I have a problem with the A518 automatic. For a year I’m driving with the A518 od/lu trans behind a 408 stroked engine. It works fine but after 1500 mile the trans start making problems. when the engine/trans is at operating temperature it just shifting up late and downshifts early when I'm letting off. When I’m driving at a constant speed it will downshift from 3rd to 2nd gear. When I turn the gas it shifts back to the 3rd gear. This happened at speeds between 2000-3500 RPM, even if the automatic is in overdrive. Oil is ok, kickdown adjustment is ok. Oil pressure is 80 psi, there is no change in pressure when the problem occurs (unasked downshift 3-2)

Its a A518 od/lu with A618 internals and a SF TFOD-jr shiftkit.

Any help is welcome, thanks.

Patrick

Check the vacuum if you are using the vaccum switch for od and L/U apply.

I'm using 2 toggle switches to control the OD/LU

How can it downshift from 3rd to 2nd if "even if the automatic is in overdrive"? Overdrive is 4th.

Aside from the overdrive reference, uncommanded downshifting from 3rd to 2nd is usually caused by worn governor sealing rings or leakage at the governor pressure tubes.

OK, thanks for the information.

The overdrive is working in all gears (1-3), thats why I don't call it the 4th gear.

The overdrive still works when the trans is downshifting(uncommanded) from 3rd to 2nd until I shut off the toggle switch.