Question: I see a lot of mechanics using grease on bolt threads and on bottom brackets, but I know that some parts need thread locker. How do I know what needs grease and what needs thread locker? From: Tom
Answer: Great question. You should always follow the manufacturers’ instructions regarding the preparation of components before assembly, but I’m happy to offer some general guidelines.
Mechanics often use grease on bolt threads to protect the threads inside a component while also preventing bolts from seizing to the component. While both of these things are important, you have to keep in mind that a greased bolt takes less torque to apply a given amount of clamping force. This means that even if you use a torque wrench to torque the bolt to spec, you run the risk of damaging the component. So, if the manufacturer specifies to install the bolt dry, or with thread locker, you need to follow those instructions. Your safety depends on it.
When it comes to threaded bottom brackets, greasing the threads of both the bearing cup and the frame will help to ensure that the cup threads in straight while also protecting the threads in your frame. You should also grease the crank spindle and any seals in the system. Be sure to grease the splines on the spindle that engage with the crank arm as well.
For pressfit bottom brackets like PF30 or BB86, a lot of people don’t know that SRAM actually calls for their plastic cups to be installed dry. However, they do call for grease on spindles, crank arm and spindle interfaces, and on seals. Shimano calls for the same preparations to their pressfit bottom brackets and crank spindles.
All cartridge bearings should get grease applied to their outer race before they are pressed in. That includes BB30 bearings.
For seatposts, you should use grease for metal on metal installations. With either a carbon seatpost or frame, carbon friction paste is the way to go. You can also use the carbon friction paste on metal frame and seatpost combinations too if you have problems with a slipping seatpost.
On rear derailleur fixing bolts, Shimano recommends a dry installation while SRAM recommends using grease.
For pedals, just about every manufacturer recommends applying grease to the spindle threads.
When it comes to brake components, all fixing bolts require thread locker. That includes caliper fixing bolts for both disc and rim brakes, disc brake rotor bolts, and road caliper brake pad fixing bolts. Each of these should get a medium strength thread locker applied to them if the factory applied thread locker has worn off. The same goes for suspension pivot bolts and chainring bolts.
Lastly, derailleur pulley bolts should have high strength thread locker applied to the threads.
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