Torque converter gear lock-up question

[labsy]

Hi,

I could not find exact info on Jatco RE5R05A automatic transmission LOCK-UP conditions. Referring to service manual it only locks-up in 5th gear (see copy below). So you run on open torque converter all up to 5th gear, meaning if you drive mostly in city, TC never locks up and mixes and heats ATF fluid all the time, not having a break at all.

Is this true?

[smj999smj]

Well, I don't see anywhere on your chart (unless I missed something) that it says it only engages "lock-up" in 5th gear. From what I've heard, lock-up can occur in 3rd and 5th gear, but not in 4th gear. As far as "mixing and heating the ATF all of the time," remember that automatic transmissions have been around a very long time and during most of those years, they didn't have lock-up torque converters and they all did just fine. It's great to have lock-up, but it is not essential for the operation or durability of the transmission.

[labsy]

Thanx, SMJ! Nice info on those 3rd and 5th gear only locking up - will pay attention in future.

How I essentially started thinking about lock-up is annoyance of gears shifting down and un-locking when - by my opinion - is not necessary. For example, driving 80 mph highway and a bit uphill, pressing gas pedal a bit gives vehicle quite an acceleration (because mine is chip-tuned to have 60 HP more and more torque).... but transmission kicks-down anyways.

Do you think there's any way to make it down-shift later, without reprogramming TCM?

[smj999smj]

Probably not since the shift solenoids are controlled by the TCM, which is part of the valve body. You may want to check with a transmission shop. That said, I haven't heard of anything or anyone that can re-program the TCM.