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question after testing a J type overdrive


Jedi Warrior
I just tested the J o/d transmission I bought for my Spitfire.

At first it didn't want to disengage, but after playing with it for awhile it started to behave correctly.

Now the question:

Using the buckeye triumph webpage write up as a model the pressure guage responded just like I hoped it would except for one thing:

There was a pressure fluxuation of about 50 lbs with it engaged, from about 425 down to about 375 or so.
To me that means one or a combination of three things,

Leaky pump,

Leaky pressure relief valve,

Leaky operating piston.

My question then:

Worry about it? or let it go?



I'd drop the screen and check for gunk buildup. Maybe pop the relief valve out and clean it up... Other than that, it's building good pressure. And your symptom description alludes to some gunk hanging up..


Great Pumpkin - R.I.P
For a Spit, the working pressure should only be 320-350 psi.

Personally, I would want to chase down the problem, as it sounds like a sticking PRV. That may also be the reason it didn't want to drop out of OD at one point; excess pressure can jam the clutches together until the springs won't separate them or of course the PRV itself can stick in the OD position. The clearances in the PRV are very tight, so the least little bit of swarf can cause problems. And if it sticks, the pressure may spike well above what you read.

Backing up with the unit stuck in OD will damage it badly, basically causing the sprag clutch to break and take the rear housing with it.

Note that there are two screens worthy of cleaning. You have to remove a plug to get to the pressure side screen.


Great Pumpkin
Just out of curiosity, what did the oil look like that came out of it when you got it? Was it clean and how did the strainer look?


Great Pumpkin - R.I.P
This might be helpful


Jedi Warrior
Here's the story,
About a year and a half ago I was reading the Classic Motorsports forum, when a fella from TX wrote in that there was a o/d equipped Spitfire in the scrapyard next to him.
I wrote him and we worked a deal for him to pull the whole gearbox and ship it to me.
When I got it he had drained it, so I don't know what the old oil looked like.

I pulled the top cover and everything was very clean, the synchro's are hardly worn at all, everything turned smoothly.

I pulled the o/d pan and pulled the HP screen, it was all very clean.

I removed the solenoid and tested it on the bench, it worked.
I put a new o ring on it and reinstalled it.
I dumped a quart of 30W in it, and made an adapter to drive the input shaft with a electric motor that I had laying around.
Just for fun, I tried it without a pressure gauge, and it would engage, but would not disengage without stopping it.
I made another adapter so I could put a pressure guage on it, and tried again.
Which lead to the first post. The more I play with it the more readily it disengages, to the point that it disengages almost immediatly.

My question is how concerned should I be over the pressure fluctuations?
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