'05 Tacoma Tranny or Speedo Problem. Help!!

Actually this would be a tranny or TACH problem, not speedo. My '05 Taco (2nd Gen) 4x4, Dual Cab, w/Auto Transmission has started doing something weird at highway cruising speed. When it rolled over 100K miles, I changed the ATF using the method found on this site of disconnecting the cooler lines and letting it suck in the new fluid and blow out the old. I ran several gallons of new fluid through it until I had clean fluid coming out of it. I used Amsoil ATF of the proper type for my Taco. And the old fluid coming out was not in bad condition - it was still red and smelled right, not brown or burnt smelling.

A couple of thousand miles later, I'm cruising down I-80 at 70 mph on my back to Missouri from Wyoming and I notice that the revs shown on the tach are about 800 rpm less than what has been normal for that truck since day one, when on flat, level ground with no bad headwind. See the photos below. Normally at 70 mph I get about 2200 rpm. For some reason it was running at 1400 rpm at that same speed.

When I stopped later for fuel, it reverts back to 2200 rpm for 50-60 miles then drops down to 1400. Several times on the remainder of that trip and ever since then, it will run for a while at 2200 rpm, for a while a 1400. It's random, but it doesn't drop down to 1400 until I've been at least 20 miles or so.

What is going on?

Could this be a problem with the tach or the tach pickup/trigger or do I have a transmission problem?

I've counted the number of shifts many times, and I'm getting five drops in rpm even when it ends up on 2200 rpm at 70 mph. I figure I'm getting four gear changes and one torque converter lockup.

The dealer is absolutely no help at all. They're about as useful as mudflaps on a sledge hammer.

Here is "normal" tach and speedo at 70 mph on flat, level ground with no headwind.





Here is where it randomly decides to run sometimes now, under the same conditions:

 

Interesting. If you manually shift it to 4th gear, where do the RPMs go? If you roll into the throttle just enough so the converter unlocks where do the RPMs go? 1400 seems low, what size tires are you running?

 

My wife's previous van used to do it. It got progressively worse, to where in the end I could stomp on the gas and accelerate from 50 to 70 and then let it back to 50, and the RPMs would stay about the same, coincedentaly also around 1400.
I could hear the engine reving (obviously), and since I gained speed like usual, there was nothing wrong with the tranny, so I think it is just something with the cable that's slipping.
In your case, since it start of accurate and then starts to go down, maybe when it warms up it starts to slip - almost like oil that change in viscosity when it warms up.
I would not be concerned about it, unless you want to have an accurate tach.

 

I'm not positive, but I would think the tach pickup would be electric.

 

If it was a trans issue , you are going to get a code stored in the trucks on board computer and malfunction indicator should also pop up .
To verify , you will need to connect a scanner and watch the tach on the scanner as well as watching the transmission upshift . The scanner is going to tell you engine rpm , vehichle speed and what gear you are in .

 

Is this scanner something that you buy, rent, or borrow that will give you this type of info??

 

Skidooman, I'm running the stock size 265/65-17" tires. Good questions you've got about the converter unlock rpms and the downshift rpms. I won't be able to find out the answers until this weekend.

 

The scanner is all up to you . You can rent , buy or borrow .

All depends on how much of the work you plan to do yourself and how much work you want the shop to do .

You can purchase a cheap scanner/ code reader for 16 bucks .
The pricey scanners have more functions and help you a little more .
Do a search on TW for scanners , there are many posts

Keep in mind that your truck is completely computer controlled .
A quality scanner will tell you when the converter is locked and when its unlocked .The scanner will tell you when the transmission downshifts and what gear you are in .

 

Do you hear the motor change RPM when it drops? I'm guessing you don't because the engine has to still be running at 2200 rpm. There is no way the transmission can spin faster than the motor while maintaining speed... Unless it drops when you are slowing down and the trans speed is being maintained by the trucks momentum while the motor is trying to drop to idle and the torque converter is letting it rather than getting that engine braking affect you should get when you let off the throttle.