92 A4LD momentary dropping out of OD or torque converter unlocking | Ford Explorer - Ford Ranger Forums - Serious Explorations

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92 A4LD momentary dropping out of OD or torque converter unlocking

XLTByAccident

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I recently rebuilt a '92 A4LD. The donor came out of the wrecking yard, so previous operation history is unknown. I replaced all the bearings, clutches/steel, bands and the OD planet assembly due to some minor bearing damage to the mating surface. Servo's have been replaced, valve body rebuilt with an A4LD junior shift kit as well as the sonnex booster valve upgrade and installed an end plug kit. I replaced the torque converter (rebuilt one). Pretty much everything you would expect in a good rebuild. I did not replace the 3-4 shift or overdrive solenoids in the VB. They tested fine, so I re-used them. I did not replace the vacuum modulator either. It is holding vacuum and does not appear to leak. Transmission shifts normally under all loading conditions. Kick down works.

Everything seems perfect...except when I am on the freeway cruising at a constant speed. About every 3 or 4 seconds, the RPM will jump 200 to 300 RPM (goes from 2000 to 2200/2300) as if the torque converter is unlocking or it is downshifting. It immediately locks up or up-shifts again and the RPM returns to normal. 3 or 4 seconds later, it does it again.

What I am trying to determine, is the torque converter unlocking momentarily or is it doing a 4-3 shift and what would cause this? Putting the shift selector in D forces a shift to 3rd and the RPM is higher (2500 RPM) than the momentary jump. So, I don’t thing it is doing a 4-3 shift. However, it happens so fast, that it could be a 4-3 shift. The only testing that I've done so far, is a pressure test. Pressure is good in all gears under light and heavy loading (to spec). When the jump in RPM occurs, pressure is running at about 90 psi. The pressure fluctuates by about 10 psi when the jump in RPM occurs. I figure this is normal as the engine RPM is changing.

A couple of questions. How do I determine for sure if this is the torque converter unlocking or the transmission doing a 4-3 downshift momentarily and then how I can narrow down the culprit? None of the diagnostics that I've read about seem to cover this one.
 
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PopRichie77

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I think the A4LD is the same in this respect as the 5R55E. While driving at normal cruising speed touch the brake pedal, this should unlock the torque converter and the RPM will go up, if it is similar to what is happening then it is the torque converter unlocking. The brake pedal switch may be going bad or there is a short in the torque converter solenoid wiring. The insulation comes off the wiring inside the pan, a common problem and causes a short.
 
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XLTByAccident

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I did a road test today and the results were a bit puzzling. While in 4th and the torque converter was locked up, a tap on the brakes caused the engine RPM to rise by about 500. (Seems kind of high to me for disengaging a torque converter)

Downshifting manually to 3rd also raised the RPM by about 500.

The RPM rise with my problem that I'm seeing is 200 to 300 and appears to cycle at about every 3-4 seconds. It's very brief and then quickly re-engages.

I drove in 3rd for a bit and could feel the torque converter lock up and stay locked up. (no cycling). I could unlock the torque converter with a tap of the brakes (forgot to write down the number of the RPM gain).

So, my problem seems to be isolated to driving in 4th only.

I think I will need to take some voltage readings of the solenoids while driving to be sure. At this point, I suspect the 3-4 solenoid is cycling for some strange reason. Anyone have a better idea on what to look for and check?
 
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PopRichie77

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You did adjust the OD band? Seems like an electrical problem, when you rebuilt did you check the insulation on the wiring in the pan? The SSC solenoid could also be the problem.
 
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SuRrEaLNJ

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the 3-4 shift and OD are both controlled electronically, the 1-2 and 2-3 are hydrolic, could be the VSS signal dropping out. could be pcm related

adjust the bands in the trans to rule out as broken band first, as thats common
 
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XLTByAccident

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Thanks for the suggestions. The bands are new with the rebuild and adjusted to spec. I'll recheck to make sure something didn't go wrong. However, all shifts are nice and firm including when it gets to 4th. The insulation on the solenoid wires was fine when I did the rebuild. I'm thinking it is electical too and possibly the VSS signal/pcm. Can't think of anything else that would cause it to drop out of 4th momentarily (I still need to confirm that it really is 4th). I won't be able to get back to this until later next week sometime after turkey day.
 
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PopRichie77

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I think you confirmed that it is not the torque converter when you said that it stayed locked in 3rd gear. 500 RPM change could be right, it depends on the stall speed of the torque converter. Check the RPM change in 3rd gear to confirm.
 
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PopRichie77

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Sorry forgot it is a 4ALD, no SSC solenoid.
 
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Jack Flash

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are you watching your coolant temp guage when this occurs ? I had an A4LD doing weird things like yours. turned out I was losing water through the heater core and wasn't aware of it. the water was cycling causing high & low temps which was causing the tranny to momentarily downship, then upshift again.

,
,

J...stranger things have happened to me :rolleyes:
 
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XLTByAccident

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I'm finally getting back to diagnosing things. I read elsewhere on this forum where people have cut and spliced into the harness that controls the 3/4 and OD solenoid for testing purposes. I didn't want to cut into my harness so I built an inline plug with a splice. I can now simply unplug my present plug, insert the new inline plug and plug my orignal plug into it. I now have a way to easily take voltage readings of both solenoids while driving. I can also unplug my original harness and supply a voltage to cause the solenoids to manually engage (as another possible test). OK. Here's a picture to show you what I'm talking about. Not very elegant, but functional (no laughs at my splice and tape job). I took the plug and receptical from my old transmission. Not sure if I will get to do a road test tonight or not, but should have some results by the end of the week.
 

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XLTByAccident

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I did another road test with 2 volt meters hooked up. One to the torque converter and the other to the 3-4 solenoid. The voltage to both solenoids is occurring at the correct times and does not fluctuate when my RPM goes up slightly. I also rechecked the band adjustments (as someone suggested earlier) and they were right on. I think I can rule out the VSS and PCM. Having driven it some more, I've noticed that the RPM rise seems to happen (or is most noticeable) under very slight load (driving 55 and accelerating very slowing).

I’m running out of ideas on what to check next, but I’m thinking that there may be something wrong in the valve body itself and in particular the 4-3 torque demand valve may be the problem. The VB was completely rebuilt and I put in an A4LD Junior shift kit in it. Also put in the Sonix boost valve as well as an end plug kit.

Before I drop the valve body, any ideas on what else to check?
 
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MrShorty

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The voltage to both solenoids is occurring at the correct times and does not fluctuate when my RPM goes up slightly.
This suggests to me that the problem is not in the electronic controls for the transmission shifts. Suggests that it is something hydraulic/mechanical inside the transmission.
 
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XLTByAccident

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Mystery solved. It turns out that the band adjustment is different if you have single or double wrap design bands. This was a production change sometime in ’92 where Ford went back to the original design and dropped the double band design. I missed this point in the ATSG update manual and was adjusting the OD band for a double wrap design which is 3-1/2 turns out. Turns out my transmission (which is a ’92) had the production change and uses the old style bands and needs to be adjusted 2 turns out. I re-adjusted the bands again (this time correctly!) and everything is perfect.

What was apparently happing at 3-1/2 turns out, I was getting an intermittent slip while under a slight load. It would slip, then grab.
 
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