BIGMIKE ? ON TUNDRA

[BCB]

HEY PUTTING THAT BODY LIFT ON WITH 315s AND WAS WONDERING IF THAT TRANNY IN THE TUNDRA WAS ANY GOOD OR ATLEAST GOOD ENOUGH TO HOLD UP TO 35 INCH TIRES,  WHAT DO YA THINK.  THINK THE TRUCK CAN HANDLE 35 INCH TIRES

[BigMike]

IF THIS IS A 5 SPEED V6 TUNDRA, THEN I DONT THINK TIRE SIZE IS RELATED TO THE STRENGTH OF THE TRANNY. THE CLUTCH WILL HAVE TO WORK MUCH HARDER UNLESS THE AXLE GEARING IS ALSO CHANGED......

IF THIS IS AN AUTO, ESPECIALLY IF ITS GOT ABS, THEN I DONT KNOW WHAT TO TELL YA. I HAVE NO EXPERIENCE WITH THIS. IVE HEARD THAT WITH ABS, SINCE IT IS CALIBRATED TO THE SPEED OF EACH AXLE, NOW THAT THE AXLES ARE SPINNING SLOWER, THE ABS WILL KICK IN EVEN WHEN YOU ARE NOT LOCKING UP THE TIRES. SO IVE HEARD THAT THE BRAKING DISTANCE ACTUALLY DECREASES.

AS FAR AS THE ECT (ELECTRICALLY CONTROLLED TRANSMISSION) GOES, I BELIEVE IT IS ALL RUN OFF OF THE VEHICLES' SPEED SENSOR AS WELL AS ENGINE LOAD. SO IF YOU ARE JUST CRUISING, I THINK IT MIGHT SHIFT A BIT LATER NOW, AND IF YOU ARE TRYING TO RACE IT THEN IT SHOULD SHIFT THE SAME.

GOOD LUCK AND LET US KNOW HOW IT GOES!!
BIGMIKE

[reklund5]

FWIW, I've put in 2 trannies in Tundras/Sequoias just this month at work.  The trannys don't like towing or any kind of excessive load when in overdrive...they seem to self-destruct.

Ryan

[guywithuglyyota]

My friends 2002 tundra just had a complete auto transmission failure. He was cruising along the freeway and bang! it had 55,000 miles, however Toyota took very good care of him, new tranny under warranty, and lots of appologies. Apparently it is very rare for them to fail especially since his trucj is bone stock. And yes I have read that any auto tranny does not like to tow or haul around big tires in overdrive. If it does not have a lockup torque converter it will just gradually overheat, and autos really hate heat. Just my     

[Bob Garrett]

IF THIS IS AN AUTO, ESPECIALLY IF ITS GOT ABS, THEN I DONT KNOW WHAT TO TELL YA. I HAVE NO EXPERIENCE WITH THIS. IVE HEARD THAT WITH ABS, SINCE IT IS CALIBRATED TO THE SPEED OF EACH AXLE, NOW THAT THE AXLES ARE SPINNING SLOWER, THE ABS WILL KICK IN EVEN WHEN YOU ARE NOT LOCKING UP THE TIRES. SO IVE HEARD THAT THE BRAKING DISTANCE ACTUALLY DECREASES.

Not true. ABS works by measuring wheel speed and comparing all 4. Changing differential ratio will not affect it

AS FAR AS THE ECT (ELECTRICALLY CONTROLLED TRANSMISSION) GOES, I BELIEVE IT IS ALL RUN OFF OF THE VEHICLES' SPEED SENSOR AS WELL AS ENGINE LOAD. SO IF YOU ARE JUST CRUISING, I THINK IT MIGHT SHIFT A BIT LATER NOW, AND IF YOU ARE TRYING TO RACE IT THEN IT SHOULD SHIFT THE SAME.

If you're referring to the ECT switch, engaging it raises the shift points, so that for a given load or acceleration rate, the transmission will shift at a higher rpm for better acceleration (and poorer fuel mileage). The ECU uses a number of inputs to determine shift points, including as you mentioned, engine load and speed. It also monitors timing advance, throttle position and engine temp. Changing axle ratios will affect shift points unless you correct the speed sensor by changing the gear or install an aftermarket calibrator.

Bob

[BigMike]

IVE HEARD THAT WITH ABS, SINCE IT IS CALIBRATED TO THE SPEED OF EACH AXLE, NOW THAT THE AXLES ARE SPINNING SLOWER, THE ABS WILL KICK IN EVEN WHEN YOU ARE NOT LOCKING UP THE TIRES.

Not true. ABS works by measuring wheel speed and comparing all 4. Changing differential ratio will not affect it

That's what happens when you increase the tire size, the axles will spin slower. And since at the end of each axle there are small ridges for the sensor to pick up the axle speed decreases. If it decreases so much as that the computer believes the tire has stopped spinning (locked up brake) then it will override your braking effort and allow the axle to spin again.....but in reality the tire really never did lock up because its has a greater diameter so the axle spins slower and it throws the calibration of the ABS system all off.
I don't believe he mentioned changing his diff gearing

AS FAR AS THE ECT (ELECTRICALLY CONTROLLED TRANSMISSION) GOES, I BELIEVE IT IS ALL RUN OFF OF THE VEHICLES' SPEED SENSOR AS WELL AS ENGINE LOAD. SO IF YOU ARE JUST CRUISING, I THINK IT MIGHT SHIFT A BIT LATER NOW, AND IF YOU ARE TRYING TO RACE IT THEN IT SHOULD SHIFT THE SAME.

If you're referring to the ECT switch, engaging it raises the shift points, so that for a given load or acceleration rate, the transmission will shift at a higher rpm for better acceleration (and poorer fuel mileage). The ECU uses a number of inputs to determine shift points, including as you mentioned, engine load and speed. It also monitors timing advance, throttle position and engine temp. Changing axle ratios will affect shift points unless you correct the speed sensor by changing the gear or install an aftermarket calibrator.

Changing axle ratios will affect the shift points and so will changing tire size, which is what he's talking about.. Since you brought up the Power/Normal switch, in Power mode it ought to act the same, but in the Normal or Econ mode I just think that it should shift a bit later now that the speedsensor is reporting slower vehicle speed.
I know that the V8 Auto Tundra does not have the power mode button(s). It is all based on engine load (timing advance, throttle position and engine temp), but I don't know anything about the V6 Auto Tundra..

One cool thing is that when the truck is cold, it will avoid using overdrive in an effort to not bog an engine with loose/cold pistons

[FIREBALL]

Towing in over drive is bad on just about any transmission. 5spd or auto. If you are going to tow, or run big tires you should always shift out of OD when climbing a hill or under a heavy load, unless your truck is built for towing. OD (5th gear) is the weakest link in the tranny.

Mike, can't you re-program the Tundra computer to compensate for larger tire diameter. Many of the aftermarket programmers, and scanners that the techs have can calibrate the computer to function properly with different tire sizes.

[Bob Garrett]

That's what happens when you increase the tire size, the axles will spin slower. And since at the end of each axle there are small ridges for the sensor to pick up the axle speed decreases. If it decreases so much as that the computer believes the tire has stopped spinning (locked up brake) then it will override your braking effort and allow the axle to spin again.....but in reality the tire really never did lock up because its has a greater diameter so the axle spins slower and it throws the calibration of the ABS system all off.
I don't believe he mentioned changing his diff gearing

If you made a HUGE change in tire size that could be true, I suppose. Although, if you regeared and/or installed a different speedometer gear, you should be fine. I ran  an 80 series for over a year with 35s (OEM tire is a 31) and stock gearing and a speedometer gear that corrected for about 50% of the error and had no problems with the ABS.

One cool thing is that when the truck is cold, it will avoid using overdrive in an effort to not bog an engine with loose/cold pistons

It also raises the shift points and disables the torque converter lock up function.

Bob