[Davecrash]

Is there a rear disc brake option (upgrade kit) for the 2008 420 straight axle? has anybody done it. a quick search on here and i didnt see anything

 

[SamUK]

As far as I’m aware it hasn’t been done and nobody makes a conversion kit. If you fancied a go yourself you might look at the old Yamaha Moto 4 for inspiration, I believe they had a floating disc and fixed calliper.

 

[fishfiles]

Dave , I don't know about 420's , I know I have one on my 450 and it seems to be about the same set up , the requirements for the kit is : brake drum has to be against the wheel , also 12 inch rims , you should call Super ATV or Highlifter and ask them if their kits fit a 420

 

[RemMax]

I've been wondering about this as well as I'm finally adding some updates to my 90 300
Currently I have a friends 400ex in the garage and was looking at the disc set up on his and wondering if the rotor mount off his straight axle would fit on my 300 axle??
Anyone know if the axles are the same diameter??
Figure I can make a adapter to hang the caliper on but attaching the rotor ain't quite as easy
I'll have to measure it when I get out later to see if they're close

 

[fishfiles]

"Max , don't know the diameter of a 400ex axle spline at the rotor hub -------- I seen a set up a guy made for disc on a 300 , and it looked like he melted the hub of of a brake drum and welded to it --- I run 250/350 rear ends in my 300's and the brake drum is in the right spot but the diameter of the axle is different than the kit and the kit wouldn't work without a custom rotor hub

 

[SamUK]

"Max , don't know the diameter of a 400ex axle spline at the rotor hub -------- I seen a set up a guy made for disc on a 300 , and it looked like he melted the hub of of a brake drum and welded to it --- I run 250/350 rear ends in my 300's and the brake drum is in the right spot but the diameter of the axle is different than the kit and the kit wouldn't work without a custom rotor hub

That’s exactly how I would approach the job, use the inner steel splined part of the drum and weld/mount the rotor/disc to that. I can’t relate to sports ATV’s I don’t know how the set ups on those work, I assume it’s a floating disc on splines with a fixed calliper? Same as the Moto4 I mentioned.

 

[RemMax]

I keep forgetting that some quads have the axle tube rear ends and not the solid rear axle like the 300's
Not sure which Daves 420 has, not up to date on newer quads so hope this helps him too

ANYWAY...... The 400ex has a axle like the 300, straight solid axle with the carrier in the middle
I'm also not big on sport quads, not enough fenders for my liking, closest I personally get to em is the one 300 2wd I have but it has same drum brake as 4wd's do
I still have my buddies 400ex outside so when I head out to put my own rear end back together I'll take some quick measurement to see if it might work cause I know id love to have disc on rear to go with kit I'll be adding to front today after UPS comes
Sure had a mess inside my brake drum I took apart yesterday, disc would be so much nicer on it!!!
RemMax

 

[fishfiles]

here is a pic of a ATC250ES three wheeler rear end in a 300 , the axle tubes go al the way to the hub on both side , with double bearings at the end of each sides tube ---- a good upgrade

all that is needed to make it work is weld a mounting plate where it attaches to the swing arm , on the ATC250ES there is the old mounting bracket which many just leave , I cut and grinded it off this one cause I am kind of OCD ---------- on the 350 A or D rear end , you need to also weld a shock mount