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Overdrive disengaging


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Hi All,

 

I have a dicky overdrive. From the plethora of gearbox and OD articles online, I think I know the problem but thought it would be worth posting...very grateful for any input. The set-up is a TR4A gearbox with Type-A OD from a Vanguard. The oil is Hyp-90 and the level is good (fill to spill).

 

The OD drops out, but only in after a period of time running (20 mins+) and only on braking or downhill... and this has led me to a conclusion around the Hyp-90 and scavenging/pumping when warmed-up. I'm looking to change to SAE40 and the article in the latest TRAction (304) has given me the confidence to press ahead.

 

However, the problem is only apparent in 4th gear. No drop-out in 2nd or 3rd when braking or going downhill. That doesn't seem to fit with my pump/oil type theory. Perhaps I am off the mark with my diagnosis? As I say, grateful for any thoughts.

 

Best

 

David

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Hi Bob, do you still run a dynamo, there could be a problem with not enough current/voltage getting to the solenoid to hold it in as the revs drop in 4th gear on overun. Are all terminals clean especially those on the back of the ammeter.

I use 80 grade gl4 oil and it's fine just a bit slow to engage for first 15 mins until warm then instant.

Chris

Edited by potts4a
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I would suspect the 3 / 4 isolator switch is only just making contact when in top, & on the overrun it looses it.

 

Bob.

I would agree with Bob. I had this on my 6 a while ago. I'm not 100% on what I did now, but I think it was a case of taking the switch off and replacing the fibre washer with a thinner one. All works fine now.

Hope that might help

Best Bill

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I would agree with Bob. I had this on my 6 a while ago. I'm not 100% on what I did now, but I think it was a case of taking the switch off and replacing the fibre washer with a thinner one. All works fine now.

Hope that might help

Best Bill

 

+1

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I found my switches had poor electrical contact.

I sprayed them with contact spray and now they are fine.

Did not open them, just sprayed along the pin.

Maybe this is not entirely the right way, as i may have dissolved the grease.

Worth checking while you are there.

Waldi

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The good thing with the original switches is you can open them up by carefully prising the peened over edge up and then strip and clean the contacts and a little grease to lubricate and they will go back together and work for another 50yrs.

Stuart.

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