flyagaricus

Hi

I have a problem where when I'm shifting up (onto bigger gears), the paddle is is just loose and doesn't do anything. I have to pump it several times to get it to 'catch'. Any idea what could be causing this? I heard it usually is to do with a a slack cable, but I have new jagwire cables and they are lubed at areas where the meet the frame. I have Shimano Deore shifters.

Thanks

urbanknight

It might be getting gunked up and need to be flushed. Try this, but my experience is that this is a temporary solution and will need to be repeated with increasing frequency until you finally give up and buy a new shifter.

deacon mark

Could be starting to fray the cable in the shifter. Shimano shifters this happens quite often after time and usually you can downshift ok but the upshift causes the problem because the cable is fraying and catching on the return. What are you running?

FBinNY 

Shifting in the "pulling cable" direction is rarely affected by anything cable related. So, my initial suspicion is gunk, keeping thebsmall engagement spring from catching. Flush with thin spray oil/solvent, shake out to dry, (outdoors, if you're married) repeat, dry, and hope for the best before doing anything else.

grumpus

​​​​​​Mostly it's accumulated dirt or hardened grease that causes this. While you're riding: several times push the lever forward and then release it so it returns rapidly by it's own spring tension - I find this can unstick the mechanism, at least for a while. To fix it properly you need to clean and lubricate the internals.

Le Mechanic

This is a very common issue with pretty much all Shimano indexing shifters. The problem is that the grease or whatever lubricant Shimano originally used in the shifters gets really thick over time. The grease turns into a tar like substance that makes the small pawl spring unable to pull the pawl back into the ratchet ring. There is just too much resistance on the shaft that the pawl pivots on. The solution is to flush and re-lube the shifters. The method to do this varies. Really hot water works. PB blaster or WD 40 can revive a dead shifter as well. The older the shifter, the more difficult it tends to be, and sometimes the shifters just wear out from lots of use, but the bottom line is, any Shimano shifter that's more than 5 years old just needs some maintenance now and again.
I made a YouTube video many years ago on how to revive a shifter with the non-engagement issue:

soyabean

Recently discussed.

https://www.bikeforums.net/23204808-post15.html

urbanknight

Is this not a problem with SRAM or Campy?

Le Mechanic

Not in the same way. Campy shifters still need maintenance, probably more often. The ratchet springs in campy shifters usually wear out or break after a few years or miles depending on how many shifts/miles they get. Sram shifters MTB and road are pretty reliable under good conditions, but generally break before they malfunction. Shimano shifters (road and MTB) are much more difficult to rebuild, use more parts, many very small and delicate, but all Shimano shifters do this eventually. Especially in cold weather.

flyagaricus

They're new cables

flyagaricus

Thanks. I guess I'll open up the shifter and take a look. It's a 1996 so it's pretty old!

cyccommute 

I can’t speak to Campy nor SRAM road but SRAM mountain shifters never have this kind of problem. They are a much simpler mechanism.

RCMoeur 

If you really want to fix it once and for all, and you have the equipment and patience:

https://www.bikeforums.net/bicycle-m...long-haul.html

urbanknight

I actually have a small ultrasonic cleaner. What kind of lube is recommended?

KCT1986

During this time period Shimano sometimes used a shift mechanism that was an integrated 'pod' that bolted to the bracket or brake bracket.

Best step is to look for the model number printed on the unit, then research the diagram and manual on Shimano's tech doc web site. This will show the parts and assembly method.

Here's an example. Part of the diagram of the XT (ST-M739). On these, the unit is just held on by 3 screws, with 2 alignment pins. Unit also has some covers that are held on by screws.

Kimmo

When you crack it open, you're looking for a tiny pawl, a little part about 6mm across, pivoting on a little pin about 1.5mm thick. It's actuated by a little hairspring, which is too weak to overcome the friction in the pivot when the grease goes gummy.

There's one attached to each lever, so it can fail in either or both directions. Depending on the model of shifter, one or the other might be easily visible or hiding under other bits of the mechanism. Once you find the pawl in question, the trick is to squirt some solvent at the pivot, and wiggle the pawl back and forth until the gunge in the pivot dissolves. You might need to use something sharp like a scribe to reach through the mechanism, and you'll have to push it in both directions until the spring can overcome the friction. It might take so long that you think it's not going to come good, but if you persist it's a guaranteed fix.

Flush the whole shifter with solvent, and make sure the other pawl is moving freely, then lube with a heavy oil instead of the original grease. After this you should never need to touch it again, because most Shimano shifters are actually extremely robust despite their complexity, and usually only ever fail due to the grease going hard.

RCMoeur 

One suggestion: if the shifter is off the bike, before you reinstall it, put the shifter in a freezer, then once it's down to the freezer temp take it out and immediately try to shift it through its entire range. If there is still old problematic grease in there, you'll be able to tell because the shifter will again be balky & missing shifts when very cold.

If it's on the bike, then see if you have a friend with a walk-in freezer for this step.