SDHawk

I'm having a problem with the pictured XT shifter. It catches briefly when trying to downshift (to an easier gear), but then disengages and stays in the same gear as the trigger slams forward with no resistance. It happens in all gears, but is more pronounced in the easiest gears...when there's the most tension on the cable. I am able to make it work by pressing upwards on the trigger while pushing it forward, and the shifter DOES hold the new gear when I do that.. It's not really usable having to do that though.

I tried the usual Blaster/heat/light lube treatment for a sticky pawl, but it didn't do anything. It doesn't "feel" like the pawl problems I've had in the past. More like the downshift trigger isn't lined up, or at least not catching well for whatever reason.

BTW, when I flipped it and removed the 3 cover screws, the cover doesn't come off, it just loosens a bit. Enough of a gap to shoot in some Blaster etc but that's all. It would be easier if it came off but I don't see how to do that.

Thoughts?

'02 nrs

pull the shift cable off (remove 2 tiny screws to remove the access door) THEN remove the 3 long shouldered screws on the underside & the round plastic piece on the underside of the lever.this will allow the lower portion of the shifter to separate where you can see the spring loaded gummed up pawls(2).good chance they needs a flush with a cleaning agent to free them from any sticky grease.test them with a small screwdriver to be sure they have good action before relubing with a light oil.

Bill Kapaun

Flushing shifters is about the only thing I use WD-40 for.
Old grease and colder temps to thicken it more....

Andrew R Stewart 

Were this my shifter I would detach it from the handle bar bracket, remove the plastic covers and soak it in a solvent (not oil). I would track the pawls (I think this shifter has two IIRC) movements as I cycled the shifter through its range (sometimes with a cable helping, usually held in a bench vise) and either confirm they are moving freely and engaging the ratchet spool or not. With the shift pod (as it is sometimes called) exposed one can "work" the pawls with a pick. One trick I use is to move the pawl up and down on its tiny pivot shaft in addition to the expected rotation working. Assuming the pawls end up working and there's no other found issues I'll use a thin oil sprayed onto/into the shifting assembly/pod and cycle the shifter through its range, again using compressed air to help drive into the nocks and crevices the thin oil. Repeat with a medium/thick oil. before reassembly I'll repeat the med/thick oil and sometimes add a little grease here and there to serve as an oil feeding reservoir.

This shifter is of the age that assuming gummy/dried out lube as the problem is what I would do. But I have seen a few that either had other issues or never responded to the full monty of flush and lube. Andy

Flush should have been "soak and blast". Flush and Lube is what we call it on service tickets but soak and blast better describes what is actually done for the bad cases.

SDHawk

Thanks for the detailed info! I took off the cover. It's not full\y exposed, but I can see 1 long-ish pawl (see pic). It engages the spool fine with no load, but was slipping under tension. I'll try the things you and others suggested and cross my fingers.

I only see the 1 pawl... do you think there's a second one?

Leisesturm

It is far more likely that the 'gumming' is at the rear derailleur/chain interface. How old is everything? Before you get too crazy on the shifter (but since you have it open you may as well WD-40 its internals) use a good drivetrain degreaser and get everything spiffy. Then re-lube everything. WD-40 all the derailleur pivots and Jockey Pulley spindles. See how it shifts then.

Andrew R Stewart 

Cleaning a drivetrain is a good suggestion and can uncover other issues that have been growing (guide pulley bushing slop being a real possibility on this old der) however the description given doesn't match up with what I would expect from der/chain issues, IME. But that is easy to find out if one works the shifter independent of the rest of the system. Detach the shift cable (pulling a section of casing out of a frame casing stop works) and while lightly holding the cable cycle through the shifter's range, one can vary the tension on the cable as the shift levers are played with. If the shifter is at fault and is fairly consistent in that (a critical aspect of assessing stuff) one will feel it as the cable will mimic the issues of actual shifting of the gears. By only testing one component at a time it's easier to track the actual conditions and problems, or that's what I have found works for me many times. Andy

Bill Kapaun

Just hose it down.

KCT1986

Had a similar issue with the same shifter (ST-M739) and upon inspection found that there was a 'chip' in the pawl. See the attached. (Sorry for the less than perfect pic, this is the only one that I seem to have saved.



The way that this pawl works is that it engages the gear and pushes the ratchet to shift to a lower sprocket. On my shifter, because of the 'chip', the 'push' of the thumb shift lever has to be upwards during the rotation for the pawl to engage the ratchet.

Try inspecting the pawl more closely to check if there is any damage. You should be able to rotate the pawl away from the ratchet to get a better view.

Let us know what you find.

SDHawk

Hmmmm, same problem with the same model, even down to the "fix" of pushing upward on the lever. I couldn't see an obvious chip, but it certainly looked more rough than one would hope (see pic below). Actually, looking at the blown up pic below, I guess that is chipped haha.

Anyway, I did most of the suggested tricks above and re-assembled. I thought maybe I had fixed it because I couldn't get it to slip when pulling on the cable by hand. Unfortunately, when I had it all hooked up, the same slip was there, no change. Btw, I did lube the RD but it was pretty clean and the level of effort needed to shift was within normal range. So, I think it's the same chipped pawl problem. I don't think it's fixable, right?

The backstory is it's from a 1992 Trek 970 I picked up the other day. The left shifter was the matching XT, but the right shifter was a newer, cheaper Shimano 8-speed. However, the shifter we have been discussing was also included... seller said it "didn't work right". I figured it was likely the usual sticky pawl issue and that I could fix it. Oh well, at least I can put the cheaper shifter back on before selling. Matching XT would have been much nicer though.

BTW, I don't think the XT shifters were original to the bike because they seem newer than 92 and are 8-speed vs the original 7. The bike had also been updated with a newer XT crank and XT v-brakes. It is a nice lugged frame in the cool Sour Grape color of that year. I'll make it as good as possible and sell for cheap.

Thanks to all for the great insight and suggestions!

Bill Kapaun

Try this for aday or 2.
When making that shift, just ease the lever up and then slowly let it back down on the "detent".
IF it holds that way, it would still indicate a "guminess" problem.
Just getting it moving again can sometimes result in the problem disappearing (day or 2) until next time, some months
? down the road.

When I'd do a WD-40 flush, I was generous.

KCT1986

That does look like a chip on the very tip of the pawl. Mines chipped at an angle, so the angle that the thumb lever was pushed had an effect large on how much of the pawl engaged.

As for fixing, since I had 2 of these shift units, and the one with the chip was going on a 'beater' bike, so not much mileage or shifts under load, I did the following.

Disassemble the shifter enough to remove the pawl. Grind the pawl to flatten out tip and thin down the concaved area between the arrows in the below pic.




The concave area needed to be thinned down to allow the pawl to clear the curve of the ratchet. It is weaker, but OK for my low stress use.

Removing the nut in the center is a little tricky. Shimano 'peened' (or whatever is the correct term) the end of the bolt to flare it for retention, and unscrewing it will damage the thread. If I were to do it again, I would grind the top of the bolt around the bolt/nut interface to try to free it up. A Dremel with a small grind stone bit possibly.

SDHawk

Thanks for the intel! Well, I didn't trust myself to perform that operation and put it back together... seemed unlikely to succeed . But your post gave me an idea to pry the pawl open and file/grind the tip in the small space available. I was able to sort of sand/file/grind it but couldn't tell if it looked any different. Whatever, it was a last-ditch effort. BTW, I only mustered the energy to try it because the cable stop on this shifter is more like a brake lever so I was able to "unhitch" the cable while leaving the cable in all the housing.

Anyway, I hooked it up and was shocked that it shifted well.... no slipping. I don't know if it was the pawl work or maybe I had the cable routed better within the shifter (it felt kinda "different" when I flipped over the shifter and inserted into the housing unit). In any case, I wasn't gonna mess with it at that point. Attached the covers and re-positioned the unit on the handlebars. It's working like a champ now!

KCT1986

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Glad that you got it to work a little better.

Possibly the sanding that you did enables the pawl to 'drop' in the ratchet better. The outer end of the pawl is what engages the ratchet and pushes it. The sharp edge of the 'chip' at the outside corner or along the outer edge may have been preventing the spring from pushing the pawl down into position.

Just hope that it is engaging 'enough' of the ratchet to keep working.

If you have trouble in the future, know that pawl can be removed and modified. It's not too complicated a procedure.