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Over drive type J not engaging

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Hi all, Help,

Looking for some ideas as what might be wrong.  So whilst driving my 1977 1500 spitfire, the other day on the motorway (bloody stupid idea, 1500 spitfire made before most of them where built or even thought of) my over drive decided it no longer wanted to play, and had a sulk.  It just switch to direct drive with no noise or vibration, and would not re engage, no matter how many times I flicked the switch.  

So so far I have checked the oil level, all good,  

checked the electrical circuit (put it in third and checked that the solenoid was making a clicking noise) all good.  What now ????

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remove the solenoid   needs thin 1" af spanner ........... big tip     dont use grips on the body you can wreck it 

give the thing a shake   

the spool valve plunger inside should rattle when shaken 

its common the o rings on this piston  inside fail 

remove the small 10mm circlip in the end and tap the piston/spool valve out and examine

then  its clean fit new rings and ...hope 

have you tried loading the gearstick to the left /right to just make sure its not the inhibitor switch needs a bit more contact with the operating cam??



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Just as an alternative to Pete's good points...  Did you let the car cool down before testing the electrical circuit? I had a Stag that used to exhibit the same completely failed overdrive only once the gearbox had got warm. If allowed to cool it would work fine again, until I'd driven far enough to properly warm it up. That was down to the inhibitor switch not making enough contact with the shaft (it's a different design on the big saloon box but the same principle) because a PO had fitted two washers under it.

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  • 3 weeks later...

Hi All,

Update on the overdrive.  I had a brain wave (not usual), I decided rather than strip all the car apart to find out if was mechanical or electrical, I thought what's the easiest thing to do first.  Check the blooming switch of course, (thought I had done this with putting it in third gear ignition on and switching the solenoid, but wanted to make sure) so I removed it and tested it with the old multi meter.  It was intermittent no contact, then contact when switching ermmm.  So went for a test drive with the contacts just sticking out of the gear leaver and putting them together by hand, and hey presto all worked fine (bloody intermittently switching switch).  Then a search of tinternet for a new one, what £12 quid plus postage for a cheap Chinese copy, no chance, so I took it apart.  Turns out it was pitted because the design is rubbish, it does not make or break the contact fast enough to stop arcing (it was working as per design intent, the little spring was in very good shape.  Cleaned it all up and now all is well with the world again (for this issue at least).IMG_2070.thumb.jpg.9236ff9ad6e8e2a180168ffbd9baf666.jpgIMG_2072.thumb.jpg.db1de55dd40d8e89baefe0742cb74aeb.jpg  Some pictures attached incase anyone wondered what was inside one of these switches.

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Handy for all of us with overdrive to know. Some many parts can be stripped down and repaired. Just needs time and care. Oh and making sure that you are working on a large piece of carpet to catch all the springs that go ping and disappear, normally into the grass or gravel.

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