Just finished up with a few projects on the bandit and thought I'd share pics. I know some of these have been done before but I'll explain everything I did as much as I can to hopefully further help anyone looking at performing any of these modifications.
The biggest upgrade was for sure the suspension and brakes. I loved the little bandit's size, shape, and power but the stock suspension and brakes just sucked, it was probably a combination of being spoiled by riding newer sport bikes previously and the fact that they had 17 years of use with no obvious maintenance. Got a set of forks, triples, clip ons, and brakes off of a 2006 GSX-R 1000. Like others have said, getting the forks on was just as easy as pressing out the bandit stem and pressing it into the GSX-R's lower triple tree. I also went ahead and put in new steering stem bearings and seals while I was in there. I had a matching white front wheel laying around from a 2002 GSX-R 1000, but between the 02 and 06 the rotor diameter and bolt pattern are different, with some research I found that a SV1000 front rotor had both the correct diameter and bolt spacing to mate a 02 wheel to 06 brakes/forks. For the time being I've gone with a single sided brake set up, like how the bandit is originally. For one I kind of wanted to preserve the look of the bandit somewhat in the updated front end, but also thought that the combination of a radial master cylinder, radial caliper, and much larger better caliper and rotor would probably by itself be a massive improvement over the stock brake set up. For the street it is fine but after a track day I'll see if I want to keep this set up or go with the dual gsxr brakes. I chose not to reinstall the gauges because I wanted the bike to have a bare minimalistic racey look, although I would like to somehow reinstall the warning lights somewhere. I also bypassed the clutch lever safety switch and removed the left hand bar switch, as well as bypassed the sidestand safety switch, my past couple bikes have all been track day bikes and never have a problem started the bike in gear with the clutch engaged. Also for the moment the bike has no signals or horn. The headlight is just a temporary solution so I can ride for the time being, but am going to probably do something very similar, just with two of the same foglights and better brackets.
With the gauges and stock headlight removed when you ride all you see is the rode in front of you, I really like how it just feels like its you and the open road, nothing in your view reminding you of how many miles are on the bike or how fast your going(if it was a gsxr 1000 or something this could be an issue, but with the bandit so far i keep finding i'm actually going too slow for the speed limit), no matter how fast your going I always feel like I'm hauling ass on this bike, even more so with no speedo to tell me what I'm actually doing.
Riding it was immediately obvious that the gsxr front suspension and brakes were a massive upgrade, but the most notable thing was how much it just exhagerated how worn out the stock rear shock was. Also the gsxr forks apparently make the bike sit a bit lower in the front, because the bike would now barely stand up on its kickstand with out want to fall over. So I picked up a rear shock out of a 2001 GSXR 750. To install it I had to remove the coolant resevoir, I replaced it with a McCormick's spice bottle, I taped part of it off so I could see the level and painted it black, drilled a hole in the top, ran the coolant hose down into it and mounted it at the front of the engine for easy monitoring and filling. I also had to push the airbox slightly forward to clear the shock's fluid resevoir. The shock itself was I guess half an inch longer than the stock bandit shock, so to make it fit I had to grind a little off of the front bottom spring plate, as well as make notches in the front and rear of the top of the shock linkage. The spring is also larger than the bandit's so I had to use spacers on the dog bones to get them to clear the spring. I also took the time to carefully clean and relube all of the suspension bearings which were caked with what ten or fifteen years ago was bearing grease, but now looked and felt more like red clay. With the shock installed the bike now sat upright again, although I would like to raise the rear ride height just slightly more still, so I may try going with a shock from a 04 or newer gsxr because I believe they are slightly longer. The difference with the new forks and shock together was amazing, I was a little concerned that the gsxr bits would make the bike too stiff, but the opposite was true, I guess the stock suspension was just too worn out or old to cope with pot holes and the like, so the ride was very very harsh despite the suspension feeling like mush. The new suspension soaks up the bumps with ease, while at the same time feeling nice and firm. I also installed a pirelli supercorsa 120/70-17 front tire, and a metzler rennsport stock sized rear tire(same tires, different names on the side wall basically). The B4 is so quick to drop into a turn with the stock squarish tires I was concerned that the more round race rubber would make the bike feel too twitchy and unstable, but riding it again the opposite was true. I can only assume it was partially from going up to a 120 front tire, as well as the changes in suspension geometry the new suspension caused, but the bike is actually a fair bit harder to initiate turn in now, necessitating more leaning with your body, but I prefer that to strong steering input anyways, and now once you get it leaned over the bike feels very very stable and planted, with the stock set up I kind of felt like the bike would just let you ride right past the edge of the tire with little warning. Increasing the rear ride height should help make it steer quicker though.
The rear brake barely worked and squeaked like hell, the rear brake pads appeared to be the originals from 1991 and the brake fluid had turned into a brown sludge, the fluid resevoir cap's screws were stripped out. So I replaced the rear rotor with an ebc contour wave rotor, new pads, and installed a cup style fluid resevoir off of a gsxr. One of the previous owners had chopped the rear subframe and installed a Ducati monster seat, it lines up perfectly with the frame and tank, and just requires two brackets to hold it to the subframe. I also installed a tail light off of a 02 R1, with the plastic housing removed, exposing the clear LED's, and painted the white backing black. I just had to trim off the two top mounting tabs and and drill holes through the rear tabs and it screwed right into the ducati seat, lining up perfectly between the subframe rails. The previous owner had also installed a M4 carbon fiber slip on off of who knows what bike, I just removed the stock rear passenger pegs and replaced the muffler bracket with a aluminum bracket I had laying around, I think from an SV650.
The bike was originally all red, whoever painted it did so with out taking a single part off the bike and not taping off much, so it had lots of over spray and many parts of red still exposed, the motor was also pretty dirty so I pulled that, cleaned it, and painted it with PJ1 stuff. The engine cases and head are Yamaha YZ silver, the side covers and valve cover are satin black, and I used Honda CRF magnesium on the sprocket cover and starter motor. I also sanded the rusted header and painted it high temp flat black. I stripped the swing arm and painted it gloss black, the frame was in pretty good shape so I just cleaned it and painted over the original black to touch up some red spots showing through. I also wanted to black out a few bits so painted the foot peg brackets, the chain adjuster plates, the rear caliper, brake rod, radiator, and its guards. I installed folding metal foot pegs off of an SV1000, which mounted right up with slightly longer bolts, and a SV1000 shift lever which was just slightly shorter than the B4 lever.
The last thing I did was install a Vortex keyless gas cap off of a 2006 gsxr 1000. Only one of the holes lined up with the bandit's tank so I had to drill and countersink the other three holes.
I also performed some much needed maintenance on the bike while I was going through it. I wouldn't be surprised if the coolant was the same which was poured in it the day it was assembled in japan, and the spark plugs were some autozone crap from the 90's, one coil was cracked, and the air filter fell apart in my hands. It was sad to see someone had not taken care of such a cool rare bike, but it felt good to give it the attention it deserves and give it some TLC. Most people don't even know what a stock bandit 400 is so I'm thinking this one will have a few people scratching their heads. Only thing I'd like to do now is maybe put in a newer shock or try something to raise the rear a little more, clean up the wiring which is a mess, and try and fashion a high mount exhaust similar to TurboFb's, get the jetting a little better. And get it on the track of course.