Hi All,

I've rebuilt a few 4l80e transmissions with the help provided from Jake, Clinebarger, the Sloppy Wiki and a few others who have generously shared with the online community but am stumped with an issue I'm having.

At a stop, quickly break-standing the thing produced the following pressure

Reverse = 270
OD, D & 1 = 180
Manual 2 = 145

I'm left to assume I have a leak in the intermediate circuit somewhere.

While driving I noticed the pressure tends to dip, then recover. In manual 2nd it dips substantially as seen in the videos below, then recovers to its original low state. starting in 1st while the selector is in D produced a less significant dip:

Manual 2nd from a roll

From a stop in D

In both of these videos my foot was planted to the floor.

I plan to blow the thing apart this weekend and replace the intermediates which are now smoked. I'll air check everything again and see if I can find a leak but don't know where else to go from here.

It's a 2004 4l80e, dual fed directs, rollerized output shaft, new bonded pistons throughout, new frictions/steels, LB1-4L80e boost valve w/stock spring, new EPC solenoid, Sonnax AFL oversized valve, deleted 3/4 accumulators and some other stuff that doesn't come to mind. Basic upgrades and this is the third 4l80e that I've given this treatment to and the other two worked out beautifully.

I checked the dipstick level when installing it and it's accurate and it's currently at the top of full.

Any guidance would be appreciated.

 

How did the intermediate over-run band look?

 

I haven't got it out yet so I don't know but doubt it's bad as the only time they've slipped have been while in D. My understanding is that the band only engages in manual 2nd.

 

I may have misunderstood you, but...

Didn't you say that using the transmission in Manual 2nd gear is when the line pressure drops?
Yes that band is only used in Manual 2nd.

Was the problem in D3 or D2? I am now confused.

 

What is the EPC amperage doing during these tests?

 

Apologies, I wasn't very clear on my initial post about that. I always drive around in D and while the trans was automatically shifting I noticed 2nd gear slipping, which led me to test pressure with the selector manually in 2nd. I never actually got it to slip while manually in 2nd as I kept the boost low when checking pressure to avoid that. When I crank it up is when it's currently slipping which is no more than 600 flywheel hp.

 

I don't actually know but assumed it was a hydraulic issue given it only affects one gear. The HP Tuners scanner shows it's requesting full line pressure. If this info is worthwhile, I can test it.

 

Understood. :-)

 

Maroon Monster was asking what the amperage was, in order to see if the EPC is doing what it should relative to what the transmission needs/ the PCM commands.

 

I'm assuming I can just tap into the harness and manually check this? If I just unplug the connector on the side of the transmission it should max out the line pressure, right? If line pressure takes the same dip while unplugged I can eliminate the EPC from the equation. I'm open to ideas if there is a better method.

 

HPTuners can just view the EPC Control Amperage
Or any decent scan tool

Yes, unplugging the harness would also be a fine way to check if the dip is still there

 

I just tested the pressure again with it unplugged and it still dips under heavy load, then recovers to some degree. I noticed the pressure was much lower while unplugged until I gave it a bit of throttle. It would sit at 30 and just about fall out of gear (or so it felt) until I tapped the throttle and it bounced up over 60.

Safe to assume the issue is hydraulic at this point. I'll have it apart Saturday but am open to any areas I should be focused as I changed out most of what I can think to change a few months ago when it was rebuilt.

 

...hmm

You should have full line pressure when you "Power-Brake"/ raise the engine speed up to 1,300 - 1,500 Rpm; with the EPC solenoid disconnected.
What was the highest readings that you found?
What gear ranges did you have only 30 Psi of line pressure... That is BAD!

 

With the selector in OD or D it produced 30 at idle, however with the connector unplugged it defaults to 2nd gear only, which leads me to believe my issue is specifically related to the intermediate circuit. Reverse had 270 psi with a slight touch of the throttle.

 

When the transmission case electrical connector is unplugged...
The transmission is supposed to only have second gear (This is because 2nd gear uses both shift solenoids off).

 

Well, my findings today were disappointing as things were worse than anticipated. Needless to say, the intermediates were not happy - the pressure plate was even deformed. Clearly this was slipping more than I realized as I just expected to see some heat spots and worn clutches. The direct drum had to be removed with a puller as the intermediates didn't want to let go.



I was also surprised to see the sun shaft bushing was wasted as this bushing was just replaced back in January along with many others. As to be expected, the main shaft wasn't happy either.





I purchased a replacement shaft and will replace the sun shaft bushing again. I've been lucky to this point and every 4l80e I've done has gone smoothly - this one apparently doesn't want to go that way. I guess I'll keep updating this thread as a log which may benefit someone later, assuming it comes to a conclusion other than me trashing it and starting with a new core. I'm open to any advice or suggestions others may be willing to offer.

Parts should arrive before the weekend when I get to go back at it again.

 

It is not uncommon to see wear-problems at the sun-gear shaft bushings when using the stock "Late Center-Lube" system.

 

Suggestions:
Inspect center support for cracks/leaks.
Make sure the center support bolt is properly torqued
Check center support to case sealing area. Make sure the finish on both is good.
Vacuum test the entire valve body.
Vacuum test the pump. Specifically the boost valve and PR valve.
If replacing the mainshaft, get an early shaft with hollow center and machine the end to get proper fit and endplay if needed.
Be cautious when replacing sun tube bushings. They are "finish in place" bushings. You'll need to drive the new bushings in, deburr the edge, then use a small brake caliper hone to get proper fit. Some need about 2 seconds with the hone, some need 30.
Check the TCC valve and circuit for leaks. D2 oil feeds the TCC circuit...make sure it's not bleeding off all the oil.
Inspect the accumulator inside the low band servo. This is another area 2nd gear fluid can bleed off.
Verify "full" level on the dipstick

 

Note: The 2nd accumulator piston seals are not the greatest...

There are plenty of guys who will use IRON sealing rings from a THM400 transmission here instead.

I found the best solution to be After-market D-rings from Precision International instead of the teflon rings.
It is common to see people use this type of ring for the 4L60E servo pistons.

Both transmissions need the corresponding bores lightly deglazed with a scotchbrite pad and cleaned out.

 

Thank you all for the suggestions offered. While going through the valve body I saw the smoking gun: It was a bone-head mistake. The TCC PWM solenoid had came loose. One of the o-rings had pinched themselves in the bore when installing it last time and kept it from sitting flush. It therefore never sat close enough to catch the clip in the right spot and was blown out of the bore about 1/4 of an inch. This was my giant leak. New intermediate frictions, steels and a pressure plate later and it's all good. The main shaft was also replaced. I just wanted to conclude this thread for future searches and thank those who offered help. 180psi in all forward gears and 330psi in reverse now.