angling_man

Hi all,

Just signed up to the forum as there's some great info on here. Unfortunately I can't find an answer to my current problem, but forgive me if I missed it in another thread.

I have a 4L80e behind an LS3 in a Shelby Cobra replica. The transmission is controlled using a Powertrain Control Solutions PCM-2000 controller.
The car has only done 2,000 miles in 3 years. Everything is fine, except recently 2nd to 3rd takes over a second to mechanically shift after being commanded. When it does shift though, it's nice and firm. There are no other signs of problems with the transmission and oil level is correct.

As I'm running the PCM-2000 I'm able to log the data and can see exactly what's happening...

All gear shifts up and down (except 2-3) occur within a few hundred milliseconds of being commanded. I can see the solenoids being switched on/off in the datalog and shortly afterwards the revs drop/rise correctly.

With the 2-3 shift, I see the computer switch on the 2-3 shift solenoid. It's then around 1.2s later that the revs drop as it mechanically shifts into 3rd. Note, I'm doing this with TCC locked up throughout the shift, so it's not torque converter slip. I can see there's no slip in the datalog.

I've checked the wiring loom earths and supplies. I've manually powered each solenoid on the loom and can hear them clicking. I've swapped out the 2-3 shift solenoid for a new one. I've checked the transmission case & engine are earthed correctly. I've tried increasing the line pressure and the shifts get firmer, but it still takes ages to shift after being commanded.

I've logged data in auto mode and in manual mode, shifting with the paddle shift. The log is always the same - computer tells 2-3 solenoid to switch on, shift occurs over a second later.

The TCC is locking up correctly too with no slip - I can see this clearly in the data logs. I can see there is no slip in the transmission either, so I'm pretty sure the clutch linings are good as when the transmission does shift, it feels nice and crisp.

So the question is, if I strip this transmission down and inspect it, what should I be looking for? What could be causing 2-3 shift to take so long after the solenoid has switched on?

Any expert opinions would be much appreciated :-)

Many thanks,
AM

Jake's Performance

iTrader: (2)

There are a few reasons for the slow shift.
You need to install a valve body kit to correct it and possibly some other mods.
We corrected this issue years ago and have a valve body kit for the DIYer.

angling_man

Hi, thanks for replying so quickly. I did suspect it might be a valve body issue, so purchased one of the Powertrain Control Solutions 6-speed valve bodies thinking it'd resolve the problem and give me a 6-speed at the same time I got 6 gears, but still had a mechanical delay every time the 2-3 shift solenoid was switched on. I've now swapped back to the original valve body. I may put the 6-speed one back in once I've solved this delay problem.

What are the other mods that help please?

Last night I found a thread on another forum. Somebody suggested removing the #8 check ball for the 3rd clutch feed. Looking at the GM Technician's Guide for the trans, it looks like doing that'll let fluid through to the 3rd clutch quicker and might solve the delay I'm getting. Not sure if it'll have any detrimental effect though. Is it a sensible thing to try?

Thanks,
AM