A4LD Servos and cover seals | Ford Explorer Forums - Serious Explorations

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A4LD Servos and cover seals

Bruce Rock

Well-Known Member
December 31, 2001
Reaction score
City, State
Kaukauna, Wisconsin
Year, Model & Trim Level
'94 XLT
My '94 4WD 4.0 Explorer (in the family since new) with about 170,00 miles on it was leaking transmission fluid from the servo covers. When checking the transmission fluid level before starting it would be good but if the transmission started to slip, I'd check it again and would have to add fluid. Than it would shift as it should.

After reading about the heat damage done to the servos and cover seals by the catalytic converter, I ordered new servos and cover seals thinking the rubber must have hardened and became brittle. I wasn't able to read the letters on the servo covers so I ordered BA/BB and AA/AB servos from WIT after reading Glacier991's A4LD rebuild diary (Post 51 of part 3, 2nd half - Reassembly). WIT sells two different series for the five different sizes of pistons. The A series stands for Alternate part and the D series stands for Dealer part. I went with the A series.

Not having a hoist, I took it to a shop to replace the servos and install new o-rings (also from WIT) on the servo covers. One of the o-rings for the servo covers was broken, don't know if it happened during removal or before, but both still had some flex to them as did the sealing lip on the used servos. Neither were rock hard as I expected.

They said first and reverse work but the transmission won't shift out of first and runs about 4,000 rpm at about 35 mph. The shop will be closed Monday and Tuesday. I will be going there Wednesday to assist in trouble shooting and would like to compile a list of what the problem could be.

1) One thing that concerns me is that the tech who did the work said he had no problem getting the covers on and the snap rings in place. This with the transmission in place but the Cat removed. I was under the impression this would be a difficult and leverage or a special tool would be required. Since the transmission shifted good before the change I wonder if removing the servos could cause the APPLY STRUTS to come loose without backing off of the adjusting screws for the bands?

2) Are the tolerances on servos so loose that the bands need to be adjusted after changing them even if the shifting was good before the change?

3) Has anyone had problems with the cheaper A series servos from WIT?

4) The modulator was also changed. The tech had problems getting the old one out (it was in two pieces on the bench with the old modulator pin) I'm assuming the new pin was installed. The new one, like the old, is not adjustable so I don't see a problem there.

Anything I missed that should be looked at? If anyone has a strong opinion where I should look first, that would be appreciated also. If it weren't for this group, I would have had to get rid of this Explorer long ago. A Big Thank You to all who contribute to this site especially Glacier991!

The bands have to be adjusted after the servos are replaced. Each servo has a different apply strut as well as a different spring. Each spring is color coded to represent a different amount of appy pressure. The apply struts have a code written on them.

Thanks for your Ultra quick reply


Thank you for your quick reply.

Your acknowledgement that the bands have to be adjusted after servo replacement along with your reputation leads me to believe it will be a simple fix. I slept a lot better last night.

If that doesn't do the trick, I'll look at your warning about dirt causing the modulator pin to stick.