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Spitfire Overdrive issue on a Spitfire

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busybrit

busybrit

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Hi Guys, looking for some direction. I'm working on an O/D for one of our club members and it's starting to stump me. The O/D works in the morning but once the engine warms up it starts to jump out. I topped up the oil. it was a little low and it ran ok for half a day. Later in the day when everything was warm, well HOT, it wouldn't work at all. Anyone had the same problem?
 
I haven't had <span style="font-style: italic">exactly</span> the same problem, but I have surely noticed a slowing of engagement time as temperature rises.

I'm not an OD expert (yet), but I am accumulating experience by the day...

Here's my best guess: Oil pressure. Hot oil "thins." If the oil pump or the accumulator or the pump check valve are sub-optimal, they will work "OK" with cold, thicker oil. As the temperature rises and the oil thins, then, whichever of these parts isn't really tight enough anymore can no longer generate (or maintain) sufficient oil pressure to operate the OD.
 
Thanks for your input, that was my thought also, hence addressing the low oil level first. I'm also wondering if the solenoid is failing due to heat.
 
I would come up in oil weight. Also, I've found that some synthetics are a little TOO slick (The best ones being Amsoil and Redline) and the OD wont activate, and in some cases, will disengage. Since changing to 30WT Castrol dinosaur oil I've had no issues at all with my OD.
 
What kind of OD? I believe Spits used either D-type or J-type.

One problem I've had on a J-type is the quick connect being just a tiny bit loose on the solenoid tab. Not enough to pull off with a tug, but enough to wiggle. Sometimes it would make contact, and sometimes it wouldn't. Crimping the wire terminal tighter solved the problem.

For a D-type, there will be a relay, and I've also had problems with the relay going intermittent. Adding a diode across the contacts seemed to help a great deal.

Also, troubleshooting an overdrive without a pressure gauge is just shooting in the dark IMO. Get a pressure gauge and use it, it will quickly lead you to the problem. There's a fellow that sells them on eBay from time to time for about $50 (including the adapter for your model of OD). I think his name is Jay (or James) Holecamp, but I don't have contact info handy.
 
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