Bicycle Mechanics - Freehub (presumably) grinds under load
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09-06-10, 03:30 PM
Long story short, I just got back to cycling recently, after a couple of years on hiatus and storing the bike. I did a general overhaul, cables and housings, all of the bearings, new BB, headset bearings, new brakes, new chain, new cassette, pedals ... I even relaced my rear wheel because two spokes were shot. I basically did preventative tasks.
Now after 200 km it started to show. No matter how hard or easy I drive it, it starts to grind over time, the drivetrain feel is almost like when BB bearings are going bad. But here's the trick, it goes even worse when I'm offroad and stays like it until I clean the freehub with brake cleaner and reoil it. No signs of dirt so I guess it is caused by vibrations.
It goes away for a while after cleaning, you can only feel it on 1, 2, 3 rear, but it goes a lot worse after a trip in every gear possible, altough first three are the worst. Just keeps on repeating.
Few other notes: when I put it in a workstand I can't feel it in my hands. It's there only when you ride it. The cassette does wobble when freewheeling, but the sound is okay, no sticking or weird feel on the drivetrain. Freehub has some axial play that I believe is probably unacceptable.
It's an 8 speed HG40-an cassette on a shimano parallax (nowadays alivio I believe) hub, 11T 8th sprocket, and a relic shimano stx rc rear derailer :D From what I remember when I last rode it everything was superb, that's why I liked this bike so much.
I just need your opinion on this issue, because I don't want to go out and buy a new hub if it does not solve my problem. I was just about to put some really nice shoes on it and now it gives me this. :lol:
Thanks a lot!
Hard to diagnose what you are feeling. I'm a little suspect that it is your freehub that you feel. When you pedaling, the freehub is "locked" (not rotating) so you shouldn't feel anything from it unless it is slipping. The first thing I'd check is chain stretch. But it could also be hub or BB bearings. Checking bearings is fairly easy so I'd do that before I'd start replacing parts.
Note also that 200km is probably a little early to be flushing you freehub unless it is getting immersed in water a lot. Those things are sealed fairly well and usually don't need much maintenance for a long time. If you're spraying brake cleaner around, you could also be washing the grease out of the hub bearings.
09-07-10, 06:31 PM
About that wheel; was it a machine built wheel? Was it retensioned? Could the rear wheel have lost a bit of tension, allowing the spokes to rub where they cross and thus creating a "roughness" under load?
09-09-10, 08:30 AM
No, I laced that wheel by myself, then took it to the shop to get it true. As I said, it goes away for a short period if I clean it and put some drops of medium oil into the freehub. Over time the situation just worsens again.
Freehub itself is a bit noisy and shell moves app. 1mm axially. I checked a new FH-M530 deore hub the other day and the freehub was surprisingly silent and stiff, with no play at all. I am going to pick it up today and I'll try to transplant the freehub onto my hub. If that doesn't help it, I will probably have to relace the wheel with that very new hub. I can't say I am positive about my effort on the wheel, but as far as my experiences go, spokes are properly tensioned, alignment is perfect. I know how loose spokes sound when they 'dance' around and reposition themselves constantly, it's like plucking them with fingers.
Forgot to add: I am very mechanically inclined because I do auto repairs and I do cleaning with parts completely or at least partially disassembled. The chain is perfect, since it's only 200 km old, the hub flange does not rub on the cassette.
I really have a feeling my pawls are about to go, because it goes with a rhythm, it's like "tck-tck-tck-tck-tck-tck" every single revolution. It does not click at any particular spot and if I let it freewheel, it comes back after the pawls grab the "ramp" and I start pedaling again (don't remember the correct term, sorry, not a native speaker :D).
09-09-10, 08:05 PM
Has your cassette lockring always been kept cinched down good and tight? A strong rider can load the cogs enough to make the dogs on the cogs bite into the splines of the freehub body. Then with each pedal stroke there will be a "grrnch" as the cog moves a little on the divots in the splines -- typically only with certain levels of load though, so not easy to track down. Oddly, often not while standing and pedalling really hard. With the cogs removed you can easily see the bite marks on the splines of the freehub body if this is the diagnosis. Keeping the lockring tight is supposed to prevent this by locking the stack of cogs together as one, distributing the pedal forces over more than just the one engaged cog. Oiling the interface between the cogs and freehub will silence the hub for a while, but replacing the freehub is the cure.
09-12-10, 04:17 AM
Hey a little update. I replaced the whole rear hub, I did everything right, then after 10 kilometers it started to come back. Then I went bit by bit and fortunately I discovered that my old cassette (HG50) is perfectly fine, visually compared to my new HG40. In a moment of desperation I have put my old HG50 back on and grinding is gone, pedal feel back to normal.
Those are both 11-30T.
There are two main differences: spacer ring, drilled sprockets and nickel vs. zync plating. I have checked holes on HG40 if there are any defects or cracks. Maybe I was the unlucky guy, but for the sake of it I cannot find anything that could be wrong on this cassette. Everything is stiff and firm. I gently pried every tooth to see if any rivet or sprocket has any play and nothing ... Is it cursed? :D Seriously, I wonder why it started this after 200 km of proper use and the old one works better than the new one.
09-12-10, 10:38 AM
... you can only feel it on 1, 2, 3 rear, but it goes a lot worse after a trip in every gear possible, altough first three are the worst. Just keeps on repeating.
...Thanks a lot!
Take a closer look at your derailer pulleys.
09-12-10, 02:38 PM
This got me thinking too since the damn thing came back on any kind of cassette I am on now! On HG50 it grunts just on lower gear, fortunately. You think pulleys are about to be replaced? I regreased them numerous times. Teeth are also still good.
I did a long trip today and 40 kms away from home I started to hear the behemoth again. It's a nightmare ...
09-12-10, 06:07 PM
I give up.
Wait... here's a long shot.
Maybe one of your cones is coming loose as you ride, and tightening up the hub bearings... and heating up in the process.
Or you didn't account for the quick release pressure, which tightens the hub bearings in the closed position. Try adjusting the wheel hub so it has a little more play, just a little click in the axle when it's out of the bike.
A little loose won't hurt anything.
When you stop to clean things, it cools or something and is ok for a while.
Is the grinding only while pedaling, or all the time?
09-13-10, 04:34 AM
Only when pedaling, coasting is fine. Next thing is to replace those damn pulleys and try different settings on my bearings, altough I already tried different settings before with no luck ... I always leave some play in them when off the bike.
Thanks again, man.
Next few steps I am going to take:
- pulleys replacement
- different rear bearing adjustment
- new chain again (KMC Z8S instead of shimano HG50; KMC Z8S was on this very bike until I replaced it and it worked fine, but was already stretched about 1.5%)
Another thing I probably didn't mention - I took off the chain and reused the ordinary pin, which obviously started to come out. I have replaced that pin with a reinforced one the very same day. Could the plate be destroyed? I am anyway switching back to KMC with a master link as I hate cleaning that shimano crap on the bike.
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