lock up when downshifting

[djms]

Hey guys, Is there a way to keep the converter locked when my truck downshifts? Like into fourth gear, we have an lbz and as soon as it downshifts the converter is locked and on my lb7 it takes a few seconds. My Dads lb7 does the same thing. Its annoying when your pulling a load and the truck downshifts and the converter is slipping for a while before it locks. I was wondering if there is a way to fix this with efi live? Thanks James

 

[Lennart]

Converter lockup is a function of selected gear and speed. You can change the desired lockup speed with EFILive.

 

[Mike L.]

I think this may shock the system too much and possibly snap a shaft. Be carefull what you wish for.

 

[Bluemax]

Might also think about a different OS if you have efi. Mine locks up pretty quick after a downshift if it's in t/h. Or you could take it to the dealership and see if they have any newer updates they can flash into your tcm that might make a difference.

 

[Bluemax]

Any chance the co-pilot has anything to do with this? I've never had one and don't know anything about them.

 

[duratothemax]

in tow/haul mine stays locked all the time.......

like If Im on the highway and throw it in 1st, it downshifts through all the gears whil staying locked the whole time.




or wait.....are you talking when you go WOT and it kicks down? If im in 5th on the highway, locked up, and I go WOT, it unlocks, kicks down to 4th, then locks again. If I am in tow/haul, it only unlocks for less than a second before it locks back up in 4th, and then shifts to 5th again. If im in normal mode, it takes probably 2 seconds to re-lock.

Every once in a while if Im at the "right speed", it will get all freaked out and not lock the converter for 4 or 5 seconds, it just sits up at 3700rpm while the TCM collects itself, then locks again.

Normally I can get it to do this "glitch" if I am at the very "top" of the 5-4 WOT downshift threshold point; meaning, im RIGHT at the "decision" point where, if I went WOT, the trans either just stays in 5th gear (because a 5-4 downshift would overrev the engine) or it does actually downshift to 4th, its at that point where I can freak it out and it will take forever to relock the converter. If Im between ~55-70 mph In 5th locked, I can go WOT and it will relock almost instantly. If Im above ~72-73mph or so it will freak out. If Im above 75mph and floor it, it will not downshift.

this is with a 2001 tcm.


input speed sensor is critical here IMO. Im 99% sure with tighter converters the TCM will lcok the converter a lot faster. I think the TCM has to see a certain range of difference between input and turbine speed before it will alow converter lockup. Because if the difference is greater than X rpm, it might be too much of a shock to things if it locked it. So it leaves teh tc unlocked, waits for it to couple and bring RPM down a bit, then once it sees that X RPM (or less) it locks.

2006+ allisons have a variable bleed solenoid on the TCC so maybe thats why its different? 5-speeds have a PWM f-trim solenoid.

 

[Bluemax]

If it downshifts when your on the throttle hard it will unlock and then lock back up in t/h or normal.

 

[Bluemax]

in tow/haul mine stays locked all the time.......

like If Im on the highway and throw it in 1st, it downshifts through all the gears whil staying locked the whole time.




or wait.....are you talking when you go WOT and it kicks down? If im in 5th on the highway, locked up, and I go WOT, it unlocks, kicks down to 4th, then locks again. If I am in tow/haul, it only unlocks for less than a second before it locks back up in 4th, and then shifts to 5th again. If im in normal mode, it takes probably 2 seconds to re-lock.

Every once in a while if Im at the "right speed", it will get all freaked out and not lock the converter for 4 or 5 seconds, it just sits up at 3700rpm while the TCM collects itself, then locks again.

Normally I can get it to do this "glitch" if I am at the very "top" of the 5-4 WOT downshift threshold point; meaning, im RIGHT at the "decision" point where, if I went WOT, the trans either just stays in 5th gear (because a 5-4 downshift would overrev the engine) or it does actually downshift to 4th, its at that point where I can freak it out and it will take forever to relock the converter. If Im between ~55-70 mph In 5th locked, I can go WOT and it will relock almost instantly. If Im above ~72-73mph or so it will freak out. If Im above 75mph and floor it, it will not downshift.

this is with a 2001 tcm.


input speed sensor is critical here IMO. Im 99% sure with tighter converters the TCM will lcok the converter a lot faster. I think the TCM has to see a certain range of difference between input and turbine speed before it will alow converter lockup. Because if the difference is greater than X rpm, it might be too much of a shock to things if it locked it. So it leaves teh tc unlocked, waits for it to couple and bring RPM down a bit, then once it sees that X RPM (or less) it locks.

2006+ allisons have a variable bleed solenoid on the TCC so maybe thats why its different? 5-speeds have a PWM f-trim solenoid.

Hmm you edited while I was typing.

 

[Bluemax]

I think the TCM has to see a certain range of difference between input and turbine speed before it will alow converter lockup. Because if the difference is greater than X rpm, it might be too much of a shock to things if it locked it. So it leaves teh tc unlocked, waits for it to couple and bring RPM down a bit, then once it sees that X RPM (or less) it locks.

I think you're right. There is a spot where I data log my truck that has a small hump in the road where the pavement is a different height and if I hit it just right it is enough of a hop that the tc unlocks. If I stay on the throttle it won't lock in at all and if I back off it will lock back up a few seconds later.

 

[djms]

Thanks for the info I guess mine is normal then.