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“So you think you might want to learn to do simple repairs to your own instruments? 
Here is a primer to help you get started.”



John D. Upchurch, D.M.E. aka the Slide Doctor

with photo and design assistance from Terry L. Robinson


In his book, The Road Less Traveled, Scott Peck relates the story about visiting his neighbor.  The neighbor had the lawn mower disassembled in the driveway.  The conversation went something like this:


Peck:  I could never do anything like that.


Neighbor:  Of course you could.  You are just not willing to take the time to learn how to do it. 


This situation covers many of the conversations I have had with players regarding their assumption that they would never consider trying to do even minor repairs to their instruments.  Further, some players relate that they took an instrument repair class in college and therein were convinced that they could never do repairs.  This is hardly a positive way to approach the subject.  As a result, we have prepared a short test to help you to assess your mechanical aptitude.

So what does this test tell us?  There are 45 positive points.  If you scored 15 points or less, you may need hypnosis to convince yourself that you are capable of doing simple repairs.  If you scored from 16 to 30 points, you are a reasonable candidate for basic repairs.  From 31 to 45 points, consider yourself a prime candidate to learn the techniques.  In the following sections, we’ll examine how trombone slides are assembled, how to diagnose why they are not working properly and how to make the necessary repairs.




To assist you in getting started, there are several basic assumptions you should adopt to be successful.

  1. Trombone parts can be replaced.  Sometimes the replacement part actually improves the quality of the instrument. The secret of success in deciding whether or not to use a replacement part is to know what function that part has and how the function may change the playing characteristics of the horn.  As an example, water key cork doesn’t have any effect on tone quality unless it leaks. Then it has a noticeable effect.  Another example is the felts in the cork barrel.  They are so simple to change that anyone can do it in five minutes but few players have a clue how to begin. Why would anyone want to change them?  Many slides have deteriorated or missing felts, which result in the slide making an ugly “clanking sound” in first position and also in the slide lock not correctly engaging with the slide lock cleat. Even if you scored less than 15 points, you can do both of these repairs!

  2. You will need to spend some money on tools.  If you want to do basic repairs, it will cost less than one of those new “designer mouthpieces” that you no longer use and that now sit, collecting tarnish on the shelf.

  3. Just like playing the horn, facility takes practice.  However, unlike performance, facility isn’t always necessary.  In fact, quite often you can do the same process over and over until you get it just right.

  4. Don’t be afraid to make mistakes.  Some of the best lessons I’ve ever learned came out of doing something the wrong way.  Not all of these were even bad.

  5. The physics of a trombone slide is really quite simple:  You have four tubes.  They need to be perfectly round, straight and the same distance apart from one end to the other.  After that, you remove as much friction as possible and you have a great slide.

  6. Finally, some players believe that lubrication is the key to having a great slide.  This is only partially true.  Lubrication can improve or degrade slide action.  FRICTION is the major cause of faulty action and lubrication cannot overcome serious friction problems.  Friction problems can be caused by having bent tubes, by having out of round tubes (ergo dents) and more often, by unclean tubes.  Much of my current work involves removing the multiple applications of a high-tech lubrication that players have allowed to build up on the inside of the outer slide tubes until the action became in-action!




Straightening a water key and changing the cork:



misaligned water key   Straightening with
duckbill pliers

It is not necessary to remove the water key to straighten it.  Assuming that it is only slightly off center, use a set of duckbill pliers to grasp the water key on the piece between the axle and the cup that holds the cork.  Most of these have a wide flat side and narrow side.  Place the pliers so that the end of the duckbill gently touches the cork cup, and the face of the pliers is on the wide flat side of the water key.  You are now ready to move the cup sideways to center it on the nipple where the water comes out.  Once you have centered it, look to see if the face of the cup is level with the top of the nipple.  You can level the face of the cup by twisting the wrist just a tiny bit to lower the high side and raise the low side.  Do this in small increments until you locate it exactly where it should be.


cork is too thin   cork is too thick   just right!

First. Look at the thickness of the current cork.  Most of the time, it is either too thick or too thin, if it was replaced after manufacture.  You’ll want to determine how thick the replacement cork should be before starting.  If it is too thick, the cup sits too high and the center of the cup won’t align with the nipple.  If it is too thin, then the cup is too low and the nipple hits the cork at the back of the cup.


trim the cork




Use a jeweler’s screwdriver to pop out the old cork.  Scrape any remaining glue from the cup. Look at the old cork to determine about how big the replacement should be.  You can use any cork you like.  Good wine bottle cork is OK. Use a razor blade to slice off a piece about ¼ inch thick and about ½ inch-square.  Trim the corners until it looks like a 3/8” circle.  Then use some 100-grain sandpaper to round it up to fit into the cup.  Check for the proper thickness by looking to see where the nipple hits on the cork.  If it is dead center, glue it in.  I use “Liquid Nails” to glue in water key cork.  If the cup sits too high, then sand the cork down to make it thinner by rubbing the face of the cork on the sandpaper.


Don’t forget to put a few drops of anti-corrosive oil on the axle.  Marvel Mystery Oil is great, but any household oil (like Three-In-One) will do nicely.


Replacing cork barrel felts and bumpers:


You’ll need to purchase an inexpensive tool to do this.  Information on ordering tools and parts will be located at the end of the article.


place the tool on the
tube & remove felt using
a slow twisting motion

The tool looks like a tube with a hook on the end.  There are two sizes.  The G41A is the smaller one for tenor slides and the G41B is used on large bore tenors and basses. 


Remove the slide lock ring (if it was designed to come off).  Place the tool on the inside tube.  Slide the tool all the way into the cork barrel until it meets the felt.  Twist the tool clockwise to push the hook into the felt and pull the felt out.  This may take several attempts to get the felt all the way out.  It is often necessary to use a slow twisting action to keep the tool in contact with the felt until the felt comes out of the barrel. Just be patient and you can work it out.


place felt in the barrel




You have two options at this point.   Rubber faucet “O Rings” work well and felt spacers are readily available.  You can also cut your own from a piece of 1/8th inch felt. Slide the felt or ring up the inside tube and into the cork barrel.  Use the outside slide tube to push the felt into the cork barrel.  Repeat the process on the other tube.


What can go wrong?  If the felt is too thick, it won’t go into the cork barrel.  Trim it until you can work it into the barrel with your fingernail.  Sometimes, the slide lock won’t work with the new felt.  This probably tells us that there is still part of the old felt remaining.


Changing a water key spring:


One of the easiest and sometimes most frustrating repairs is to change the water key spring.  Not all springs are created equal and you must have one designed for your instrument.  That sounds simple enough, except that the same model instrument sometimes has different sized water key axles.  Once you determine what size you need, purchase at least one backup spring and keep it in the case.


With the exception of King slides, most others have a screw that threads into the water key saddle and through the axle of the water key.  (Most, but not all King slides, have a straight bar with a tab on the end.)  Remove the screws with a jeweler’s screwdriver.  King slides without threads can be pulled out with pliers, twisting gently as you pull it.  Yamaha’s have a Phillips head screw, so you’ll need a jeweler’s Phillips head for them.  Clean the area under the water key and around the saddle with a little 0000 steel wool to remove any residue.


Remove the old spring from the water key by pulling one side off of the axle.  Open the new spring (in the middle of the spring is a loop that fits under the water key lever) enough to get it over the axle and then squeeze the spring back together so that it fits on the axle. Now things get interesting.  If the water key lever is straight, just pull the legs of the spring back along side the lever and slide the water key back in place.  Reinstall the screw and lubricate the axle with a few drops of anti-corrosive oil.

remove the screw   place the spring on
the key
  pull the legs back,
align, & replace screw
  trim the legs


If the water key lever is bent at an angle, you may want to buy a spring installing tool. The Ferree’s model number on this is D49. It is a metal tube, shaped like a “U.”  The ends of the spring legs go into the open ends of the “U,” allowing you to get leverage on the spring and hold it “without the legs touching the slide or saddle until you san slide the water key into place.





Touch Up Lacquer:


One of the easiest ways to improve the appearance of your slide and to protect the metal from wear is to touch up missing spots.  Here is a simple process to consider:


Start by polishing the area with Wright’s Brass Polish. If there is a good deal of reddish oxidation on the brass, a gentle application of 0000 steel wool will help to remove it. Once you have the brass looking very shiny and clean, you will need to remove any dirt, grease or oil.  Do this by using a clean paper towel and wiping the area with denatured alcohol. Be sure not to touch the area after you clean it.  Tiny spots can be filled with clear fingernail polish.  Larger areas should be sprayed with clear lacquer. You can get serious and purchase lacquer designed for musical instruments, or use either automotive lacquer or any fast drying clear lacquer.  A hair dryer will come in handy to speed the drying process.  Several thin coats will prevent the lacquer from running. The “pro’s” will shoot it on in one coat, but several thin coats will work just fine.


Adjusting the Width of the Handgrips:


Every so often, a crook is manufactured a little wider or narrower than standard size.  When this crook is used, it is not unusual to see the dimensions between the outer slide tubes different at each end.  For an outer slide to work well, the tubes need to be exactly the same distance apart on both ends.  A caliper will allow you to measure the distance at each end. If they don’t match you can adjust the right hand brace in or out. If this repair is necessary it will probably be necessary to reset the left hand grip.


Outer slides are often assembled as a group and inner slides are also assembled in batches.  This can lead to manufacturing defects.  The first example occurs when the right hand grip (or brace) is assembled too narrow or too wide to match the crook on the outer slide.  A caliper is used to measure the distance between the outer tubes, just above the crook and also just below the sleeves on the upper end of the tube. If there are no sleeves, measure just below the flange on the handgrip brace. If one sleeve is short and the other long, measure just below the longer sleeve.  If the two ends are not exactly the same, you’ll need to loosen and re-solder the right hand brace bar. Once the outside geometry is correct, you’ll want to check to see if the left hand brace is the correct width for the outer slide. You can hold the slide in a vertical position, with the outer slide about an inch below the bottom end of the cork barrel and see if the inside tubes drop dead-center into the outside tubes.  Chances are that they don’t.  If you notice that the first and second position action is much slower than from third out, you may wish to heat the joint at the brace and ferrule on the inner slide and make the left hand grip wider or narrower to match the outer slide.


measure the width at
the crook with a
caliper & lock
  measure the width at
the hand brace. above
example is too narrow
  heat the hand brace
with a torch until solder
is fluid
  adjust to the proper

Before doing any repair, it is a good idea to measure the distance between the outside tubes at the crook end and at the handgrip end .  Be sure these are the same.  If they are not, you’ll want to fix the outer slide first.


the inner tubes should
be in the exact center
of the outer slide
  heat the handgrip until
solder is fluid and
allow outer slide to
"guide" inner tubes for
perfect alignment

To adjust the width of the inner slide handgrip, use a propane torch and make the flame as small as practical, about 3/4th inch to one inch long.  Heat the area where the left hand brace meets the ferrule, on the lead pipe side, until the solder melts. Open or close the joint as necessary until the tubes drop dead center.  It is OK to set the size several times to get it just right.  If you burn the lacquer, clean the burned area with 0000 steel wool and follow the touch up lacquer instructions.






Advanced repairs will require that you purchase several tools.  You will need two expandable dent rods models N-11 and N-11A from Cliff Ferree and a level stone.  While this is a substantial investment, the payback in personal satisfaction and security may be worth the investment. If you know that you are capable of dealing with most any emergency that may arise, it can add greatly to your comfort level.  You should read the emails I receive from panicked players with minor problems and major responsibilities.  Learning to fix these may be good for your performance and even better for your blood pressure.


We will divide the advanced repairs into to two categories: slide tube alignment and dent removal.




Using the Level Stone to straighten tubes and check for torque:


Telling you how to use the stone is almost as difficult at describing the taste of roast beef. Imagine reading a book on glass blowing and then trying to do it the first time.  That is probably how you will feel about using the stone.  Don’t let this feeling keep you from learning to straighten tubes.  It isn’t all that difficult and like Yogi Berra said, “You can observe a lot by just watching.”


the gap of light should
remain consistent over
the length of the tube

Cliff Ferree’s stone is made so that the ends of the block are slightly higher than the face.  When you place a slide tube on the stone, you will see a gap under the stone.  I place a florescent light behind the stone to make the gap obvious.  Rotating the tube will show you if the gap remains the same or changes as you rotate the tube.  A straight tube will have the same amount of light showing under the tube all the time as you rotate the tube.  Because the tubes are attached you’ll need to be creative to see all four planes.  Lets look at inner tubes first.  Place the stone on the edge of a table so that the about an inch or a little more of the stone is forward from the top of the table.  You can now place the top inner tube on the stone and allow the bottom inner tube to hang over the edge of the table, directly below the top tube.  Slide the tube along on the stone and observe the distance between the tube and the stone. It should be the same except when the stocking of the tube meets the stone.  Stop there for now.


Grasp the lower inner tube about 2nd position and slowly and gently, pull it outward and upward to rotate the top tube on the stone. Again, watch the gap between the tube and the stone.  When you reach the point where the inner tubes are side by side you can see if the tube is bowed sideways.  Right now, you are just looking.


hang the slide on the
  rotate while looking at
the gap between the
slide and the stone

Swap the ends of the tubes and place the top inner tube on the stone again. This will allow you to observe the other two planes of the tube.  Even though the tube is round, think of it as being square and having a top and bottom plane and a left and right plane.  Once you have determined where the bends are located on the top tube, repeat the process on the bottom tube.  Locate the bends first, then plan your strategy to straighten them.


slide is torqued




Lay both tubes on the stone and see if they lay flat or if one tube is raised above the stone.  Heating the left hand grip until the solder melts will allow the tube to drop into a flat position.


repeat the process for
the outer slide
  be sure examine all
sides of all tubes!

The same process works for the outer slide.  Look at all four planes on the outer tubes.  Is the gap the same all round?  Lay the outside slide on the stone.  Does it lay flat or will it wobble on the stone because one tube is not laying flat?


Now lets look at how to fix these problems.




Chances are that any tube you look at will have some bow in it.  Sometimes it is severe and sometimes minimal.  Every bow should be treated as if the tube will break with little effort until the tube proves otherwise.  The pictures below will show you how to bend inner and outer tubes to get them straight. When the tube is perfectly straight, you will see the same amount of light under the tube any way you place that tube on the stone except on the stocking area.


Here are a few hints to get you started:  Always begin the straightening process either just above the crook or below the sleeve (or handgrip flange if it is a lightweight slide).  Once you have the correct tiny amount of light showing at both ends, work your way to the center of the tube from both directions.  When you think that the tube is straight, check the length by sliding the tube along the stone from the sleeve to the crook.  Does the light stay the same?  If so, move to the next tube.


one technique for straightening is to apply pressure while sliding your
hand along the length of the slide
alternatively, you may slide the slide over the knee while applying
pressure.  Start off with light/medium pressure and check your progress
often.  Don't over correct!

When both tubes are straight, place the part you are fixing on the stone to check to make sure that the tubes lay flat on the stone.  If not, heat the left hand grip on the inner slide until the high tube drops.  On the outer slide, you’ll need to heat both ferrules on the crook to loosen the solder joint.  Once this joint is free, you can usually just gently press the outer tubes onto the stone to get them level.  If they are stubborn, it may be necessary to hold the crook with a rag and gently twist the crook until the tubes lay flat on the stone.  Let it cool and allow the solder to firm up before you move the piece.

inner slide tubes are
not aligned properly


Check to see if the 7th position ends of the inside tubes align properly with the openings of the outside slide.  If not, you may want to reheat the left hand grip with the inner slide inside the outer slide.  Work the inside tubes in and out of the outer slide to make sure that they move freely.




Remember that any crash that is powerful enough to cause a dent will have knocked the tube out of alignment.  Even if you have a dent removed by a competent technician, you’ll need to make sure that the tube is also straightened after the dent has been removed.


In the following picture sequence, you’ll see a simple process to remove dents to make the slide playable in an emergency.  It may not be perfect, but it will get you playing again.


There are two schools on proper dent removal.  Both schools have good points and not-so-good points.  One uses a roller to burnish out dents.  The other school hammers out the dents.  Both methods result in some thinning of the metal.  The secret is to lower the ridges on the sides of the dent and to avoid thinning the metal as much as possible.


Here are the steps to repair a dent on an outside tube:

  1. Place the correct size adjustable rod inside the tube so that the expanding end is about ¼ inch past the dent.  Place your hand on the rod to measure the location and then slide the rod in until the tube reaches your hand. Tighten the wheel only finger tight.  Use care not to tighten the wheel beyond a 1/8th turn after the point where you feel restriction.

  2. Use the Lucite end of a

    measure the location
    of the dent in relation
    to the length of the
      place the expandable
    end of the rod 1/4 inch
    past the dent and
    finger tighten
      gently tap and finger
    tighten 1/8th of a turn. 
    repeat until dent is

    screwdriver as a hammer.  Start on the outside edge of the crease and tap gently.  Move to the other end of the crease and tap gently.  After 8-10 taps, you’ll probably feel that the wheel has loosened.  If it has, tighten it just another 1/8th of a turn.  Tap again on the ends and work toward the center.  You should see the crease flattening as you tap on the shoulders of the crease.  Take your time and be gentle.  Lots of little taps are the best way to go on this.  When the tube starts to become round again, you’ll hear a very different sound when you tap.  The first sounds will be fairly high pitched.  A good description is that it will sound like “tink.” When the tube is about right, the sound will be lower in pitch and more “solid” sounding.  It may sound like “top.”

  3. Straighten the tube and try the inside tube in the outside tube.  If you can’t feel the dent, you are done. If it still is noticeable, continue the tapping process. Just be careful not to expand the tube and make it larger in diameter with the dent tool.

Most of the time, it is smarter to not remove dents from inside tubes.  Just straighten the tube and see if it will work properly.  Inside tubes with severe dents require lots of experience to get them working without expanding the tube and ruining it.


Please understand that this is a “Reader’s Digest” version of how to do these repairs.  If it is any consolation, this is a great deal more than I was ever able to read when I started this over 30 years ago.


The next article will deal with chemical cleaning and  treatments to make your slide even faster.


Tools mentioned in this article are available from Ferree’s Tools Inc., 1477 E. Michigan Ave., Battle Creek, MI 49017


Neither the Slide Dr. or the On-Line Trombone Journal assume any liability for accidents or damage done by the reader using the techniques described in this article. The attempt to make any repair constitutes some risk.  Persons making repairs do so at their own peril and assume all responsibility for any damage incurred.

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