ST-MC35 maintenance

Arnev

New member
Hi,

My Shimano STX ST-MC35 won't shift properly. At shift 5 it stops and it won't go futher. I want to open, clean and rebuild it.
Is there any video about it? Because to get the parts out won't be a problem, but get them togehter will be I think.

Greetings,
Arne
 
Hi,

My Shimano STX ST-MC35 won't shift properly. At shift 5 it stops and it won't go futher. I want to open, clean and rebuild it.
Is there any video about it? Because to get the parts out won't be a problem, but get them togehter will be I think.

Greetings,
Arne

Hi Arne,

This Shimano PDF might give you a rough overview of the mechanism:
https://si.shimano.com/en/pdfs/si/R220B/SI-R220B-000-00-ENG.pdf

Service without (a full) disassembly

Take this with a grain of salt as I don't remember the exact model service, but it is a general guide for most Shimano shifters:

You can usually remove the cover without disasembling the mechanism fully. That lets you see what's going on.

Also, very often, you can just spray WD-40 inside, without even opening the cover - just spray with the nozzle through any opening. Spray liberally, you are trying to wash the insides off any dust, dirt, or caked-up (gummed-up) grease.

Click it through gears after that, and then repeat.

After that, you can lubricate it with some fine oil. This oily (not dry) MOTIP PTFE spray is available for about 6 euros in Serbia and works well:
https://lavauto.rs/product/sprej-teflon-motip-500ml/6237/

On the German Amazon, I can only find the expensive "dry" variant (Amazon.de affiliate link) which I haven't tried myself. When it comes to the dry spray lubricants, for the past month I've been experimenting with WD-40 Specialist PTFE Dry Lubricant Spray (Amazon.de affiliate link). That one works well for the fine mechanisms (locks, shifters etc.), and doesn't attract dirt because it leaves a dry film. However, I'm not sure about its durability (dry lubricants can't replentish themselves on the surface once sheared off from it). The first-noted oily Motip PTFE is tried and tested - not too much dirt attraction, with good lubrication.

Disassembly​

There often is a twisted coil spring inside. The tricky part is getting it back, and snapping the rest of the mechanism in place without the spring flying off.

Note: if you find a mechanic who doesn't clean their shop floor, make them work on mechanisms like these and they'll start cleaning enthusiastically. A very bad place to service shifters is on a balcony, grass or rough surfaces with many objects (ask me how I know :) ) - it's impossible to find the small parts when they fall.

Free tip: :)
For the clean floors, the stuff often bounces a lot further than you would expect. It sometimes helps to intentionally drop a similar item, and watch where it bounces. That gives you some idea where to look (10% chance, but better than nothing). :)

Edit: Withoud cable it works fine, and with cable it gets stucks at the sixt gear?

Try to loosen the cable from the derailleur and hold it tight with your hand.

That will let you feel if the cable slides freely when you shift up and down.

The problem you've described sounds like either gummed-up internal mechanism, or frayed/dirty cables or housing.

You can (that's what I do) try the above-described WD-40 washout before (fully) disassembling the shifter.

Having said that, on one occasion, I've had the spring slide out of its place inside the shifter cause a similar malfunction. That required a full disassembly (that's when I found the problem), cleaning, lubrication, and re-assembly.

Hope this helps at least a bit.

Relja
 

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