Fitting rear undertray mod.. Courtesy of Odd Jobb (I followed this and did mine.. it worked brilliantly. Egg)


Right here goes.  I hope I haven't forgot anything, and I hope you can follow it.

First of all remove the seat and rear hump/seat. Remove grab rail if fitted. Remove battery. Remove the rear body upper section. This is held in place by 2 allen bolts either side at the front, 2 posi-drive screws on the top near the front, and the 2 bungee hooks (these have a hex key slot in them). The top bodywork is also connected to the undertray with plastic buttons (3 on each side), remove these. You may find some of these buttons break when removing, as you will need them to re-fit the new undertray it is advisable to get some spares beforehand. Remove the 2 screws holding the rear seat lock to the subframe.  Unplug the wiring to the rear light. Gently prise apart the upper bodywork section and lift off and set aside.

Unstrap the ECU (this is held in place with a rubber band).  I found that my alarm had been fitted to the rear undertray so you may have to remove yours if fitted here. Unplug the wiring to the indicators. There are 4 bolts securing the rear undertray, 2 at the front beneath the tray and 2 at the rear. Remove these and the undertray will almost be ready to be removed. You will find that a brake pipe is routed through the undertray from the reservoir to the cylinder. To save having to disconnect this pipe I found it easier to cut the undertray either side of the pipe to allow it to be pushed to one side and allow removal of the tray.  Remove the undertray. Remove the numberplate from the undertray (and don't forget the petrol tank stay).

This is where the fun starts, as you now have to butcher the old undertray to re-use the battery box.  I also thought it would be better to keep the old ECU mount as well.

Before you cut anything measure the old tray from the front mounting bolt holes to the rear light recess. You will need this measurement later.

Using a Dremmel or jigsaw, cut out the battery box and ECU housing from the old tray using the following picture as a guide. (click for larger picture)

Now sit the cut out piece on top and in front (if you see what I mean) of the new tray. The ECU housing should slid over the new tray whilst the battery box sits in front.  You need to align the two pieces so that the overall length is the same as the old tray.  Remember that measurement made earlier !!!

Using a 6mm bit, drill four holes though the two pieces at suitable locations, and bolt the two pieces together using the plastic nuts & bolts supplied. Just be careful that the bolts don't interfere with the mounting of the ECU or battery.  Also drill 2 holes horizontally through the raised lip  at the very rear of the ECU mounting plate BUT NOT THROUGH THE UNDERTRAY. You will need these later.

Now fit the indicators to the rear of the undertray. If you are re-fitting the original indicators you will need to cut out an oblong shaped hole on each side. If you look at the mounting point on the indicators you will see a raised shape in the centre around the mounting bolt. This shape has to fit into the hole that you make in the undertray (this stops the indicators from spinning around).  Fit the indicators to the undertray.

If you have purchased alternative indicators then refer to the fitting instructions supplied with them.

You are now ready to re-fit the undertray.

Slide the undertray assembly under the subframe and into position. If you have a hugger fitted it is a good idea to place an old towel over it to protect it. Ease the brake pipe back into the side of the battery box. Fit the two front mounting bolts and tighten. You will note that the rear of the undertray is sagging. Remember those two holes you drilled in the ECU mount. Using 2 heavy duty cable ties, fasten the ECU mount to the subframe, ( going through the drilled holes and over a subframe brace immediately behind). Now re-fit the ECU, battery, and indicator wiring. (And any other items fitted to the old tray).

Now re-fit the rear top bodywork, (the undertray sits inside the top bodywork when you view it from beneath), and tighten all mounting bolts, screws, etc. Don't forget to plug the rear light back into the harness, and re-fit the seat/hump lock.

Now look at the rear assembly from beneath and you will see 3 holes on either side of the top bodywork. Using a 5mm bit carefully drill through these 6 holes into the undertray.  Using the buttons/studs removed earlier, fix the bodywork to the undertray.  Now re-fit the number plate. I found that the number plate mount would not fit straight onto the undertray, so I cut a piece of plastic from the old undertray and made a new mount. You may need to experiment a bit here to see what works best for you.

And that's it.  You now have the rear end of your Busa looking how it should have done when it left the factory.

Good luck