Sudden high speed shift (1 Viewer)

[MontereyHZJ77]

Hey everyone! Long time viewer, but just signed up as I recently took possession of a 94 HZJ77. The truck has been amazing so far, but recently and suddenly developed what I think is an issue. About three weeks ago, while cruising around 60-70 kph the truck started to shift odd. A/C was on and outside temp approx 90F
The truck seemed to have shifted into a higher gear. RPMs went from around 2100 to 1200 and back up to 2100. This happened several more times all within 2-10 seconds of each other. It almost feels like the truck is upshifting and does seem to gain a small amount of power, but not much, and definitely none going uphill. Turning O/D off eliminates the problem.

This has continued nearly every day since and happens no matter what now: if A/c is off, outside temps are cooler, rain/shine, all of that. Usually it only occurs on the expressway at speeds above 60 kph and all of the time at 90.

The transmission fluid was disgusting- not sure if the previous owner ever changed it. I had the fluid replaced by Toyota (here in Japan) this weekend, but it did not improve anything around this issue. It actually caused the problem to present itself sooner into the drive, even with a/c off.

I have been searching all over the interwebs, including here, but cannot find the exact issue I am experiencing. Hoping to sort out any bugs before I bring the truck stateside next year.

Anyone else seen something like this?

 

[Blomdala]

Hey everyone! Long time viewer, but just signed up as I recently took possession of a 94 HZJ77. The truck has been amazing so far, but recently and suddenly developed what I think is an issue. About three weeks ago, while cruising around 60-70 kph the truck started to shift odd. A/C was on and outside temp approx 90F
The truck seemed to have shifted into a higher gear. RPMs went from around 2100 to 1200 and back up to 2100. This happened several more times all within 2-10 seconds of each other. It almost feels like the truck is upshifting and does seem to gain a small amount of power, but not much, and definitely none going uphill. Turning O/D off eliminates the problem.

This has continued nearly every day since and happens no matter what now: if A/c is off, outside temps are cooler, rain/shine, all of that. Usually it only occurs on the expressway at speeds above 60 kph and all of the time at 90.

The transmission fluid was disgusting- not sure if the previous owner ever changed it. I had the fluid replaced by Toyota (here in Japan) this weekend, but it did not improve anything around this issue. It actually caused the problem to present itself sooner into the drive, even with a/c off.

I have been searching all over the interwebs, including here, but cannot find the exact issue I am experiencing. Hoping to sort out any bugs before I bring the truck stateside next year.

Anyone else seen something like this?

Based on your info, you need look into the control system. You said turning O/D off stops the issue, so either something is confused about commending that solenoid, or that solenoid/connection is unreliable. I would check your TPS on the injection pump, and the cable to the transmission that is mounted there to make sure that those easy items are happy. Baseline the transmission control system then go from there. To go further, you are going to have to start disassembling things.

 

[MontereyHZJ77]

Been a while, but finally have an update for this problem.

Truck eventually lost 3rd and 4th gear and was unusable. Had a mechanic here in Japan run a full check on the transmission. After about two weeks in the shop, mechanic discovered that the problem was something with destroyed wiring in the transmission. Wiring was replaced and problem has been solved. Truck runs like a dream now.