped it on the output shaft and in the carbon fiber disk until it is well seated against the cap and put a drop of CA glue to glue it to the carbon fiber disk.

http://i177.photobucket.com/albums/w.../th_mccd18.jpg

Now install the CD in your ERBE and enjoy some trouble free CD action for racing. Next posts will be the Traxxas TRA3985X output gear installed on the scjrss and CowboyRay CDs.

(Mistercrash)
TRA3985X output gear on the scjrss CD - <!-- status icon and date --> <!-- status icon and date --> 09.01.2009, 11:57 AM <!-- / status icon and date --> <hr>
<!-- message --> So here's how I installed the Traxxas output gear on the Hyper 7 CD that scjrss made. Here's the cap made from the Hyper 7 spur gear with the 4 holes that are threaded with M3 threads.

http://i177.photobucket.com/albums/w...scjrss_cd1.jpg

The red you see in the holes is just something I am trying to stop lube seapage between the threads and the screws. It's very sticky and tough tape used to tape the seams when you put vapor barrier on your house's walls.

http://i177.photobucket.com/albums/w...scjrss_cd2.jpg

Here's the CD assembled ready for the output gear.

http://i177.photobucket.com/albums/w...scjrss_cd3.jpg

Other than the center hole that was trimmed to let the 8X12X3.5 bearing go deeper in the gear, it didn't need any more modifications. The thick spokes of the output gear are lined up between the threaded holes of the cap.

http://i177.photobucket.com/albums/w...scjrss_cd4.jpg

Four M3X16 mm flathead screws that were trimmed down to 14.5 mm in length to secure the output gear to the CD.

http://i177.photobucket.com/albums/w...scjrss_cd5.jpg

And here is the final product ready to use.

http://i177.photobucket.com/albums/w...scjrss_cd6.jpg

(Mistercrash)
TRA3985X Traxxas output gear on the CowboyRay CD - <!-- status icon and date --> <!-- status icon and date --> 09.01.2009, 12:06 PM <!-- / status icon and date --> <hr>
<!-- message --> Finally here's how I put the Traxxas output gear on the CowboyRay CD. Here's three shots of the machined diff cap. This is a well used cap so that's why it looks a little grungy.

http://i177.photobucket.com/albums/w...boyray_cd2.jpg

A shot of the stock Traxxas output gear on the left and the modified one on the right. Some grinding was needed in the spokes for the screws to meet the holes in the cap and some grinding of the spokes from underneath the gear so it would fit on the cap's elevated portion.

http://i177.photobucket.com/albums/w...boyray_cd1.jpg

Here's the CD assembled.

http://i177.photobucket.com/albums/w...boyray_cd3.jpg

And here is the output gear on the cap lining up with the cap's holes for the screws.

http://i177.photobucket.com/albums/w...boyray_cd4.jpg

The finish CowboyRay CD with the Traxxas output gear using 4 M3X8 mm flathead screws to secure it to the diff cap.

http://i177.photobucket.com/albums/w...boyray_cd5.jpg
<!-- / message --> <!-- sig -->

(Sjcrss)
Here is the 4 hole drawing dimensions
here is the drawing for the bolt pattern to drill & tap the 3mm holes in the ofna ring gear, after i finish my shafts, I'll get those dimensions and add them to the drawing as well....FYI, scroll down a bit, pic is at the bottom......sorry dang scanner placed it there...lol
http://img.photobucket.com/albums/v4...oltpattern.jpg

If I missed anything let me know or just add it directly to this thread, thanks everyone for the contribution

Very awesome guys. Glad all this info is in one place now and can grow even larger. I'm not even finished with my first one yet and already the wheels are turning on what to do next! Thanks for all the hard work everyone has contributed to make this easier on less experienced people like myself.

I can't access my Photobucket account for some reason. All I get when I click one of my pics is this message:

The action that you were trying to perform has failed.

Even if I try to log in to my account from the Photobucket page, I get the same message.

All is fine now, I wanted to get this and post it, it's sjrcss's. Or Shane's.

http://i177.photobucket.com/albums/w...r_drawing1.jpg

Here's my first question for the new thread: what are the smaller two o-rings used for in the Thunder Tiger diff internals?

You won't have to use them, they went on the original outdrives of the Thunder Tiger EB4 S3 diffs and center diff.

Thanks, next question: what is the purpose of the new bearing you've fitted on the cap/spur side of the diff?

The 8X12X3.5 bearing is simply to center the TRA3985X output gear perfectly on the spur/cap. An 8X12 bushing would do the same but I couldn't find one so I went with the bearing. It will not move or turn so even an old gritty bearing will do fine.

Got my parts into the machine shop today. Should have them back by tomorrow or Thursday. I'll post a pic of the finished product when I have it all pieced together.

What weight oil is everyone running? Heaviest I have on hand is 10k, but I'm not sure if that is a good starting point?

I run 50k, center and 30k F/R, I think Mc runs 100k center, not sure on F/R, looking forward to the pics, and your input on the CD as well..... glad you enjoyed the build....

Well, today was a very bad day. The machine shop called and said they drilled the holes in the output shafts but that the hardened cap was too hard and they weren't even able to make a dent in it. I can't see how this is possible. I told them people have drilled/tapped these in their home workshops and they just said "I don't know what they did but we can't do it, it's too hard". I think the are BSing me and just didn't want to do the work for the price they quoted me. When I first talked to the guy he said "I don't think this is as hard as everyone has told you". Yeah right....

So then I go pick everything up thinking "Well at least they drilled the output shaft pin holes" and the holes are drilled too far in on the shafts. The shafts aren't flush with the gear, they stick out past them. I had written 0.229" on my drawing but I haven't measured yet to see if they drilled the wrong distance or if 0.229" is wrong. It's my own fault for not double checking it myself.

At this point I don't even know what to do. Output shafts can be ground down to make them flush, but they might be too short now, and I guess I'll have to try drilling/tapping the hardened cap myself without having access to proper tools. Everything was going so well....

EDIT: I'll post some pictures of the shafts with gears when I get home, maybe you guys can see if I'll still be able to salvage them.

Take your output shafts and mount them in the diff with all the gears and pins and gaskets and O rings but mount it dry, no lube in the diff. If you can tighten the screws of the spur gear in the diff case all the way down tight and snug that will be good. Now if the output shafts turn with no excessive binding then you're fine. If the shafts really are too long for you to tighten those screws on the spur then grind them down a tiny bit and still you will be fine. Remember that what bolts on the output shafts are ''slider'' shafts so even if you're off by 0.005'' it won't make a difference, it will still work fine.

Here are the output shafts with gears mounted in their current state. The pinholes are exactly 0.229" (5.8mm) from center to the end of the shaft, so please note that isn't the correct measurement to use. I did make the shafts a tiny bit longer just in case something like this happened. If they were going to be off I wanted them to be long. My main concern is that the part of the driveshaft that mounts to the outputs will be too close to the trans case and hit it or rub.

Currently the shafts are 29mm and 41mm. Each shaft wil have to be ground down another 2.5mm to be flush with the gear. This will leave the final lengths at 26.5mm and 38.5mm.

Compared to the original measurement suggestions (27.2mm and 40.6mm) the smaller shaft will be 0.7mm short and the larger shaft will be 2.1mm short. So the total length I've lost is less than 3mm. As you can see by the difference in the 2.1mm and 0.7mm I wasn't very accurate in my original cuts, but hopefully that will work to my advantage since they are longer than suggested. Hopefully this won't be as big of an issue as I first suspected. The 0.7mm isn't much, but the 2.1mm lost from the longer shaft is what I'll be most concerned about.

Now drilling/tapping the hardened steel, that will be a much more difficult issue. I still think there is something weird about the machine shop saying they couldn't do it. It's not a shop in someones garage, it's a huge shop with thousands of dollars of CNC mills, lathes, and other heavy duty machinery. And they want to tell me they can't do a job multiple people here have done in their basement workshops? Just doesn't add up...

Anyway, I'm going to keep on trucking. I've put a lot of time (and a modest amount of money) into this and not going to give up now. Sorry to clog up the official thread with a bunch of my ramblings. Maybe it will help someone avoid the same mistake in the future. I'll post the exact measurement from pinhole center to the end of output shaft once I grind them down and make them flush against the gears.

Thanks for all the help you guys. Wouldn't have been able to do this without everyone else helping. I know it will be awesome once everything is finished!

http://i47.photobucket.com/albums/f1...3/P1020362.jpg

I went in the garage and dug up the original output drives of my Ofna diffs and you are correct in saying that 0.229'' is wrong. I gave you that info and I'm sorry. I measured 0.190'' and that is from the original output drives of the diffs, not some bogus calculations from CAD drawings like I gave before. When putting the original output drives in the gear, they do stick out a little bit but definitely not as much as your pic shows. The part that sticks out on the OFNA drive I measured as 0.018''. As for the total length of both of your output shafts you'll be left with after you shorten them, you will have to try them to see if the drive shafts fit without rubbing on the tranny case like you said. That machine shop with the tens of thousands of dollars, if not hundreds of thousands of dollars in equipment should invest in a 20 dollar carbide drill bit and an 80 dollar carbide M3 tap. Unbelievable that they said they can't do it. I suspect they just don't want to do it and they should be honest and just say so and explain why.

No prob mistercrash. You were trying to help me and I should have been responsible for checking my own numbers and measurements. Worst case I'll probably be able to use the short output and might have to replace the longer one. No big deal.

I ground down the output shafts to make them flush with the gears. The overall total length of the assembled diff is now 72mm. The short shaft sticks out of the cup side a hair less than 13mm, the long shaft sticks out of the spur side 16mm. I forgot that I still need to wait for my 8x12 bearings to arrive before test fitting.

I went to two different industrial tool shops today and everyone told me "If xxxxx machine shop couldn't drill/tap that metal I don't know what to tell you." They also said carbide is very brittle and I should try cobalt drill bits? I kept telling them that people have done this plenty of times with carbide and it can be done, but they didn't seem to want to listen. It's getting very frustrating. I think I'll just order the carbide bits online.

What about trying to soften the metal a bit? Is that even in the realm of possibility? Might not work but I want to explore any options to make this easier.

I just ordered a drill and tap. Hopefully these will get the job done:

http://www1.mscdirect.com/CGI/NNSRIT...PMPXNO=2209799
http://www1.mscdirect.com/CGI/NNSRIT...PMPXNO=1897620

Annealing the metal to make it soft, then drilling & tapping, then re hardening is something I've seen mentioned before on the subject of drilling difficult metal parts. May need to look that shizz up though as Im no blacksmith...

I have been doing a little bit of reading:

"Spot-Annealing Hack Saw Blades and Other Hardened Steel:

Spot-annealing requires a drill motor and a nail or other steel rod about the diameter of the desired hole. Cut off the nail head and smooth the end, then chuck the nail into the drill motor. At high speed, attempt to drill a hole in the hardened steel. The attempt will fail, but the resulting friction will heat the metal until the point of contact turns straw, then bronze, then peacock, and, finally, blue.

Stop the heating process and allow the steel to cool while you replace the nail with a drill bit of the desired size. At low speed, using a cooling/lubricating fluid, drill the hole through the softened steel."

Anyone think this is a possibility? Seems like a weird way to heat up the metal, but maybe it would work? Otherwise I'm thinking of just heating up the cap with a torch.

I never had any problems drilling hardened shaft with carbide bits and my mini drill press.

It is true that carbide bits are very brittle, I drill at the lowest speed my drill press can go and I go slow, especially when the bit is just about to go through to the other side, that's when I am extra careful because that is the point where I lost a couple bits because they snapped like glass. I just go very slowly, not much pressure is needed because the bit just cuts through the metal like butter. I also have a set of numbered bits that I used successfully to drill in the hardened steel of the spurs. I have no idea what they are made of, I got them from an old neighbor, her husband had died of cancer and he was into model trains, she let me in his shop and let me pick whatever I wanted at a yard sale price. Only the tools, she wanted to keep the trains.
I don't know what the heck is wrong with the machine shops in your neck of the woods, looks like they're a bunch of woosses.

Do you think it would be helpful to get some type of cutting fluid or other machining lubricant?

I don't use cutting oil when I make the holes in the spur with a carbide bit. I don't let the bit get warm and the metal is relatively thin. I would use cutting oil with cobalt bits. I used cutting oil when I made the threads, it's more like a wax. Something like this.

http://www.fastenal.com/web/products...3126544&ucst=t

I posted on a CNC machining forum yesterday to get a bit more advice. People recommended trying to do some spot annealling by taking a butane and/or propane torch and heating the cap for 10-15 min. (blue point of flame directly on area to be drilled) and then letting it cool to room temp. They said it should be a bluish tint after the process and that should mean the steel has softened up a little.

I'm going to try that. Then, I'll try the cobalt bits with the cutting fluid. If that doesn't provide any results I'll move on to the carbide bit.

The place I ordered the bits/tap from actually had a free upgrade to next day shipping. I left a note for the UPS guy to leave the stuff at the door. Hopefully they won't need anyone to sign for it, but I'm not sure since it's next day service. I really would like to be able to finish this project over the weekend so there better be a package waiting for me when I get home!

Why don't you just use the carbide bits right away instead of trying the spot annealing and cobalt bits? To me, that's just a waste of my time. Work smarter not harder. Lowest speed setting on your drill press with the carbide bits work wonders when drilling hardened steel.

By the way, in order to prevent the bit from wandering initially due to the coating on the hardened steel, I sand or gring the surface to roughen it up.

SUCCESS!

I annealed the metal, made a divot with some diamond dremel bits, and then drilled with carbide bit and tapped with cobalt tap. Couldn't believe how easy the drill and tap went through. I almost wonder if I softened too much or if the bits just made it that easy? I wasn't that surprised at the carbide bit chewing through the steel, but the tap was also much easier than I expected, barely required any force. The threads seem solid though and the drill bit was 2.5mm.

I feel kind of dumb now. I had this turned into such a big deal in my head and it turned out to be no problem. Oh well, it's done now! Going to do a test fit and see if anything else needs to be changed. Thanks again for all the help guys!

http://i47.photobucket.com/albums/f1...3/P1020363.jpg

Looks good, great job, I would make sure the heads of the bolts don't interfere with anything inside, I don't think they will, i can't remember off of the top of my head right now...sorry, but great work ..

Test fit confirms everything is A-OK including the shortened outputs. The screws are very close to the inside of the trans case, but a few shims on that end gave them enough clearance. Rotation is smooth all the way around with no binding. All there's left to do is fill it up with silicone oil and make sure everything seals up tight.

I'm so glad it's finally done :lol: Just joking SC :mdr: If everything checks out, if it rolls nice and free inside the tranny and there's no big leaks then go out and enjoy it, you'll love it for sure. Great job. :party:

It was definitely a learning experience. Knowing what I know now I could probably put one of these together over a weekend. To anyone thinking about making one of these diffs: if I can do it, anyone can. Don't be intimidated by the hardened steel, it's very do-able with the right tools and right advice.

EDIT: One more question about the silicone oil. 50k and 100k seem very high to me for a 1/8 diff. Is that just the nature of the E-revo to need heavier fluids even with this hybrid diff? Or do you guys just like the diff to be very firm? I figured once I swapped all my diffs to 1/8 diffs I could run similar setup to a truggy (7k/10k/3k for example), but now it seems like I'll need heavier weight oils?

Here is a article I typed up out of RC driver some time ago, it should help explain the basic concepts behind diff oils...
http://www.rc-monster.com/forum/showthread.php?t=5050

Great article there scjrss, I think that the weight of the truck and the amount of suspension travel it has are a big part of the reason why the center diff needs heavier oil than a Truggy would. The E-Revo squats quite a bit in the rear on acceleration, the front end wants to go way up in the air because of the power of the MMM. Anyway, the truck looses a lot of front traction on acceleration because so much of its weight is transferred to the back wheels. With that said, if the CD has thin lube in it, the front wheels will just spin like crazy and overall acceleration will suffer. Weight transfer can be controlled a bit by putting the front pushrods in the most outer hole of the suspension table, less droop. Putting the hinge pin of the rear suspension arms in the lower hole helps two I've heard. Using the extended rear arms for a longer wheel base and puting your batteries to the front of the battery compartments.
With 10k in the CD, your truck will not wheely, but it will feel sluggish on acceleration and the front tires will look like pizza cutters. With 50k, you will be able to wheely moderately on high traction surfaces, less unloading to the front but still a lot if you don't use throttle control. The acceleration will be much better. With 100k, you can wheelie on demand on asphalt and grass, but not on dirt. High wheelies that make the rear wing touch the ground but the truck won't flip on its lid. Throttle control is a must on start ups, accelerations are explosives on asphalt and grass but a little squirrely on dirt (throttle control fixes that)
This is just from what I have tried up to now, I also tried 30k and I thought it unloaded too much to the front, less than the 10k but not by much.
From what I have experienced and according to MY preferences, the ideal weight lube for me would be around 68.24k to 72.86k :lol:

Now about those machinists you talked to and wouldn't help you, go back to them and show them what you did.

Thanks MC, I agree about the machinists, go back and show them what you did......since they said it couldn't be done....as for the diff oil, I like mine at 50k, but I also have throttle, ect and a few other things set on my radio, and this helps me control my erevo, but it still can wheelie on asphalt as well, still kinda tweaking it.....

Anyone have any new developments?

I still need to get silicone diff fluid, then I'll be dropping in all of the 8th scale diffs. Decided to start at 10k front, 50k center, and 10k rear. Not sure if the F/R diffs will be thick enough? I have the 10k fluid but I need to get 50k. If the 10k is too thin i will need to also order some 30k and run 30k/50k/10k or 30k/50k/30k. What do you guys think?

I use 30k/50k/30k in mine..it works for me