Silicone Damping Fluid

Turntables use silicone damping fluid in a variety of capacities, all to dampen the motion of the tonearm.  The most common application is slowing the drop rate of the needle when the cueing mechanism lever is moved down.  There’s also a thicker fluid for use as an oil bath for a monopivot damping well.  Three other thicknesses are available for arm motion damping troughs.  Turntable Tuneup has five different thicknesses of silicone damping fluid, each for a different purpose.

 

Silicone Damping Fluid 10cc Syringe
Silicone 300,000 cSt in a 10cc syringe

For tonearm cueing mechanisms: 300,000 cSt

Over the years, the cueing mechanism, which lifts the needle off of the record, and lowers the tonearm to drop the needle gently onto the record groove, can leak or dry out.  Usually the up-down lever will continue working, but it will drop the needle too quickly onto the record, resulting in a loud thump, and possible damage to the phono cartridge.

Removing tonearm rest from cueing mechanism piston
Removing tonearm rest from cueing mechanism piston
Cueing mechanism with tonearm rest removed from piston
Cueing mechanism with tonearm rest removed from piston

To restore proper operation of the cueing mechanism, you will first want to disassemble it.  First, remove the tonearm rest from the cueing mechanism shaft.  Then, remove the cap from the cylinder and remove the piston.  At the bottom of the piston is a small cam, which is supposed to lift the piston when it is rotated in one direction, and allow it to drop when rotated back to its original position.

Loosening set screw to allow removal of cueing mechanism from yoke
Loosening set screw to allow removal of cueing mechanism from yoke

Removing cueing mechanism from yoke
Removing cueing mechanism from yoke

What keeps the piston from dropping too quickly is the thick silicone fluid inside the cylinder.  You don’t want to fill the cylinder with fluid, but only to add enough to coat the cylinder wall when the piston travels upward.  That coating of thick fluid will create enough friction to slow the motion of the piston when the cam is rotated to its resting position and the piston is allowed to drop.  If the cylinder is over-filled, then the piston will not be able to move in either direction.

Cueing mechanism, removed from yoke, with tonearm rest and rest-mounting screw
Cueing mechanism, removed from yoke, with tonearm rest and rest-mounting screw

Cueing mechanism with cap removed from cylinder
Cueing mechanism with cap removed from cylinder

Cueing mechanism cylinder with return spring removed
Cueing mechanism cylinder with return spring removed

Looking down the cylinder bore at the lever-operated cam
Looking down the cylinder bore at the lever-operated cam

You can use a cotton swab to clean out the cylinder before reinstalling the piston and adding the new fluid.  Add a little at a time, reassemble and try it out.  The correct final amount to add will fill the cylinder perhaps a third of the way, but you will need to experiment with the fluid level to achieve the drop rate you want.

The variables which determine the drop rate are the thickness of the fluid, and also the distance (tolerance) between the edge of the piston and the cylinder wall.  Different manufacturers build different tolerances into their designs.  More loosely-fitting pistons will require a thicker fluid, and a piston with a very tight tolerance will probably want a thinner fluid.  While most tonearm cueing mechanisms work properly with 300,000 cSt (centistoke) silicone fluid, some people find that they can only achieve a slow enough drop rate with a thicker fluid, and in these cases, the fluid which is normally prescribed for monopivot damping wells (600,000 cSt) will also work well for the cueing mechanism.  If the piston is dropping too slowly, then a thinner fluid (100,000 cSt) will fix the problem.

Silicone Damping Fluid for Tonearm Cueing Mechanisms 300,000 cSt, 10cc




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For Monopivot Damping Wells: 600,000 cSt.

 

Most tonearms have two sets of bearings; one allows the arm to swing left and right, and the other lets it rise up and down.  These bearings are visible from the outside.  But some arms have a single post at the pivot point with a pointed tip, and the arm balances and swings on that point.  This tip is hidden inside the arm shaft at the pivot point.  This pivot must be lubricated and also dampened with a very thick silicone fluid.

 

Damping DampingWell1a tonearm’s motion at the pivot point serves a few purposes.  First, it allows the arm to move very smoothly across the playing band of the record.  But while allowing it to move, a thick damping fluid will also remove a lot of the chatter that results from small vibrations in the turntable base and inhibit skating forces upon the needle that make the arm want to fly toward the inside of the record.  Proper damping will also provide more stable azimuth alignment; monopivot arms can rock like a boat in choppy water as well, if they are allowed to.

All of these tiny vibrations and chatter in the tonearm will, of course, result in a confused, unstable signal during playback.  Keeping the arm quiet and still is a major goal of tuning up your turntable for proper playback with minimal interference and error.

Silicone Damping Fluid for Monopivot Damping Wells 600,000 cSt, 10cc




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For motion damping troughs: 30,000 cSt, 10,000 cSt and 100,000 cSt

Tonearms with bearings at the pivot points also frequently have fluid damping systems that involve a paddle attached to the bottom of the tonearm, about an inch from the pivot point, which projects downward into a trough filled with a more lightweight damping fluid.  The fluid in an arc-shaped trough needs to have less viscosity because it exercises its resistance to motion at a much greater radius than the fluid in a monopivot damping well.

There are three variables which determine the effect of this damping system: the viscosity of the fluid, the depth of fluid in the trough, and the width of the paddle.  For most tonearms, 30,000 cSt works best for damping the motion of the tonearm and maintaining smooth playback.  However, experience has shown that some tonearms require thicker or thinner fluid, and for this reason we also offer 10,000 cSt and 100,000 cSt fluid, which many people have found optimal in their own systems.  Any of these fluids can be mixed together to achieve custom thicknesses as well.

Tonearm motion damping systems do not replace anti-skate mechanisms, but do reduce the severity of the need.  Skating forces are imposed on the needle by the spinning record groove, and make the tonearm want to fly to the inside.  Fluid motion damping systems help the tonearm resist moving quickly toward the inside of the record, and help dampen chatter and vibrations in the tonearm wand, while allowing the inexorable need of the needle to follow the record groove smoothly toward the end of the playing band.  in the tonearm are much stronger than bearing chatter and vibrations that disrupt smooth playback.

Silicone Damping Fluid for Tonearm Motion Damping Troughs (most common) 30,000 cSt, 10cc




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Silicone Damping Fluid for Tonearm Motion Damping Troughs (light) 10,000 cSt, 10cc




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Silicone Damping Fluid for Tonearm Motion Damping Troughs (heavy) 100,000 cSt, 10cc




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