Author Topic: New XT rear mechs  (Read 2486 times)

New XT rear mechs
« on: 06 May, 2018, 08:57:48 pm »
I have an XT rear mech from earlier this century. It looks like this:



It looks fairly shiney as I've just cleaned it up, but it's getting a bit tired.

What would a more modern equivalent be?

Something like this: Shimano XT M772 9 Speed Rear Derailleur

or this: Shimano XT M771 9 Speed Rear Derailleur

And would I need medium or short cage? I'm a bit out of the loop with Shimano stuff....

Rings are 26/38/48 cassette is 11-34.

Ta.
Those wonderful norks are never far from my thoughts, oh yeah!

Kim

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Re: New XT rear mechs
« Reply #1 on: 06 May, 2018, 09:03:43 pm »
I've got a couple of bikes with the long cage M771.  They just work.

One has an 11-34 cassette and 26/36/48 chainrings, but the mech is a hand-me-down, so I'm not sure if the long cage is actually required or not.


That M772 looks like they've employed a designer who used to do computer cases for gamers...

Re: New XT rear mechs
« Reply #2 on: 06 May, 2018, 09:05:39 pm »
either will do but they are not the same (see my comments in another thread for details).

You need one with an arm that is at least as long as the one you have. Depending on the model this may be described differently; 'medium' and 'long' mean different things in different mechs. The one you have looks like an SGS model, i.e. the longest then available.

cheers

Re: New XT rear mechs
« Reply #3 on: 06 May, 2018, 09:24:46 pm »
Ok, ta.

Just thought to check my MTB (d'oh!) and it appears to have the M772. The cable comes in at a weird angle and would mean the shiftmate on my tourer wouldn't fit properly. The M771 looks like the cable comes in pretty much the same as the current mech. So it looks like the M771 would be the way to go. Or I could just leave the existing one alone. It's worked fine for about 30,000 miles....
Those wonderful norks are never far from my thoughts, oh yeah!

bhoot

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Re: New XT rear mechs
« Reply #4 on: 06 May, 2018, 09:32:18 pm »
Unless you are set on the newer design you could still get an old style one if you don't mind "downgrading" to plain Deore eg http://www.wiggle.co.uk/shimano-deore-m591-9-speed-rear-mech and save some money.
I had the same as you on my touring bike and replaced it with a Deore LX which seems very similar. The advantage (possibly) of getting the old style rather than a newer "shadow" design is that the cable routing would be the same, also the older model has the adjuster at the derailleur which I think the newer ones don't (but I rather like).

Re: New XT rear mechs
« Reply #5 on: 06 May, 2018, 09:37:55 pm »
Unless you are set on the newer design you could still get an old style one if you don't mind "downgrading" to plain Deore eg http://www.wiggle.co.uk/shimano-deore-m591-9-speed-rear-mech and save some money.
I had the same as you on my touring bike and replaced it with a Deore LX which seems very similar. The advantage (possibly) of getting the old style rather than a newer "shadow" design is that the cable routing would be the same, also the older model has the adjuster at the derailleur which I think the newer ones don't (but I rather like).

Ah! Good idea. I'm sure a regular Deore would be just fine. Cheaper too :)
Those wonderful norks are never far from my thoughts, oh yeah!

Re: New XT rear mechs
« Reply #6 on: 06 May, 2018, 10:05:59 pm »
mllePB has the Deore on her machines whereas I have the ST as per yours Bobb.  To be perfectly honest neither of us has had rear mech issues since I first started tinkering with mllePB's bikes at the back end of 2000.  Our turers, audaxers and mtbs have been very reliable.

Kim

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Re: New XT rear mechs
« Reply #7 on: 06 May, 2018, 10:29:17 pm »
The bike with the hand-me-down XT had a Deore on it until a plastic bag tangled the derailleur cage with the spokes.  It was fine - main gotcha is probably that the barrel adjuster, while useful, is prone to seizing up if neglected.  I had that happen on an old LX mech of similar design.

I think the XT has slightly nicer jockey wheel bearings, but that might just be because it's newer.  IME the teeth are likely to go before the bearing does, anyway.

Torslanda

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Re: New XT rear mechs
« Reply #8 on: 06 May, 2018, 10:49:52 pm »
No, Kim, the XT jockeys are nicer bearings. Funnily enough I recently had cause to dismantle an ancient Huret Svelto mech. Actual, real, ball bearings in the jockey wheels...
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: New XT rear mechs
« Reply #9 on: 06 May, 2018, 10:57:33 pm »
RD-M771 is the older design, with a sprung B pivot, and the cable entry will suit a shiftmate I think.

See my post herehttps://yacf.co.uk/forum/index.php?topic=107877.0 for some comments re the difference between these mechs.

XT pulleys are much nicer than the plain deore ones; a proper ceramic bushing at the top and a well sealed ball bearing at the bottom.

BTW if the OP has a shiftmate, could the mech not be chosen to match the shifters properly to begin with? IIRC there is a current shimano mech that matches campag 9s cable pull, for example.

cheers

Re: New XT rear mechs
« Reply #10 on: 06 May, 2018, 11:08:22 pm »
BTW if the OP has a shiftmate, could the mech not be chosen to match the shifters properly to begin with? IIRC there is a current shimano mech that matches campag 9s cable pull, for example.

I dunno. The shifters are 2006 Campag Centuar 10 speed....
Those wonderful norks are never far from my thoughts, oh yeah!

Re: New XT rear mechs
« Reply #11 on: 07 May, 2018, 10:33:44 am »
well in a nutshell a 9s RD (shift ratio ~1.7) needs ~2.55mm per click to work properly on a 4.35mm pitch 9s cassette (2.55 x 1.7 =  4.325) and the campag shifters pull ~2.8mm per click, so this tells you what difference the shiftmate is making (reducing shift pull to ~91%).

The current shimano 11s road mechs (and tiagra 4700) have a shift ratio of ~1.4. Thus 2.8 x 1.4 = 3.92mm so your shifters with a shimano 11s mech ought to  work almost perfectly on a shimano (or SRAM) 10s cassette, which has a sprocket pitch of 3.95mm.

Weirdly if the shiftmate pulley is flipped in the housing, it will multiply the pull by x1.098 which will cause an 11s RD movement of 2.8 x 1.098 x 1.4 = 4.34mm.

 In other words if you use an 11s shimano road mech with your shifters, I think the extant shiftmate (with pulley flipped) can be used to increase the cable pull to work with a 9s cassette, or omitted for it to work with a 10s cassette.

cheers


Re: New XT rear mechs
« Reply #12 on: 07 May, 2018, 01:56:31 pm »
No, Kim, the XT jockeys are nicer bearings. Funnily enough I recently had cause to dismantle an ancient Huret Svelto mech. Actual, real, ball bearings in the jockey wheels...

OT but how do you "dismantle" a Svelto? From memory they were all rivetted apart from the bottom jockey, which could be unbolted to get the mech on and off without splitting the chain (although, also from memory, the bottom jockey could be taken apart for cleaning and regreasing) - or does the arm with the top jockey unbolt as well? Some of the later Taiwanese copy Huret mechs were genuinely dismantleproofed.

Re: New XT rear mechs
« Reply #13 on: 07 May, 2018, 05:51:56 pm »
IIRC the lower knuckle in a Svelto comprises a bolt that is threaded into the steel knuckle plate, secured by a special locknut on the outside.  If you remove the locknut the bolt then unscrews and then the guide pulley can be removed.

  Later versions of the svelto had one ball bearing pulley and one plain bushed one. The parallelogram in a Svelto is indeed riveted together and cannot be dismantled.

Such adjsutable ball bearing pulleys (like campag ones from early GS mechs) are wonderful apart from one thing; in wet weather the ballrace fills up with water. It would have been better if there were drain holes to let water out of the 'groove' in the main part of the pulley.

cheers

bhoot

  • MemSec (ex-Mrs RRtY)
Re: New XT rear mechs
« Reply #14 on: 07 May, 2018, 10:39:04 pm »
BTW if the OP has a shiftmate, could the mech not be chosen to match the shifters properly to begin with? IIRC there is a current shimano mech that matches campag 9s cable pull, for example.

I dunno. The shifters are 2006 Campag Centuar 10 speed....
I run my 9 speed Deore LX with Campag Daytona 10 speed shifters and connect the cable using the "hubbub" method to get the cable pull correct, no shiftmate needed!  Check out Chris Juden's "Shimergo" info.

Re: New XT rear mechs
« Reply #15 on: 07 May, 2018, 10:53:54 pm »
if you want to be able to use the hubbub cable mount method, you need to choose RD-M771 not RD-M772

cheers

Re: New XT rear mechs
« Reply #16 on: 07 May, 2018, 11:10:55 pm »
The hubbub method always seemed a bit of a bodge to me, which is why I use a shiftmate. It's worked absolutely fine for years. I'm sure the hubbub method works fine too, or people wouldn't use it, but seeing as I have a shiftmate and I'm happy with it, I'll continue with it.

I may or may not get a new rear mech - if I do (and it would probably be the Deore) the only reason for doing so is for piece of mind before setting off on a 2000+ mile tour. The mechs are just about the only things left from the original build. The shifters are too actually, but they got a refurb at Condor a little while ago.

The front mech seems fine, but the barrel adjuster on the rear is seized and the adjustment screws are very rusty. I could probably nick some from another mech actually....
Those wonderful norks are never far from my thoughts, oh yeah!

Torslanda

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  • Just a tart for retro kit . . .
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Re: New XT rear mechs
« Reply #17 on: 07 May, 2018, 11:32:43 pm »
No, Kim, the XT jockeys are nicer bearings. Funnily enough I recently had cause to dismantle an ancient Huret Svelto mech. Actual, real, ball bearings in the jockey wheels...

OT but how do you "dismantle" a Svelto? From memory they were all rivetted apart from the bottom jockey, which could be unbolted to get the mech on and off without splitting the chain (although, also from memory, the bottom jockey could be taken apart for cleaning and regreasing) - or does the arm with the top jockey unbolt as well? Some of the later Taiwanese copy Huret mechs were genuinely dismantleproofed.

I remember the bottom jockey coming out fairly smartly. The top was a bit harder. Come to think it might not have been a Svelto. Certainly had Huret stamped on it thobut.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: New XT rear mechs
« Reply #18 on: 19 May, 2018, 05:18:27 pm »
If anyone is remotely interested, I went with the bog standard Deore mech in the end:



I got a new chainset whilst I was at it  :)

I *think* I've just about got a low enough bottom gear now  :P

Just been for a ride and everything is just fine...
Those wonderful norks are never far from my thoughts, oh yeah!

Torslanda

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  • Just a tart for retro kit . . .
    • John's Bikes
Re: New XT rear mechs
« Reply #19 on: 19 May, 2018, 07:46:05 pm »
Yep. Looks low enough to induce lactic acid after 800 yards!
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: New XT rear mechs
« Reply #20 on: 20 May, 2018, 09:46:41 am »
Blimey, that's low. 24/34?

Re: New XT rear mechs
« Reply #21 on: 20 May, 2018, 09:52:41 am »
Blimey, that's low. 24/34?

Yup  :)

I tried it yesterday up the steepest hill I could find and it was great!
Those wonderful norks are never far from my thoughts, oh yeah!

Re: New XT rear mechs
« Reply #22 on: 20 May, 2018, 11:52:04 am »
yup that is a twiddle-tastic low gear alright.

The biggest differences between the mech you have and an XT one is a small weight difference and the quality of the pulleys. IME regular cleaning and greasing of the pulley bushings will result in a much longer life than otherwise. In particular I would strip and regrease new pulleys, because they are usually little better than bone dry when new.

cheers

Kim

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Re: New XT rear mechs
« Reply #23 on: 20 May, 2018, 09:56:35 pm »
Blimey, that's low. 24/34?

Yup  :)

I tried it yesterday up the steepest hill I could find and it was great!

Proper gearing, that is.   :thumbsup: