A4LD overdrive problems

[XploreAlaska]

So I don't have OD, and think it may be the 3/4 shift solenoid. Did a little searching on here couldn't really find what I was looking for. I've read the sticky about valve body rebuilds and am havin a hard time picturing what I'm going to be looking for (I've never worked on trannys before, gotta start somewhere) so here's my question, first, what does this solenoid look like from the outside? How do I test it? When (if) I find it to be faulty, after you drop the pan, where do I go from there?? I've got the new solenoid, and a gasket for the pan, what other gaskets or O-rings will I be needing? I've got till next weekend to scrape all my parts together, going to spend next saterday working on it.

 

[BrooklynBay]

Test the solenoid with an ohm meter at the 3 prong connector to see if it's within 25-40 ohms. Test your TPS, and VSS. The PCM needs to make a decision when to command a ground signal to the 3-4 shift solenoid. Other possibilities could be a leaking overdrive servo, out of spec or broken band, leaking modulator, valve body issue, defective valve body gaskets, loose valve body bolts, defective 3-4 shift solenoid or internal damage to the front overdrive section.

 

[Jack Flash]

if you're going to drop the pan and the valve body, you will need 2 valve body gaskets (an upper and a lower). you will also have to drop the rear servo, so I would buy a new gasket and replace the orings on the rear servo.

"an ounce of prevention..."

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J

 

[BrooklynBay]

They make 2 thicknesses for those gaskets. I like to use the thinker ones. They are mostly used on older valve bodies which might be slightly irregular.

 

[NiceExploder]

couple overdrive questions

can anyone explain a little further about the OD servo, and the modulator? How to fix? What symptoms come with these parts going bad? I think I'm all set on the other stuff I've seen mentioned on this site(valve body rebuild, shift corr. kit, solinoids, band adjustments, etc.)

 

[BrooklynBay]

The servos apply pressure to engage the bands. A dried out servo will either not engage the band or apply partial pressure, then slowly pinch off. It might feel a little like a shift flare where there is a high RPM then a slip after engagement. The modulator is vacuum regulated to assist with shifts along with the kickdown cable linkage. Bands, some modulators, and the kickdown cable are adjustable. The low/reverse servo is not adjustable on the A4LD. Some transmissions such as the AOD, AODE, and 4R70W don't have adjustable bands.