RD-M772; would you put your bike in for a service like this?

[Brucey]

I occasionally salvage parts that would otherwise end up in the scrap. Recently I retrieved a well-used RD-M772-GS rear mech; I thought it might be both useful for spare parts and interesting so see how they can wear at high mileages; I have a couple of these mechs and mine have not done a lot of miles yet.


shiny newness

The provisional verdict on wear is that the upper mounting appears not to be very prone to it, but the main (A) pivot (which has a bushing which is quite short in this design) can wear a bit and the parallelogram pivots can also wear. Obviously the pulley bearings can wear too. However the parallelogram pivots are set far apart, so the effect on the whole mech is not catastrophic.

As with all RDs with a diagonal tension spring inside the parallelogram, the spring preloads all the parallelogram pivots nearly all the time; this helps prevent movement (arising from vibration) and therefore wear. However when the RD is set in top gear and the high gear stop screw is loaded, the tension spring does not preload all the pivots in the same way as normal; under this condition any wear is more evident, and moreover riding the bike far in top gear also wears everything faster than normal. I've seen similar things on 'shadow' mechs eg RD-M4000 (which are basically a cheaper version of the same thing, but with a barrel adjuster, plus more steel parts and fewer aluminium ones). No way of knowing if the posh bushings in the XT version are much harder wearing than the Alivio version, but the pulley bearings are, for sure.


The bike this mech came from may have had a 'full reset' service but apart from that the main reason the mech ended up in the scrap was because the pulleys didn't go round easily any more.... and the reason that was the case was that the pulleys were as badly encrusted with crud as any I have seen. I could hardly believe it; I was, if you like, quite incrudulous.... IME these 'crud monsters' are made of road dirt bound together with excess chain lube. When it is nicely dried, I think you could build houses from it.

the scrap mech, together with most of the crud

So would you expect your gears to work with that much crud on them? Would you put your bike in for a service like that?

To date (when not populated by crud monsters, obviously) RD-M772 seems like a pretty durable mech; anyone else have anything to report re durability? FWIW I've seen a few RD-M4000s go into wheels and they mostly didn't break, they just bent (in a 'straighten it and you will probably get home' kind of way) mainly at the top link and in the pulley cage. Being mostly steel, I think RD-M4000 is less likely to break than a similar mech like the XT one with more aluminium parts.

cheers

[fastpedaller]

Would you put your bike in for a service like that?

Why would you clean it yourself, then pay a guy to do it?

[willcee]

BRucey.. just finished a repair on a friends work colleague commuter bike or cheap full sus Halfords 27.5 wheeled BSO .. and i have yet to witness a worse case of gross miss use.. wish i had taken some pics.. however my chum asked me to have a look at this chaps bike, warning me not to part with it until he had paid for the repair, ''this guy could bend a crowbar in the ''moss'' he says, rough as all get out on any bike..it wasn't working and he had parked it at their business yard, i had a look and saw immediately the BB was totally gone the left cup had disappeared into the bb shell, the adjusting ring was sellotaped to the crank!!! the right d/s cup was twisted so that the back side was 4mm from the edge of the cup with the front side where it should be.. don't ask how i got it out.... it was a basket case ..no LBS with any sense would have tried the job and would have said skip it.. 3 hours later i had a new BB in it crankset back on and checked the gears without me resetting anything it was as sweet as a new machine, then the real dirty work began.. the chain and derailleurs were so thick with congealed lube dirt and grease that i couldn't see if the jockeys had teeth..after a clean and relube and many pairs of work gloves it was delivered in working order.. i will take some pics of the bb axle for you to see.. the axle ridge where the bearings run on the drive side was ground away.. seriously.. ground away.. there was about 3inch play side /side in the bb so the chain was coming off that's why he wanted it repaired!!! [moss is soft peaty wet ground lots of it in N Ireland]..will

[Brucey]

Would you put your bike in for a service like that?

Why would you clean it yourself, then pay a guy to do it?

In this case the dirt probably stopped the bike from working altogether; its not like the bike was totally neglected, with the local soil hereabouts you don't usually get crud monsters without there being chain lube present, so the chain was almost certainly oiled.... but not cleaned in any way....

Also NB, the repair shop in question make it abundantly clear that they don't clean bikes, but they do repair them. Folk who bring them a clean (or at least cleanish) bike to work on get the best out of them, for sure. [ BTW this will vary from place to place but I've known LBSs turn away bikes that are too dirty, or make a (not insubstantial) separate charge for cleaning them.]

In this case I have little doubt that the cassette and chain were knackered and went in the bin. Possibly this mech was (rightly or wrongly) deemed sloppy enough that it wouldn't last out the next cassette and chain. In any event at workshop rates you wouldn't bother cleaning an RD if you thought it was probably knackered and/or the customer had agreed to/asked for a new one anyway.

BTW Will may have seen something similar but I have seen pedals where the ball bearings have all come out, and the bike has then been ridden far enough that the edges of the bearing cups in the pedal body have worn through the pedal spindle....

cheers

[francovendee]

A good friend who also cycles a bit never cleans his bike and maintenance consists of squirting more oil onto the chain.
It's a right mess and I'm waiting for the day when his chain comes off and he has to touch it.

[Samuel D]

Cleanliness of drivetrain varies from person to person as much as cleanliness of home toilet or clothing.

I have riding companions who always show up with a spotless bicycle and gleaming drivetrain. They are not necessarily mechanically talented (I recall one of these compulsive cleaners arriving with a rattling-loose head bearing). But they are fastidious about keeping their bicycles clean, and I suppose that goes a long way to minimising other problems.

My drivetrain is black more often than silver but seems to work anyway. Of course I don’t let grunge build up to the extent of Brucey’s example, but where should you draw the line?

This is what mine happened to look like on the day of my recent crash. (Was trying to photograph the derailleur scuffs but missed focus.)



Honest opinions, then: is this clean enough?

It’s fairly typical for my bicycle. Once it gets a little worse than that I clean it.

Curious to see grime build-up on the chain ahead of the pins but not behind, with respect to the chain’s direction of travel.

[ElCani]

I’d say I’m similar to you. When mine got like that I’d be thinking “time for a clean” but it’d be no surprise if I left it a bit longer.

[Brucey]

Cleanliness of drivetrain varies from person to person as much as cleanliness of home toilet or clothing....

but they (for better or worse) don't all go hand in hand.....

It’s fairly typical for my bicycle. Once it gets a little worse than that I clean it.

Curious to see grime build-up on the chain ahead of the pins but not behind, with respect to the chain’s direction of travel.

that could indicate something to do with the relative speed of the chain vs the plume of crud off the front wheel (on both bottom and top runs), but it might also be something to do with exactly how the chain was wiped after it was last lubed, too; wiping in one direction may leave more chain lube to one end of the outer side plates, and it is this which makes crud most likely to stick?

FWIW I've seen plenty of chains get grimier than that in a single ride.

cheers

[fastpedaller]

looks just like mine

[Samuel D]

[…] it might also be something to do with exactly how the chain was wiped after it was last lubed, too; wiping in one direction may leave more chain lube to one end of the outer side plates, and it is this which makes crud most likely to stick?

I wrap a paper towel or rag around the slack run of the chain while pedalling backwards to make it not slack, so that would fit your theory. Good observation.

[alexnharvey]

Are chain lubes getting messier? I bought a bike a little while ago with terrible accretions of gunk that had set hard and were very hard to shift.

[The utility cyclist]

I've seen RDs in far worse condition, I've encountered one's were the pulley's were worn to a round and the chain simply skated over them as they were stuck in place. If whatever you're rescuing actually functions then it doesn't really matter what it looks like cosmetically, it doesn't take too much time to get the gunk out from under the bearing cover or scrape the hardened on concrete mix from the pulley's so you can get them working in decent fashion without too much effort.
A 772 is higher end so you'd expect the body and springs/pivots to be of decent quality/robustness, some of the lower end RDs are junked in a short space of time with misuse, the amount of slop in them makes gear changes vague at best and as the bodies are plastic on these low end jobs they are peone to cracking at the pivot points quite easily thus rendering them useless, you might be able to reuse the pulleys if they aren't too badly worn, probably the highest quality aspect of these lower end derailleurs.

[Mike_Ayling]

BRucey.. just finished a repair on a friends work colleague commuter bike or cheap full sus Halfords 27.5 wheeled BSO .. and i have yet to witness a worse case of gross miss use.. wish i had taken some pics.. however my chum asked me to have a look at this chaps bike, warning me not to part with it until he had paid for the repair, ''this guy could bend a crowbar in the ''moss'' he says, rough as all get out on any bike..it wasn't working and he had parked it at their business yard, i had a look and saw immediately the BB was totally gone the left cup had disappeared into the bb shell, the adjusting ring was sellotaped to the crank!!! the right d/s cup was twisted so that the back side was 4mm from the edge of the cup with the front side where it should be.. don't ask how i got it out.... it was a basket case ..no LBS with any sense would have tried the job and would have said skip it.. 3 hours later i had a new BB in it crankset back on and checked the gears without me resetting anything it was as sweet as a new machine, then the real dirty work began.. the chain and derailleurs were so thick with congealed lube dirt and grease that i couldn't see if the jockeys had teeth..after a clean and relube and many pairs of work gloves it was delivered in working order.. i will take some pics of the bb axle for you to see.. the axle ridge where the bearings run on the drive side was ground away.. seriously.. ground away.. there was about 3inch play side /side in the bb so the chain was coming off that's why he wanted it repaired!!! [moss is soft peaty wet ground lots of it in N Ireland]..will

How much did you charge him?

Mike

[Brucey]

FWIW if you ever have to remove crud monsters from the pulleys, or are dealing with a truly filthy bike, a hot pressure wash shifts nearly everything. But most folk don't have that as an option, so there is a trick to getting the worst of it off. With the bike in the workstand, turn the transmission and use a flat blade screwdriver almost as a lathe tool on the pulleys as they turn; most of the crud on the pulleys themselves will soon come off this way. The worst of it can be removed in a couple of minutes.

However the mech upthread took a lot longer to deal with; it was no longer on the bike, and the crud (much of which was near the pulleys rather than stuck to them) had dried to a consistency that made it difficult to remove. I had a spare ten minutes but it took at least that long just to get the stuff off that you can see in the photo.

To finish it off, I might yet stick it in the dishwasher....

cheers

[nigelnightmare]

A small tub (Chinese takeaway) with petrol.
Put the derailleur in, put lid on and agitate (shake it).
Check and repeat until clean, the use of an old tooth brush helps.
Let it dry,
Then strip, lube (I use a dry chain lube) & re-assemble. I usually grease the jockey wheel bearings.

I prefer the Alivio as it has a barrel adjuster whereas the M772 doesn't. Jockey wheels are easy to upgrade.

Dishwasher= Me standing at kitchen sink with hot water & WUL (fairy).