Hello all,

I'm working on an older MTB - mid-90s perhaps - and it's got Shimano m739 components ...

I'm looking for replacement parts for the FD and the right 8-spd shifter. I've found parts on ebay, but I have a couple of questions:
- the FD I need is for a 31.8mm tube, but the one I found on ebay is a 34ish with a shim ... are shims a reliable way to install a derailleur, or are you just inviting slippage?
- I can't seem to find the right shifter - only the left - the right shifters I've found on ebay are contained in sets and the entire set is going for $150-200+ ...

Speaking of the shifter ... any repair ideas? When it's off the bike and detached from the cable, it works and indexes fine, but when it has tension on it, it sounds like it's stripped ... is there a way to get in and only repair the innards without replacing the entire shifter?

In any case ... I found a right shifter for an m738 ... how can I determine if this is compatible? I've got v-brakes on it.

Otherwise - any of you know a good source for some of these older parts? I'm pretty new to diy bike repair stuff.

Thanks in advance for your advice,
bsker

If you are sticking with your V brakes then look out for the rapid fire brake/gear lever combo sets, I've seen quite a few XT sets lately for 8 and 9 speed, a good upgrade and the pair won't brake the bank.

The shims supplied with derailleurs are customized to fit well to both the derailleur and tube and are quite secure.

Good advice - hopefully I can find some ... So ... how would I ascertain what FD would work with my BB and crankset, and also what shifter would work with my RD?

In general, the innards aren't repairable by ordinary mortals. There's been some people who have done it, so it's not impossible, but it's not something I would try myself.

You can try to gain access to the mechanism by taking off the indicator and the outer housing. Since it "sounds" stripped, I would look for pieces of broken-off cable inside it.

Also, clean it out thoroughly and lube with light oil before reassembling. Many old Shimano shifters get sticky due to old grease. A good cleaning keeps them working.

Here's an exploded view:

Any Shimano MTB front derailleur made for small (less than 48 teeth) chainrings will work, and any Shimano shifter (except for early Dura-Ace and Dyna-Sys) will work properly with your rear derailleur.

It could just be gummed up. Over time, the lubrication in the shifter becomes a lot less effective, preventing the shifter's pawls from engaging. Before giving up on the shifter, flush it thoroughly with WD-40, then re-lubricate with something like Tri-Flow.

Pretty much any Shimano 7/8 speed triple mountain bike derailleur (Altus, Acera, Alivio, Deore, etc.) should work, so long as:

1) The derailleur isn't designed for a chainring smaller than yours. If you've got a 53 tooth chainring, don't use a derailleur designed for a max 42-tooth ring.

2) Its cable pull direction matches your frame's cable routing. If your derailleur cable runs along the top tube, then down the seat tube, you need a "top pull" derailleur. If your derailleur cable runs along the downtube, then up from the bottom bracket to the derailleur, you need a "bottom pull" derailleur.
and its cable is designed to be pulled from the right direction.

...and so long as you've got your crankset matched to a bottom bracket whose spindle is the appropriate length. If the spindle is too long or too short for your crankset, the derailleur might have a hard time reaching all your chainrings.

If you need to replace your shifters, just about any 8-speed Shimano or Shimano-compatible mountain bike shifter should work. For example, Shimano Acera SL-M310 8-speed shifters, which are available for about $30 per pair online. They're not considered high-end parts -- you'll need to scout used parts for "high end" 8-speed stuff -- but they're perfectly serviceable and reliable for day-to-day riding.

Had done all this, and as far as I can tell, there are no loose pieces - the springs seem to work, the pawl seems to engage and disengage quickly as it's supposed to, the innards *look* clean, at least ... was hoping I could see the actual teeth of the gear inside, but that's the part I don't have access to when I take off the housing. When the cable's disconnected, it's the last click that strips, and that cog is not visible without taking the whole thing apart. When the cable is connected, I can only shift from the innermost ring to the 3rd (of 8) rings before it strips out beyond any hope of shifting further.

Even though the current levers are combined brake/shifters? How would I know that a M310 SL would fit to the M739 BL? I found some ST-M950s online, including the combined shifter/brake levers ... according to the chart at Shimano '97 Shift & Brake/Shift Lever Specification Table - the Buyer's Guide, 2015, the M950 is the only set that's equivalent to the Deore XT M739s, right? I'm trying to match a new SL to an existing BL - or is this a lost cause? Is there some sort of Shimano document that indicates whether or not a particular shifter (SL) would connect to a different brake lever (BL)? For example, I've found that the ST-M738 is NOT for v-brakes, but could I just get the SL-M738 and attach it to the BL-M739, or is that a no go? Do I need to replace the entire BL/SL combination?

The primary issue is simply that I can't seem to find M739 shifters/levers for reasonable prices (i.e., for prices I'm willing to pay )... but I have found M738 and M950s, which I'm hoping could work ...

I hope my questions are clear enough - Thanks for all your input!
bsker

SL is just a shifter, which may or may not bolt on to the brake lever assembly.
ST is the combined brake/shifter.
They both came in 738/9.
If you have the ST type, just get some EF ST51's or 65's, of the proper speed.
They come in 2 & 4 "finger" versions.
The 4 finger can be used on either V or Canti brakes, while the 2 finger is V brake only.
There will be either a 2 or 4 in the suffix. Not all vendors list the suffix however.

I've had 51's & 65's on the same bike (after the 51's were stolen, along with the bar, pedals....)
The 65's did shift better. (9 speed)

BTW, if you're interested in going to 9 speed, now would be the time.
All else you would need would be the cassette & chain. Maybe your old cassette & chain have enough miles on them that they are toward the end of their life anyway????

Any thoughts on this one? I've currently got a top pull, top swing, FD-M739 triple with 22/32/42 chainrings and an 8-speed cassette.
https://www.amazon.com/SHIMANO-Alivio-Derailleur-FD-M412-34-9mm/dp/B00BQ7UGVO

Thanks for your input!! It's not that I want you to do ALL my shopping for me, but summer's running out and I'd hate to waste time buying the wrong parts!!