Why does my bottom bracket creak?
Why does my bottom bracket creak? It's very annoying. This article helps you to identify the problem and get it fixed quickly!
This article is about general bike maintenance and not specific to LaVita bikes.
This article is mostly about press fit bottom brackets; we hope you also find it useful for identifying your bottom bracket type and then diagnosing the problem.
There are three types of bottom bracket in modern usage.
This is a guide only – always use appropriate force to avoid damaging your bike and if you’re not sure consult a local bike shop for help.
Square Taper bottom bracket
This is the oldest of the three styles of bottom bracket in modern use. The crank has a square hole and the bottom bracket has a square peg that pokes out, which is part of the crank axle which passes all the way through to the other side of the bike. The square hole has a slight angle, so the square is bigger on the bike side and smaller on the bolt side. When the bolt is tightened the pedal is squashed onto the peg. You will need a special tool to remove this sort of crank.
Taper bottom bracket (crank removed)
Threaded & press fit cranks
In both threaded and press fit bottom brackets, the cog side of the crank has the axle permanently attached. Simple undo the non-cog side little bolts and the non-cog side crank should come off without force. Then slide out the cog side crank.
Straight crank used with both threaded & push fit bottom brackets
Diagnosing bottom bracket bearing failure
For threaded & press fit bottom brackets you can put your finger into the inside surface of the bracket, where the crank touched it. This should rotate freely without roughness or wobbly movement. Any grinding or stiffness means the bracket needs to be replaced.
Threaded bottom bracket
The threaded bottom bracket has a left and right side, and usually a tube lightly fitted between them to keep out muck. Both sides have a thread, and this is threaded into the bike frame. Note that some styles of threaded bottom bracket use a reverse thread on one side so check carefully. Shimano standard is different from ‘Italian’ threaded.
You will need a special tool to remove a threaded bottom bracket. This is usually a job for a local bike shop.
Press fit bottom brackets
Press fit bottom brackets are commonly used on higher end carbon fibre bikes (there’s limited point using them on aluminium or steel where a thread can be simply made into the metal, and where weight is less critical).
There’s an open debate about whether press fit bottom brackets are a ‘good thing’. They are a tiny bit lighter than a threaded equivalent but do have a reputation for creaking. Some high end bikes continue to use threaded brackets.
Here’s a cross section through a press fit bottom bracket and crank. Imagine looking from the rear wheel axle on your bike and looking towards the front wheel, with X-Ray vision.
The press fit bottom bracket has three parts
- Bearing cup (blue) – the ball bearing race is pressed into this. Made of reinforced nylon plastic (where alloy, this becomes a hybrid bracket which we will discuss elsewhere. The ‘Hambini’ style of bottom bracket is a hybrid, not a press fit.)
- Ball bearing race (black); ball bearings running in a groove between an inner and outer metal hoop. Most have covers on each side to stop muck getting into the balls. Made of hardended steel.
- Sleeve – this is pushed into the inner side of the ball race, and the crank slides inside the sleeve. Made of reinforced nylon plastic.
Ball bearing race
The press fit bearing cup has a very tight fit with the frame and is pushed in using considerable force. It’s held in place other than the friction caused by the pressure on it. A certain minimum pressure must be maintained to keep the cup in place.
The ball bearing race and sleeve stay in place due to friction.
The crank axle is then slid through the sleeve, usually with a little light grease. It should have a close fit with the sleeve but due to tiny misalignment and bending of the parts under the force of pedalling there will always be tiny movement between the crank and the sleeve. There needs to be small permitted movement to avoid wear between the axle and sleeve. Higher precision on the bike frame and installation of the bottom bracket will reduce wear between the crank and sleeve.
So why DOES my bottom bracket creak?
Well, usually because the bearing cup loses its press fit with the frame; ingress of oil, water or mud will cause damage to the surfaces of the frame and cup and over time the pressure will reduce and made worse by any contaminant, the cup will slide. This will cause creaking.
It’s possible that the creaking is related to the ball bearing race corroding or seizing. If this happens, it will cause increased wear to the axle, sleeve and accelerate a loss of press fit pressure between frame and cup. The bearing cup could have started slipping and this damaged the ball bearing, or the ball bearing could have got stuck and this caused damage to the bearing cup. Either way, both are likely to be damaged.
How do I fix my bottom bracket creak?
This is definitely a job for your friendly independent bike shop as removing and refitting of a press fit bottom bracket requires special tools.
These suggestions are for those that are comfortable to make their own decisions about their bike maintenance.
By the time you notice the bottom bracket creaking it needs to be replaced. Note that with Hollowtech 2 both sides of the crank are 24mm into the sleeve. For reasons unknown ‘GXP’ type cranks are 22mm diameter on the non-cog side. This article does not cover bottom bracket sizing.
- Remove the bottom bracket
- Clean the frame surfaces using soap and water, then white spirit, then a non oil cleaner such as standard paint thinners, Isopropyl alcohol (IPA), paint surface wipe, etc.
- Examine the surface of the frame; if there’s damage you should consider using a gap filler. Various bike and other manufactures have various chemicals for this job. Most are liquids that cure to a solid when air is removed – anaerobic. We have had good success with Loctite 222 Threadlocker. 222 will not ‘glue’ to the nylon material of the bearing race; it will creates an exact mould to its surface. It may make disassembly more difficult. Apply a small amount on the frame and bearing cup.
- Press new bottom bracket into place as usual.
We hope you have found this article useful; please feel free to post comments! Good luck!
We’ll be back shortly to discuss ‘Hambini’ hybrid style bottom brackets which are a solution to persistent creaking on press fit frames.