Very Bad defueling. Need help :o

[Cknight199]

Okay so these symptoms are not of my truck, but of a friends. We have tested everything as far as electronic tuning goes, turned stuff off that is rarely messed with from tuners just to see if it would change anything and nothing... Been through several Tcm tunes, no luck.

Trucks info:
Lbz 6 speed Alison built by Trent Nell, Unknown what his kit consisted of, standard ml converter with an adjusted stall (so we think). Engine is a built motor, the daily driver tune should be around 750 hp which is what we are testing it on.

Symptoms:
Since the build it's been doing this like crazy, and it has trouble locking the torque converter. Normally It won't lock till 4th gear. We have always thought the problem was just it was lacking a lockup controller, and now we installed one and it made the defueling more noticeable on the shifts. It's not your average defueling, it falls flat on its face then picks itself back up again when it gets in gear.

There was a trans with similar symptoms in the past (hondarider552) but his was only on the 2-3 shift. He had a blown valve seal on the c4. So my question is can a different valve seal blow that will affect all of the shifts? The c1 is what I have heard but just want to get some insight before we tear down a transmission... Are there any other ideas that come to mind to try? We are going to swap his and my Tcm tomorrow and see where it goes from there.

Thanks in advance,
Caden

 

[03spoolindmax]

My truck does it really bad on a 1-2 shift. Only thing I can think of is defueling. I've never changed the tune so I'm not sure. It did it before my TCM tuning though too. I thought all defueling was done threw the ECM and not TCM so I don't think changing Tcms will affect anything. I could be wrong though. Hopefully some one can chime in with more knowledge on this subject and help you out.

 

[mike diesel]

Its not that the torque converter is having issues locking because we all know the Allison inhibits lockup once horsepower is bumped up. The issue is that it plain and simple just blows past every shift point and hangs the gear for a solid 1-2 seconds before shifting the next gear. 1 second being about average and 2 seconds being the more than not "extreme".

We installed a BT lock up box tonight and the box works flawless...but shifting is still suffering terribly.

The trans shifts smooth all around and feels good as far as actually performing and shifting...no bangs, no clunks, no limp mode (never been limped at all) and no abnormal noises/smells/sights. No codes either. It just blows right past every shift point and hangs the gear really bad then shifts like normal and revs to 3600 rpm IIRC and then hangs the gear again really bad and repeats. Best way to descride it is that it just feels like some seriously gnarly defueling.

Were swapping TCM's with a known good, un molested TCM to help rule out any electronic issues. Every effort has been made to fix the shifting issues as far as ECM/TCM tuning is concerned with no luck. Regardless of what limiters and tables are changed it still blows past every shift point.

At this point were leaning towards internal/hard part "issues" but are hesitant to tear the trans apart because with our luck, there will be 0 issues internally...like stated above, trans was built by Trent nell with unknown parts other than a precision ml converter. Truck has dynoed 1080+ horse before but has seem to had this shifting issue regardless of what tune it is on since day one. Only info that was given was that the trans "needed a lockup box" and it will be "good"...so here we are. By all means, this isn't a "bash Trent thread" so please don't turn it into one. Were just looking for solutions to the shifting issues and if anyone knows what Trent may have done/does to his trans builds, that would be great.

 

[hondarider552]

sounds like torn c4 apply piston like my GMC did.
It would hang 1-2 and 2-3 at only WOT
Go in the taps cells in efi scan tool for the 1-2 shift and see what the values are. Is the shift always late on the 1-2/2-3 only at 90% throttle and up?

Kory helped me a lot with my GMC, he even tried to bring the WOT shift down to 2000rpm and mine would still hang at 3400, I feel your pain.


PM'd you my number.

 

[GMC_2002_Dmax]

Who is tuning it ?

 

[Mike L.]

Open up the sump filter and see what's in there.

 

[mike diesel]

sounds like torn c4 apply piston like my GMC did.
It would hang 1-2 and 2-3 at only WOT
Go in the taps cells in efi scan tool for the 1-2 shift and see what the values are. Is the shift always late on the 1-2/2-3 only at 90% throttle and up?

Kory helped me a lot with my GMC, he even tried to bring the WOT shift down to 2000rpm and mine would still hang at 3400, I feel your pain.


PM'd you my number.

We actually referenced back to your thread and figured a torn apply piston but this hangs every gear. As far as I know riding in it yesterday on a 700 horse tune it does it on at least the 2-3, 3-4, 4-5 shifts every time.

We will check out the taps today and the sump. All filters are fairly new as well, maybe 2000 miles on both internal and external with no change in performance when either was replaced. Trans has roughly 20,000 miles on it and has done it since day one is what I was told by my buddy.

It has dynoed 1082 horse 1 time and then weekend driven on the 700ish horse tune ever since with minimal "abuse". And yes it seems to only hang the shifts above 80-90% throttle. If you back off the throttle right before the shift, it seems to make the shift fairly normal.

The owner of the truck is actually a salesman for Starlite diesel, so this truck has had Zachs full attention in the past trying to at least electronically mask the issue so we can figure out what may be causing it and get it fixed the right way.

Thanks for the replys!

 

[mike diesel]

This hangs gears so bad that it has been to the track 1 time and ran a low 14 second quarter mile on the 700 horse tune...other factors may have contributed to the low 14 at that time but as far as I'm concerned even with a terrible 2.0 60', and rolling off the tree, it should still be able to at least break a 12 no problem on that tune.

Last night playing around with it on the highway in my truck, if your in the higher gears so that it only hangs the 4-5 shift, it will walk away from my truck no problem and I have ran a 12.91 on the tune I was running against it with but if we both mash it from down low, I can keep up with it almost no problem.

 

[Mike L.]

I would pull the trans for inspection. Assume everything is wrong until you confirm it's right. Look carefully at the stator support area. Make sure the shaft itself hasn't moved out or twisted. Inspect the C1 valve retainer as it is known for breaking.

 

[Cknight199]

Only question is hondarider said his wasn't shedding any clutch material and all the filters were good, but once he swapped tcm's he found the filters had stuff in it. Just hoping that my Tcm won't screw up his trans...

 

[mike diesel]

I would pull the trans for inspection. Assume everything is wrong until you confirm it's right. Look carefully at the stator support area. Make sure the shaft itself hasn't moved out or twisted. Inspect the C1 valve retainer as it is known for breaking.

Sounds like this is the next step and I appreciate your input very much as well as everyone else:thumb:

 

[Chevy1925]

Only question is hondarider said his wasn't shedding any clutch material and all the filters were good, but once he swapped tcm's he found the filters had stuff in it. Just hoping that my Tcm won't screw up his trans...

ignore that fact. he never opened his trans filter the first time

 

[Cknight199]

sounds like torn c4 apply piston like my GMC did.
It would hang 1-2 and 2-3 at only WOT
Go in the taps cells in efi scan tool for the 1-2 shift and see what the values are. Is the shift always late on the 1-2/2-3 only at 90% throttle and up?

Kory helped me a lot with my GMC, he even tried to bring the WOT shift down to 2000rpm and mine would still hang at 3400, I feel your pain.


PM'd you my number.

He did say it was more noticeable when at WOT than rather at 90% throttle