AOD slipping in 4th

my 1988 crown victoria lx with 5.0L and AOD trans.

Yesterday, detected engine flare in 4th on acceleration. No slipping in m1 , m2, m3 or R. Completes all shifts normally. Trans fluid is in great condition and at proper level.


Want to air check the overdrive band servo...Can I do it without the special test plate tool? If I can't; was going to change it out the servo.

Is there anything else I should check or replace while the valve body is off?
If the servo doesn't fix it I will be pulling the trans and rebuilding.

Any tips or advice is appreciated as I'm not familiar with ford's or ford trans.

Sounds like a worn band. They're usually the first to go on these transmissions considering the band is tiny for the power and weight it has to handle.

If you opt to rebuild, you can put in a lighter servo spring on the OD band servo. It will cause 4th to engage quicker and therefore less wear on the band.

Be careful not to lose the valve body check balls and make sure you know where they go after you remove the separator plate.

I'm not 100% sure on an AOD but you may be able to do a certain number of tweaks on the valve body separator plate and the 1-2 and 2-3 accumulators to increase shift firmness if desired. (google J-mod). It really gets rid of that excess, unnecessary clutch engagement slipping which keeps things cooler and makes the clutches last longer.

Will look into the jmod, servo spring and other upgrades at rebuild time. Can't get to it untill May so will let you know what I find when its all apart. Time start pricing stuff out I guess.

I will pull off the valve body this weekend and see if anything jumps out. Will the band stay in place when I pull out the o/d servo?

The car has 230 000km and is 23 years old so I can't complain.

Thanks for the advice.

If you remove the servo, the band will have to be pushed back into place with a screwdriver through another hole to put pressure on it so the servo can grab it when re-installing.

finally had time to check this out. Was something easy; (when does that happen) the throttle valve cable retainer had broken off from the throttle linkage. reattached it and everything ok.

Should have clued into the early upshifts and late downshifts. At least no trans rebuild needed...yet