Overdrive pressure question

Hello all --

My overdrive has been slow to engage (and sometimes slips) when hot. I thought I had licked the problem with heavyweight oil and an operating valve adjustment a few years ago (which did help enormously), but it seems unhappy again on hot days at slow speeds....

Measured cold (with 50 weight oil), I got ~275 psi @ 1500 RPM in 4th. I then a) replaced the spring on the non-return valve, b) replaced the accumulator spring, and c) added a 1/16" washer in the accumulator piston.

Now (cold, still with 50 weight oil) I get ~510 psi @ 1500 RPM (and ~540 psi @ 3000 RPM) -- guess I didn't need the washer! -- BUT, the pressure now drops rapidly to zero as soon as I stop the transmission spinning.

I assume either the operating valve isn't seating or I messed up the accumulator piston rings? Fiddling with the former didn't seem to help, and how bad can the accumulator rings be if I'm seeing >500 PSI?

So I guess my question is, should I care? Everthing seems happy (at least on jackstands), except for the pressure dropping quickly. Or any troubleshooting ideas?


Thank you ever so much!

That is a bit high 300 to 450 are good enough numbers IMOP

I once had similar issue

the problem was that in the opreting valve, in the little hole under ball (see section G6 in the workshop manual) there was a little bit of oil crude who prevented
the correct flow of the oil and the lifting of the ball. i just cleaned away the tiny bit of crude and the overdrive worked perfect again.

But there could be a lot of other reasons. Hope my input helps.

Hello and have a nice from Sunday from Switzerland.

Norman Nock also recommended tapping the tiny ball (that is lifted by the operating lever) lightly to get a good seat/seal to keep the pressure from leaking down.

Bingo -- I cleaned the operating valve seat with a clean cloth, tapped the ball lightly with a drift, and gave the spring a tug to stretch it out a bit.


Now, when stopped, pressure gently falls to 300 PSI, but then holds there steady for what seems like forever.


Thank you! Now to button it up and get it on the road ASAP....