2020 Tacoma off-road won’t shift from 4th please help

Holy shit, 13 mph over the speed limit?!! I’ll bet there’s an APB out on him already.

 

Idk. Not my problem. He lied about his speed anyway.

FYI it’s not called an APB anymore. Cmon man try to keep up.

 

Lol, regear, regear, something wrong with your truck
With your speedometer way off with your larger tire size and doing an actual 87 mph+ with cruise control you’re gonna see 5000+ rpm. Turn off cruise on grades, drive 70-75 mph gps actual speed (7-8 mph less than your speedometer erroneous indication), problem solved.

 

I'm confused why everyone keeps saying regear. All a regear will do is let him be in a higher gear in trans but the engine will still need to turn those rpms to keep the truck at those speeds. What's the difference of being at 5300 in 4th with gears vs 5300 in 3rd without them? How does that solve the "issue"?

 

Because lower geared axles will raise the RPM level at a certain speed and put the engine into the power band. When larger tires were installed they lowered the RPM of the engine at speed to where it's no longer in the power band which results in a shift down and higher RPM's. Older vehicles tended to ''lug'' when larger tires were installed [taller] while on newer vehicles, it results in the computer selecting a lower transmission gear and putting the engine back into the power band.

 

Oof. That’s not how it works. I recommend doing some research on gearing.

 

Oof. That is how it works. Not saying he can't use a regear. He can but it's not the answer to this. Regearing doesn't magically give you power. It's irrelevant if you're in a lower gear with taller rearend or higher trans gear with a shorter rearend gear you'll get overall a similar final ratio.

His is a power/tunning issue.

 

That's what I'm saying. A regear will allow him to run a higher gear in the trans but the rpms will need to be up regardless of the gear he's got to cruise at that speed. I didn't do the calc but let's say the regear effectively makes 5th the same final ratio as 4th prior to the change. Now he can run in 5th but will still need the rpms to make the power. It doesn't change anything other than the gear the trans is in.

 

Gears are a torque multiplier. I run 5.29s and 35s and no issues with 5th and 6th and I’m not running at 5300 rpms

 

You are correct. However, if the gear change puts the engine in a better power producing RPM band of the engine, the transmission might not have to shift shift down to get to that ''sweet spot'' that makes the best power.

 

A lower differential gear (higher ratio) results in higher torque at the wheels for a given engine rpm, it’s a torque multiplier. For a given speed the rpms will be higher than with a higher diff gear (lower ratio) when in the same gear. Beyond that I can’t say how it affects shifting since I don’t know how the Tacoma shift maps work, but could prevent downshifting early for an automatic.

 

Yep. You beat me to it

 

The rear end gear + tire combo is too tall, so the transmission is downshifting to compensate. With a lower rear end gear, the transmission can be in OD, the engine won't be screaming, and all the gear reduction will be happening in the rear axle.

 

I understand gears multiple torque. What I’m saying is it’s irrelevant how you get that multiplication. You can get it either by using a lower gear in the trans or higher numerically rearend ratio. His complaint isn’t that he can’t use 6th it’s that the engine is at 5300 rpm.

a regear will allow him to run a higher trans gear no doubt. But it will not chnage the power required to move the truck at that speed. And for the engine to make that power it will need to be in the higher rpms.

 

I never understood why the V6 auto comes with a 3.91 differential especially with the low torque at low rpms due to the Atkinson cycle. My 2TR-FE 4 cyl has good torque even at 1500 rpm with the 4.30 diff based on dyno charts I’ve seen as well as my butt duno lol.

 

When you re-gear to a higher numerically number R&P you will raise the RPM of the engine in any gear at any given speed. That compensates for the taller tires.

 

Hwy gas milage I guess? I dunno, it seems weird.

4.30 + 4 cylinder is a good combo though, mines a hoot to drive around town.

My nissan has 3.55 rear gears, and is definitely not lacking for torque but still cruises down the hwy comfortably at 2200 or so. They got that drivetrain juuust right.

 

Maybe I’m looking at this wrong or explaining it poorly. I get 100% what you’re saying. What I’m saying is all a regear will do is allow the trans to run in a higher gear.

As a simplified example if 4th with 4.30 gears is the same final ratio as 5th with 4.88 what benefit do you get by running in 5th with the 4.88s vs 4th with 4.30s? Unless your goal is use 5th but that’s not his complaint here.

 

It is his complaint because he wants out of forth .

 

The benefit you get is the usage of the full range of gearing. Instead of having to run around in 4th on the highway, you get to use 5th and 6th. Which means that at lower speeds, you get to use 4th again, and so on down. It just shifts the whole powerband back to where it should be. If you follow the logic all the way down to first, 1st gear ends up being too tall, which means more strain on the transmission and torque converter every time you start out. Putting in the correct gear ratio for the tire size takes that strain away.

I also think that is his complaint - the truck keeps downshifting into 4th because it can't hold either of the OD gears.