What Toyota got wrong with the 2.7 AT

The purpose of this post is to relate an anecdotal account of replacing the differential gear in a Toyota Tacoma with a new ratio.

My truck is a 2017 Tacoma with a 2.7l, 33 inch tires, and a 6 speed Automatic. The automatic has 2 overdrive gears. This truck originally had 3.90 gears. While it ran nice on perfectly flat ground, it does not do well pulling hills at highway speed and at times has to drop to 3rd gear near 5000 rpm to maintain speed. I recently took a trip on I25 between Albuquerque and Las Cruces where there are moderate hills and observed as low as 11 mpg.

This is totally stupid. In general, unless on perfectly flat ground or going down hill the two overdrive gears are seldom used. The truck basically runs in 3rd and 4th gear. The difference in gear ratio between 3rd and 4th gear is significant, so when ever the truck needs to operate at a slightly higher rpm for a little more torque it has to go all the way to 3rd and run a much too high rpm.

I just had 4.88 gear installed. The shop where the gears were installed is about an hour and a half away. The (crappy) picture below if from my drive home where I got roughly 2mpg better mileage than the trip there. I purposefully took a route home over very hilly and picturesque mountainous terrain because I would be stopping and waiting every 20 minutes.

This is a completely different truck with 4.88s. It now runs in 6th, 5th and 4th gear at highway speed. The difference in gear ratios between these gears is very moderate, so the transmission easily finds an appropriate rpm range for the motor. It drives easy, and manages highway speeds very well. Only on the very steepest hills will it drop into 4th. At highway speed it normally runs between 2K and 3K RPM.

I don't know what Toyota was thinking. It looks like they put the 2.7 behind the same Transmission and diff they used with the more powerful 3.4l and saved a pile of money by not doing any more work to the truck.

If you are on the fence about doing gears, DO IT. This is how Toyota should have set the truck up to begin with.

I had the Eaton TruTrack put in at the same time. The tru-track is a limited slip but uses gears instead of clutches. The older tacomas had limited slip differentials and not having that come with the truck is a disappointment. If you are going to work on the diff, leverage the labor and get the most out of it.

 

What are the transmission ratios for the 2.7? Is it the same as the 3.5 ?

 

I can't say definitively, but all my research and observations (using the http://www.grimmjeeper.com/gears.html gear calculator, with gps speed and RPM) seems to indicate it is the same transmission and ratios.

 

Running 488s my self, even with a manual the factory gear ratios were stupid

 

Yeah and 15 years ago when I put 33s on my 4 cylinder 4runner it needed 4.88s too.

Went to an aggressive tread pattern with more rolling resistance, +3" of diameter, +1.5" width and +28lbs per tire.

 

Were you in Las Cruces to get the gear swap done? Just wondering, since I'm in LC and would like to know who you used.

 

I live in AZ. Had the swap done in Tucson, used Western Differential. It was just on that stretch of road I was doing mpg logging about a month ago.

 

The 5 speed manual is 1900 rpm at 55 mph stock in 5th gear.

 

See the gearing table in my signature.

 

you have 33 inch tires?

 

I'm not sure what else you expected when you jumped that significantly in tire size. People bitch enough about how it runs stock with a V6 let alone putting bigger, heavier tires on a four banger.

 

I have a 2020 SR with 2.7L and 6 speed auto 4X4 . Isn't the rear differential on that 4.30?

 

Simple. They were thinking final gear ratio / EPA MPG test based on OE sized street tires.

Sometimes one modification leads to another, whether that was the goal or not.

Glad you're happy with the drive-ability now. But it sure made that tire change out expensive........

 

Yes

 

So, you bought a 4-cylinder, automatic truck and proceeded to throw heavier tires on it and can't use your overdrive gears up a grade in mountainous terrain?

Albuquerque, NM elevation: 5312 feet
Las Cruces, NM elevation: 3900 feet

Dumb, but then you seemed to expect the same performance out of the truck with 30" P-rated street tires as 33" A/T tires.

 

Thanks JNG !

 

The trans sucks with the 3.5 too lol

All 3rd gen ATs need gears

 

I agree. Toyota over did it with OD ratios IMO.

 

The internal ratios are not the problem, IMO. It's the overall ratios with the 3.909 gearing combined. Heck, I wouldn't have minded a slightly taller 6th in the MT, but I have zero real complaints with what they are along with the 4.30 gears. Pretty much similar to the ATs with 5.29s.

 

The only time it really works is under 55 mph.. but most people dont or cant always drive that slow.

It still amazes me how much differently the AT and MT drive. You’d think if someone testing for Toyota drove them both they’d be like hey guys we have a problem.. It was immediately noticeable for me how poorly the AT is geared.