Confused about fluid coupling issue
- Thread starter N2BRK
- Start date
How much power are you running? Usualy 400/500 rpm differential between the turbine and output ss will not command t/c lock till 4th gear.
Who’s ecm and tcm files? I think James is onto something with it being TCM tune related. My old TCM tune was crap at any positing besides WOT. My new file is much better. Some trucks with higher stalls, even when they’re told to lock, won’t lock which is why I use a lockup box when I’m messing around or at the strip. That way I can ensure it locks when I want and stays locked.
I had nothing but lazy lockups on my LLY with a stock TCM and a ATP tuned ECM when my truck was a Danville 68R 4094 with 60% and a 10mm. As soon as Rob tuned the TCM it was a joy to drive (Suncoast 1058) as lockup was consistent and much smoother.
I've been told that stock TCM files don't like larger stall converters as they don't know how to handle the slip.
I believe that for sure. What concerns me is that everything ran fine for a few years like this on the ML and then in the last year it acted like this, making me think the ML was damaged, and now out of the box the K is acting exactly the same. It has me thinking the trans has other issues.
It is possible your old converter was hurt/worn out, and that was causing it to slip too much to lock with a stock TCM tune. With the new converter, you probably want a trans tune to move the lockup apply & release points around to take advantage of it.
I run a high-stall converter, and it drove like ass on a stock TCM tune. With a good TCM tune, it is a joy to drive. Hit the throttle, RPMs come up to 3000-3500 for a second, truck instantly lights the turbo and starts pulling hard, it commands lockup after I pick up some MPH, pulls RPMs down to ~2600 and stays locked up from there through the gears.
You will be much happier with the truck once you have the TCM commanding lockup at part throttle. I have mine lock up at 55 MPH when I am below 1/3 throttle. I've played with locking it up in 3rd/4th, but it makes the truck too twitchy in town for my tastes, so I only do that in tow/haul mode.
If you want, I can post up my trans tune so you can see what I've done. It's a 5 speed, but you can copy those values and make up something similar for 5-6 and 6-5 and see what you think. Heck, just disable 6th if you just want a quick test. I run a 71mm turbo and a stupid cam, so I rarely let the truck drop below 2000 RPM if I'm touching the throttle at all. Might be a bit more extreme that you need/want. And tow/haul mode needs a lot of work, so ignore that for now. Let me know and I can post the tune if you want to look at it.
I run a high-stall converter, and it drove like ass on a stock TCM tune. With a good TCM tune, it is a joy to drive. Hit the throttle, RPMs come up to 3000-3500 for a second, truck instantly lights the turbo and starts pulling hard, it commands lockup after I pick up some MPH, pulls RPMs down to ~2600 and stays locked up from there through the gears.
You will be much happier with the truck once you have the TCM commanding lockup at part throttle. I have mine lock up at 55 MPH when I am below 1/3 throttle. I've played with locking it up in 3rd/4th, but it makes the truck too twitchy in town for my tastes, so I only do that in tow/haul mode.
If you want, I can post up my trans tune so you can see what I've done. It's a 5 speed, but you can copy those values and make up something similar for 5-6 and 6-5 and see what you think. Heck, just disable 6th if you just want a quick test. I run a 71mm turbo and a stupid cam, so I rarely let the truck drop below 2000 RPM if I'm touching the throttle at all. Might be a bit more extreme that you need/want. And tow/haul mode needs a lot of work, so ignore that for now. Let me know and I can post the tune if you want to look at it.
Thank you! I will spend some time after work tonight and see how I make out. I'll reach out if I need -- thanks so much!
My next step is to send in the ML as fast as possible - it's got a little warranty left. If they find no issue, then I know it's a trans problem. If they come back that there's some bending etc. then what you say must be correct and nothing is wrong with the trans that a TCM tune can't cure.
Thanks for the patience guys.
My next step is to send in the ML as fast as possible - it's got a little warranty left. If they find no issue, then I know it's a trans problem. If they come back that there's some bending etc. then what you say must be correct and nothing is wrong with the trans that a TCM tune can't cure.
Thanks for the patience guys.
Thank you! I will spend some time after work tonight and see how I make out. I'll reach out if I need -- thanks so much!
My next step is to send in the ML as fast as possible - it's got a little warranty left. If they find no issue, then I know it's a trans problem. If they come back that there's some bending etc. then what you say must be correct and nothing is wrong with the trans that a TCM tune can't cure.
Thanks for the patience guys.
I really think you're over-complicating this. I believe Dave hit this on the head. If the ML was slipping it would cause the issue you're experiencing. A larger stall converter really should have a trans tune with it to adjust lockup and shift points etc.
I get that, and I'm not above saying I'm over complicating or just dead wrong. But what I am seeing is far and away different than another truck with the same setup. He's telling me that he's coupling and locking and I am sitting there at redline spinning away. It makes it hard to believe that all is ok.
Does he have a trans tune? What generation truck? Like has been said, lockup is purely computer controlled. If it was a transmission hard part problem you bet the truck would be throwing a code. The Allison TCM is extremely in-depth with self diagnostics/monitoring. If your converter isn't locking (and its being commanded to from the TCM) it will set a code. Your ECM tuning also is pulling torque out down low to protect stock parts.
I don't want to de-rail the thread, but reading it got me interested in the underlying principles of torque converters. I think I understand them but I have a question. A stock duramax makes peak torque at around 1600 rpm I believe, but the stall of the stock converter is at around 2000 rpm. Does this mean that you typical trying to match the stall with the peak horsepower instead of peak torque? What is the typical criteria for trying to select a torque converter?