Monster Beetle Blackfoot Gearbox

[berman]

I had a search using my topic thread in the search engine but didn't find anything relative.

I'm getting a clicking noise on take off or har, low speed turns when accelerating, I'm guessing it's either the mesh of the spider and bevel gears slipping,

or the hex driveshafts slipping inside the cups. I'm sure I've read something about this before, but I cant find anything.

Help?

Cheers

Neil

[mymonsterbeetleisbroken]

Your correct

It's almost certainly the diff gear slipping. It happens due to wear of the metal gears, and the flexing of the aluminium gearbox side plates under load. These two issues combined together cause the diff gear to slip and make that cracking sound.

The more worn it gets, the easier it slips.

You can replace the parts with ones from the re release frog or brat. The gearbox side plates can be flexed back into shape with the aid of "careful hammering" and a block of wood, or bent back by hand if you're up to it

[berman]

Your correct

It's almost certainly the diff gear slipping. It happens due to wear of the metal gears, and the flexing of the aluminium gearbox side plates under load. These two issues combined together cause the diff gear to slip and make that cracking sound.

The more worn it gets, the easier it slips.

You can replace the parts with ones from the re release frog or brat. The gearbox side plates can be flexed back into shape with the aid of "careful hammering" and a block of wood, or bent back by hand if you're up to it

Awesome! Cheers MMIB

Well I have enough spares to build another gearbox but are mostly secondhand parts, so i will compare with the ones in my current gearbox.

Although it's probably just easier to replace them with new ones than have some seconds lasting 3 months and doing the same thing aye?

The motor side plates flexing, that explains why there is another thread on here for custom made 3mm thick alloy ones.

I'm guessing it's around the diff cups where the motor plate flexs and needs some gentle persuasion?

Thanks again for your help!

Cheers

Neil

[mymonsterbeetleisbroken]

I'm guessing it's around the diff cups where the motor plate flexs and needs some gentle persuasion?

Thanks again for your help!

Cheers

Neil

No problem

Yep, the diff cups are where the flexing happens, so concentrate efforts in that area when bending them back.

Forgot to mention the white plastic bearing housing that the differential sits in. those while plastic parts rub against the gearbox side plates and can wear down too, adding to the sloppy differential problem. CRP used to produce yellow ones made from harder plastic.

[Blacque Jacque]

For a more permanent fix, try the oldfrogshot mod:

http://www.tamiyaclub.com/showroom_model.a...74&sid=3142

Basically, you cross bolt the diff cups thereby stopping anything spreading apart.

I've done this to my Monster Beetle & it's had loads of run time since, with no more cracking from the gearbox. I also have a Brat, as yet unbuilt, but I've already prepped it for this mod.

The design flaw was addressed in the Super Blackfoot gearbox & those that followed it.

[berman]

No problem

Yep, the diff cups are where the flexing happens, so concentrate efforts in that area when bending them back.

Forgot to mention the white plastic bearing housing that the differential sits in. those while plastic parts rub against the gearbox side plates and can wear down too, adding to the sloppy differential problem. CRP used to produce yellow ones made from harder plastic.

Cool thanks for that I might invest in some brand new plastic housings (brat/frog/hornet ones?) then, as no doubt they are worn.

For a more permanent fix, try the oldfrogshot mod:

http://www.tamiyaclub.com/showroom_model.a...74&sid=3142

Basically, you cross bolt the diff cups thereby stopping anything spreading apart.

I've done this to my Monster Beetle & it's had loads of run time since, with no more cracking from the gearbox. I also have a Brat, as yet unbuilt, but I've already prepped it for this mod.

The design flaw was addressed in the Super Blackfoot gearbox & those that followed it.

That's a pretty cool mod. So when the differential is working whilst turning (as both drive cups wont turn the same speed), does the drive cup with the head of the screw, just spin on the screw head?

Thanks for your help guys!

Cheers

Neil

[Blacque Jacque]

That's a pretty cool mod. So when the differential is working whilst turning (as both drive cups wont turn the same speed), does the drive cup with the head of the screw, just spin on the screw head?

Thanks for your help guys!

Cheers

Neil

Correct, the screw mustn't be tight, otherwise it will lock up the diff totally.

I've built several of these now & I find it best to screw it up finger tight, then slacken just a fraction before the Loctite starts to set.

[berman]

Correct, the screw mustn't be tight, otherwise it will lock up the diff totally.

I've built several of these now & I find it best to screw it up finger tight, then slacken just a fraction before the Loctite starts to set.

Yeah I figured as much. Do you drill a recess/countersink with a larger drill bit in the drive cup to sit the screw head in? Or is there enough clearance for the hex shaft?

Thanks for your help. I think I have nearly enough parts for a spare gearbox so I might build one on the side. Might get new bevel gears and B parts (those little white bearing spacers). I'm guessing the rere brat uses different ratio to the blackfoot due to it's smaller wheels? Otherwise I would replace the counter and diff gears aswell.

Neil

[Blacque Jacque]

I have a suitably small countersink bit which I run into the cup & match it with an M2.5 x 25 csk stainless screw.

[rc-martin]

I've used this mod on my wild one gearbox also, but instead of a 2.5mm screw I used a 3mm screw because I already had the taps and a box full of screws. Works a treat.

[berman]

Thanks guys, I will go to my local engineering shop tomorrow. Good excuse to buy a new tap n die set

[berman]

No such luck with the 2.5x25mm ss csk anywhere, can only find 16mm in 2.5mm

On a side note, I rebuilt the current gearbox with spare parts today...

Nasty.

Have all brand new parts for the other gearbox (apart from a pinion), but would've liked to have done the oldfrogshot mod first.

[Blacque Jacque]

No such luck with the 2.5x25mm ss csk anywhere, can only find 16mm in 2.5mm

On a side note, I rebuilt the current gearbox with spare parts today...

Nasty.

Have all brand new parts for the other gearbox (apart from a pinion), but would've liked to have done the oldfrogshot mod first.

Ooh, that's unpleasant.

PM sent too

[Leethal Driver]

I've been planning to sell my Thorp diff (to offset my recently bought Scorchers) but haven't as yet due to same issue: 2.5mm x 25mm countersunk screws are as rare as rocking horse poo.

Which is nice, cos I love my Thorp, but I really would like to get a couple of said screws.

Russ, don't suppose you can spare me a couple could you? Can trade for 1 x 50mm

[berman]

Mmm thorp...

Loaded them all in the car today and took them out for a bash at a newfound pozzy, king cab rear was screaming like a banshee...

what is it, International Diff Repair Week? *grizzle grizzle*

[Jack_Truck]

I have hadd this problem a few times. All I did to fix it was to tighten the screws on the gearbox.

[Jeep-Power]

For a more permanent fix, try the oldfrogshot mod:

http://www.tamiyaclub.com/showroom_model.a...74&sid=3142

Basically, you cross bolt the diff cups thereby stopping anything spreading apart.

I've done this to my Monster Beetle & it's had loads of run time since, with no more cracking from the gearbox. I also have a Brat, as yet unbuilt, but I've already prepped it for this mod.

The design flaw was addressed in the Super Blackfoot gearbox & those that followed it.

Sweet-

I spooled (epoxied the diff together) my Blackfoot years ago, but I think the new addition of the 35T motor & 2C LiPo has caused one of the bevel gears to break loose-- (it pulls wheelies *hard* from a stand-still)

I was worried that I'd have to dig for parts, but I'm pretty sure this will do the trick. Thanks for posting that link!!!

[chris350z]

make sure your metal plates are flat, as they tend to bow out

chris

[Jeep-Power]

I know what you mean. Fortunately, with the diff locked together, it takes most of that 'pushing-out' force away. The bevel gears are not trying to push themselves away from the spider gears.

I tore into mine last night-- it wasn't the differential gears. It seems I never upgraded the counter gears' bushings-- they were worn to heeel and thus allowed the smaller intermediate gear to eat itself & diff gear.

Luckily I had a bunch of Wild One / Fast Attack gears in the parts bin. These gears are a little 'taller' (48 teeth vs. 47 on the Blackfoot diff gear), but that's ok-- I can use a little more top speed--

The new set is epoxied together & ready for install.