[erastusboy]

So I have to build a bike for an interview audition? whatever, I'm not really worried about it very much except f'in limit screws. Any of you mechanics have any advice about limit screws, secrets or tips. I know how to adjust the rest of the drivetrain but I never quite get the limit screws right. Maybe its just lack of patience. Also anyone have any other tips, I have built tons of bikes mostly frame up but this interview is freaking me out.

 

[binary visions]

Limit screws are really easy. The rear derailleur is a great mystery for some reason but it's really not bad.

Just look at the derailleur from behind the bike, so you are getting a parallel view of the chain, derailleur cogs and cassette cogs. Shift into the higest gear (small cog), and start screwing in the H limit screw. Eventually, you'll see the chain/derailleur cogs start to come out of parallel with the small cassette cog. Back the screw off until they're just parallel.

Then, do the same thing with the big cassette cog - shift into low gear, screw in the L screw until it moves out of parallel, back it off until it's good again. Then try your gears. You can back both of them off a little bit more if it doesn't quite shift right.

Just think about what they're doing - they're keeping the derailleur from shifting past the edges of the cassette and thus into your spokes/frame. That's all. So tighten them down until they do their job

 

[GotMyGED]

One thing to keep in mind is that each time you make limit screw adjustments, it will affect your cable tension.

Also remember that when backing off a limit screw on the low side, it will take more cable tension to push the derailleur out to the limit.

I think an understanding of cable tension is far more important than an understanding of limit screws.

Just pray the the rear derailleur isn't rapid rise. Rapid rise isnt hard just backwards.

 

[binary visions]

One thing to keep in mind is that each time you make limit screw adjustments, it will affect your cable tension.

Also remember that when backing off a limit screw on the low side, it will take more cable tension to push the derailleur out to the limit.

This is only true if you are actually using the limit screws as an adjustment/setup mechanism. If you have the chain installed and the cable tension set properly, and the shifting works, setting the limit screws as an afterthought won't affect anything if done properly.

When the shifter cable is not installed and the cable tension is not set, the limit screws will, of course, push the derailleur around. Once you have everything installed and set up (which I prefer to do before I touch the limit screws, since they're just a fail-safe and don't even need to be there to have your setup working fine), you should just be able to screw in the limit screws until they are just keeping the derailleur as you have it and not actually moving anything.

 

[erastusboy]

Thanks a ton, I knew "how" to do it but didnt really understand what exactly i was doing. Really its cable tension to make sure you have good shifts and limit screws to make sure your wheel doesnt eat your derailleur.

 

[binary visions]

Thanks a ton, I knew "how" to do it but didnt really understand what exactly i was doing. Really its cable tension to make sure you have good shifts and limit screws to make sure your wheel doesnt eat your derailleur.

You got it. The limit screws are a "fail safe" to make sure that your chain doesn't jump off the cassette; you can have a functional, flawlessly shifting drivetrain even if the limit screws are completely removed from the derailleur.

 

[sanjuro]

One thing to keep in mind is that each time you make limit screw adjustments, it will affect your cable tension.

Also remember that when backing off a limit screw on the low side, it will take more cable tension to push the derailleur out to the limit.

I think an understanding of cable tension is far more important than an understanding of limit screws.

Just pray the the rear derailleur isn't rapid rise. Rapid rise isnt hard just backwards.

Limit screw adjustment and cable tension is more critical in front derailleur adjustment than the rear. You could have a correctly shifting rear derailleur without playing with the limit screws (if you are lucky) because the cable tension will prevent overshifts. However, as soon as the rear derailleur got out of tune, you could easily shift into the spokes if the limits were not set right.

The way I adjust a rear derailleur, is after I have the cable taunt but not too tight while on the "slack position" (small cog normal, big cog rapid rise), I check the high limit (low for RR), then pull on the cable manually to check the low limit (high for RR). After that I shift to the third cog and check cable tension.

On the front, limit screws are critical for proper cable tension. Before even tightening the anchor bolt, I adjust the low limit so the inside plate is about a MM from the small ring. Then I pull the cable as much as possible then tighten the anchor.

 

[erastusboy]

Thats a good point, anyone else have any front dereailleur tips, I guess thats where I really need help.

 

[dhpimp]

Thats a good point, anyone else have any front dereailleur tips, I guess thats where I really need help.

Easiest way to set up a front derailleur is to start with the limit adjustment screws. Clamp the derailleur on the frame and align the outer plate to be parallel with the big ring. Now set the height - make sure to follow the little orange sticker on the FD for the height of the FD. If this sticker is lacking, use a #2 flat head and make sure the bottom of your outer plate is 1mm from the top of a tooth on the big ring. Now, start by setting the low limit adjust. Screw in to push the derailleur away from the frame. You only want about 0.5-1mm of space between the inner plate and the chain when in the granny gear. Once set up clamp the cable onto the FD and pull on the cable with your hand and turn the cranks to get the chain to the big cog. Don't try adjusting the shifting at this point, just set up the upper limit screw. Again, 1mm of space between the chain and outer plate. Now that you have the limit screws set, drop it back to the small cog. Undo your cable, turn the barrel adjuster 2 full turns, pull on the cable and clamp it onto the FD. Check shifting and adjust barrel adjuster on the shifter as needed. Presto, your done.

 

[dhpimp]

Just pray the the rear derailleur isn't rapid rise. Rapid rise isnt hard just backwards.

Rapid rise is piss easy ... The great thing about these is that the derailleur automatically sits in the big cog - LOW gear. Adjust the limit screw, pull it towards the bottom cog and adjust the HIGH gear. As long as a mechanic understands what the H and L are, there is no problem. However, for any newb High and Low is counter-intuitative as a lot of the times they thing High means Big cog!

 

[dhpimp]

So I have to build a bike for an interview audition? whatever, I'm not really worried about it very much except f'in limit screws. Any of you mechanics have any advice about limit screws, secrets or tips. I know how to adjust the rest of the drivetrain but I never quite get the limit screws right. Maybe its just lack of patience. Also anyone have any other tips, I have built tons of bikes mostly frame up but this interview is freaking me out.

For some reason no one touched on the B-Tension and I wanted to. The easiest way to setup the B-Tension is to put the derailleur in the biggest cog, and then screw in the b-tension until there is 2.5mm between the top pulley wheel and the cog (or 1.5 chain links between the two). If your blind then just screw it down until there is no more noise