Welcome to the first of many articles in the self-proclaimed popular series of “Huggy in the Workshop” technical articles, which are aimed at helping the novice bike mechanic to demystify some of the more involved technical issues. This is your chance to take some info on board or better yet sit back, grab a beer and get ready to deliver some armchair expertise.
Much has been written on the trials and tribulations of the Mavic Freehub design. The Mavic Freehub uses a ratchet system with an internal cut gear which is engaged by hardened metal “pawls” when the cyclist applies power to the wheels. When coasting, the pawls are spring loaded and simply “tic” over much like the little needle ticking over the pegs on Burgo’s wheel of fortune.
There are many possible dramas with the freehub but this article will be dedicated to fixing a binding Mavic Freehub. The tell-tale symptom is that the freehub starts to bind and instead of being able to coast or freewheel it turns itself into a fixie and the cranks continue to rotate. If the rider decides to freewheel, the Mavic Freehub becomes disagreeable and will instead pull on the chain and you will hear your rear derailleur being pulled forward on a rhythmic basis.
First of all, I’m assuming you have at a bare minimum disassembled and re-oiled your freehub to eliminate the potential issue of lack of lubrication. If so, the problem is likely to be at the rear axle. Instead of being constrained properly the axle is not rotating true. This lateral play is diagnosed most easily at the rear cassette. If your cassette is able to be rocked back and forth by pushing to and fro on the largest cog then there’s your answer.
If this is the case, then your failed component, in ascending price of repair, will either be:
1) The nylon bushing in the freehub body. This costs about $10 to replace, see my mate TheHubDoctor for some new parts.
2) Or, as in my case, the issue was a wheel bearing. The balls contained inside the cartridge bearing were well and truly worn out, permitting a large degree of movement between the bearing inner and outer race, in turn allowing the axle to rock. You will need some replacement cartridge bearings, which can be bought off many a supplier including TheHubDoctor, for about $30. No doubt you might consider purchasing ceramic balls but as this was a training wheel, the extra expense was not warranted.
If it’s the nylon bushing that’s the issue it could either be cracked or, more commonly, you haven’t re-oiled your freehub often enough. In my case, I don’t ever remember re-oiling the freehub in 4 years, who knew? Surprisingly, it’s the aluminium wheel hub nose that tends to wear, rather than the bushing.
A new hub will measure 0.983”, at least. If this is the case you will be able to replace the nylon bushing with a 0.000″ i.e no oversize bushing. Any more wear on the hub (e.g. 0.983 -0.980”) and you will want the 0.003″ oversize bushing that TheHubDoctor makes. If things get really dire you can always go to the 0.005” oversize, but after this you’ve probably worn the hard anodize off the hub nose and your wear rate increases exponentially.
Basically, TheHubDoctor accounts for the outer diameter of your aluminum hub wearing by adding material to his nylon bushing inner diameter to account for the wear, such that you get a nice snug fit. This snug fit is responsible for keeping your axle running concentrically; conversely a loose fit will allow the axle to rock and cause the freehub to bind. If you’ve replaced the nylon bushing and still no love, you will probably find it’s the wheel bearing.
My Askium wheel bearings were cactus after some fairly constant riding at about the 15,000-20,000 km mark. As a rough guide you probably want to overhaul your wheel bearings every 5000 km, which for most of us is about once a year. You may like to do your pedals and bottom bracket while you’re at it.
The steps involved in diagnosing and correcting the problem are outlined below. If you are Rainman and only require the pictures to do the job, scroll down to the photos.
To replace the nylon bushing:
- Remove cassette with chainwhip, spigot and socket set.
- Undo the freehub assembly, using a spanner at one end and an Allen key to fit inside the axle on the freehub side.
- Remove the freehub body assembly carefully. Be prepared for the spring loaded pawls which will no doubt fall out and mark your nice new carpet (in our case, cream-coloured).
- Inspect the nylon bushing for cracks and wear, inspect the cartridge bearing in the freehub assembly. Does it rotate freely, is there any lateral play in this bearing?
- Ideally, measure the wheel hub at the base of the hub nose using a pair of Vernier Calipers right down near the rubber seal. Anything less than 0.983” will indicate excessive wear and the likely source of the issue. If it’s not worn excessively, as in my case, the issue lies with one of your 3 bearings; either the one in the freehub assembly or one of the wheel bearings. (Note: my caliper reading of 0.983” in the image. F##k, this is not the problem, then! What else…….?)
- The nylon bushing is not easy to remove. I dare say the only method is destructive and will require you to cut it out.
Assuming that the issue was not the nylon bushing and is therefore the wheel or freehub bearing……
To remove the freehub bearing:
1) Place the appropriately sized socket over bearing and whack with a rubber mallet. You might need to get creative and try some thick fabric with a metal hammer, assuming rubber mallets are a scarce commodity at your house.
To remove the wheel bearings:
1) You will be able to knock out the smaller bearing side first by using a hammer and a well sized piece of dowel. Alternatively, you can use the arse-end of an appropriately sized drill bit. If these are your Dad’s drill bits he will be furious when he catches you blunting the point of the bit, so you will want to think about your exit strategy.
2) Repeat the same “Mavic-approved” method to knock out the larger bearing if need be.
Before putting the whole thing back together do yourself a favor and put some new oil in the freehub. It must be a light grade oil (consider using sewing machine or purpose made freehub oil or equivalent). Grease will not work as a substitute as its viscous nature will make the pawls stick and you won’t be able to fire that 500 Watts of power instantaneously into the pawl and ratchet system no matter how many squats of you’ve been doing in the off-season.
And now for the the pivotal steps required to fix the Mavic Freehub binding issue in pictures:
Hopefully this article provided you with enough information to fix your Mavic Freehub. Feel free to post comments and suggestions and start the tech discussion. Blotto members might want to consider sharing some of their innovative technical solutions.