92 Explorer: No Overdrive 3/4 Solenoid?

[strikefast]

92 Explorer: No Overdrive 3/4 Solenoid bad or screen clogged?

I have a '92 Explorer 4x4 4.0L with the A4LD transmission. The overdrive isn't working, but the torque converter still locks in 3rd gear at highway speed with the gear selector in D (and OD, for that matter, but D just double-confirms that what I'm observing isn't the OD shift). There is no engine braking with the gear selector in 1, 2, or D. The transmission shifts and behaves fine otherwise.

I've read in other posts that one possible cause of the OD problem might be the 3/4 shift solenoid, or the wiring/signaling to it. (Thanks a TON to Glacier and MrShorty for their numerous posts on this topic!) Using the wiring diagrams on Autozone's website as a guide, I checked the 3/4 (and TCC) solenoids via the appropriate wiring harness that sits under the hood on the driver-side front fender well. Normal resistance of ~30 ohms was found across both solenoids. No leads were shorted to ground. So, wiring integrity seems to be OK.

The KOEO test returns 111 codes (all OK). I used the output state test to investigate further. It appears to me that the resistance between the purple/yellow and orange/yellow wires on the computer side of the connector and ground is ~70 ohms when de-energized, and drops to 0 when energized. This seems fine to me. KOER test also returns 111's. The red common from the computer side is supplying +12V.

Based on the output state test, it looks like the computer can signal the shift. As for whether it chooses to, that's more difficult for me to tell since I don't have a breakout box, etc. I don't know if it's realistic to hook up my cheap analog sweep multimeter to the computer wiring harness inside the passenger kick panel for a road test or not. Cruise control works, so I think the speed sensor is OK.

The results of the +12V click tests are quite interesting, in my opinion. I applied +12V to the common red lead. Results of grounding each of the following:
orange/yellow (3/4): audible click on de-energize, none on energize
purple/yellow (TCC): no audible click on either energize or de-energize

I feel 99% certain the TCC solenoid works based on my driving observations of torque converter lockup, even though I can't hear it "click" during the above test. This is interesting, because I expected the opposite results based on the symptoms (i.e., silent 3/4, and audible TCC solenoid). I have verified the results a few times. Does a click really mean that the solenoid is working properly? For example, I have had starter solenoids go bad on other vehicles where they would click loudly without actually energizing the starter...

In any case, I'm less inclined to think that the problem is electrical based on what I've done so far. To me, it seems more likely to be a mechanical malfunction in the solenoid, or something else wrong within the transmission.

My '92 was manufactured 10/91: I wonder if that makes it old enough to definitely have a screen around the 3/4 solenoid? If so, perhaps it is plugged as per Glacier's experiences... Does anyone know when Ford stopped using the version with the screen?

I realize that many other things could be causing my overdrive problems as well, but I was trying to focus on something short of a full overhaul/rebuild. Taking the valve body down to inspect/change the solenoid scares me a bit since I've never done any transmission work other than dropping the pan to change the filter/fluid and replacing the pan gasket. The thought of those check balls falling out and rolling across the floor turns my stomach!

I'm struggling to recall now, but it seems like there was a period of time where the OD struggled to engage before it stopped working totally. In other words, you almost had to let off the gas completely to get the OD shift, but my memory is faint there. Not sure if that might be indicative of a screen that was slowly getting plugged up...

I'd like to think that the lack of engine braking is not directly related to the OD issue, although I guess it could be. Fortunately, I don't live in a mountainous area, so I don't miss the engine braking ;-) I imagine that fixing the engine braking problem would almost certainly involve more serious transmission work. Neither OD nor engine braking have worked for at least 2-3 years now. I can't say whether both problems appeared simultaneously or not. Other than the modulator problem I also learned about on the site (and fixed), I've had no other trouble with the transmission and have treated it pretty well (no off-road 4x4 driving, light on the gas pedal, etc.)

Questions:
a) Is there any way to diagnose a plugged screen other than by visual inspection? In other words, I presume the electrical properties/tests would all check out "normal" in that case. Does the above sound like a scenario where this might be happening?
b) Any way to tell whether my 3/4 solenoid has a screen other than by visual inspection?
c) Can these transmission solenoids click, yet still be faulty?
d) Any point in further diagnosing whether the computer chooses to signal a 3/4 shift?

Sorry for the long post, but wanted to get all the available info out there in one shot.

Any advice or thoughts?

 

[BrooklynBay]

No engine braking could be a broken one way sprag, and would require a rebuild. No OD could be the result of many things. There is an OD servo on the side of the transmission that gets rotted out after a period of time from the heat of the exhaust. The OD band could need an adjustment. The PCM takes inputs from the VSS, TPS, and brake on/off switch to control the OD, and TCC to engage, and disengage. The solenoid could be clogged as well as the screen, and passage ways in the valve body. Start with a band adjustment. That servo is very difficult to replace while the transmission is still in the vehicle, unless you remove the catalytic converter. You've mentioned a lot of things in the above description, except how many miles you have, if this is the original transmission, and how regularly you've replaced the fluid, and filter. By the way, the valve body balls won't fall out if you remove the valve body, only if you open up the valve body. There are a few torx head screws holding it together.

 

[strikefast]

Thanks for sharing your insight, BrooklynBay. Let me address a few of the areas you mentioned. The vehicle has 254K miles currently. It has been "in the family" since it had about 55K and was <2 years old (it saw a lot of highway mileage early on as a corp. lease vehicle). It is the original transmission as far as I know (pretty sure)--hasn't been replaced/rebuilt by anyone after the 55K mark anyway. I have had it for about 6-7 years, and put about 12K/year on it. I can't speak to regular fluid/filter flushes throughout its life, but I did do it myself about 5 years ago (used a TopSider suction tank to draw out as much fluid as possible from the fill tube, dropped the pan, changed the filter/pan gasket, cleaned the pan magnet, and did a few more fluid exchanges with the TopSider once I got it back together to flush it out well). The old fluid did not have that awful smell that you can encounter when the fluid gets "burned"--never a good sign for a transmission when you run into that. The transmission had been and continued to work fine at that point, and there were no "parts" or anything lying in the pan . Sometime after that, it started using a fair amount of fluid, and so by keeping it filled up it effectively kept the fluid flushed/fresh over time. I figured it had been going out the overflow tube or something. (I recently learned this was due to a bad modulator diaphragm, which I fixed--no more fluid consumption ) The transmission pan gasket still doesn't leak a drop (wish I could say the same for the oil gaskets in the engine--the rear one leaks Mobil 1 like a sieve!)

Now that the transmission fluid consumption is fixed, and with what I have learned in these forums, it seems like a good time to drop the pan again for fluid maintenance. However, that also seems like the best time to attempt a minor repair if indeed it is something within my ability.

I do remember a few threads about that OD band. I see a couple in your useful threads section. Given that mine is a '92, I wonder if I have a single or double OD band (-2 or -3.5 turns?) I'd need to find an in-lb torque wrench it seems...

 

[BrooklynBay]

You could find out if there is a single, or double band by determining when it was manufactured. Look at the sticker on the inside of the driver's side near the door. You do have very high mileage for that transmission. If you decide to drop the valve body to rebuild it, then you could get a better look at that band from the bottom. There are some upgrades that are available for the valve body that you might want to consider, such as 2 kinds of shift kits, anti shudder spring, high ratio boost valve with O ring seals, new TCC filter, manual valve index sleeve, valve body end caps with O rings, and a Transtec viton seal kit for the
low/reverse servo.

 

[BrooklynBay]

This is from my band specification chart thread:

Band specification chart.

--------------------------------------------------------------------------------

A4LD:
All Intermediate bands are single wrap. Single wrap band = 2.0 turns back.

1990-1992 Overdrive bands are double wrap, except in mid 1992, which went back to the single wrap band. Double wrap band = 3.5 turns back.

 

[strikefast]

The driver-side door label indicates it was made 10/91. Not sure if that qualifies it as a "mid-92" or not... Yes, I do feel I've had pretty good luck with the transmission so far (knock on wood), given some of the stories/mileage I've seen on the forums. It has a lot of highway miles, though, and almost zero towing/offroad operation. I guess that has helped me get this far with it.

I appreciate the suggestions on the upgrades. If I do decide to pull the VB, I'd probably consider it a resounding success if I could get the Z-link and other things to fit back together properly I was just looking at bulkpart.com, and would definitely replace the TCC filter. Guess I'd need new upper/lower VB gaskets as well. I'd probably install a new 3/4 solenoid, but likely stop short of a full VB rebuild since this is still my primary vehicle. Might change my mind if I get something else and keep it, though.

Does the low/reverse servo need to come out to remove the VB? I suppose getting the ATSC manual might be a good idea as well, in the absence of having any other manuals on the subject (besides the resources on this forum, of course!)

 

[BrooklynBay]

There is the regular ATSG manual, and the update manual. It is a good idea to buy both. Ford makes a 3 ring binder with a hard covered blue cover. That has pretty much everything. The ATSG manual is handy for doing the actual rebuild. It has a lot of step by step diagrams. You do have to drop the low/reverse servo, but it's not a scary thing. It is held in place by a metal cover with 4 bolts, and a hard gasket under the cover. You will see this servo come out with a big spring. The servo has 2 seals. One is big, and the other is small. If you are already rebuilding the VB, then you might as well rebuild the whole thing. There are some places that you could buy an already rebuilt VB, but I think you will be better off rebuilding it on your own. You will then know exactly what is being upgraded in it.