Lock / Semi-Lock Differential Options / Trade-Offs

[squidchief]

My apologies, I'm sure this question has been addressed a hundred times but I did try the search function and could not find what I was looking for.

Apparently it is normal that when you start off hard the front lifts just high enough to allow a lot of the power to go to the front wheels, ballooning them up and a reduction of real 4 wheel drive traction, not to mention the accelerated wear to the middle part of the tire tread - tires being about $50 for just one pair you'd want to avoid premature wear. Here are some things I've read about locking down the center differential:

- Mash silly putty or silicone earplugs in there;
Q: which is "safer" to avoid damage to the differential itself?
Q: which is more reversible if I decide to go back to stock oil later on?

Q: What common (automotive, marine, etc...) thick-ass grease could I put in there to stiffen but not lock the differential?

- Creating unacceptable stress / damage to the front and rear drivetrain;
Q: True or not?

- Makes steering control harder / worse;
Q: True or not?

Q: What are the trade-offs of doing this, is it "worth" it? (subjective, I know).


Thanks!

 

[KevinC]

1) use earplugs before putty,.or use proper 20 million oil. I’ve never used earplugs personally.....just diff fluid.
2) you won’t want to reverse your choice back to stock after you see the results.
3) Lucas red and tacky......it will do nothing to stiffen your diffs, it’s used on the gears outside the diff cups.
4) I think not
5) mine steers just fine. I use an upgraded servo though. diff fluid does affect steering to some degree. More experienced guys can chime in.
6) worth it.


Put 1 million in your front and rear. The stock copperheads balloon a lot no matter what fluid is in the diffs. Pick up some belted duratrax....lockup’s or six packs.

Remember you said you aren’t going to spend hundreds of dollars?.......this hobby is like Heroin bro. It’s a natural progression. I see a Hobbywing Max5 combo in your future......

cheers,
kev

 

[squidchief]

Kev,

You are awesome, thank you very much for your input! Yea, already put more $$$ into it in one month than I thought I would all year (parts, tools, etc...).

On the Duratrax Six-Pack X, I know you need to expand the center hole to 18mm, and most people apparently just use a step-bit. My concern doing it that way is how can I ensure that the drilled hole is absolutely perfectly centered? I don't have a drill press to lock the tire to be perfectly centered on the drill bit, so I'd have to do it with a hand drill. At $56 a pair, I don't want to screw it up.

Thanks.

 

[KevinC]

The duratrax 6 packs and Lockups now sell specifically for the Arrma 8s rigs......meaning the hole is already big enough (18mm) to fit over the stock wheel hex. Just make sure when you order those tires, you get the right ones. The banditos also sell with a proper fit.....but they’re road tires.

If you happen to mis-order and get the tires with the smaller hole, no worries.......I have never used my kick ass drill press to ream these out.....always my trusty dewalt with the step bit. I was very worried as well the first time I did this. Go slow, switch the tire around so you are drilling from the outside and inside.....equally. Keep in mind, the tire/hex fit is “Hexcentric” so if you are off a tiny bit, it’s the hex that determines the wheel fit......not the hole you’ve drilled.

Again, this won’t be a worry now that they sell them to fit your rig.....

Are you going to take the plunge and do your diffs? You won’t be sorry. I couldn’t wheelie mine at all stock, but when I did the the 1mill/20mill/1mill........pure magic bro.

cheers,
kev

PS.
Have you installed the 23 T pinion?.....I can’t remember if you did or not. If you haven’t......you going to want that on this rig.

 

[squidchief]

Kev,

I looked deeper into the bowels of the internet and found the 18mm versions of the six-pack and lockup. Thanks!
Unfortunately they won't be in stock anywhere until some time in March.

On Horizon Hobby's web site I put the pages of the DTXC5587 (six-pack belted) and the DTXC5586 (lockup belted) both side by side and aside from a very minor difference in the tread pattern, the writeup, features, size, and specs are identical. Even the non-belted versions have the exact same writeup (so basically the same writeup for 4 different tires). Uhggg. Duratrax's tire chart only goes up to 5583, so it isn't even updated showing the new tires.

So:
- What is your (or anybody reading this) opinion on if there is any tangible difference between the two?
- Go belted or non-belted? Pros & Cons of each?

- Thoughts on doing the threading a fishing line through the nobbies, 3 times around and across 3 rows to stop the tires from ballooning thing?

Yes, going to shove some silicone earplugs in where the sun doesn't shine as soon as I get the chance. Looks like I'll have to heat up the 4 screws with a soldering iron or a torch to get the screws hot enough to loosen the Loctite from what I've come across reading about it.

Still running the 17T pinion, have not put the 23T in yet. The wheelies are cool but for now maximum control and good handling is what I'm going for.

 

[KevinC]

The difference in tires will be negligible.
Id go belted if possible, they balloon less.
The fishing line trick........seems to work but I’m far too lazy to go to those lengths.

Yes, the Center differential can be a real pain to deal with. I’ve busted some screws even after using a torch......

Since your going to do this, it’s a good time to change out that pinion......the rig is going to be apart anyways so I’d take advantage of that fact. Use heat on those motor mount screws too....

cheers,
kev

 

[squidchief]

Thanks, yea figured as much on the tires, like diet coke vs coke zero. Got the mounts out - as soon as I felt resistance on the screws I took out my little mini butane torch - which is GREAT since it has a very small but pin-point blue flame and I can pretty much only get the head of the screw and hardly any overlap to the surrounding metal. Got the 23T standing by for install.

Next up is the differential gear.

 

[squidchief]

Center diff all done. My mini butane torch was perfect, was able to concentrate the small blue tip right on the outside of the red case where the threads were behind. Didn't even melt the 3 plastic spacers. I did not even need to directly heat the tops of the screws - just as well because of the proximity of the spacers. Screws came out with a little resistance but nothing near enough to damage them. YEA!!! OMG was that sucker HOT . Cleaned out all of the old threadlocker paste from the internal threads as well as the screws so not only do I have good metal to metal contact but also a nice clean surface for the new threadlock application.

What I did not expect was the grease inside was black and at least 3 times as hard as the silicone ear plugs. I wouldn't even call it grease. It was so hard that I was able to scoop / pry it all out with a mini screwdriver. Weird, the car only has less than 2 hours run time on it. Chopped up the ear plugs into 4ths, mashing them in one layer at a time as I put the gears back in, got 3 full plugs in there.

Before I put everything back together, going to put 2 long square steel stock bars underneath the chassis plate, attaching the bars at multiple points by drilling and tapping holes in them with the screw heads on the inside top of the chassis plate. I'm willing to sacrifice 1/4" of ground clearance to help reduce the chances of the chassis bending. Might incorporate the length of the rods to beef up the strength of the front and rear bumpers.

Also ordered carbon fiber tubes on amazon to put over the 2 top red support rods to prevent them from bending at all.

 

[KevinC]

“What I did not expect was the grease inside was black and at least 3 times as hard as the silicone ear plugs. I wouldn't even call it grease.”

Thats because it’s not grease, it’s the 20 million silicone oil Arrma now installs in that diff. After you run a while with the earplugs and do a further oil change down the road, your earplugs will look black and chunky too......the same texture as the stuff you pulled out. It be what it be. My 20 million oil looks like the Ganges river bottom if the water was drained when I do an oil change.

Glad you got the screws out no problem. It’s a major pain when they break off inside that case. I know......

It’s a pricey hobby, particularly as you move up in scale......s#it gets more expensive. I wish you all the best with the chassis mods but if you stick with the hobby the compulsion to make your rig the best it can be will overwhelm you and you will acquiesce...........M2C, Hobbywing, or Castle will creep into your mind and take over. FWIW, my stock chassis is still straight, but I changed it after 4 months ‘cause that’s what the cool kids were doing.

Resistance is futile.

Then.....you’ll buy another rig because this is the BEST HOBBY EVER, and the process starts again.

cheers,
kev

 

[Arrma15T68]

Hi Kevin I was reading your thread and liked and agreed with everything you wrote. Then I saw Brantford ,Ont ! Cheers from Caledon .