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XT RD M772 like grandfather's axe?

Posted: 12 Oct 2020, 9:56pm
by mikeymo
I seem to have missed the chance to get a new or NOS XT RD M772.

But there are several "lightly used" ones kicking about. I see some parts are available. Is it possible to replace all the (important) parts, grandfather's axe style? And so end up with a more-or-less-new one?

Thanks.

Re: XT RD M772 like grandfather's axe?

Posted: 12 Oct 2020, 10:30pm
by Brucey
you can see what spares might be available in the EV techdoc.

But if the parallelogram pivots are worn or parts are bent, it is 'game over'.

In general RDs are consumables; they wear out or get broken; getting hung up on obsolete models is best avoided, unless you have a big stash of them.

cheers

Re: XT RD M772 like grandfather's axe?

Posted: 12 Oct 2020, 10:37pm
by peetee
Don’t panic just yet. I have had well over 20 years service from a M735 rear mech with just one replacement Jockey wheel. It still changes faultlessly.

Re: XT RD M772 like grandfather's axe?

Posted: 12 Oct 2020, 11:02pm
by irc

Re: XT RD M772 like grandfather's axe?

Posted: 12 Oct 2020, 11:12pm
by mikeymo
irc wrote:What about the Deore shadow?

https://www.rosebikes.co.uk/shimano-deo ... eur-368015


Yes, thanks, I've seen that. I was just fancying the famously robust M772. I wish I'd got one a few months ago, when they were still available. I've got a NOS M771, but the M772 goes up to 36 teeth. I suppose if the XT M77x range is as robust as claimed, then sourcing a "lightly used" one should be OK. Or two.

Opinion generally seems to be that Deore isn't as solid as XT, but at least the M592 is actually available. And at that price I could just buy two. That would probably see me out.

This is all part of my "make my 9 x 3 setup last until I die" strategy.

Re: XT RD M772 like grandfather's axe?

Posted: 13 Oct 2020, 11:56am
by irc
Will the 771 not go up gto 36T anyway. I thought Shimano were a bit conservative with their specs.

I know the feeling with 1x9. I run low normal rapid rise derailleurs on my 3x9 tourers. Currently have 2 nearly new ones on my two touring bikes and two brand new on the shelf.

I'm happy with 34T at the back though. 22/32/42 on the front.

Re: XT RD M772 like grandfather's axe?

Posted: 13 Oct 2020, 5:37pm
by mikeymo
irc wrote:Will the 771 not go up gto 36T anyway. I thought Shimano were a bit conservative with their specs.

I know the feeling with 1x9. I run low normal rapid rise derailleurs on my 3x9 tourers. Currently have 2 nearly new ones on my two touring bikes and two brand new on the shelf.

I'm happy with 34T at the back though. 22/32/42 on the front.


Thanks. I'd like to be able to go down to a crankset that size, but it isn't as simple as I first thought. It seems that most cranksets like that are for MTBs, and at the crank there isn't the same MTB/Road compatibility as there is at the back end. Could I ask:

1. Is this a drop bar bike with STIs (or similar)
2. What crankset is it?
3. What BB is it?
4. What FD is it?
5. Do you know what the chainline is?

Thanks.

Re: XT RD M772 like grandfather's axe?

Posted: 13 Oct 2020, 7:45pm
by irc
mikeymo wrote:
irc wrote:Will the 771 not go up gto 36T anyway. I thought Shimano were a bit conservative with their specs.

I know the feeling with 1x9. I run low normal rapid rise derailleurs on my 3x9 tourers. Currently have 2 nearly new ones on my two touring bikes and two brand new on the shelf.

I'm happy with 34T at the back though. 22/32/42 on the front.


Thanks. I'd like to be able to go down to a crankset that size, but it isn't as simple as I first thought. It seems that most cranksets like that are for MTBs, and at the crank there isn't the same MTB/Road compatibility as there is at the back end. Could I ask:

1. Is this a drop bar bike with STIs (or similar)
2. What crankset is it?
3. What BB is it?
4. What FD is it?
5. Do you know what the chainline is?

Thanks.


Drop bar tourers using bar end shifters . A Surly Long Haul Trucker and a Spa Steel Tourer. The bar end shifter allows Deore Hollowtech 2 cranksets with HT bottom brackets and MTB XT front shifter.

I realise that isn't much help if you use STI's.

Only tip I can offer if you are on STIs is this device (below) for adjusting the inner/outer position of front derailleurs which may help with one aspect of getting STIs to shift on an MTB chainset or move a road front deraileur further outboard if required. . The other way with Hollowtech bottom brackets which could be used in conjuction is putting only one of the 2.5mm spacers on the drive side and two on the non drive side which shifts the chainrings 2.5mm to the left.

https://www.sjscycles.co.uk/gear-spares ... hed-split/

Re: XT RD M772 like grandfather's axe?

Posted: 13 Oct 2020, 9:36pm
by mikeymo
irc wrote:
mikeymo wrote:
irc wrote:Will the 771 not go up gto 36T anyway. I thought Shimano were a bit conservative with their specs.

I know the feeling with 1x9. I run low normal rapid rise derailleurs on my 3x9 tourers. Currently have 2 nearly new ones on my two touring bikes and two brand new on the shelf.

I'm happy with 34T at the back though. 22/32/42 on the front.


Thanks. I'd like to be able to go down to a crankset that size, but it isn't as simple as I first thought. It seems that most cranksets like that are for MTBs, and at the crank there isn't the same MTB/Road compatibility as there is at the back end. Could I ask:

1. Is this a drop bar bike with STIs (or similar)
2. What crankset is it?
3. What BB is it?
4. What FD is it?
5. Do you know what the chainline is?

Thanks.


Drop bar tourers using bar end shifters . A Surly Long Haul Trucker and a Spa Steel Tourer. The bar end shifter allows Deore Hollowtech 2 cranksets with HT bottom brackets and MTB XT front shifter.

I realise that isn't much help if you use STI's.

Only tip I can offer if you are on STIs is this device (below) for adjusting the inner/outer position of front derailleurs which may help with one aspect of getting STIs to shift on an MTB chainset or move a road front deraileur further outboard if required. . The other way with Hollowtech bottom brackets which could be used in conjuction is putting only one of the 2.5mm spacers on the drive side and two on the non drive side which shifts the chainrings 2.5mm to the left.

https://www.sjscycles.co.uk/gear-spares ... hed-split/


Thanks. This is all new to me.

I've got a pair of Dura Ace DT shifters on the shelf, and sometime I'll try them out. But I'd like to keep at least the option of STIs.

So if I've got this right:

1. If I'm using road STIs, I need a road FD (like I've got).

2. But the main problem is that most MTB chainsets are expecting a MTB chainline, which may be 50mm (or even 54mm with Thorn cranks) and then the FD isn't in the right place. Because road FDs are expecting a road chainline, of 45mm.

3. As far as I can tell, and please correct me if I'm wrong, the actual chainring to chainring spacing on a triple MTB chainset isn't substantially different to the spacing on a road triple chainset. And I can always make it wider with chainring spacers, but not narrower, obviously.

So I need a way to get the FD further out, the chainset further in, or a combination of those.

The Jtek eccentric shim (which would work on my bike, 28.6 seat tube) would do the first thing. And by changing the BB (if ST) or doing the thing with the shims on HT, I might be able to do the second thing, at least until I ran out of space on the BB. At which point the (road) FD would be "centred" over the chainset.

As the whole point of this is to use smaller chainrings, I assume that I'm less at risk of them catching the chainstay if I'm moving them inboard.

And as a matter of fact I read somewhere that with 135 OLN, like mine, the chainline should really be 47.5 mm. I'll measure it sometime.

Am I on the right track?

PS, the reason I'm interested in the Thorn Cranks - https://www.sjscycles.co.uk/cranks/150-thorn-10464-pcd-triple-crankset-mk2-black/ - is that they are about the only cranks that will take a 22 tooth inner, and also have 165 crank arms available, which is what I have, and like.

Re: XT RD M772 like grandfather's axe?

Posted: 13 Oct 2020, 10:09pm
by Brucey
mikeymo wrote:
1. If I'm using road STIs, I need a road FD (like I've got).


it is worse than that; as I have tried to explain in several previous threads: If you want indexed front shifting to work properly on your bike you need a mech that is

- shimano

- 'road'

- triple

-for your chainring sizes and intervals

- at the correct chainline

- and the FD should have all the other boring details correct eg chainstay angle, chainstay clearance, mudguard clearance, frame fitment, cable pull direction.

as soon as you ditch the infernal nonsense that is the indexed left shift, you will have a much easier time of selecting suitable equipment, especially if you want different gear ratios than shimano anticipate.

cheers

Re: XT RD M772 like grandfather's axe?

Posted: 13 Oct 2020, 10:57pm
by irc
mikeymo wrote:PS, the reason I'm interested in the Thorn Cranks - https://www.sjscycles.co.uk/cranks/150-thorn-10464-pcd-triple-crankset-mk2-black/ - is that they are about the only cranks that will take a 22 tooth inner, and also have 165 crank arms available, which is what I have, and like.



Spa Cycles do a crank with a165 option which takes a 24t inner. Close enough? As they are sq taper you could get correct chainline for your current front deraileur..

https://www.spacycles.co.uk/m8b0s109p20 ... chainrings

I have no experience of getting road front deraileurs to work with smaller chainrings though so have no idea how small is workable with which model front derailleurs.

Re: XT RD M772 like grandfather's axe?

Posted: 13 Oct 2020, 11:12pm
by mikeymo
irc wrote:Spa Cycles do a crank with a165 option which takes a 24t inner. Close enough?


Quite probably, especially if I can wrangle a 36 sprocket onto the back.

Thanks.

Re: XT RD M772 like grandfather's axe?

Posted: 13 Oct 2020, 11:15pm
by mikeymo
Brucey wrote:
mikeymo wrote:
1. If I'm using road STIs, I need a road FD (like I've got).


it is worse than that; as I have tried to explain in several previous threads: If you want indexed front shifting to work properly on your bike you need a mech that is

- shimano

- 'road'

- triple

-for your chainring sizes and intervals

- at the correct chainline

- and the FD should have all the other boring details correct eg chainstay angle, chainstay clearance, mudguard clearance, frame fitment, cable pull direction.

as soon as you ditch the infernal nonsense that is the indexed left shift, you will have a much easier time of selecting suitable equipment, especially if you want different gear ratios than shimano anticipate.

cheers


Thanks for you input, as always. Apologies if I'm boring you with my questions.

Just looking at your list then, for my proposed set up:

Shimano - check
Road - check
Triple - check
Cable pull direction - check
Chainstay angle - just calculated it, check
Chainring sizes - I'll drop to 42-32-22, so check. I'll even put a 31 in the middle, if anybody makes one.

The various clearances might be difficult to check without trying to fit, but I daresay a sunny afternoon measuring - "if this were 5 mm further that way, what would happen" might flag up any problems.

The big one is getting the chainline out. That Jtek eccentric shim seems like a way forward.

Still, at least one user has posted getting the the same FD, with the same shifters, as I'm proposing to use as working just fine with a 44-34-22 XT chainset. So not impossible.

As I've said before, I'm an eccentric millionaire who enjoys collecting spare 9 speed parts.

Re: XT RD M772 like grandfather's axe?

Posted: 29 Oct 2020, 4:32pm
by mikeymo
Brucey wrote:But if the parallelogram pivots are worn or parts are bent...


I've got an M772 now. Well, two, actually. I've tried twisting the parallelogram and can't really feel any play. Would worn pivots only become apparent in use?

Thanks.

Re: XT RD M772 like grandfather's axe?

Posted: 29 Oct 2020, 7:00pm
by boblo
mikeymo wrote:<snip>
Still, at least one user has posted getting the the same FD, with the same shifters, as I'm proposing to use as working just fine with a 44-34-22 XT chainset. So not impossible.

As I've said before, I'm an eccentric millionaire who enjoys collecting spare 9 speed parts.
<snip>


That might have been my XT triple? I hadn't thought about the chainline but I do remember using 2 spacers on the 'wrong' side which would account for the 45mm-50mm difference. At the time, I did it just to get stuff working rather than spend any time over it in deep thought :wink:

So XT 44/32/22 with an XT M772 rear dérailleur, Sora front dérailleur and Sora 3x9 STI's. It shifts perfectly. I used bar ends before and held off migrating to the Sora's for years as I didn't want to risk moving to something potentially not as good without a compelling reason to do so. An enforced new build was that reason.