MaroonMonsterLS1

Rebuilt my 4l60e a couple weeks back and it's been working great. I put 250 easy miles on it, then took it to the track. just 1/8th mile, so I never got into 3rd at wot.

Here's the deal, when in normal driving conditions, everything is perfectly fine. It shifts great. no 2-3 flare, no problems.

When under WOT, it will hit 1-2 just fine, then hit 2-3 just fine, hold for about a half second, then seems to "fall" out of gear. Like 3rd is just slipping. If I let out of it, and roll back into the throttle in 3rd, it will carry solid all the way up until 4th gear, then pull hard into 4th with no slipping. If I'm cruising and force 3rd (D) and lay into it WOT, it will hold and pull just fine. It seems as though the only time it acts up is if i'm doing a continuous 2-3 WOT pull.

The trans has an 8 friction GPZ setup in the 3/4. corvette servo, ultra wide carbon band, 5 pinion planets, HD2 shift kit, 3rd apply drilled to .110, .500 boost valve, molded applies, etc etc. I just can't seem to wrap my head around it.

with how strong it holds in 3rd and 4th, the normal driving conditions being just fine, etc i'm reluctant to blame the clutches. Does anybody have recommendations, experience, etc with a similar problem? Thanks

mrvedit

Do you have HP Tuners?
A log of various trans and engine parameters might indicate where the problem is.
Or hook up a pressure gauge and watch it while driving; perhaps the pressure is dropping during the period.
Also, if you have the stock shallow pan, overfill it by 1/2 quart or consider getting a +1Q deeper pan. The impact of the 2-3 shift might be causing the fluid to move away from the filter pickup; fraction of second later it slips due to low pressure.

MaroonMonsterLS1

Never even thought of the low fluid issue. I do have a pressure gauge and will definitely get it put on when I get back home from my trip. It was fine when I first checked it with a gauge on the first drive, but again, never got into 3rd at WOT with it so that still could be an issue

I do not have HP tuners. I need to get it and am more than confident I could learn it pretty quickly, but I just don't think i'd do enough with it right now to validate the $500 purchase.

I'll throw the gauge on it and watch. Also, would someone like to chime in as to how the truck pan works on our cars? I don't want to worry about scraping the thing every time i pull into a sonic! I have 3 or 4 at the shop and could easily take the 10 minutes to drop the pan and swap em out.

mrvedit

Try the extra 1/2quart first. If that fixes the problem, consider the truck pan.

MaroonMonsterLS1

Sometimes it's the simplest things. Filled it 1/2 qt over full and it pulled hard all the way up into 4th. Might have to look at running the truck pan

clinebarger

Works fine on my car, Stock ride height though.

mrvedit

Glad to hear the 1/2Q overfill worked.

MaroonMonsterLS1

picture is a little tough to see. How far would you say it hangs down past the oil pan?

98CayenneT/A

Here are a few more pictures I just took. I am at stock ride height and clearance is not a issue. Even if I was lowered clearance would not be a issue.
From my concrete floor to the bottom of my pan it is 6 inches on the nuts.

MaroonMonsterLS1

So I got the chance to get the car out of winter storage and took the car for a nice rip. Was disappointed to find the issue is back. Checked fluid level and it didn't change a bit.

Did some thinking and realized that when I previously did my testing, I had a different tire size. So, I did some more testing. It seems like when I use the 245/50r16 drag radials I have, the thing will make back to back 2-3 shifts and just keep on freight training.

If I put in the 255/50r16 tires, it will go back to the odd 2-3 activity. It hits 3rd hard, then acts like it slips. Rpm doesn't jump, motor still behaved like there was a load on it, but the car didn't accelerate, merely maintained speed.

Car is 100% stock tune. Could such a minor tire height change affect the trans? I wouldn't think so but I'm hoping someone else can chime in with some help so I can get this thing ready for some full 1/4 mile passes!

mrvedit

Sounds like your trans is right on the edge of flaring a bit during the 2->3 shift.
Put your pressure gauge on it and report what it reads during the shift.
Drilling the 3rd apply hole a bit bigger might help.
Did you ever put the truck pan on?

MaroonMonsterLS1

I'm out of town for the week, so I won't be able to put the gauge on till I get back, I have not put the truck pan on but plan to the next time I do a fluid change.

I can't remember exactly for sure what the hole is drilled to but I believe .100 is what I used for the 3rd apply.

Once I get the gauge on i will report back. What pressures will be most helpful? Reverse @ idle, 1st @ idle, then each gear while driving?

mrvedit

Blipping the throttle even in Park/neutral generally gets close to the max line pressure.
Reverse also get up there. Best would be to keep an eye (just one) on the gauge while at WOT on the road. If not close to 225psi we should address that.
Drilling the 3rd apply to .100 should be plenty.

MaroonMonsterLS1

Put a gauge on the thing and road tested it
Here are the results:
Park(idle):60psi
Reverse(1500):150
Reverse (2000):180
1st (1500):140
1st(2000):155

1st(WOT):210 drops to 175 as rpm increases

2nd (WOT):150 drops to 120

3rd (WOT): 150 Drops to 120

All shifts were done in d3 and executes flawlessly, pulling strong through all gears with no flare and no "odd slip"

These were all tested with fluid 1/2 1st over fill and with the trans warm.

Seems WAYYYYYY low to me considering I have the transgo hd2 shift kit with boost valve

What's the best place to start trying to correct this problem? Do i start with the force motor, the boost valve,boost valve spring, the pump, etc

MaroonMonsterLS1

Here is a video I took of the gauge. The increments are a little hard to see, but it's 60 at idle while I flap my gums, then the increments are 30psi from there. Hope this video is in some way useful

mrvedit

Diagnosing such a significant drop in line pressure as both the RPM increases and in higher gears is outside my experience.
My guess, and this is just a guess, is that the drop as RPM increases is due to a pump problem. Do you know if the HD2 kit's high pressure pump spring was installed? Perhaps not and perhaps the original stock one is now very weak.

Hopefully one of the pros has some suggestions.

MaroonMonsterLS1

The pump has new hardened rings, new spring, and new boost valve. Not sure what could make it leak away almost 70psi worth of pressure that should be there

Game ova

I have zero experience with the 4l60. But I'm assuming you have the iron rings on your pump/forward drum.... and elsewhere in the tranny. We're the areas that those rings are located still snooth.....or were they worn? Just thinking maybe that's where the pressure loss is.

MaroonMonsterLS1

Everything looked great when it went back together. The only real reason for the hardened rings in the pump is for high rpm applications.

MaroonMonsterLS1

I'm wondering if the pump spring could be the problem here. It seems like since the pressure falls off with rpm, it could be a matter of the pump slide spring.

Can i install the sonnax slide spring space part #77917-RV
ALONG with the slide spring itself part #77722-01K

Does this seem like a logical solution to my problem, or is there something else more likely to be causing my problem?

Lastly, before i buy parts and tear the whole trans apart, could I just turn the EPC solenoid screw i a 1/4 turn and see if there is any positive result? That would let me know if I'm bleeding off the pressure or if the pump is just physically maxed out.