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Thread: overdrive problem

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  1. #1 overdrive problem 
    regular forum contributor Club Member
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    Hi All
    I have a problem with my overdrive which I think had not been operated for some time (ie. 10yrs+).
    I was testing some wiring that I had renewed with the gearshift in neutral, turned on the ignition then starter motor, all OK. After approx 15mins I realised that the overdrive switch was in the ON position. From there on I have not been able to put it in any of the forward gears. Reverse is still obtainable.
    I am thinking that the clutch inside the overdrive won't dis-engage. I have checked the solanoid switch is off and taken apart and checked the operating valve. The lever on the right hand side of the overdrive moves very little. Have tried taking a piece of wood and a decent hammer to the rear casing to try and free the clutch but no joy.
    I would be glad of any guidance. The gear box is an A type from a 2.5pi and Laycock overdrive.
    PS. I removed the oil some 3 mths ago and had no cause for concern re metal filings. Oil was on the low side and I haven't replaced it yet.
    Barry
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  2. #2 Re: overdrive problem 
    frequent forum contributor Club Member b_caswell's Avatar
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    Hi Barry

    The overdrive should only actuate when the car is in 3rd or 4th gear so having the switch on in neutral wouldn't make any difference.

    Even if the overdrive clutches have stuck the gears would still be available.

    If you ran the engine even with the car in neutral with no oil in the gearbox/overdrive you have probably damaged the gear box as

    the input to mainshaft bearing would be working along with the lay gear bearings.

    I suspect the damaged bearings are now dragging and preventing gear selection.

    You should be able to select the gears without the engine running if not you have me foxed??
    Ben Caswell probably not the last word on anything here!!
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  3. #3 Re: overdrive problem 
    frequent forum contributor Club Member stevejgreen's Avatar
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    I would echo Ben’s thoughts.
    Even in neutral, with the engine running, all the gears are in motion, power only reaches the output shaft when one of the selector dogs is engaged. All the time the gears are spinning, oil is circulated/splashed over every internal part of the gearbox, it’s a veritable storm of oil in there, all the time there is oil available to circulate.
    Reverse gear is slightly different as it has a separate idler gear to reverse the direction of rotation.

    I would pop the top off the gearbox and look closely at the selector dogs for damage or signs of overheating, but it sounds serious.
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  4. #4 Re: overdrive problem 
    frequent forum contributor Club Member greyV8pete's Avatar
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    Yep! I agree with Ben. I think the overdrive is a red herring.

    BTW the O/D valve lever doesn't move very much normally. If disturbed / undone the lever needs resetting. IIRC by using a dowel (3/16” comes to mind) through the non solenoid side lever into the setting hole in the O/D body and with the solenoid switched on you clamp up the operating lever. Check the workshop manual for yours to be sure. Peter.
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  5. #5 Re: overdrive problem 
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    Hi All
    Thanks for your input. Food for thought. I will let you know how I get on.
    Barry
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  6. #6 Re: overdrive problem 
    forum contributor jimfer01's Avatar
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    I agree that the overdrive isn't likely to be the culprit.

    If my memory serves me right, the solenoid doesn't actually move any gears, it just opens a valve to allow oil pressure to activate the overdrive gear.
    Thus, it doesn't work when sitting idle, particularly if there is no oil in the gearbox.

    Jim
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  7. #7 Re: overdrive problem 
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    Ref my overdrive problem, initially I removed gearstick then tried changing gear with a lever. All gearshafts moving as should. Tried unjamming drive shaft at exit of gearbox using a spanner on joint bolts. A bit of movement left and right and, with some persuasion, something popped free (overdrive clutch?). From then on shaft was easy to turn, so now refitted gear lever taking care of instructions. All gears now obtainable. Reset overdrive operating lever and started engine. All forward gears obtainable and running (car is up on axle stands). Reverse engage was very rough to the point of stalling the engine at tickover. Not so on forward gears.
    Drive shaft moves freely one way but not the other. Also overdrive solenoid is working in all gears but is only moving approx. one sixteenth of an inch to engage. It that right? The overdrive is not actually working. I think something is horribly stuck inside so will have to take all apart. Any other suggestions gratefully received.
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  8. #8 Re: overdrive problem 
    frequent forum contributor Club Member greyV8pete's Avatar
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    Quote Originally Posted by batman3481 View Post
    Ref my overdrive problem, initially I removed gearstick then tried changing gear with a lever. All gearshafts moving as should. Tried unjamming drive shaft at exit of gearbox using a spanner on joint bolts. A bit of movement left and right and, with some persuasion, something popped free (overdrive clutch?). From then on shaft was easy to turn, so now refitted gear lever taking care of instructions. All gears now obtainable. Reset overdrive operating lever and started engine. All forward gears obtainable and running (car is up on axle stands). Reverse engage was very rough to the point of stalling the engine at tickover. Not so on forward gears.
    Drive shaft moves freely one way but not the other. Also overdrive solenoid is working in all gears but is only moving approx. one sixteenth of an inch to engage. It that right? The overdrive is not actually working. I think something is horribly stuck inside so will have to take all apart. Any other suggestions gratefully received.
    It sounds as though the overdrive roller clutch was jammed. This is not the cone clutch outside of the epicyclic ring gear. It is inside the very back of the overdrive This will jam if the car is allowed to roll backwards with the overdrive still switched on. Owners handbook for original car usually warns against this.

    The solenoid travel is not very much as it only lifts a valve open enough to allow oil under pressure from the accumulator piston to actuate the two pistons that move the epicyclic gear assembly to enable engagement of the o/d cone clutch. See my previous post for how to set this valve lever using a dowel. If you haven't undone the pinch bolt on the solenoid lever this shouldn't have moved, but worth checking anyway. Peter.
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  9. #9 Re: overdrive problem 
    frequent forum contributor Club Member greyV8pete's Avatar
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    BTW in the unlikely event that you do need to remove the overdrive from the gearbox, let me know on this forum and I can give you some tips and warnings how to go about it. Peter.
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  10. #10 Re: overdrive problem 
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    Quote Originally Posted by greyV8pete View Post
    BTW in the unlikely event that you do need to remove the overdrive from the gearbox, let me know on this forum and I can give you some tips and warnings how to go about it. Peter.
    Hi Peter
    I'm fairly sure that I will have to take the overdrive and gearbox out of the car and would be grateful for any tips you have.
    Thanks in advance
    Barry
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