Derailleur Question

[neptune]

About a month ago, I fitted my pushbike with new chain, rear sprockets [freewheel] and new rear gearchange mechanism and inner cable. Although rideable, gear changing has not been 100% since. Whether changing up, or down, I often have to move the revoshift too far, and then back a bit to change gear. Changing up seems
to be worst., that is when you are slackening the cable. When changing down, the action seems quite heavy, so it is not lack of spring tension in the mechanism.

I am starting to suspect wear in the revoshift twistgrip itself. I have looked on ebay for a replacement, but can`t seem to find the exact one. My question is, basically, are all Shimano 6 speed revoshifters interchangable?

 

[Zebb]

Have you got the correct distance on the hanger from the rear coggs.
So the top cogg in the hanger needs to be close enough not to collide with other coggs but not to far away, which can put too much tension on chain and make changing gear clunky. Hope that makes sense.

 

[D C]

Also check the outer cable for any kinks or sharp bends which could prevent the inner cable from moving smoothly.

 

[Aushiker]

A couple more suggestions. If you have a derailleur hanger check that is aligned properly or not bent. I recently had a slight bend in one of mine. Putting it in the vice helped otherwise you can get a tool to check the alignment.

Another aspect to check is the where the cable is attached. I have a SRAM X 9 rear derailleur having the cable attached on the inbound side throughs out the shift. Moving it to the outbound side fixed my shifting problems. Seems alignment is pretty sensitive.

I would check for a groove and make sure the cable is running through this groove when you tighten the cable.

Good luck.
Andrew

 

[Deleted member 4366]

I think that's fairly normal for those cheap revoshift free-wheel gears. I've never ridden one where they weren't like that. I guess wear makes them worse. Correct adjustment makes them a bit better. Don't forget that you have a cable adjuster on the revoshift that can compensate for a bit of cable stretch/wear. Even when mine's correctly adjusted, I still need to over-shift to change up to some gears. These cheap system work, but at a tenth of the price of Shimano Deore XT, you can't expect the same level of precision.

 

[flecc]

My question is, basically, are all Shimano 6 speed revoshifters interchangable?

My e-bikes have always used the SRAM twistgrip shifters which are Shimano compatible and much better in my view.

Here's an example on this link, select number of gear options, they are made for 3 to 8 speed. Mine are the 6 speed MRX type.

Read the first review on that link, it sums up how well they perform.

 

[neptune]

OK guys and many thanks for the suggestions. I bought this bike brand new, and the gears changed perfectly for many thousands of miles, so I may have been lucky. I do not expect miracles, and am quite happy to "overshift" a bit if necessary. I said that I suspected the Revoshift changer itself, and I was probably right, because it has now reached the stage where even with the cable disconnected, I am unable to move the shifter to gear positions five and six.

So a new shifter is needed. The original is a Shimano SL-RS31-6. These seems to be unavailable now, although I bought the bike only three years ago. There is one on ebay, but it is in the USA and shipping would be prohibitive.

Pretty well all the ones on Ebay in the six speed category, are described as Shimano Tourney RS45-6. The only difference in the external appearance is that the gear indicator is behind a clear plastic window. The big question is, would one of these be compatible with my existing system? In other words, would the cable move the same distance per click?

 

[flecc]

I would think so since the SRAM is compatible with all Shimano derailleurs, but cannot be certain. However, for myself I'd buy the SRAM MRX from Wiggle that I linked to, since mine have been unfailingly reliable on Shimano 6 speed derailleur systems.

 

[Alan Quay]

I bought one of these last week:

(sorry, gave up trying to insert the link, ebay "shimano rs35", I paid about £8.50")

..as you say, its just about the distance per shift that's important. I fitted this to a 6 speed freewheel, with an old SIS derailer. Works ok, but as others suggest, it's not the same as the more expensive stuff.

 

[RobF]

Any six speed shifter should work because the distance between the sprockets has almost certainly not changed for a lot of years.

 

[neptune]

Again thanks for the useful info from all. I have ordered the SRAM type that flec suggested, should be here tomorrow.. What you say is true, however I wondered if differences in the rear mech might affect the necessary length of pull required from the cable. I suppose its all about leverage and angles. It would be nice if there was standardisation accross different brands/models, but life is not like that.

 

[Alan Quay]

.... It would be nice if there was standardisation accross different brands/models, but life is not like that.

I take a different opinion here Neptune. I am constantly amazed by the compatibily between brands. My experirinces with mid and low end bikes is that the parts are largely interchangeable. Any old 6 speed freewheel will work with Any old 6/7 speed derailer and chain, and any old 6 speed changer. One of my bikes mixes Shimano, Clark's, and Sram in the drive train alone.

Also, while seat post diameter varies, the seats themselves all fit on the same mount in the mid range stuff. Most handlebars are 22mm.

I expect things change once you go really high end.

 

[neptune]

OK mike. My opinion was based on technology other than bikes, mainly washing machines where there is next to no standardisation. It is refreshing to know that there is some standardisation.

My SRAM shifter arrived today, and I have fitted it. Setting the indexing was a bit fiddly, but I am now at the stage where gear changes are reliable and predictable, with no overshifting needed. I particularly like the cable adjuster on the SRAM shifter, which enables fine adjustments as you actually ride.

The shifter came with a new inner cable, so i fitted that, and cut the excess length off the end. Most bikes have a crimped fitting to put on the cable to prevent fraying. There was not one supplied. Modern inner cables are probably stainless steel. I tried to tin the cable with solder before I cut it, but the solder wont stick. Instead, I bound the loose end of the cable with fine nylon thread, and applied some glue to it.

I have used solder on older cables, as that enables you to unthread and rethread the inner cable through the outers for maintenance. This is not necessary on modern bikes, as the outer is in two pieces, and you can just slide them along to expose that part of the inner that is normally covered, facilitating cleaning and relubricating. All in all, I am well happy.

 

[flecc]

I'm glad you've found the SRAM shifter ok Neptune, I've found mine perform well above their price level.

 

[Deleted member 4366]

I've seen lots of broken ones. There's a little plastic bit inside that isn't very strong. I don't know why they broke - maybe ham-fisted amateurs, but be careful not to over-stress it just in case.

 

[Alan Quay]

OK mike. My opinion was based on technology other than bikes, mainly washing machines where there is next to no standardisation. It is refreshing to know that there is some standardisation.

My SRAM shifter arrived today, and I have fitted it. Setting the indexing was a bit fiddly, but I am now at the stage where gear changes are reliable and predictable, with no overshifting needed. I particularly like the cable adjuster on the SRAM shifter, which enables fine adjustments as you actually ride.

The shifter came with a new inner cable, so i fitted that, and cut the excess length off the end. Most bikes have a crimped fitting to put on the cable to prevent fraying. There was not one supplied. Modern inner cables are probably stainless steel. I tried to tin the cable with solder before I cut it, but the solder wont stick. Instead, I bound the loose end of the cable with fine nylon thread, and applied some glue to it.

I have used solder on older cables, as that enables you to unthread and rethread the inner cable through the outers for maintenance. This is not necessary on modern bikes, as the outer is in two pieces, and you can just slide them along to expose that part of the inner that is normally covered, facilitating cleaning and relubricating. All in all, I am well happy.

I never have those crimps to hand, but I always have a load of bootlace ferrules. I find the black ones fit just right, and look quite smart. I always leave a couple of inches sticking out, so In can cut and 're-crimp if I need to.

Here's what I mean:

 

[neptune]

Today, I was out early. It was cool with very little wind, and I did fourteen miles before breakfast. The gears performed perfectly. I found myself changing up and down needlessly trying to cause a missed change. Couldn`t make it happen.

That got me thinking about philosophy and bike maintenance.{Did anyone else read a book back in the sixties called "Zen and the art of motorcycle maintenance?"} Niggly little faults appear on a bike, and we automatically ignore them, hoping they will go away. But they don`t go away, they gradually get worse. Sometimes the progress is so slow that we gradually adapt, and create a work around solution.

Then one day we get a wake up call, and things go pear-shaped. At that point we take the bull by the horns, and do something about it. Then we suddenly wonder why we struggled with dodgy equipment.

Added Later;
I took my old original shifter to pieces, to find out how it worked.I was surprised to find that the mechanism incorporates an epicyclic gearbox. Its purpose seems to be to enable the cable drum to move at a different rate to the hand grip. I am not sure if it works as a step up gear or a reduction gear.
The planet gears are mounted on an extension of the cable drum. The inner ring gear is part of the hand grip. and the outer ring gear is a stationary part of the outer casing.

I think it works as a reduction gear, but to me it seems a complex solution to a simple problem. Anyone got any theories?

 

[neptune]

Please note my update to my last post

 

[flecc]

I agree Neptune, I've always been happy with the longer travel of the direct acting SRAM shifters, and as you've found, they are unfailingly accurate. The one on my Q bike has been in use for 7 years now and is as good as when it was new. I haven't been gentle with it either, normally changing multiple gears at a time in either direction, which is why I use twistgrip shifters in preference.

I can understand Shimano aiming for a short and quick action, they have always worked towards quicker gear changing in their systems, but they sometimes go too far. I think this is one of those occasions.

 

[neptune]

My eyesight is poor, especially for close up work, so I have just examined all the gears in the epicyclic gear train with a magnifying glass. As I suspected, one of the planetary pinions has a tooth missing. The remains of that tooth is embedded between teeth on the inner ring gear, or sun pinion. I always feel that it is very satisfying to be able to pinpoint the precise cause of a problem, even if it is beyond repair.

I can`t really complain, as this shifter has been in service for about thirteen thousand miles. It is amazing to think how a precise mechanism like this can be manufactured at such a low price. Imagine if it had to be built by a craftsman using hand tools. It would cost so much that it would only be available to the very rich. This is true of so much of today`s gadgets.

I feel that there is a danger in using complex technology for the sake of it, and there is a lot to be said for simplicity.