Shimano XT hub FH-T780. Wheel is a little over a year old. Riding conditions are not extreme in terms of mud, dirt and dust.
When I pedal and then coast the freewheel sticks. That is, the upper part of the chain slacks, and then the freewheel releases, and I coast normally. This does not happen all the time, but maybe 2 or 3 times on a 2 hour ride. It does not seems to depend on cadence.
I removed the casette, cleaned the freewheel as much as possible, and sprayed some WD-40 through the end section. This didn't seem to improve the situation much.

Any ideas or recommendations are appreciated.

YannisG

I'm very confused. Is it a freehub or a freewheel? Cassette and freewheel are two totally different and unrelated things that perform the same task. A cassette slides off the freehub which has splines and is held in place by a lockring and needs a chain whip to remove. A freewheel is the cogs and ratcheting mechanism all in once unit that unscrews from the hub itself.

Most modern bike shop brand bikes come with freehub based wheels these days.

But the term cassette and freewheel are not interchangeable and used with the same parts on a particular wheel.

The best way is to remove the freehub from the shell (instructions available on the internet) so you can give it a real soaking, in solvent and flush clean. This can be done on the bike, and using a so-called "freehub greasing" device makes it much easier, but you'll have a mess as oil, dirt and solvent gets all over the wheel.

Once the freehub is flushed clean, oil and reassemble.

The early versions of the new generation xt freehubs were often duds. You should replace the freehub body. This may be covered under warranty depending on the age, etc.

- joel

Bobotech,
Thanks for yr response. Sorry for the confusion. I meant freehub, and not freewheel.
YannisG

The quick/dirty method is to remove the rear wheel from the bike and lay it across a trash can sprocket side up. Spin the cogs with your fingers and notice how hard it spins and what spins with the cogs and what stays still. Spray a little WD40 onto that crack and let it soak in for about 5 minutes. Spin the cogs with your fingers again. If they spin more freely than before, you're good-to-go.

Thanks for the response.
The sprocket spins freely. That is, it doesn't grab at all. I had sprayed it with WD-40, but I can't say I noticed any difference in the spinning.
YannisG

If it isn't the freehub, maybe one of the jockey wheels are sticking.

A sticking pulley cannot cause the upper loop to slacken.

Only a sticking freewheel (or freehub) would make it possible for the spinning wheel to spool the chain forward into the upper loop. It doesn't take much, and often isn't mechanical, but the result of stuff packed behind the cassette and binding the wheel and cassette together.

Sporatic sticking is often because of dirt, or even rust damaged pawls, and flushing, either via the dunk or sprayed WD-40 method helps, but you have to spin the freewheel to work stuff loose and hopefully out via the bottom gap.

It does not have to actually grab - an increase in friction is all that's necessary. Keep in mind that the wheel is turning fast and at a constant rate when you are coasting, so what seems to be OK when you spin it by hand may be deceiving. As FB points out friction in a freehub or freewheel is the only thing that can cause a droop in the chain. The hub is essentially driving the freewheel forward through a very mild clutch action, and as you are not turning the pedals the forward rotation makes the chain droop.

Thanks for the correction FB.

Thanks for the response,
Since squirting WD-40 into the freehub and then dripping light oil in between the freehub and hub the sticking seems to happen less often. However, I have never been able to simulate the sticking with the bike on the work stand.
YannisG