Weird Shift behavior between 4th and 5th (Automatic)

I've been noticing everyday when I get on the freeway, at mid acceleration, maybe 2500 rpm in 4th gear, right before it shifts into 5th, it goes into neutral, I dont take my foot off the gas, engine goes up to 3000rpm then the ecm cuts power to the engine and it shifts into 5th.

Doesn't do this in any other gear, or at slower accelerations through 5th. It also seems to only do it in the morning. The shift isnt hard or anything, its just a surge in rpm between 4th and 5th but still a smooth shift.

What I've just become accustomed to is putting the shifter in 4th, and right as I move the shifter to 5th I let off the gas and it shifts normally.

This seems kinda similar to the behavior of the transmission at WOT. Where it will cut engine power for a split second between shifts?

I did a couple back to back fluid drain and refills about 10k ago. Went through the whole checking fluid level process as well.

I'm guessing this isnt normal behavior?

 

I'd say not normal.

First thing I'd check is the fluid level using the Temp Check mode. Adjust as needed.

After that, off to Toyota or a tranny shop.

Mileage?

 

Get it flashed. My is doing the same but I’m too lazy to fix it

 

Check fluid level.

a 4 to 5th flare can be common, its possible that at that acceleration you end up in 4th lockup, then before it shifts to 5th it lazily unlocks the torque converter and then shifts to 5th causing the flare.

The 4 to 5th flare is even more common on the supercharged trucks.

 

Good to know. Mine is supercharged

 

Oh yeah, the 4th to 5th flare around moderate acceleration on the stock TRD calibration for the supercharger is well known.

 

Mileage: 160k

I just did a level check using the temp check mode. Added fluid until it poured out the overflow, waiting until trickle and closed, all at the correct temp.

 

Where and/or with what tool?

What specifically needs to be adjusted here?

 

Did you do the proper procedure for the fluid level check? Spark notes are basically: cycle through every gear while running, reach the proper temp, and then keep the truck idling on level ground while taking out the check plug?

Edit to clarify the check plug, not fill plug

 

Correct, I am sure the level is correct.

What is actually happening that causes the rpm to surge when shifting? And is the computer trying to correct by cutting power? Would this eventually destroy the transmission? Would letting up on the gas before the shift prolong the life of the transmision?

 

Its a combination of things. The biggest being that as far as i can tell on our 5 speed autos by looking at the whitepapers, the shift between 4 and 5 "goes through neutral". Meaning, unlike the other previous 4 gears where the shifts are a clamping of a band or clutch pack, the shift between 4 and 5 actually releases everything for a split moment where you have a neutral condition then goes into 5th. Most of the time this is seamless and never felt. But given the PERFECT combination of load and throttle input you get what you describe, a shift flare. A tune via HPtuners can adjust the trans torque table to reduce the propensity for this to happen quite a bit.

Will it hurt anything as it stands, likely not, its not a flare under high load conditions (like at WOT), and doesnt occur every time.

 

Awesome, that makes me feel better. I try to monitor fluid levels and the temperatures are always at 130F in winter, and never above 175F in the summer. So I feel my transmission life should be fairly long. I will continue to release the throttle in the 4 to 5 shift to ensure it remains as seamless as possible.

 

Have you guys found a solution to this? I got my truck tuned and seemed to not change much. I am re-tuning now with new gears and hoping it will help. Went through fluid checking multiple times. Only does it first drive and sounds just like what you are explaining. It feels like it's slipping but sounds like it shifts to neutral real quick then shifts because depending how much gas I give it adjusts how severe it does it. Still shifts smooth and isn't jerky when it shifts but the action feels like a slip which made me worried.

 

Not to beat a dead horse, but you sure you doing the fluid check properly? Cant count how many times people have done it thinking they are right but end up a few qts low for one reason or another.

Also, this is just my opinion but I don't think tuning does much on 2nd gens unless you have something else going on like forced induction. How many miles?

 

I just checked the lvl yesterday and it's spot on. Put it in AT temp mode then once the light illuminated pulled the check plug and it had a small consistent stream so put the plug back in.

First drive in the morning only. Never does it again the rest of the day. It feels like a slip but just revs in-between the shift of 4 and 5. No harsh engagement or anything. Still shifts smooth.

 

I have this exact shift flare issue in mine. Feels like it goes into neutral between the 4-5 shift, revs up and then catches into gear, slowly goes away as I drive and it warms up. Definitely worst in the winter months. Have flushed the fluid and checked level. Transmission only has about 70k miles. Has anyone considered/tried to replace the valve body for this? Not sure what else to try other then just getting a trans from a wrecker and being done with it.

 

@gearcruncher recommended doing one of these valve body kits. I haven't gotten to it yet. Probably going to do it within the next month. If I shift from reverse to drive a couple times before driving first thing in the morning it doesn't do it. So it seems like it's something in the valve body where fluid isn't getting to where it should be quick enough. Your part # might be different depending on the year of your truck.

A750E-A761E-ZIP

 

Could it be this?




https://hgmelectronics.com/blogs/hgmelectronics/toyota-a750-transmission-control-with-the-compushift

Main Forward Clutch Failure
Inside the A750 transmission are 7 clutches in total, with an 8th clutch inside the torque converter. However, there is one clutch that has the smallest friction surface area that during one particular shift takes the entire load of the engine. This clutch is the main forward clutch or C1. The shift in question is the 5-4 kickdown.

With modern engines producing more and more power, the thirst for more power in older vehicles becomes greater. This is where the C1 clutch failure shows itself. Due to larger turbochargers, superchargers or high flow injectors, the increased torque available at lower throttle positions means the amount of torque delivered to the C1 clutch becomes too great and slipping starts to happen.

Enough slipping of this clutch can result in the clutch welding itself on permanently. If this happens, the resulting fault reported by the driver will be the absence of 5th gear. This is because the C1 clutch needs to disengage for the 4-5 upshift.

The only way to fix this is through a transmission overhaul, and a reduction in engine torque to a more suitable level. That being said, there has been many cases where an engine upgrade chip has caused failure due to incorrect calibration. If your engine runs any form of upgrades it is imperative to monitor transmission pressures.

 

It's possible. This seems more applicable to someone that adds a supercharger or something. I would assume an issue like that would be more consistent and do it almost every shift from 4 to 5. Not just the first shift after sitting cold then goes away.

The guy who did my my tune after I regeared said that most people who add superchargers get shift flare. Which feels similar to a slip and this issue we are talking about.

 

Agreed hopefully this is normal and we are just overanalyzing...

I get a very similar issue on my AM DD to work, pretty much only notice on the first on ramp to the highway. The shift from 4 to 5 hangs when I'm speeding up to get on the highway for like 3-5 seconds longer than it should typically right around 2,500 rpm.

I feel like the transmission has always been a little clunky. So I try not to worry about it.

I drain and fill my transmission every 50k/miles. Did a pan drop and new filter for the first change, but did not really find much debris. I've got an '07 4.0 prerunner.