When designing a full traction/diff replacement for the Axial Yeti & EXO control arm setups, we wanted to make something similar to our regular FI spool, but it HAD to work with stock differential output shafts, e-clips, etc.
To be named "FI" it had to be indestructible, simple, cost effective, reasonable weight and of course offer a very, VERY tight fit to your axle shafts to eliminate slop.
So, we came up with the Lunchbox version of our awesome FI Spool.
"Lunchbox" because it drops into your stock carrier, similar to a 1:1 lunchbox locker... but because there is no differential action like a 1:1 Lunchbox, it's still a spool.
The full steel construction completely fills your stock differential carrier. So there is no slop.
The steel is "wall to wall" and fills the carrier better than an Axial HD locker. So you won't have pins and gears smashing through the carrier like the stock setup.
Because the setup is 2 halves, it is actually easier than our regular FI Spool to test fit your differential output shafts outside of the vehicle and ensure you get a perfect, custom fit.
This hardened steel setup is great for you if you need 100% traction, 100% of the time.
These 0.61oz spools are sure to get you through the toughest trails and have stood up to our worst abuse. They are "F*****g Indestructible ... hence "FI".
Replace your wimpy stock "locker" with our FI Lunchbox Spool and prepare to conquer all!
These are designed to offer THE tightest fit possible with stock differential output shafts (AX30381). Our tests have shown that stock differential output shafts will require a hair of "love" on the edges of the flats for a perfect fit.
Aftermarket parts may require a bit of force or polishing to get the tang to comply.
This "fitting" process is due to the variances among manufacturer measurements, tolerances, etc.
This is the only way we are able to make these spools work with no slop for all the various parts out there.
Because of this, we suggest you test fit your differential output shafts outside of the axle prior to final assembly.
We also suggest using our Copper Anti Sieze Grease
This helps with shaft removal after extended periods of use.
Spools are sold individually.
Tested to fit:
HPI RS4 (Customer tested)
The center slots are "In Phase" which can help to minimize drivetrain harmonics.
NOTE: Installing this locker in place of an open differential can result in component failure.
Applications with factory dogbones, high power, high speed, etc can see frequent failures due to the additional stress.
We highly suggest aftermarket axle shafts for these applications.
Shown installed in a stock diff carrier (not included):
"Fun Fact" from fyrstormer
The FI Lunchbox spool also works in the HPI RS4
A spool in the front is a quick and easy way to make most touring cars
handle more consistently when cornering hard, but nobody makes spools
for the RS4 for some reason.
This convenient crossover is brought to you by the fact that Axial
copied many of the critical dimensions from the HPI RS4 / MT2 / Wheely
King / Crawler King diffs, and the FI Lunchbox spool was made to fit
inside an Axial diff.
"It was a bone-stock diff case. I used
factory-upgrade "HD" drive cups, but the normal drive cups are the
same size and shape. The drive cups fit VERY tightly into your Lunchbox locker,
but I suspect that was intentional on your part, and either way I'm not
complaining -- I can just hammer-out the drive cups if/when I need to replace
them.The diff I posted pictures of was for a RS4 2, and the
Lunchbox locker dropped right in. The RS4 3 uses a gear-driven diff instead of
a belt-driven diff, so it was made from a different mold and the Lunchbox diff
had to be pushed in with some force instead of dropping in, but I still didn't
have to modify anything to make it fit."