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Chattering Overdrive solenoid


Guest TR2Man2

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Guest TR2Man2

Can any one give me an answer  to why the overdrive soleniod has started to "chatter" when energised. Also the overdrive is not coming in. Is it a case of adjustment, I have carried out procedure as described in w'shop manual.

Any thoughts would be appreciated.

 

John

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There are two coils-in-one inside the solenoid.  The "pulling" coil draws about 25 amps to pull up the plunger.  Inside the top of the solenoid is a small "normally closed" switch that the plunger opens when it gets up to the top.  With the plunger up and this upper contact open, the 2nd coil takes over.  The current drops to about 1 amp.  This is called the "holding coil".

 

Therefore your plunger is being pulled up by the action of the "pulling" coil, then the contact opens but the "holding" coil is not working, so the plunger drops about 1/8 inch where the "pulling coil draws it up again - hence the chattering noise.

 

You need to replace the solenoid.  Or if you are handy, remove the solenoid, hold the solenoid body gently in a vice and roll back the rubber boot protecting the top.  If your solenoid is an original LUCAS unit, it may need to have a tiny wire re-soldered inside.  If you find this to be the case, make sure you screape off the polyeurethane insulation from the end of the wire that you want to re-solder to the post.  After this, connect it to a battery and test it before re-installing it.

 

I always carry a spare.  Whichever I last repaired becomes my next spare.  The original one is stamped LUCAS 2/54 (Feb. 1954) on the body of the solenoid.  The newer one is from 2001 and they use gobs of RTV silicone in the top end which can get loose or gummy causing a problem.

 

I cut a hole in the side of the tunnel near my solenoid and it takes about 20 minutes to take out the carpet, remove a 3" diameter rubber plug (like for the jack hole in the floors) and I drilled 2 other holes about 6" higher up for access with a long screwdriver to un-screw the two retaining screws for the solenoid.  These smaller holes I fill with smaller rubber plugs like are found on the bulkhead.

 

Don Elliott, Original Owner, 1958 TR3A, Montreal, Canada

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