So, the transmission issue I mentioned my trip report last year (here) has reared its ugly head again. I’ll summarize the series of events chronologically.
Following a day of driving across Oklahoma (towards Utah) with a particularly strong headwind, lock-up in the 4L80E started to get fickle. It would continuously slip in and out of lock-up so I had to ease back on the speed to minimize the heat that was undoubtedly being generated in the torque converter.
All of the driving around Utah was relatively low speed so I never needed lock-up, but the drive home was a miserable 50-55mph for 2,175 miles.
A while after I got home, I got the Cruiser in to a see a good transmission guy (aka Wizard). Lo-and-behold, he could not recreate the problem. I figured I’d have to settle with the embarrassment that, during his diagnostics in which he checked the electrical connectors for moisture and shifted through the gears (including a low gear that I didn’t realize was there), he knocked a valve loose or some other inexplicable change that made lock-up work again. Automatic transmissions are built on sorcery.
I then drove it down to Ocracoke, where lock-up functioned wherever I needed it over the course of the ~800 mile trip.
Most recently, I drove to KY and back and on the way to KY, after about 300 miles, lock-up began acting erratically again. By the time I was return to VA, lock-up was just as unreliable as it was coming home from UT.
I have the programmer for the transmission and it’s currently set to shift at certain speeds:
1st -> 2nd @ 10mph
2nd -> 3rd @ 20mph
3rd -> 4th @ 30mph
4th -> LU @ 55mph
I understand the ideal scenario is to have the transmission shift at set RPMs, but as of now, my tach doesn’t work.
Poking around on various forums, I’ve found the following possible culprits
1. The brake switch is bad and the 4L80E is supposed to drop out of LU whenever you hit the brakes. However, I’m not sure that this transmission even has a brake switch (I hit brakes while in LU, and it didn’t instantly fall out of LU). That’s on my diagnostics-to-do-list.
2. A heat sensor. I think the 4L80E has a sensor that will keep it from locking up if the transmission gets above a certain temp.
3. Sensitivity to dropping out of LU is programmed incorrectly. I believe there’s a setting in the programmer that lets you determine what criteria will cause the transmission to drop out of LU (RPM, speed, etc.)
The above are all things I need to investigate further. I wanted to pose the following questions though:
1. If I get the tach working, given the 4BT à 4L80E combo, does anyone have any suggestions on shift points?
2. Can anyone think of any other causes for erratic LU behavior?
Following a day of driving across Oklahoma (towards Utah) with a particularly strong headwind, lock-up in the 4L80E started to get fickle. It would continuously slip in and out of lock-up so I had to ease back on the speed to minimize the heat that was undoubtedly being generated in the torque converter.
All of the driving around Utah was relatively low speed so I never needed lock-up, but the drive home was a miserable 50-55mph for 2,175 miles.
A while after I got home, I got the Cruiser in to a see a good transmission guy (aka Wizard). Lo-and-behold, he could not recreate the problem. I figured I’d have to settle with the embarrassment that, during his diagnostics in which he checked the electrical connectors for moisture and shifted through the gears (including a low gear that I didn’t realize was there), he knocked a valve loose or some other inexplicable change that made lock-up work again. Automatic transmissions are built on sorcery.
I then drove it down to Ocracoke, where lock-up functioned wherever I needed it over the course of the ~800 mile trip.
Most recently, I drove to KY and back and on the way to KY, after about 300 miles, lock-up began acting erratically again. By the time I was return to VA, lock-up was just as unreliable as it was coming home from UT.
I have the programmer for the transmission and it’s currently set to shift at certain speeds:
1st -> 2nd @ 10mph
2nd -> 3rd @ 20mph
3rd -> 4th @ 30mph
4th -> LU @ 55mph
I understand the ideal scenario is to have the transmission shift at set RPMs, but as of now, my tach doesn’t work.
Poking around on various forums, I’ve found the following possible culprits
1. The brake switch is bad and the 4L80E is supposed to drop out of LU whenever you hit the brakes. However, I’m not sure that this transmission even has a brake switch (I hit brakes while in LU, and it didn’t instantly fall out of LU). That’s on my diagnostics-to-do-list.
2. A heat sensor. I think the 4L80E has a sensor that will keep it from locking up if the transmission gets above a certain temp.
3. Sensitivity to dropping out of LU is programmed incorrectly. I believe there’s a setting in the programmer that lets you determine what criteria will cause the transmission to drop out of LU (RPM, speed, etc.)
The above are all things I need to investigate further. I wanted to pose the following questions though:
1. If I get the tach working, given the 4BT à 4L80E combo, does anyone have any suggestions on shift points?
2. Can anyone think of any other causes for erratic LU behavior?
