A rubber seal cut to the outline and hole pattern of the Bafang BBSHD controller, the finned box that bolts to the back of the motor. Fit it whenever the controller comes off, or when the old seal has flattened, torn or let water in.
On a BBSHD the controller is not tucked away in a bag on the frame. It is the finned aluminium box bolted to the back of the motor, right under the bottom bracket, and it holds the power electronics that switch up to 30 amps into the motor windings. The joint where it meets the motor casing is sealed by a rubber gasket, and that gasket is the only thing keeping road spray off the board.
FILFEEL cuts this replacement to the BBSHD controller's outline, with holes placed to line up with the fixing screws. The material is rubber, and the maker lists four jobs for it:
The title also lists BBS01, BBS02, BBS03 and BBS04. BBS03 is Bafang's name for the BBSHD, and the features describe a part made for the HD controller. The BBS01 and BBS02 use smaller controllers, and Bafang has changed housings between generations, so treat the wider list as a claim to check against your controller rather than a promise.
The package weighs 15 grams and fits in a 2.36-inch square box. It is a small, cheap-to-stock part that decides whether a 1000W motor keeps working through a wet winter. Where the unit sits and what it does is mapped in the controller guide.
| Spec | Value |
|---|---|
| Brand | FILFEEL |
| Part type | Controller gasket, sealing washer |
| Material | Rubber |
| Designed for | Bafang BBSHD (BBS03) mid-drive controller |
| Other motors named | BBS01, BBS02, BBS04; confirm outline before relying on it |
| Location | Joint between the controller housing and the motor casing |
| Main job | Keeps water, dust and contaminants out of the controller |
| Secondary job | Vibration damping at the joint |
| Fit | Custom outline with precise hole positioning |
| Installation | Controller off, old seal out, new seal seated, controller refitted |
| Electrical connections | None |
| Package dimensions | 2.36 x 2.36 x 0.79 in |
| Package weight | 15 g |
Controllers get hot, which is why a cheap seal earns its place. Forty minutes of climbing with a loaded bike pushes heavy current through the controller's transistors, and the housing and the air inside warm up with them. When the ride ends, or the bike rolls through a cold stream, the air inside cools and contracts.
A good seal holds that pressure change out. A flattened, torn or poorly seated one lets the housing breathe, and each cool-down draws in a little outside air. On a wet day that air carries water, which condenses on the cooler metal inside and settles at the lowest point of the board.
Signs the seal has already let water in:
None of this means the gasket was bad from day one. Rubber takes a set after repeated heating, and a seal that has been disturbed once rarely seats as well a second time. The rest of the wet-weather checks on the motor are in the maintenance guide.
FILFEEL calls the swap quick and simple, and on the bench it is. The work is mostly in removing the controller carefully, because it connects to the motor inside the housing. Allow half an hour, and do it with the battery unplugged.
Skip the sealant unless the gasket seat is damaged. A bead of silicone can help an old, scarred casing, but it makes the next removal messy, and a new rubber seal on clean metal does the job without it.
If you are opening the controller anyway to fit a higher-current unit, fit the new gasket at the same time. Put the cables back along the routing from the install guide.
A gasket is prevention and cleanup, not a cure for a burned controller. If the bike still runs normally and you are opening the housing for any reason, fit a fresh seal as routine. If water got in and the bike now cuts out, dry and clean the board first, then fit the gasket and see whether the fault clears.
Some faults do not come back from water damage:
In those cases the answer is a new controller, and the BAFANG replacement controller page covers versions and ports. Fit a new seal with it, since the old one will not seat well again.
First, find out which controller generation you have. Bafang's newer controllers have a different housing size from the old ones, so a gasket cut for one outline may not match the other. Lay the old seal over the new one, or count the screw holes on your controller.
A few habits make the new seal last longer. Rinse the motor with a gentle hose rather than a pressure washer, which can force water past any gasket. Park wet bikes upright so water drains away from the joint instead of pooling against it. And after a long, hot climb, let the motor cool in the air before a stream crossing or a hose-down, so the housing does not suck in water as it contracts.
Do not confuse this part with bottom-bracket spacers. The Auto-plaza washer set is metal and goes on the motor's shaft to position it in the frame; it does nothing for the controller joint. For water sealing, a rubber gasket like this is the part.
Between the controller housing and the motor casing, at the back of the motor. It seals that joint against water, dust and grime.
The title names BBS01, BBS02, BBS03 and BBS04, but the features describe a BBSHD fit. BBS02 and newer controllers use different housings, so compare the outline and holes first.
Not usually. A new rubber gasket on clean surfaces seals well, and sealant makes the next removal harder. Save it for a damaged seat.
Only if the cause was moisture that you can dry out. A controller with burnt parts needs replacing, with a new gasket fitted at the same time.