wanting10s

I have a 4L60e that was just installed by a reputable transmission shop. The trans has been built specifically for high drag application. The trans performs very well except for

one issue that they have not been able to solve; under WOT it has trouble shifting into 3rd gear. It will hit the rev limiter and not shift into 3rd, even if you back off for a

split second and go again it will not up upshift until you back right off and let the box settle. I have taken it back a few times any they are able to fix it temporarily with

tuning and other adjustments, but the issue comes back after 2-4 weeks (three times now). The problem is more likely to happen if the wheels had been spinning in 2nd. When it

does shift into 3rd the shift is tight.

They have tried dropping RPM and road speed values in the tune but this has not solved the issue.


Vehicle details
supercharged LS1 - approx 600 HP engine power
approx 3500 RPM stall converter
3.9 diff gears
factory drive-by-wire setup
factory 6250 RPM rev limiter

mrvedit

Sounds like your 3/4 clutch is slipping due to a poor build, plain parts, low line pressure or a combination of those.
Think of your tires at a launch - if they spin/slip, you have to back way off to get traction again, but can then go WOT again without slippage. Same with a clutch in a transmission.
I would want to know the following:
The actual measured line pressure during that shift - a $35 pressure gauge can tell you that.
What frictions and how many were used in the 3/4 clutch - the shop should be able to tell you that.
What size was the 3rd feed hole drilled in the separator plate - the shop should be able to tell you that.
What boost valve was installed? The shop can tell you that.
Was the Sonnax HD 2-3 shift valve installed? The shop can tell you that.
If not you should be dragging in OD and not D3. Iff installed, you should drag in D3.

Get the answer to at least the shop questions and we can tell you whether the trans was built to handle 600HP.

wanting10s

Hi mrvedit. Thank you for responding.

I should clarify. When I took the car to the drag strip it shifted 2-3 every time, nice and sharp. The issue that I'm experiencing occurs when I am on the street and floor it in 2nd, if the wheels spin (even slightly) it will not shift into 3rd, just bangs the rev limiter.

I will get some of the details you've requested from the detailed invoice, and contact the shop to get the rest - it usually takes a few days before I get a response from them.

mrvedit

Thanks for the additional info.
It would help if you connect a scanner that reads/logs the gear shift commands from the PCM. If the PCM commands the shift to 3rd and the trans doesn't immediately do it, you might have a trans issue. I say "might" because the PCM should also be commanding max line pressure during high throttle operation.
It could be that due to some characteristics and/or tuning, that the PCM is not commanding max line pressure causing the 3/4 clutch to slip.

wanting10s

Thanks mrvedit for your continued assistance with this.

Following your recommendations I am going to try and get my hands on an OBD2 scanner that can extract live stats about the trans. Does anyone know if there are any reasonably priced Android or Windows apps that can do this? I already have an ELM 327 cable to use.

Also, I've attached the details I have about the box build. Hopefully this can provide some clues about what might be happening?

MaroonMonsterLS1

I use dash command and paid the extra $10 for the vehichle specific package. Commanded gear, trans temp, timing pulled (for viewing torque management), etc.

soloman369

iTrader: (13)

That built sheet does not look like a drag build for a 4l60e JS....

wanting10s

Thanks for your suggestion MaroonMonsterLS1. I will check out that one.

Also thanks Soloman369. I was a bit worried to begin with when they suggested a 600hp box build from my specs; I told them from the start that my car made 375rwkw through the old auto. Also it's supercharged so possibly making a lot of torque.

What extra bits would you expect to see in this list?

mrvedit

I'll assume the "Input Drum strengthening kit" is the Sonnax Reinforcement kit, which is good. The "Custom Shift Kit" probably includes a bigger boost valve, which is good.
However, there is no mention of what frictions are used in the critical 3/4 clutch.
A 600HP build should also have 5-pinion planetaries (not mentioned) and perhaps a billet output shaft (also not mentioned).

My current guess is that the PCM is not commanding max line pressure in all situations where it should. With the SC the max line pressure should be commanded at a much lower throttle position.

RevGTO

iTrader: (12)

With your converter and wheelspin, the PCM could see a discrepancy between vehicle speed and engine rpm and throw the tranny into limp mode, effectively defeating the 2-3 shift. This happened to me at the track a few times after doing my burnout following the install of my 3600 converter. The tranny would not shift out of second.

If this is the problem, the fix is to tune various DTC's (P0502, 751, 752, 756, 1870) to no report.

wanting10s

Thanks mrvedit. Even when I have this problem solved I'm wondering just how long this box is going to last

Thanks RevGTO. Will any/all of these codes be logged in the ECU? Because the only fault I have seen is P0102.

RevGTO

iTrader: (12)

Oftentimes this doesn't throw a code at all, but the only one I saw was the VSS low voltage P0502.

A tuning factor that could be an issue could be a conflict between the WOT commanded shift at vehicle speed and the WOT commanded shift at RPM. But if this was the case, it wouldn't ever upshift normally.

wanting10s

I have some more info about the problem; I have just now followed MaroonMonsterLS1 recommendation of using Dashcommand. I have tested a few times and have observed that the PCM is not commanding 3rd when the issue occurs. Data shows 6400 RPM, 117km/h, throttle is 99.6%, but commanded gear is still 2nd.

RevGTO, do you think this backs up your suggestion, even considering none of these faults are logged? Is there any free software I can use to check if reporting of the codes you've listed have been disabled? I thought the guys who setup the trans would be on top of this???

mrvedit

Well its kinda good news that the PCM is not commanding 3rd because it now sounds like your trans is working OK. Fixing PCM/Tune issues might not necessarily be easier, but generally cheaper and definitely cleaner.

RevGTO

iTrader: (12)

Yes, I would think the tranny guys would be on top of it, but apparently not. The only way to address these issues is with tuning software. So tuning out those DTC is one approach. The other is to make sure that the VSS upshift command occurs BEFORE the RPM upshift command at WOT.

wanting10s

I've messaged the shop asking if they can email me shift tables and details about any fault codes that have reporting turned off. I might be able to research and find the problem then get a local engine tuner to fix the issue.

Getting the car to the trans shop is a one-day round trip for me. Having to leave it there over night is even more of a headache.

MaroonMonsterLS1

Why do you say to make sure the speed command doesn't happen before the rpm command? This is opposite of what I've come to understand.

Both speed and rpm need to be satisfied for the shift to happen, so, many guys will have the pcm see the speed parameter met first then it waits on the rpm parameter to be met and initiates the shift. Either way should work but many tune based on rpm being fulfilled 2nd.

RevGTO

iTrader: (12)

After thinking about it, you're right, I had it backwards. It's been 10 years or so since I did a lot of tranny tuning and my memory was fuzzy ... I do remember having it the wrong way tuning a friend's car and it wouldn't upshift.

OP, please note and I will edit my post above.

wanting10s

I think we're getting somewhere with this. Hopefully the shop will be able to email me the tables and other details then I can carefully review them. I will post up more info as it comes through. Thanks all for your valuable input.

wanting10s

Looks like we can put this one to bed! I saw my local tuner today and we fixed the issue!

We set codes 751 752 756 and 757 to No report, and the issue hasn't happened since (despite some rigorous testing.)

My tuner was a bit surprised but suspects that when the stall converter was serviced (after the old box died) the bearing clearances had changed and caused the stally to respond differently, hence triggering the codes.

*** Please note that at no point were any of these codes logged ***

Thanks again for all the help provided here.