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Bike front derailleur limit screw problem, stripped?

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Bike front derailleur limit screw problem, stripped?

Old 03-09-20, 04:42 PM
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Bike front derailleur limit screw problem, stripped?

Hello,

I can't tighten/screw past a certain point in the high limit screw on my front derailleur.

Once I hit the point, it just spins.

If I push hard with the screwdriver, the screw gets pushed in but it springs out again and doesn't catch.

Is the part it screws into shot?
Can I do anything other than replace the derailleur?

Keep in mind, if the cost of whatever I need to fix exceeds that of a basic derailler, might as well just replace.
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Old 03-09-20, 04:50 PM
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If you can maneuver a tap into the space, I would guess you can just tap it and use the matching-sized screw as a limit screw. This is a rear mech with a stripped limit hole that I tapped to M5. (Notice the black screw under the "Suntour."). I found it at the coop for $2.50 and overhauled it -- it was otherwise in great shape.

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Old 03-09-20, 04:57 PM
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What's a tap?
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Old 03-09-20, 05:36 PM
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Originally Posted by user_1 View Post
What's a tap?
If you have to ask it's probably not something you should do yourself
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Old 03-09-20, 06:35 PM
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Originally Posted by dedhed View Post
If you have to ask it's probably not something you should do yourself
That's a really stupid thing to say.
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Old 03-09-20, 06:45 PM
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Originally Posted by user_1 View Post
Originally Posted by dedhed View Post
If you have to ask it's probably not something you should do yourself
That's a really stupid thing to say.
Actually, it's excellent advice.
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Old 03-09-20, 07:07 PM
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I guess, if I've never seen a need to re-tap anything and hence have never investigated what tools are required to do so, it means I'm re tarded and shouldn't attempt to fix this myself.

AnkleWork and dedhed - get lost!


I'm here to learn.

..
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Old 03-09-20, 07:13 PM
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Originally Posted by user_1 View Post
I guess, if I've never seen a need to re-tap anything and hence have never investigated what tools are required to do so, it means I'm re tarded and shouldn't attempt to fix this myself.

AnkleWork and dedhed - get lost!


I'm here to learn.

..
They are correct!
You just got "lost" on my ignore list.
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Old 03-09-20, 07:59 PM
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Bill,
Just for snicks and giggles can anyone new to being a mechanic explain to me what a trunion is, or even a trunion bearing?
"Turbo Encabulator" the original. I'll be waiting for replies.... Smiles, MH
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Old 03-09-20, 08:38 PM
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Originally Posted by user_1 View Post
I guess, if I've never seen a need to re-tap anything and hence have never investigated what tools are required to do so, it means I'm re tarded and shouldn't attempt to fix this myself.

AnkleWork and dedhed - get lost!


I'm here to learn.

..
Because tapping aluminum by hand is easy without experience or training, right?
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Old 03-09-20, 08:46 PM
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Originally Posted by noobinsf View Post
If you can maneuver a tap into the space, I would guess you can just tap it and use the matching-sized screw as a limit screw.
Originally Posted by user_1 View Post
What's a tap?
A "tap" is a tool used to cut threads into a workpiece to accept a bolt of the same thread spec as the tap.

I suspect the cost of a tap would approach that of a replacement derailleur, and a new derailleur would carry no risk of inadvertent damage.
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Old 03-09-20, 09:04 PM
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Originally Posted by Mad Honk View Post
Bill,
Just for snicks and giggles can anyone new to being a mechanic explain to me what a trunion is, or even a trunion bearing?
"Turbo Encabulator" the original. I'll be waiting for replies.... Smiles, MH
If you ever worked on an old closed knuckle front 4X4 solid axle you were familiar with trunnion bearings.
On the other I try to stay away from Mopars in general
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Old 03-09-20, 09:13 PM
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Dedhed,
On the GM models they were called spurbing bearings, but served the same purpose. Smiles, MH
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Old 03-09-20, 09:17 PM
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Originally Posted by user_1 View Post
I guess, if I've never seen a need to re-tap anything and hence have never investigated what tools are required to do so, it means I'm re tarded and shouldn't attempt to fix this myself.
I'm here to learn.
No, it means it's probably cheaper, faster, and easier to have someone who already has the correct tap drill, tap, holder,and experience do the work.

Part of learning is knowing you limits or when something is not cost effective.
Personally, depending on what the bike and/or derailleur were, I'd stuff some fine steel wool in the hole, crank the screw back in, and call it good.
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Old 03-10-20, 05:48 AM
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Originally Posted by Mad Honk View Post

"Turbo Encabulator" the original. I'll be waiting for replies.... Smiles, MH
OK Mad, I'm with ya. I even have a poor photocopy of the original GE service advice. That takes me way back to my Power Systems Sector I&SE days. Wow. Great piece of technical writing.

update: OK I should not be surpised that the contraption has such a large presence on the ole "dub.dub.dub".

Last edited by Prowler; 03-10-20 at 05:53 AM.
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Old 03-10-20, 11:41 AM
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"Before rebushing the lower grunnion banjos....."

Originally Posted by dedhed View Post
Personally, depending on what the bike and/or derailleur were, I'd stuff some fine steel wool in the hole, crank the screw back in, and call it good.
Redneck heli-coil. Not that I've ever tried anything like this....
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Old 03-10-20, 12:02 PM
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Originally Posted by JohnDThompson View Post
A "tap" is a tool used to cut threads into a workpiece to accept a bolt of the same thread spec as the tap.

I suspect the cost of a tap would approach that of a replacement derailleur
This is what I was thinking.

I may just live with it since the bike is older and has other potential issues. Just means have to be very careful not getting the cable tension too tight.

As is, I had to replace the front gear shifter and have been having a lot of problems getting the indexing right since the old one was not indexed to the gear and fine adjustments were possible with the old one.

I've read it's not good for the chain to open the link - any truth to that.
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Old 03-10-20, 03:08 PM
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If the screw threads in part way and then slips, the screw is the problem. The threads are damaged in the area of the screw where it starts to slip.
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Old 03-10-20, 04:44 PM
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Originally Posted by dsaul View Post
If the screw threads in part way and then slips, the screw is the problem. The threads are damaged in the area of the screw where it starts to slip.
Except it may not be easy to find a matching screw.
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Old 03-10-20, 04:59 PM
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Originally Posted by user_1 View Post
I've read it's not good for the chain to open the link - any truth to that.
Modern riveted chains (used on clusters with more than eight sprockets) do not like to have pins reused once they have been pushed out to open the chain. Instead, they use a "master link" that can be repeatedly opened and closed:



The master link will look slightly different from the other links. Ideally, a "master link pliers" is used to open the link, but a needle nose pliers, carefully applied, is often sufficient.

N.B. the width of the master link must match that of the chain to which it is attached, so a chain for a 9-sprocket cluster will use a "9-speed" master link.
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Old 03-10-20, 05:13 PM
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Originally Posted by user_1 View Post
Except it may not be easy to find a matching screw.
I can only tell you what is wrong, based on the symptoms you described. If the low limit doesn't need to go in as far, maybe swap it with the high limit screw. Otherwise, take the screw to a bike shop and see if they have one in their junk parts box.
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Old 03-10-20, 05:18 PM
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^^^^^ Those screws are quite standard. I was missing a limit screw on a Shimano FD, probably a Deore, on one of my MTB. Happened to be on that bike when I spotted a cheap big-box store bike in a dumpster, with a bottom-of-the-line Shimano FD. Whipped out my Leatherman, unscrewed one of the limit screws, dabbed a little grease on the threads from my seatpost, and was back in business.
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Old 03-11-20, 06:01 PM
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If the screw itself is ok, you may be able to get the screw to grab properly by inserting a piece or two of monofilament fishing line into the hole, then screwing in the screw. Fiddle around with the mono size (8lb, 10lb, 12lb) you get the drift. A bike shop may have an extra screw or a broken RD in parts.
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