TOPIC:

My first RC car was back in '86. Bought a Black Foot used from a friends brother. It came with an RS-540SD Endurance motor (wish I still had that!) I was great once I'd saved up enough for an Airtronics XL2-p. When I finished 6th grade that year I'd made honor roll all 4 quarters and as a gift my parents let me drag them down to Jim's RC in Derry NH and I got a Tamiya RX-540SD Technipower to replace the "Techniblack" I had. That turned out to be the death knell for the Black Foot tranny After a zillion sets of Diff/spider gears I parked it and it was lost to a bunch of moves and time.

This one came almost as you see it...showed up last week.
It needed tires and electronics, so I happily obliged with a brand new RS-540 Sport Tuned Black motor as a nod to my younger days I popped in an HPI ESC and a Spektrum RX and Servo. The tires are a spare set I had for my Monster Beetle Project{s}. Body has no cracks and just needs a sunroof and rear window....maybe some black paint on that grille and some color for the driver. Need to put the rear bumper back on

It's just as fun to drive as it I remembered but I'm taking it a bit easy until I fab up some braces for the tranny to fight the side-plate flex (the cause of the nukes diffs of yesteryear).

The truck is a survivor and I'm just going to play with it gently. No big resto, just smiles.

Since it arrived I gave it some of the parts I never could when I was a kid...Monster Beetle CVA shocks, bearings and some CRP Suspension pivots and rear bumper/tranny brace. I wiped it down and just have been having a ball driving it.

I build scale 4wd rigs and while I truly enjoy both the zen of the build as well as the nirvana of driving a scaler, the Blackfoot pastes a HUGE smile on my face.







From last week before the CVA's etc...

nice to see the monster truck surviving through all the fads

In another topic I suggested replacing the gearbox sideplates with copies made from say 18swg stainless, or just anything stiffer than the standard ally ones. Seeing as you're already looking at modding, maybe you're an ideal candidate to try this?

Again, in another topic it was suggested that Tamiya specified the techni-wotsit motor as a hop-up & I immediately fell about laughing at the idea of extra power being put into this gearbox, seems you confirmed my suspicions!

I have in the past also thought about just writing off the MB/Blackfoot box as a bad job, & thought about the possibility of just grafting in a better 'box, eg Wild One or similar - I'm fairly sure it would be much easier & more final than trying to make the original do what it's supposed to

Nice blackfoot and its great to see it being used and not restored to immaculate condition. The used look seems to suit it

before I ran the truck I kept thinking back on all my failed diffs and how to deal with the root cause. Back then, a friend actually milled the plastic part down a few thou on each side...this kept the plates sandwiched in tighter and worked well.

Once I got this beasty going I assumed I'd have issues everywhere as the specs on the Black Sport Tuned motor, and my 8.4 volt NiMh battery were far beyond what I put to mine even back when I popped the Technipower (on beat up old 7.2's) in there.

The upshot here is that I have not had a single diff failure and I've been having a blast with the truck. I think the reason has two parts...the first is that I have the CRP rear bumper and and the mount is a brace for the tranny sides. The second is that I've nuked 2 spur gears. They're old and seem to be the sacrificial element. They splinter the teeth off before the diff can see the torque.

I'd planned on just welding a few beads along the case sides to stiffen them and I may very well do it. The weld bead would certainly add rigidity without the need of having someone tool up a CNC machine (lots of cash!)

RJ

eddrick wrote:

In another topic I suggested replacing the gearbox sideplates with copies made from say 18swg stainless, or just anything stiffer than the standard ally ones. Seeing as you're already looking at modding, maybe you're an ideal candidate to try this?

Again, in another topic it was suggested that Tamiya specified the techni-wotsit motor as a hop-up & I immediately fell about laughing at the idea of extra power being put into this gearbox, seems you confirmed my suspicions!

I have in the past also thought about just writing off the MB/Blackfoot box as a bad job, & thought about the possibility of just grafting in a better 'box, eg Wild One or similar - I'm fairly sure it would be much easier & more final than trying to make the original do what it's supposed to

The "usual" fix is to drill out one drive cup, tap a thread in the bottom of the other & screw the two together (with threadlock) to stop the diff expanding in the first place ... can say I've tried it myself, but IIRC someone on here did so recently

Like the idea of weld beads to stiffen, but won't that anneal the ally & make it softer?
If I were doing the stainless plates thing, I wouldn't faff about with CNC, I'm fairly sure some careful transfer dot-punching & drawing around the profile would be good enough.

Possibly a dumb idea, but what about converting a cartridge type diff to fit/work?
Along the lines of a Mu/TLT/Highlift diff unit, with a correct size ring gear grafted onto it, a'la FG diff?
Mind you, that won't help the strippy counter gear, so back to the "different gearbox" suggestion then....

Big wheels & hot motors on weedy standard buggy components are never a good combo!

Yes the weld would anneal it, but in this application it wouldnt be much, if any of an issue. The weld would lend an edge of stiffness to solve our issue and unless the welds were far too hot, there would be minimal degradation of the plate.

In practical terms, the easiest fix is a bar that is drilled to use two of the trannys stock bolts. The bar should span the space across the plate, as close to the output as possible. There are a few of these available on ebay and making and installing a set would take far less time than even welding.