a4ld lost OD, possible easy fix? ha-ha

[tac0meat]

I lost my overdrive a few years ago. Everything else works fine, simply no 4th gear. Putting the trans in D or OD makes no difference, TC locks up around 55 like it always has, just no 3-4 shift. There is no hesitation or noise at 45 when it would normally shift into 4th or any indication of an attempted shift into 4th. OD acts the same as D, like they are the same setting. Selecting 2 or L will do just what think, either put the trans in 2nd or first and hold it there. I have had it rebuilt many times prior to losing OD, but beyond the loss of 4th gear, the trans has been solid, shifts fine.

I have been seriously contemplating a manual swap, but if a relatively easy/cheap fix will get my OD back, then it will make highway travel a bit more friendly until I get all the parts together for the swap.

My hope is its the 3-4 solenoid or maybe some kind of loose wire? I have had the fluid changed and it is clean (no metal shavings). I guess my question is, is there a way I can diagnose and possibly fix this in my driveway? and how would i go about determining if its a solenoid/something simple, or something that will require a rebuild?

 

[Vargas]

3-4 solenoid is a $35 part. I don't if there is a diagnostic for it or not. If not, it's a relatively cheap guess.

 

[tac0meat]

How bad is it to change out the solenoid? I am thumbing through my shop manuals and it looks like i can get to it just by dropping the pan. Is it something I can change without having to drop the whole valve body? If its something I can knock out in a couple of hours, it might well be worth a shot.

 

[Vargas]

I have no idea how much is involved in changing it. I did a quick search (A4LD OD solenoid) and learned a couple of things. The 3-4 shift is commanded by the PCM, not by the internals of the A4LD. So other things can cause the loss of OD, not just transmission components. Are you sure the solenoid is plugged in? I don't know where to look on the case to find it. If it is a problem internally, you may want to read up on adjusting the OD band. OD drum or band failure is more common than solenoid failure.

 

[MrShorty]

The 3-4 shift solenoid circuit is a pretty basic DC circuit. It shouldn't be overly difficult for someone with some basic understanding DC circuitry, a wiring diagram, and a voltmeter to track down an electrical problem (if any) in that circuit.

I'd probably start by putting a voltmeter across the solenoid, then put the PCM in output state test mode (see my "notes on pulling EEC-IV codes" thread), then see if you can see the PCM changing the solenoid's state (on - off).

 

[Jack Flash]

Since you're gonna drop the pan to get to the solenoid, look for debris in the pan. I've seen a lot of OD units that have mechanical problems. You say it has been overhauled...was the OD servo replaced ?

I'm also guessing that the OD band was replaced in the overhaul. Has it been readjusted lately.

Look in the stickies for the procedure to test the OD solenoid.

,
,

J..all my old mind can think of at this hour.

 

[tac0meat]

I like the idea of testing to make sure it is getting a signal before I tear into it. From what I can tell, there are only 2 electrically controlled functions in the transmission, the 3-4 shift and the TC lockup, both of which come through the same connector on the outside of the trans. I haven't gotten under there yet because it has been poor weather and that job thing is taking up a lot of time. I have looked over mrshorty's post on the EEC-IV codes and putting it in test mode.

If I understand this correctly, I can pull the codes, and I might possibly get an error relating to a transmission or other fault that might cause the transmission to not shift. If I get no codes (pass/11/111), then I can enter the test mode and signal the solenoid. It looks as if I just push the throttle while in the test mode to cycle the various solenoids, but how do I know when I have activated (or at least sent a signal to) the 3-4 solenoid? will the CIL flash to indicate which function has been activated?

 

[MrShorty]

It looks as if I just push the throttle while in the test mode to cycle the various solenoids, but how do I know when I have activated (or at least sent a signal to) the 3-4 solenoid? will the CIL flash to indicate which function has been activated?

It's been a while since I've used the output state test, but I think the CEL turns on and off with each press of the throttle just like the other solenoids. Every tested solenoid is cycles with each press of the throttle, so there really isn't a question of knowing when it has tested the 3-4 solenoid. The 3-4 solenoid should cycle each time you press the throttle. If you have your voltmeter hooked up to measure voltage drop across the solenoid, you should see it cycle from 12V to 0V and then 0V to 12V as you press the throttle.

Does that make it as clear as mud?

 

[tac0meat]

It's been a while since I've used the output state test, but I think the CEL turns on and off with each press of the throttle just like the other solenoids. Every tested solenoid is cycles with each press of the throttle, so there really isn't a question of knowing when it has tested the 3-4 solenoid. The 3-4 solenoid should cycle each time you press the throttle. If you have your voltmeter hooked up to measure voltage drop across the solenoid, you should see it cycle from 12V to 0V and then 0V to 12V as you press the throttle.

Does that make it as clear as mud?

So, it basically cycles all the solenoids at once?

I ran the codes this afternoon and got 11 in the KOEO test and 11 in the KOER test. it took me a few tries to figure it out, but man I wish I had known about running the codes years back. I pulled out my wiring diagram and I located the harness under the hood (it was pretty hot and greasy underneath). I didn't check the voltage, but tested the solenoid with my DVM and came up with 33 ohms, which I think is within range.

I am starting to feel that it is most likely the 3-4 solenoid (or something else internal to the transmission) because the TC lockup still works fine.

 

[IronIndian]

Any updates?

 

[SuRrEaLNJ]

adjust the bands. if you can adjust the bands then that most likely rules out band breakage.

when i lost my od it was because of an internal fault in the pcm causing it to see erratic vss signals. something to keep in mind

 

[MrShorty]

So, it basically cycles all the solenoids at once?

Yes.

33 ohms through the solenoid suggests that the circuit is intact. I'd probably still run the output state test to make sure the PCM can communicate with the solenoid.

 

[tac0meat]

I have been going non-stop the past week or so, but I am going to try and get back under there in the next couple of days to test the signal to the solenoid and ive read all about adjusting the OD bands and will give that a shot too. I did some light towing this weekend and ran it in OD instead of D, hoping to feel any kind of shudder, indicating that the OD band might not be tight enough.

 

[tac0meat]

finally got out and tried to adjust my OD band. I torqued it to 120 inch pounds and backed it off 3.5 turns. Tightened the lock nut, and took it for a drive, and still no OD.

While driving, I started to move my shifter between D and OD while driving along at about 60. I couldn't feel any difference when I shifted from D to OD, but when going from OD to D, I could feel a very slight change. It felt like a very slight, very subtle tapping of the brakes. Again, this was very very subtle. I don't recall if it ever did this before the adjustment, so it might not be anything new.

I am wondering if maybe I should have backed it off 2 turns instead of 3.5? Mine is a 91, so it should have a double wrapped band, but it has been rebuilt several times in the past 10 years, so is it possible that it now has a single wrapped band?

 

[Wakeboy1337]

The slight change you felt was the torque converter I think.