Replacing rear gear shifter

esuhl

I've got a Decathlon b'Twin Rockrider 8.1 mountain bike with SRAM X7 gear mechs & shifters.

Both shifters were surprisingly stiff when I bought the bike (3 yrs ago), but the right has become so stiff that it really, really hurts my thumb!

Also, something snapped when changing gear. Now when on that particular gear, the gear lever just clicks and only changes gear when it's moved all the way back. (Normally, the first click also changes gear as well.)

I could live with the last problem (for a bit), but the stiffness makes it unusable. I've tried using WD40 to loosen the shifter a bit, but it hasn't helped.

EDIT: I loosened the gear cable and the shifter isn't stiff at all, so the problem seems to be with the rear mech, rather than the rear shifter as I thought.

Do I need to replace the rear mech with an identical one (SRAM X7) so I can use it with my SRAM X7 shifters, or could I use, say, a Shimano rear mech?

Given that the rear shifter isn't working perfectly anyway, would it be worth replacing the shifter and rear mech?

Can anyone recommend anything fairly decent (rugged and reliable for off-road use)?

Nebulous2

How is the cable, when last was it changed?

I haven't worked much on mountain bikes but if the cable runs under the bottom bracket it is very susceptible to getting dirty/ gummed up.

The 'something snapped' sounds as though it could be damage somewhere, but remove the cable at the rear and see what happens to the mech. On a roadbike it moves out to the smallest cog and you should be able to move it in against the spring to the biggest cog quite easily (it helps to have the chain off, but isn't essential.) If that moves freely then it doesn't sound like the mech is damaged. They are susceptible to bent hangers but that is a different problem.

I think, but I'm not sure, that some mountain bikes are the other way round. The mech is held in line with the biggest cog and you have to move it out against the spring, but I don't think that is common.

andygb

It could be the cables need replacing, particularly if they are the originals. You can get cables with a special teflon coating which make gear changing very light.
I would advice taking the rear gear mechanism and cable off, then trying to move the gear cage by hand. It sounds as if the whole thing needs cleaning , then lubricating.
I have rear gears (Shimano and Campagnolo) on my bikes which are over thirty years old and still work fine.

Norman_Castle

As above, disconnect the cable and check if the rear mech is the problem. The cable may be poorly routed or damaged inside the cover. If the rear mech moves freely replacing the cable is very cheap and easy.

esuhl

I slackened the gear cable by unclipping part of the plastic cable housing from the frame. The "missing gear change" is a problem with the shifter itself, but I can live with that for a bit... if I have to...

If I pull back on the cable to provide a bit of tension, the shifter changes gear and the gear cable moves easily. It's the original cable from when I bought the bike 3yrs ago, but it seems fine.

It's only when I take the slack out of the cable so it moves the rear mech that it's so incredibly stiff. (It's days since I last rode and my thumb is still aching and throbbing!)

I sprayed WD40 into the hinges on the rear mech and flexed it back-and-forth in my hands. It seems to move fairly easily, but I when I try to move it using the gear lever it's still just as stiff. Also, with the chain removed, as I release the tension with the gear lever, the mech doesn't snap back into position like it used to -- it gradually moves over 2 or 3 seconds. I guess there's either a lot of grit in the hinges, or it's damaged.

The rear mech got bashed a few months ago when I was hit by a car (who stopped to give way to me, then floored it as I went past). I'm amazed there wasn't any major damage at the time, but maybe the knock has made the stiffness worse...?

I'll give the rear mech a proper clean, let it dry, and WD40 it again. But if that doesn't work, I guess I'll need a new one. Do I need to replace it with the same make & model so it will work with the gears and shifters...?

ev70

First - Stop using WD40 on your bike. It is not a lubricant, it is a Water Displacer (No. 40). To lubricate use a light chain oil or TF2 or GT85. Just be very careful, you must make sure that none gets on any braking surface.

If the bike has the original components that are three years old then the first thing that I would suspect would be the gear cable. Over time water, dirt, road salt, etc would corrode the cable and damage the outer of cable internally. This would cause extra friction slowing down the movement of the mech/shifter.

If you need to replace the rear mech then you will have to use a SRAM mech designed for the number of gears that you have on the rear. SRAM uses 1:1 gear cable pull and Shimano uses 2:1. This normally makes SRAM a little stiffer than Shimano, but it is designed for off-road use.

You say that the rear mech had been hit in an incident. This can cause the mech. hanger to bend and that will cause shifting problems. Also in this time if other drive-train components have not been checked you may have other worn out parts which can contribute to poor performance.

If you have not got all the tools or are not sure what you are doing find yourself a friendly local bike shop. They would certainly get your bike working again.

Norman_Castle

Unhook the cable outers from the frame, slide them along then clean and check for damage. Any damage or wear, especially to the outer directly above the rear mech can make a difference. With the cable loose is the rear mech still stiff?.
Hopefully a daft question. You are changing gear when peddaling?.

With the thumbshifter, loosen the bar clamp bolt and move it around the bar so it is upside down. Remove the small screw and cover and spray inside with GT85 or similar. This may get the missing clicks back.

esuhl

ev70 wrote: »

First - Stop using WD40 on your bike. It is not a lubricant, it is a Water Displacer (No. 40).

Oh... really? Yeah, I know what WD40 stands for, and there's no way I'd use it on the chain, but the back of the can does say that it's a lubricant (twice!)... and has a picture of a bike amongst other things... :huh:

Ah well, too late -- I'd already WD40'd it!

I took off the gear cable outers and inspected the cable. There is a tiny kink in the cable at the point it first emerges from the housing near the shifter -- that seems to be causing a bit of friction and it's the part of the housing with the greatest curve (hence more friction anyway). But other than that the cable looks completely brand new.

Anyway, I went for a short ride today and the WD40 on the rear mech seems to have (at least for now) fixed the stiffness -- gear changes have never been so easy!

I probably need to get a new rear mech and cable at some point (... and chain... and gears), but if I can put it off for a bit with WD40 (okay, okay, I'll use the proper stuff next time! ) then that'll keep me happy!

Is it worth replacing the gear cables with ones that have full-length housing to keep out all the grit?

Norman_Castle wrote: »

Hopefully a daft question. You are changing gear when peddaling?.

Oh, yes! I'm not that silly!

Norman_Castle wrote: »

With the thumbshifter, loosen the bar clamp bolt and move it around the bar so it is upside down. Remove the small screw and cover and spray inside with GT85 or similar. This may get the missing clicks back.

I'd already tried that with WD40, but I'm pretty sure something's broken inside. It sort-of clicks when I change down from gear 4 to gear 3, but there's no resistance in the gear lever until it moves back to the next "clicking" position, which does click properly and does change the gear.

Anyway, thank you all for your help and suggestions. I'll probably treat my bike to a full-on service later in the year, but for now at least I can nip to the shops to get my shopping! :T

Richard53

WD40 is a water displacer and a lubricant (the two aren't mutually exclusive). The drawback as a lubricant is that it is very light, so it tends to dissolve and remove heavier oils and greases (which makes it a great cleaner) and it evaporates, so you need to keep re-applying it. But for freeing up and lubing small mechanisms it's brilliant.

I have a Raleigh Amazon which is 22 years old. The rear mech has always been lubricated with WD40, and it still works perfectly. Little and often is the key.

My money is on the small kink in the cable, by the way

andygb

I have been thinking about this a bit more, and think that it could be the gear shifter to blame. Years ago (back in the mid nineties) I made the mistake of buying Campagnolo Veloce Ergo shifters (along with the matching gears and chainset. All was well until the end of the second season, when the front shifter would not change at all, and the rear was really stiff.
It turned out that the internal mechanism of the ergo levers had siezed up, probably from salt (roads and sweat), and they could not be fixed.
I went back to downtube levers again after that - at least they were cheap to replace.