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duncanhyams

A type overdrive problem

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Hi chaps,

A few weeks ago while driving, on excelleration in third gear overdrive it came out of overdrive and excellerated then went back into overdrive, this would also happen in fourth as well without touching the switch, Today I have no overdrive at all,

So could this be a symptom of a failure waiting to happen, and now has. I have read fault finding points to check on but was hoping you guys may have encountered a similar fault in the past,

 

Thanks in advance

Duncan.

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Hello Duncan, I'm not an expert, but my old TR4 had an 'A' type overdrive, and whenever the gearbox oil needed topping up (it leaked oil quite badly), the overdrive behaved exactly as you describe. Maybe a quick check of oil in the gearbox would be a good start. Let us know what you find. Best wishes, Austin

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Cheers Austin, this was one of the first things I was going to check but getting someone who has the same fault was exactly what I was hoping for,

Regards

Duncan,

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The same applies for the J type. Check oil first.

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Hi Duncan

 

Had this problem a few years back 1974 TR6 J Type

Yes check gearbox/overdrive oil level

My fix was a very loose electrical connection on the overdrive solenoid new spade terminal fitted jumping out of overdrive fixed.

 

Alec

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You should hear the 2 solenoids click when the overdrives engaged/ disengaged with the key "on" but the engine not running .One solenoid is on the passenger side of the engine bay and the main solenoid is on the same side of the gearbox.

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There aren't two solenoids - one is the relay. Certainly, you should hear the actual solenoid on the O/D itself "click" if you turn on the ignition (don't start the motor), put it in the requisite gear and switch the O/D. Depending on the type and location of the O/D relay, you may or may not hear it. Mine is a modern relay located in the passenger footwell, but I can't hear it when I engage the O/D with the motor off.

As for the original O/D issue, the first things I would check are consistent solenoid switching and fluid level (with the car on level ground, fill the transmission until fluid pours back out the fill hole - why they didn't install some sort of tranny dipstick escapes me). I have always used 30 wt Non-Detergent oil for my tranny+A-type. A faulty relay could switch in and out unpredictably, generating the symptoms you describe. Even if you're interested in originality, you should be able to temporarily plug in a modern 4-contact relay (~$5 at your FLAPS) to see if that's the issue. If the replacement relay alleviates the problem, then stick with the new relay or buy a period-correct reproduction.

After that, I would investigate oil pressure - you should be getting >400 psi at the actuating valve. You can test this with the tranny in place. If you're not getting pressure, this suggests that your pump is shot, the non-return valve is shot, or the accumulator cylinder is worn. Either your pump isn't attaining sufficient pressure, or your accumulator isn't maintaining sufficient pressure. Investigating these would be best done with the tranny on the bench

Edited by Litespud

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Thank you guys for your replies, I can hear solenoid and relay working so checking the oil level when I can will be my first task,

Regards

Duncan

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Hi Duncan,

if it only happened under acceleration then check the fitting of the rubber gaiter around the gear stick.

If this is fitted with a boas it may push the gear lever ever so slightly and knock it out of OD. As OD is switched in then it may resume upon deceleration.

 

Roger

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