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Discussion Starter #1
I just bought this truck about a month ago, it only has 90k on it. Runs and drives just fine, however the transmission behaves weird under certain circumstances. When accelerating from a stop or low speed under very light load (e.g. proceeding down a grade with very light throttle) the transmission tends to linger too long in 4th gear. Like excessively too long. Then, when it finally does shift into 5th it'll flare briefly (like its disengaged) before it makes the shift. The flare doesn't always occur, but it ALWAYS lingers in 4th gear under these very specific circumstances.

There is one location I travel through on my route to work in the morning where I stop at an intersection and make a left turn onto a long downhill grade. Usually there's slow moving traffic in front of me so my rate of acceleration is very slight. It always lingers in 4th gear until I get all the way to the bottom of the hill and level out. It aggrevates the hell out of me. :| Just wondering if anyone else ever experiences this. There is no CEL, however I have not run a scan with my scanner.
 

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I wonder if it could be a symptom of the moderately-common "transmission shudder" issue, but you did mention coming down a long grade, and I could see this being totally "normal". I would typically just leave the truck in '4' instead of '4D' so to avoid the shift entirely.

Have you had the fluid flushed? at 90K you should, despite what any dealer says.

I have seen the seemingly crazy shift patterns explained in other threads before....usually by @FJtest . Some of it is on purpose.
 

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Discussion Starter #3
No, there's no shudder or slippage going on. This is a controls issue. I suspect it's a bug in the software that is related to MAP values (slight throttle angle and no load) and ground speed. It's confused about the necessity for a shift. At least that is what it seems like to me. I was just wondering if this might be a common issue or not. I am planning to change the fluid in it. I'm reletively sure it's never been done. On a positive note, this truck does not have a hitch on it - so this trans has never been abused.
 

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I think what you are describing is the transmission programming. I find with downhills where I am not pushing on throttle that my FJ will hold its speed rather than upshifting and running away like everyone else seemingly does. For example, I may be coming down a hill at 40 mph and as long as I am not hitting the throttle will laregely maintain that speed whereas everyone else will tend to runaway and be doing 45-50 by the time they hit the bottom of the hill. People behind me probably find it annoying because they have to brake while I am continuing at the speed limit.

Most other vehicles I own would simply upshift due to small throttle opening and high vacuum and tend to 'runaway'.

Of course there may be something else going on like fluid being too low and only noticing on hills, etc or some variant of the 4-5 shudder.
 

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This is entirely normal, and is part of the A750F's sophisticated shift control algorithm.

Based on the input from many different driveline sensors, and the pattern "learned" from recent driving, the transmission will inhibit upshifting if the ECM senses reduced or closed throttle while descending a downgrade.

If the transmission "believes" the driver's intent is to maintain (or reduce) speed on the downgrade, under certain conditions it will automatically downshift to 4th or even 3rd gear.

In cases where the descent condition is not quite enough to trigger a downshift, the transmission WILL downshift instantly when the brake pedal is just touched, just enough to trigger the brake switch without invoking any actual braking.

Here is a graphic showing how the A750F "with road condition support control" responds to various load conditions.

1121276
 

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If in fact your driving habits are part of that pattern as noted..... might try and disconnect the battery for a while so to 'reset' that and let it relearn. Not sure how all that works much either!
 

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Discussion Starter #8
If in fact your driving habits are part of that pattern as noted..... might try and disconnect the battery for a while so to 'reset' that and let it relearn. Not sure how all that works much either!
Well, I just got it a few weeks ago. So it's going on someone else's driving habits most likely lol.
 

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And for your peace of mind and to be on the safe side get the transmission flushed and also install a oil cooler if there isn't one.
 

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Discussion Starter #10
I am planning to change the fluid. Adding a cooler probably isn't necessary, especially one that isn't thermostatically-controlled like I suspect a lot of people are probably installing. They're probably doing more harm than good. Modern automatic transmissions with modern lubricants in them can function just fine - long term - operating at temps upwards of 210*F. I have built lots of automatic transmissions in my time. Lots.
 

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I am planning to change the fluid. Adding a cooler probably isn't necessary, especially one that isn't thermostatically-controlled like I suspect a lot of people are probably installing. They're probably doing more harm than good. Modern automatic transmissions with modern lubricants in them can function just fine - long term - operating at temps upwards of 210*F. I have built lots of automatic transmissions in my time. Lots.

A cooler will drop your temps 40-50 degrees. Its incredible!. If you never offroad or tow, or really get stuck in traffic, then you are probably right - no need. Cooler fluid can only prolong its life though. Its also a stupid simple install. With no cooler, you are probably above 210 a good bit in the summer. With a cooler it tends to stay around engine temp at its highest.
 

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Reviewing 5 years of Torque Pro logs, and I've seen a peak torque converter outlet temperature of 244F. This is climbing long, moderate grades with an extremely light foot on the throttle (not towing).

That's why I installed at transmission fluid cooler, which immediately reduced temperatures by about 30F.

Regarding a transmission cooler potentially doing "more harm than good", please elaborate. I can't think of any real "harm" other than increased viscous drag adversely affecting fuel consumption, slightly harsher shifts, etc.

Toyota trucks that are factory equipped with true towing packages do have a thermostatically controlled combination transmission fluid heater/cooler.
 

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Since early 80s when I got my license I have been putting transmission coolers on every automatics I have owned from early Trans AM GTA to the latest FJ Cruiser I have now. This is the first time I hear that transmission cooler does harm than good. At twenty thousand my transmission oil was dark and my Torque Pro would show upwards of 230 doing hills and it was regularly 200 doing stop and go. I guess all them shuddering transmission that folks go through is the effect of using transmission coolers.
 
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