Help: A518 problems

Posted By: 408barracuda

Help: A518 problems - 03/15/10 07:39 PM

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

Posted By: stumpy

Re: Help: A518 problems - 03/15/10 08:21 PM

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

Posted By: 408barracuda

Re: Help: A518 problems - 03/15/10 09:13 PM

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

Posted By: John_Kunkel

Re: Help: A518 problems - 03/15/10 09:51 PM

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.

Posted By: 408barracuda

Re: Help: A518 problems - 03/16/10 10:37 AM

OK, thanks for the information.

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

Posted By: John_Kunkel

Re: Help: A518 problems - 03/16/10 07:20 PM

Quote:

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

Huh? Explain.

Posted By: 408barracuda

Re: Help: A518 problems - 03/16/10 08:55 PM

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

Posted By: MarkZ

Re: Help: A518 problems - 03/17/10 03:25 AM

Quote:

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

If you leave OD on, yes, it will down shift as the car slows. The kickdown lever however, will have absolutely no effect if OD is left on and the throttle is pushed in.

If you toggle OD on/off by a switch, like I do, then it should be off when decelerating.

Posted By: John_Kunkel

Re: Help: A518 problems - 03/17/10 09:35 PM

Quote:

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

I questioned your statement that "The overdrive is working in all gears (1-3)". The OD can't work in 1st because it doesn't have fluid pressure available to the OD until after the 1-2 shift; there is no pressure available for the OD in 1st.