The current GSXR shock is nearly a drop-in on the 400, and seems to fit even better than
on previous models. I'm sure that an Ohlins, K-Tech, etc. is better, but it's hard to beat the value of a cheap 3-way adjustable GSXR shock from eBay and the minor adjustments needed to make it fit.
The 400 shock now has an eye for the bottom mount, as opposed to the clevis used on the 250/300/500. You'll want to get a shock that looks like the one below.
2011-2019 GSXR 600 is the default model to look for.
As usual, you can take off that top mounting bracket, so you're left with just the horizontal bushing. If yours happened to come with the knuckle stuff on the bottom mount, you can get rid of all that too.
The GSXR shock is 315mm long vs. 320mm on the stocker. You can do a direct drop-in install, but you'll lower the rear end about 5/8". This change in suspension geometry will result in slower steering and less swingarm angle, which is the exact opposite of what most people want to do with these bikes.
The simple, cheap solution is to remove the shock mounting brackets from the rear of the engine, flip them upside down on the opposite sides, and reinstall. They're sort of L-shaped, so this moves the shock mounting hole from the top to the bottom, giving you about 15mm of extra height. Combined with the 5mm shorter shock, that's +10mm overall, which is a reasonable increase for the rear.
The worst part about this mod is that the shock mounts have little ears for the ECU tray to bolt to. To get to those screws, you have to pull the ECU, which requires pulling the tank, which requires pulling at least some of the fairings. The flipped mounts mean you no longer have those ears for the tray to screw into as well.
Once again, Norton to the rescue with their
GSXR Shock Adapter Brackets. They're simple L-shaped brackets that slip on the mounting bolts next to the shock mounts and provide replacement mounting points for the ECU tray. They're not strictly necessary if you're trying to save every penny/ounce you can, but they're a very nice product to restore that secure mount if you're a perfectionist like I am.
Here's a pic of someone else's install with flipped stock mounts. They removed the ears from the mounts and refinished them, then added the Norton brackets. If you did want to return to stock after this, you could still use the Norton brackets in place of the missing ears on the right-side-up stock mounts.
If you do happen to be a perfectionist like me, or if you just want some more adjustability, you may be interested in
Spears' Variable Ride Height Adjusters too. These are replacement shock mount brackets with reversible inserts resulting in either +5mm or +10mm height on the shock. Once again, combined with the shorter GSXR shock, you end up at stock or +5mm height. In theory, you could make inserts for anywhere between +5mm and +10mm, if you wanted to get really precise about it. These mounts lack ears, but the Norton brackets above handle that. Some alternative fasteners are included for securing an aftermarket undertail, but I'm not sure exactly how that ties into swapping the shock mounts.
One last little bit remains. The lower mount bushing on the stock shock is 40.5mm wide. The GSXR's lower mount is only 36mm wide. The OEM bushing is 18mm OD while the GSXR's is 17mm OD, so you can't just transfer the OEM one over to the GSXR shock. However, M10 washers are about 2mm thick, so one on each side works great. See the two washers in the Norton bracket pic above? This is what those are for.
It was annoying to try to hold the washers in place while lifting the rear tire to align the shock and knuckle to get the bolt reinstalled. I don't plan to be removing this frequently, but if my OCD gets to me, I may have a longer piece machined so I don't have to bother with the washers anymore.
And here's a final shot of the top mount. You can see the Norton and Spears parts, and how there's plenty of room all around the shock. No need to cut the battery tray or undertail or anything like that. The shock's adjusters are easily accessible. The rebound on the bottom is probably the worst, as it's partially behind the dogbone. I was able to adjust all of them after pulling into a parking lot while riding.
Final Notes
The 600 listed in the beginning has a spring rate pretty close to the stock spec. As with the previous Ninjette GSXR swaps, this is a reasonable choice as long as the stock spring works decently for you. The current 750 and 1000 seem to use the same shock, with different spring rates. If the stock rate doesn't work well for you, a different model may fit better.
Here's the same chart I've posted before, adjusted for 400 riders (based on Norton's spring rate chart). Note that most of these shocks
won't be a direct bolt-in on the 400, but the spring from an older model may swap onto a current shock (cheaper than buying a spring from RaceTech or something). I measured my GSXR 600 spring as 3.0" OD x 2.25" ID x 7.5" free length. The last three lines are from a member on another forum, who actually bought those shocks off eBay and had his local suspension shop measure them. The shocks themselves looked identical.
Code:
BIKE MODEL RATE (kg/mm) RATE (lb/in) RIDER (lb)
EX500 OEM 5.4 300 X
EX250F OEM 7.9 440 X
EX250J OEM 9.3 520 X
EX400H OEM 10.0 560 190-220
98-00 GSXR600 6.4 360 90-120
01-03 GSXR600 8.0 450 120-150
04-05 GSXR600 7.6 425 115-145
06-09 GSXR600 9.4 525 170-200
11-13 GSXR600 10.1 565 195-225
00-03 GSXR750 7.2 400 95-125
04-05 GSXR750 7.3 410 100-130
06-07 GSXR750 9.5 530 175-205
08-10 GSXR750 9.5 530 175-205
11-13 GSXR750 10.5 590 210-240
01-02 GSXR1000 7.7 430 115-145
03-04 GSXR1000 8.6 480 135-165
05-06 GSXR1000 8.1 455 125-155
07-08 GSXR1000 10.1 565 195-225
09-11 GSXR1000 11.6 650 240-280
18 GSXR600 10.3 577 200-230
17 GSXR750 9.3 520 165-195
11-16 GSXR1000 10.7 600 215-245
The larger GSXR spring is close to hitting the dogbones. Some people have reported some very minor rubbing. The preload adjuster is about 1/8" smaller than the ID of the spring, so it does have a bit of room to wiggle around. Try to make sure the spring is centered on the adjuster to keep it in the middle and avoid hitting the dogbone on either side.
Also, the top shock mount is about 10mm narrower than the bottom. The upper and lower shock bolts are different lengths. Even if you're really anal about setting your parts out while you're working, it's possible to get them mixed up and not notice until the bottom bolt is too short, and you realize that you have to take it all apart again to swap the bolts.
