Hardy Boys Solve The Mystery Of The Nylon Gear Failure On The BBS02 - E Smart Way

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Hardy Boys Solve The Mystery Of The Nylon Gear Failure On The BBS02

Posted by Tom Lee on

In the past, I’ve told people when they replace the nylon gear (instructions are here) to use heavy axle grease on it as the Lithium grease that it ships with is incredibly light and tends to just spin-off the primary reduction gears when they are spinning at around thousands of RPM. After 5 minutes of Internet research, I’ve found that doing this is a terrible idea and can actually CAUSE your nylon gear to soften and fail prematurely (it was really a ploy to help sell more nylon gears for Bafang).

This takes me back to my original nylon gear failure about 6 months ago and I distinctly remember that the gear was 1/2 white (toward the motor) and 1/2 black grease (toward the drive unit) leading me to believe that this heavy axle grease had seeped through the bearing and possibly caused the nylon gear to soften and fail prematurely. For a video that proves my point check out this video from our favorite Aussie speed freak Bruno where he takes apart a BBS02 with 6000km on it. SPOILER ALERT : It has totally turned to the dark side.

Do I know for sure that this is what caused my failure? Absolutely not. Am I sure beyond a reasonable doubt? The more I research it, the more it looks to be true. The gear failed at high RPM under not-that-much load on a slight 5 degree grade hill going about 15mph in a very low gear. Considering how hard I usually thrash on my drive units there is no way this should have failed under those conditions.


This is the nylon gear fresh out of the drive unit with the nasty black axle grease side facing up.


I’ve sorted through my photos of my nylon gear replacement and the more I look at them the more clear it seems to me that the axle grease is getting through the bearing. Is there any way to prevent this? When I lube up my secondary reduction gear on the other side I use a lot of black axle grease. Using too much grease and using the wrong kind might be allowing the grease to seep through the bearing.

In the future I plan on only using lithium (white) non-petroleum based grease on both the nylon gear side and the secondary reduction gear (axle) side. This way even if the grease seeps through the bearing it will not cause the nylon gear to fail. The grease I am going to use is Mobil Grease 28 which is safe with nylon and aluminum and should last about 10 years. You can get about 14oz online for ~$12 right here.

Clean this chamber out with a toothbrush, then clean off the toothbrush and carefully return it back to its owner without getting caught.

You can see the grease on the back side of the unit is a much darker grey color, almost black. It must have seeped through the bearing. Egads, that drive unit is FILTHY.

Will the BBSHD have a similar problem? It’s hard to tell, but from now on when I take it apart I’m not going to clean the black grease off the 2ndary reduction gear and replace it with my axle grease. I’m also going to be extra careful to never get any black grease in the nylon reduction gear. Use only white lithium grease when you have to replace this gear after failure. I found this very informative tidbit by “callpocket” on this post here.

Back several years ago when I rebuilt a few VCR machines, all the manuals had big notes written in red telling the techs to only use white lithium grease to lubricate the plastic gears because petroleum grease would cause damage to the gears. I found this to be the case also (from experience) to use this white lithium grease on the plastic or nylon rollers used in window mechanisms for many older vehicles. Owners and shade tree mechanics had used vaseline or axel grease to lube these and the nylon or plastic rollers came apart. I always replaced them and used the white lithium after I saw the damage from the other lubricants.

Makes me hungry just looking at it.

The side of the nylon gear that faces the rotor is almost entirely Lithium grease. It does kind of look like a VCR gear.

Thanks to Dieter Spiller for pointing out the blatantly obvious to me. I told him to use KY Sex Lube in his Nylon gear and he rightly refused to. If only everyone was smart enough to ignore my great advice. There is a special place in hell for people who use petroleum-based grease on their nylon gears, and I’ve already got my one-way ticket.

Ride On.





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