Locking The Diff

[Davewins13]

Hi all,

Can someone please explain the reason for locking the diff?

Can it be done to a Lunchbox?

Does it improve the handling?

Under what conditions is it most efective?

Can someone tell me how to do it? (pics will help)

Thanks guys

Dave

[mobias]

Locking the diffs on monster trucks enables better traction for crawling and general mucking about but obviously comes at the cost of cornering performance because the inside wheels on a turn aren't free to have less revolutions. If you've got a big 4WD truck like the TXT or High Lift you can get away with just locking the rear diff and it doesn't have too bad an effect on cornering and gives you much better traction. On a small 2WD truck like the Lunchbox cornering will be effected because you've only got drive from the rear wheels although your trucks ability to hill climb and crawl over mud and rocks will be improved. In a small gearbox like the Lunchbox you could probably just use very heavy duty grease. There's stuff which i think is called JB-Weld which people use in the TXT's gearboxes which all but glues the diff together.

[Davewins13]

Thanks,

The only use the Lunchbox gets at the moment is when my son comes to stay and we go over the park. I noticed that it sometimes get's stuck in long grass because one wheel is left spining. If I locked the diff would this help?

Someone mentioned on another site that it could be locked with blu-tac, would this be ok.

Also do you know how I could prevent the front wheels rubbing on the shock springs during reverse and cornering?

Cheers

[skip665]

Locking the diff on a lunchbox isnt easy as the gears to transmit the power to the driveshaft are part of the driveshaft themselves. Someone may prove me wrong here but I dont think its straight forward...

[markbt73]

It's hard to use grease or other sticky stuff on that diff because it's open - there isn't any way of keeping the sticky stuff in. It will just get flung off the gears by centrifugal force, and you'll be back to an open diff again.

If you really want to lock the diff permanently, you can epoxy the spider gears together. But there's no going back unless you get a new set of gears. If you want to try it, I'd suggest getting a second set of diff gears and rear axles, and epoxy the whole thing together and install it as a unit. Then, if you don't like how it drives, you can always put the original gears and axles back in.

Oh, and FYI, to make parts shopping easier, the rear axle on a Lunchbox is the exact same thing as on a Midnight Pumpkin, and all the Grasshopper and Hornet models. Very common and easy to find parts, especially since they've all been re-released.

[mymonsterbeetleisbroken]

Oh, and FYI, to make parts shopping easier, the rear axle on a Lunchbox is the exact same thing as on a Midnight Pumpkin, and all the Grasshopper and Hornet models. Very common and easy to find parts, especially since they've all been re-released.

they share the same spur gear, diff gears and drive axles, but the plastic gearbox case itself is very different! The hornet and grasshopper have less plastic bracing around the axle tubes, so they are weaker than the pumpkin/lunchbox ones.

[markbt73]

they share the same spur gear, diff gears and drive axles, but the plastic gearbox case itself is very different! The hornet and grasshopper have less plastic bracing around the axle tubes, so they are weaker than the pumpkin/lunchbox ones.

Really? Huh. You learn something new every day. I have both at home; I'll have to look at that when I get home.

[pearce_jj]

Really? Huh. You learn something new every day. I have both at home; I'll have to look at that when I get home.

Another reason to lock the diff is to get power-slides and doughnuts on loose-ish surfaces. The problem with the diff in the LB is that as soon as you start to slide, the wheel with the weight on it looses all power because the other wheel is spinning like crazy, hence ending the slide

[Davewins13]

I had I tinker last night and although I have not locked the Diff yet I did mess about with the rear suspension. I have compressed the springs with some of those spacer things. I also locked the whole lot to the main chassis. Where those little return springs are that always break I have taken them off and drilled small holes at the bottom the treaded a screw through the hole into the pivot points of the gear box housing. THis now means that the rear suspension no longer rocks from side to side and keeps the wheels on the ground at all times. It pops wheelies more but seems to be more stable. The real test will be tomorrow when I take it out with my son.

If it works well i will post pictures of what I did.

[mymonsterbeetleisbroken]

That does work but now your rear suspension can only go up and down, it can't articulate.

check out this thread for something called the 3rd shock mod:

3rd shock mod

[Davewins13]

That does work but now your rear suspension can only go up and down, it can't articulate.

check out this thread for something called the 3rd shock mod:

3rd shock mod

Yeah I have seen the 3rd shock mod before. I don't have the parts and can't really afford to get them just yet. When I can I will.

Cheers

[mymonsterbeetleisbroken]

Yeah I have seen the 3rd shock mod before. I don't have the parts and can't really afford to get them just yet. When I can I will.

Cheers

Cool

Its a worthwhile mod and can be done with most shocks. I bought a second hand set of monster beetle ones when i modded my midnight pumpkin. The only other bit you'll need is one of those little alloy shock mounts that came with the kit.

[Davewins13]

Well I tried to lock the Diff this weekend and it did not go well.

I first tried the blu-tac and as predicted it all got flung off and I spent the next 2 hours cleaning the sticky gunk off the cogs.

I then tried blocking the gearing with rolling cigarette filters, this worked for about 2 mins then they got shredded.

Next I tried to superglue some pits of plastic cut from the part mounts in the kit. The idea was to prevent the small cogs spinning but they only worked for 2 mins again before being ripped off.

I did not want to permanently lock the diff because I don't want to have to buy a replacement just yet.

Does anyone else have any ideas for locking the Diff?

Cheers

[skip665]

I have fitted polymorph to my Mud Blaster diff and it appears to work well - although I have not used it in anger yet - for a couple of quid its worth a go - easily removable without ruining the diff too...

Do a search on eBay for "polymorph"

[terry.sc]

Hot melt glue will also do the job and can be peeled off.

I used Polymorph to lock my Clod crawler diffs, which use the same diff parts as the Lunchbox. Heat it up, put it in all the gaps, assemble the diff and make sure you keep it squeezed together until it sets. Diff is now locked, but the polymorph doesn't stick to it so it can be removed easily.

[Rabiedmushroom]

Don't use Tamiya Putty; that just goes hard and shatters. An alternative to temporary blue tack; RCDaggerweb.com seem to favour Silly Putty (but that's internal for a Dagger/Twin Det). I may try it in my own!

[pearce_jj]

So clod diffs fit the lb?? Like this: http://www.thundertechracing.com/balldif.htm

[mymonsterbeetleisbroken]

So clod diffs fit the lb?? Like this: http://www.thundertechracing.com/balldif.htm

Nope, sadly.

the clod diff gear has much larger teeth than the lunchbox, as its a much larger truck.

although the diffs are similar in size and appearance they are not interchangeable. I've just checked and it looks like the only parts shared between them are the 3 small bevel gears inside the main diff gear, that must be what terry.sc was talking about.

[Davewins13]

I spent ages last night working on the problem and I have found a perfect solution which does not involve putting anything messy in the diff.

I took out all of the smaller cogs and threaded a small piece of rubber tubing over rod holding the cogs in place. I then put the cog back on so that the tubing was pushing it inwards to the central of larger cog.

Now the small cog is being pushed into the middle and locking itself against the central spokes.

I have run a couple of batteries and so far nothing has gone wrong and nothing is broken.

Is this an original idea? Have I finally been able to answer the question asked by all frustrated Lunchbox owners?

Dave

[terry.sc]

So clod diffs fit the lb?? Like this: http://www.thundertechracing.com/balldif.htm

No, I said diff parts, as in the bevel gears. any technique used for locking a clod diff will work for a LB diff as the gear teeth are the same size.

[markbt73]

I spent ages last night working on the problem and I have found a perfect solution which does not involve putting anything messy in the diff.

I took out all of the smaller cogs and threaded a small piece of rubber tubing over rod holding the cogs in place. I then put the cog back on so that the tubing was pushing it inwards to the central of larger cog.

Now the small cog is being pushed into the middle and locking itself against the central spokes.

I have run a couple of batteries and so far nothing has gone wrong and nothing is broken.

Is this an original idea? Have I finally been able to answer the question asked by all frustrated Lunchbox owners?

Dave

So it adds some resistance to the small bevel gears, and also forces them against the large gears...

You're talking about just a very thin slice of tubing, right at the backside of the gear?

[Davewins13]

So it adds some resistance to the small bevel gears, and also forces them against the large gears...

You're talking about just a very thin slice of tubing, right at the backside of the gear?

Thats right, it works really well and does not gunk up the gears with glue so can be removed if needed.

[markbt73]

Well, to quote another guy who drove a van: "I love it when a plan comes together."

I did a little research, mainly because I was curious about how a limited-slip diff in a "big" car worked. And a quick Googling uncovered this:

http://auto.howstuffworks.com/differential4.htm

Basically, by slowing down the diff action by making it overcome some static friction, exactly like your little slices of tubing do. There are more complicated designs, but the one most often used, and in production since the Fifties, works exactly the same way, except it applies force to the two large outer gears, instead of the three inner gears.

I was thinking of how to do something similar with springs and thrust bearings on either side of the axle, but your solution is simpler, and more elegant.

Congratulations; your Lunchbox now has Positraction. And I hope you don't mind if I steal your idea for my 'Box.

[Davewins13]

Well, to quote another guy who drove a van: "I love it when a plan comes together."

I did a little research, mainly because I was curious about how a limited-slip diff in a "big" car worked. And a quick Googling uncovered this:

http://auto.howstuffworks.com/differential4.htm

Basically, by slowing down the diff action by making it overcome some static friction, exactly like your little slices of tubing do. There are more complicated designs, but the one most often used, and in production since the Fifties, works exactly the same way, except it applies force to the two large outer gears, instead of the three inner gears.

I was thinking of how to do something similar with springs and thrust bearings on either side of the axle, but your solution is simpler, and more elegant.

Congratulations; your Lunchbox now has Positraction. And I hope you don't mind if I steal your idea for my 'Box.

Be my guest.