Sudden downshifting with A442F and help locating transmission wiring

[varenc]

hey folks!

I'm on a weekend trip in Truckee and have a new problem on my '93 FZJ80 with the A442F automatic transmission (there's also an HDT-1 engine swap). I'm not too knowledgeable about cruisers so forgive me if my questions are a bit easy.

So I'm getting sudden downshifting when driving on the highway. It seems like it'll suddenly go down a gear, I'll watch the RPMs rev, and then it'll jump back up to the correct gear. Happening maybe once a minute or so and it's pretty jarring and can feel unsafe. The rpms aren't redlining so it seems like it's only going form 4th to 3rd, but if I turn off the O/D it seems to pop form 3rd to 2nd randomly as well. (or maybe it's always jumping the 2nd?)

I called a transmission shop, and they can't look at it soon but they suggested the problem might be as simple as a corroded transmission wiring harness. That sound like a possible culprit? I want to try their advice, disconnect the wiring, clean and check the wires a bit, and then try again.

Now my stupid question: Where in my engine compartment can I actually find the transmission wiring harness? The Toyota A442F manual just says to do this:

Unfortunately, that's not quite enough info for me.

I also know from the manual the wiring should look something like this:

But looking around my engine I wasn't able to locate this. Any tips on where in the compartment I can find that connector? Will it involve removing other parts of the engine to make it accessible? If anyone happens to have a picture of their transmission's wiring's location around, that'd be super helpful.

I'm traveling in Truckee at the moment and just hoping I fix this at least enough to make it back home to the bay area where I can really dig in on the problem.

hope everyone's rigs are holding up better than mine!
cheers

 

[ppc]

You are in the mountains at high elevation. Sounds normal to me. Not only will the transmission downshift/upshift but the torque convertor is going to unlock/lock both which cause RPMs to jump.

 

[varenc]

I've done this drive many times in my rig and never gotten this behavior before! The downshifts are very sudden and correct themselves a second later even when on flat ground. I'm fairly sure it's not normal behavior and the sudden jerks cause a sharp deceleration which can feel unsafe on the highway.

 

[thatcabledude]

About midway up the trans on the driver side.

 

[MidwayLC80]

Hi,
From your original post, I'm assuming this happens on a straight flat road and you did say 1-HDT
When this happened to me it was the throttle position sensor, sat on top of the injection pump.
Basically the carbon track is worn out, (think crackly volume on your Hi-Fi). Gearbox ECU doesn't know what the throttle opening is.
Mine wore out at 170K, next one still going at 351K
Hope this helps.

 

[Sd1975]

Hi,
From your original post, I'm assuming this happens on a straight flat road and you did say 1-HDT
When this happened to me it was the throttle position sensor, sat on top of the injection pump.
Basically the carbon track is worn out, (think crackly volume on your Hi-Fi). Gearbox ECU doesn't know what the throttle opening is.
Mine wore out at 170K, next one still going at 351K
Hope this helps.

Reviving this thread as I'm over a thousand miles from home with the family on vacation and mine is doing this bad. We are in a hotel room as I type because I didn't want to continue. Was it the TPS?

 

[Xland]

I’m encountering this exact same issue. My 1994 80 down shifts suddenly then recovers . Happens more frequently when I’m light on the throttle, maybe close to a down shift. Also seems associated with left turns. Might just be the light throttle when turning. Things I’ve checked:
-transmission fluid hot running level (perfect)
-kickdown cable adjustment (perfect)
-TPS (perfect)

Have others resolved their scary down shifts? What was found to be the issue??

 

[Kernal]

FWIW the A442F Automatic transmission has more issues with it's solenoids (causing odd shifting behavior) compared to the later A343F.

 

[bski90]

This isn't totally relevant, however I had a Honda Accord that exhibited the same behavior on the highway, eventually it wouldn't upshift and then keep downshifting. Eventually it wouldn't go past first gear. The issue was the solenoids would clog with clutch material. This sounds somewhat similar to what you're experiencing, and it sounds like you may need to replace the solenoids.

My A442F would shift terribly also, it would start in 2nd gear at times. Replacing the solenoids fixed all issues. Cheap and fairly easy job.

 

[Xland]

I had a full motor reseal done after developing the dreaded timing cover pry point leak. My transmission had run cool and flawless prior to that. Frustrating because it seems like a setting/adjustment issue.

 

[Xland]

I spent a ton of time researching solenoids and was about to purchase new ones when I found another A442F thread here on mud detailing how the transmission throttle cable tends to stretch and the gap between the rubber stopper and the nub on the cable is often bigger than the FSM details. I began inching mine out a little at a time and noticed at the point where my shift lockup began to firm slightly, the nasty slip behavior vanished. That’s all it was
EDIT: classically, that’s not all it was. The No.2 speed sensor on your A442F will trigger crazy downshift behavior if the wiring disconnects. Posting a final diagnosis and photos below:

 

[ubguessin]

I spent a ton of time researching solenoids and was about to purchase new ones when I found another A442F thread here on mud detailing how the transmission throttle cable tends to stretch and the gap between the rubber stopper and the nub on the cable is often bigger than the FSM details. I began inching mine out a little at a time and noticed at the point where my shift lockup began to firm slightly, the nasty slip behavior vanished. That’s all it was

So is your cable tighter or looser. Like does it have flex in it or not? I am have these same issues

 

[Xland]

So is your cable tighter or looser. Like does it have flex in it or not? I am have these same issues

I lightly tightened the cable (less slack) a very small amount at a time until I felt the shifts firm up. That helped around town but, be warned, it REALLY firms up the shifts in low range.. like neck-snapping firm. It was actually the No.2 speed sensor wire on the A442F periodically disconnecting that produced the scary down shifts. I’ll edit my post above, and post some pictures of what I found.

 

[Xland]

My crazy downshifts began after I had my motor out for a timing chain cover reseal. The sad shorter story is that I could never find a clear cause. Replaced my TPS, No.1 and No.2 speed sensors, shift solenoids, and trans fluid and filter with no improvement. Figured my friction plates in the trans were toast and just slipping. Started looking at rebuild/replace options, and did a bit more research on available kits. Found some discussions on Mud about the gear selection sensor and issues with the electrical connection to the main harness rotting out due to its location near the wheel well. Checked mine out and discovered it had been ripped apart when the shop pulled my motor. The socket and retainer were broken. I got the ohm meter out and started testing wires back to the TPS, selection sensor, and speed sensors. I found an intermittent open circuit in my No.2 speed sensor wiring. It was touching just enough to run normally until the harness shook or twisted. I built a replacement wire and swapped it in. Problem ACTUALLY solved.

 

[Xland]

 

[Xland]

 

[Xland]

 

[ubguessin]

My crazy downshifts began after I had my motor out for a timing chain cover reseal. The sad shorter story is that I could never find a clear cause. Replaced my TPS, No.1 and No.2 speed sensors, shift solenoids, and trans fluid and filter with no improvement. Figured my friction plates in the trans were toast and just slipping. Started looking at rebuild/replace options, and did a bit more research on available kits. Found some discussions on Mud about the gear selection sensor and issues with the electrical connection to the main harness rotting out due to its location near the wheel well. Checked mine out and discovered it had been ripped apart when the shop pulled my motor. The socket and retainer were broken. I got the ohm meter out and started testing wires back to the TPS, selection sensor, and speed sensors. I found an intermittent open circuit in my No.2 speed sensor wiring. It was touching just enough to run normally until the harness shook or twisted. I built a replacement wire and swapped it in. Problem ACTUALLY solved.

Thank you very much for this write up and pics. I am waiting for my TPS to arrive then will definitely have to check out my wiring next. I just had a rebuilt motor and trans put in.
Originaly my trans was not going into lockup. And now it's "erraticly" shifting in and out of lockup and som gears between 18-25mph/ 35-45mph and 50-60mph

 

[Xland]

If you’re suffering from strange shift behavior, start at those connections to the transmission. They’re right next to the wheel well and very likely corroded.. mine were busted..

 

[Xland]

Thank you very much for this write up and pics. I am waiting for my TPS to arrive then will definitely have to check out my wiring next. I just had a rebuilt motor and trans put in.
Originaly my trans was not going into lockup. And now it's "erraticly" shifting in and out of lockup and som gears between 18-25mph/ 35-45mph and 50-60mph

Mine did the same thing after it worsened. it would jump in and out of lockup. And flare really bad when I hit bumps.