roshea

I'm trying to get an old bike up and running again and have run into a problem with the rear shifter, a ~1994 M737.

When I'm trying to shift to an easier gear (lower lever), there is no resistance when moving the lever - it just doesn't engage. Shifting the other way (upper lever) is fine. A friend suggested pulling it apart and making sure the pawls aren't gummed up or something, so I am trying to get the cover off to reveal this:



The large Allen bolt in the centre (holding on the cover?) turns freely in both directions without the cover actually loosening or tightening. The screw at 5 o'clock comes out but that doesn't change things for me.

View from below:



Is this because something is stripped or do I need to remove the cable before the cover will come off? I detached the cable at the derailleur end but that didn't help matters.

Scratcher33

I'd post this in the mechanics forum

Ingleside

It has been a while since i took one of these apart but here is the run down.
I belive you have to remove the small phillips screw in addition to the larger 5mm allen screw.
Sometimes on the top side of the shifter there another screw or bolt you may have to remove.
If the shifter has an gear indicator window there are sometimes two small phillips screws you have to remove. Also remove the cable from the shifter.
Essentially you need to drop the lower section from the upper section to expose the guts. Once you do and can see the inside like in your first picture you are going to want to free up the arm/pivot i have pointed out. A few drops of oil on the pivot should do the trick. The arm should snap back when you move it back and forth. Once the arm moves freely I suggest adding some oil to the other pivots and then reinstall the unit.

roshea

Thanks for your reply Ingleside!

This is the part I'm having trouble with. Loosening the Allen bolt and removing the Phillips screw on the bottom of the shifter doesn't get the cover off, so I now need to find which other screws and bolts need undoing. There IS one of the gear indicators (which doesn't work since I loosened the Allen bolt). Can you please suggest which screws / bolts to attack next and also how to remove the cable from the shifter?





Edit: parts diagram for this shifter, which might help in working out what goes where, is here:
https://manualer.happymtb.org/shimano/sh-stm737.gif

Hi-res version in German:
https://bernd.sluka.de/Fahrrad/Shiman...-M737_1994.gif

Ingleside

Thanks for the hi res doc.
It seems like you will need to unscrew the cable adjuster out of the shifter body.
Also looking at the doc you need to remove the screws that the number (2) in the "Richter Hebel" box.
As for the allen screw on the bottom, the important one, it screws into a threaded nut that slides through the internal unit. If it is indeed the style pictured in the doc, sometimes this nut gets pushed out of its seat and will spin freely. I don't know if there is any way for you to apply downward pressure on the allen screw but by doing so the nut may find its way back into the seat and the allen screw will be able to unthread from the nut allowing you to access the internals.

If you can get it all apart then you'll be able to get things freed up and moving. The shifter indicator has a small pin that points downward and fits into a smal hole on the top of the shifter internals. I belive that it is a white plastic part that has the hole for the indicator pin. Make sure you shift down into the last gear on the shifterand alighn the indicator to gear 7 (or 8 if it is an 8 speed shifter) so the pin will easily align with the shifter body.

Hope this helps.

cs1

Be careful with Shimano shifters. They have a lot of small parts that are easily lost. Sometimes it's easier to clean them as an assembly. Usually that's all that's wrong with them. Good luck

CercaMemorial

Actually I just cleaned out one of those shifters earlier this week while refurbishing my trek 930. The older (and some of the current) models have that problem. I just stuck it in our parts cleaner at work and ratcheted through the gears while it was submerged. The light blue solvent turned black with all the de-gunking. This was with the top and bottom covers removed. Then I sprayed some teflon oil in there and it working tons better. If you are concerned about not being able to put it back together after the fact, keep it assembled while cleaning it.

roshea

Thanks to all for the help so far!

Ah - very useful too! So I'm stuck with the question - exactly which screws and bolts need to be removed to take the covers off?

My understanding so far is that I need to remove:

- bottom Allen bolt (currently just rotates and bottom cover is loose)
- bottom Phillips head screw
- cable (necessary?)
- top Phillips head screw (upper one labelled "2" in the diagram linked above) (?)

Do all of these need to come out +/or any others?

Thanks again.

roshea

Bump - I still have more questions than answers! Anyone able to help with the above list?

Iowegian

I doubt the cable needs to come off to remove the cover but since the models vary I don't know for sure. To remove the cable you usually shift to the smallest cog and then push the cable back into the shifter. There is probably a small plastic screw or something similar that covers the hole where the cable goes in/out.

To get the covers off I'd just remove all the exterior screws then GENTLY try to pry the covers apart. You don't want to crack the plastic but sometimes the two plastic cover halves get stuck together by old grease.

Definately do NOT try to disassemble the shifter mechanism. It's not really that complicated but you need to hold about 4 springs and small parts together simultaneously to get it all back together correctly. Highly not recommended. Just use some solvent to loosen up the old grease and apply some new oil.

Most likely there is a pawl that is not moving freely on its post and is not engaging the rachet with the small amount of spring force on it (see post 3). You won't be able to remove the pawl without taking the entire mechanism apart so just clean the entire mech with some solvent (I like ether, does a great job on the whale blubber and isn't too toxic) then add some oil.

Good luck!

sonatageek

Let me chime in by repeating what many have already said DO NOT take the shifter apart.

Get a can of WD-40 and flush the heck out of it. Work the shifter levers and flush some more. My experience with these Shimano shifters (out of 8 bikes with a problem like yours this fixed it on 7 of them) is some gummy grease just needs to be softened up.

roshea

Thanks for all the advice!

Yup, I am just hoping to free up some gunked-up internals! As it stands, the big Allen nut in the centre of the bottom cover just goes 'round and 'round, so I can't loosen OR tighten the cover. I am hoping to be able to remove the cover so I can get that nut seated again after drenching the internals in Prolink.