# Optical Forums > Optical and Ophthalmic Equipment >  American Optical exam chair model 14200

## CRM

Our chair has a mechanical locking mechanism for the recline.   Recline up motion - it locks fine / Recline down the "teeth" slip and the chair falls back when leaned on.
I tightened the two cables from the two levers that run down to the mechanism- still it fails.   Suspect the teeth are damage in the one direction.
Looking for service adjustment procedures please - or service advice.

thnx
CRM

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## Howard Gorin

I just saw this post.  The tilt lock is problematic.  Tightening the cables will not solve the problem.  There are three different tilt lock mechanisms.
The first is rarely seen the two common ones are adjustable sometimes,  The rack and lock will wear if they slip.  Two things to try.  Remove any lubricant from the rack teeth and lock.  You should see a coil spring that pulls down the locking bar.  Replace the spring with a stronger spring.
If all else fails jamb the lock so it cannot disengage.  Sadly the tilt lock is the weak point of the chair.

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## CRM

Thanks for the reply --- in fact, I did lock out the tilt function initially, until I enlisted the University Machine Shop to rebuild the mechanism.    Teeth and spring were worked on just as you described.    The chair is used in a research area here.

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## Howard Gorin

They are about the best chair ever made.  Salesmen hate them, the chairs last too long. Lift cylinder can leak after thirty years, they are rebuildable.  Also the linear bearing races can fail, I make better ones.  Please forward my compliments to the staff at the University Machine Shop.  In my lifetime I have seen five different models of chairs and stands sold by AO or later by Reichert.  Each succeeding model was inferior to its predecessor.  So there have been four levels of deficiency which are touted as improvements.

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## JFK

The fix is actually tightening the screw which holds the mechanism tightly engaged. It’s a flat head screw and keeps the teeth engaged so they do not slip. It’s seriously that simple.

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## JFK

Tighten the flat head screw which keeps the teeth engaged.

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## Howard Gorin

There are many possible fixes.
You found the one that works!
Congratulations

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