Shimano XT 780 Hubs.

[Bowedw]

Having recently had a set of 26 inch road wheels built with the Shimano XT780 hub the cassette freewheel has seized solid. A total mileage of about 200 miles has been done on the hub and to say I am disappointed would be an understatement.
I purchased the hubs on line but the supplier only has 32 hole replacements and not 36 like I have so if they ask for the complete hub back under warranty I have a problem there.
A complete hub is £34 approx. and a cassette freewheel only is about £44 from the importer? I need to get the bike up and running asap.
Reviews seem to suggest, that I would be throwing more money away on a poorly designed product and that I should cut my losses and have a sealed cartridge bearing hub fitted.
Anyone had a similar experience with these hubs,or am I just unlucky as so many other people who review them seem to have been.
Apart from the fact that I could have had a nasty accident as it jammed solid going down a steep hill I had to ride it home like a fixie which was an odd experience on a derailleur bike.
Having no confidence in your bike is not a recipe for a happy ride.

[Brucey]

I would expect to be able to warranty the freewheel body separately, or have the vendor cover the cost of rebuilding your wheels. What they happen to have in stock or not at present is irrelevant; it is their responsibility to make good.

BTW I would be interested to hear if these hubs still have the date code on them or not; one theory is that recently manufactured parts ought to be OK but older ones may not be. If you hubs were old stock they may not represent what you would get now.

Another theory is that the design is idiotic, and in the event that there is the slightest free play in the freehub bearings, the pawls see high loads at the corners, which then breaks them because of the stupid design. Once the corners start breaking off the pawls, the freewheel jams because the corner parts of the pawls are the parts that the springs bear against so that the pawls are properly located.

Whilst these hubs continue to fail in the warranty period, I won't get much of a chance to poke about inside them. If anyone has any failed bodies they would like a second opinion on, do let me know.

cheers

[irc]

Anyone know if this issue is specific to current XT hubs. I've just bought a pair of hand built wheels from Spa. I went for LX hubs. Do I need to be concerned?

[Bowedw]

No apparently not. There is a post for Shimano LX rear hubs, which is a bit dated at 2010 but seems to indicate the LX are better than XT. Seems everything is better than XT from what I can glean now with hind sight.
Thanks to you Brucey as well. I will try to be patient and wait if I can get a freehub under Warranty but the long term reliability issue will still be there. You are probably right about the pauls chipping as it sounds correct and the bits to jam the hub have to come from somewhere.
I am not a fan of cup and cone hubs but allowed price in this instance to rule my decision. I may decide to remove the hub and send it back for a refund which is an option with Chain Reaction and have a sealed bearing hub, one recommended by my LBS. The loss for this mistake will amount to about £50 to £60 for the labour and spokes. Buy cheap buy twice wins again.

[irc]

No apparently not. There is a post for Shimano LX rear hubs, which is a bit dated at 2010 but seems to indicate the LX are better than XT. Seems everything is better than XT from what I can glean now with hind sight.
Thanks to you Brucey as well. I will try to be patient and wait if I can get a freehub under Warranty but the long term reliability issue will still be there. You are probably right about the pauls chipping as it sounds correct and the bits to jam the hub have to come from somewhere.
I am not a fan of cup and cone hubs but allowed price in this instance to rule my decision. I may decide to remove the hub and send it back for a refund which is an option with Chain Reaction and have a sealed bearing hub, one recommended by my LBS. The loss for this mistake will amount to about £50 to £60 for the labour and spokes. Buy cheap buy twice wins again.

In fairness Shimano hubs are usually reliable. All my touring and commuting has been done on Shimano freehubs and I've never had a failure. My weight varies from 15-17 stone and I use a low gear of 22x34 so with a loaded tourer I'm getting a fair amount of stress on the hubs.

I've used a mix of 2008 XT 770s and various lower end hubs.

I suspect if there has been a huge increase in failures then it was a recent design change. You may just have been unlucky.

I have read that the LX is a steel axle rather than the aluminium axle in the XT which was why I went LX this time. I prefer steel for highly stressed components.

[Brucey]

the rot set in when they went to a large diameter aluminium axle in the XT series hubs. LX hubs with steel axles are not similarly afflicted.

You can see here;

http://cycle.shimano-eu.com/media/techdocs/content/cycle/EV/bikecomponents/FH/EV-FH-T780-3176_v1_m56577569830758219.pdf

that the FH-M770 is the same as the FH-T780 body. The FH-M770 body is also interchangeable with others as indicated here;

http://bike.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/FH/EV-FH-M770-2699A_v1_m56577569830646670.pdf

cheers

[irc]

Thanks Brucey. No issues after around 15k miles loaded touring on my XT770 rear hub. Either lucky, or maybe being a spinner rather than out the saddle rider helps.

Anyway my XT770 rear wheel has been relegated to my local use bike. Sounds like I'm good to go with the LX wheels for touring.

[Brucey]

some failed 'earless' pawls



My theory is that a relief grind on the back of the pawl corners would prevent corner loading and therefore pawl failure, but possibly it is something else, like brittle pawl material instead.

The freehub body can even burst open if it is ridden on whilst there are loose bits of broken pawl inside....







cheers

[Bowedw]

Thanks all for your information. The bottom line is that this hub is RUBBISH and I have decided to cut my losses and go with a sealed bearing hub.
I cannot have this unreliability factor hanging over me when miles from home or on a tour. All shimano freehubs seem to suffer from no or poor weather seals but do function for respectable mileages and do not seem to fail as drastic as this XT.

[Brucey]

personally I have never broken a shimano one in use (or indeed a shimano-knock-off come to that). This relatively recent design is something of a disappointment by contrast to my experience of older designs.

If I were in your shoes I would probably get an LX one. This would count double if I were carrying a load; cartridge bearing freehubs are inherently weaker than the classic shimano design, because the axle sees large bending stresses.

BTW did you find the date code on your XT hub? If you are ditching it, are the remains available for forensic purposes?

cheers

[PhilD28]

Shimano hubs are excellent for heavy duty touring use. This is a problem specific to this incarnation of XT, earlier xt models nor current LX models suffer from it.

I have been using xt and LX hubs on my expedition touring bikes on long arduous camping trips all over the world for the last 30 years - not a single failure. In fact I am still riding a 91 xt hub and it is perfect, I normally get about 5 years out of the bearings and more from the cones, a quick rebuild with grade 20 balls and off they go, good for another 5 years.

It would be easy for me to harp on about how much better cup and cone bearings are on touring bikes over cartridge bearings but I'm sure it's all been done before by Bruce. My own work as a Chartered Mechanical Engineer coupled to a lot of real world touring experience has led me to this conclusion.

Good luck with the sealed cartridge bearings.
Phil

[Bowedw]

I will agree with you all that defend the Shimano hub in general, it's just that I put my faith blindly into this particular model of hub without reading any reviews. Your experience PhilD 28 certainly is testimony to their durability and value for money.
I have sent a Warranty claim form and await an answer. They will probably want it back and may just replace the hub or may decide otherwise.
So unlikely to be available for a dissection but will bear your request in mind Brucey should it be available.

[Threevok]

Quite shocked at some of the results in this thread. I am not familiar with XT 780 hubs, but I would have thought they would better than that.

I have a pair of 26" XC-717s with Deore FH-M525'a that did 6,000 muddy miles with no servicing (I'm lazy in that respect) before the rear started to give out (the front hub is still fine). They are sitting in a box, waiting for me to rebuild them (again - lazy)

[Brucey]

it is all down to the revised freehub design in those hubs with aluminium rear axles. I think it is a design cock-up, but I can't prove that (not even to my own satisfaction) unless I can examine a few more failed units (that are not completely converted to shrapnel within... )

AFAICT all the shimano freehub designs that use steel rear axles are still reliable in normal use, just like they always have been. I earnestly hope not be proven mistaken, even for the sake of my own usage!

Ironically the new XT design was clearly intended to be stronger; there are more, larger, pawls within it.... hey ho....

cheers

[fastpedaller]

I've no direct experience of one of these newer hubs - I'm thankful for that having seen the above. I can only guess this is a result of the "gain" provided by using something lighter which is really not up to the task.