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I seem to remember that it is capable of making 200 psi in "D", and 275 psi in "R" when no current gets to the EPC solenoid. Sounds OK to me...
Right. Actually a bit high in Reverse.
I just don't see how the EPC can significantly reduce the Reverse pressure (below 75psi) unless something is really ****-eyed in the boost valve area.
I know the Reverse feed pressurizes between the ***** of the boost valve, but don't see how that moves the boost valve to increase pressure. However it must work because Reverse normally has much higher pressure than Park or Drive. The PCM cannot distinguish Reverse from Drive and therefore the PCM/EPC cannot be increasing the line pressure in Reverse.
Guess we'll see the result when the OP installs the Sonnax boost valve.
You are diagnosing problems with professionally built transmissions.
I'm often diagnosing problems due to missing/wrong parts or wrong assembly by amateur builders.
Any time you have a spool valve with different sized lands such as the boost valve in a 4L60E, the valve will be hydraulically pushed toward the larger of the two lands, but only by the amount of the difference in surface area of the two lands.
Example: an OEM .471" boost valve has a diameter of .471" on the small land, and a diameter of .505" on the larger land. The size of the portion between the spools is .275". If you figure the surface area of all of those, you can figure out how much force a valve will generate.
Small land surface area: .1742 sq.in.
Large Land surface area: .2002 sq.in.
Portion between the lands: .0593 sq. in.
So, the small land has an acting surface area of .1149 sq.in (.1742 - .0593 = .1149 sq.in.). And the large land has an acting surface area of .1409 sq.in (.2002 - .0593 = .1409 sq. in.). So, the difference, and thus the surface area that will actually generate force to act on the pressure regulator valve is only .026 sq.in. (.2002 - .1742 = .026 sq.in.). That is not very much area at all, which is why there is not much boost from the R/I pressure acting on the boost valve.
100 psi of pressure on the .471" land (EPC oil) will produce 17.42 lbs of force on the end of the PR valve. That same 100 psi of pressure between the lands of the boost valve (R/I oil) will only generate 2.6 lbs of force on the end of the PR valve.
EPC is the main source of line pressure boost in both forward and reverse...
What's wrong with the servo pin? I pretty much don't ever have to replace servo pins. How much servo clearance do you have? You're slipping in 2nd because you don't have enough line pressure...
Check out post #54, OP Says, "I was able to get under the car to check servo play tonight and it was definitely close to 1/4". I put 1 gold shim in and the trans still slips. I'll have to order some when I order the pressure gauge."
The servo pin should have around an 1/8" of movement from what I have read. I hope someone can chime in and concur or refute this.
If you have 1/4" of servo travel then either your band is wasted, or the R/I drum is undersized (or both). You ideally want .060-.080" for a good 2-3 shift.
The gold shim in the Transgo kit is an attempt to tighten up the servo clearance on a worn band to help the 2-3 shift. While it does decrease servo travel, it is a band-aid for a worn out band.
Any time you have a spool valve with different sized lands such as the boost valve in a 4L60E, the valve will be hydraulically pushed toward the larger of the two lands, but only by the amount of the difference in surface area of the two lands....
Thank you for the detailed explanation. Guess I didn't notice the difference in diameter of the two lands.
I have a completely disassembled 4L60E in the basement for such research/learning and to answer assembly questions.
I've compared my tune file to base tunes and don't really see anywhere that could be causing me to have tune related issues. If anyone wanted to look at the tune, feel free.
"While it does decrease servo travel, it is a band-aid for a worn out band." It is not a Band-Aid for a worn out band. The shim is to adjust band clearance only. TransGo will tell you that the kit does not fix worn out clutches or band. The transmission must be in good working order for their kit to work.
Put everything back together and just played with VCM controls while watching the pressure gauage. I started at 0 mA and went to 1A and did not see pressure move at all(Since I started at 0mA it just stayed at 250psi+). Unfortunately I don't have a good way to route the pressure hose so I will need to do the test drive without actual pressure.
EDIT: Just took the car out while commanding full line pressure...clutches are toast. Only have 1st gear and a little bit in 4th.
Last edited by NJNETSFAN; Jan 31, 2016 at 12:00 PM.
"While it does decrease servo travel, it is a band-aid for a worn out band." It is not a Band-Aid for a worn out band. The shim is to adjust band clearance only. TransGo will tell you that the kit does not fix worn out clutches or band. The transmission must be in good working order for their kit to work.
If your band isn't worn out or your R/I drum isn't worn undersized, you won't need a shim. With a healthy band and drum, you shouldn't need more than an OEM 2-groove servo pin to get your servo travel set where it needs to be. If servo travel is too much with that setup, you have something worn excessively, and your transmission is no longer "healthy".
Transmission is out of the car. I took the servo out and saw a lot of clutch material in the fluid there. I will see how much I tear down tomorrow before the super bowl.
Was able to get the a decent amount done today. It's amazing how quick things come apart when you've already done it once. The 24 band did not look back, there was some slight discolorating on the reverse input drum, but the band itself still looks new. The 34 clutch pack was toast just from checking the end play.
Where did that Reverse Input drum come from? I always use a new AC-Delco RI drum when using a "wide" 2/4 Band, Drums from trans part suppliers are usually "Turned" OE drums & are undersize! You should not have 1/4" travel with that much "meat" on the band.
The Band looks fine, The 3-4 clutches will burn down first. You needed to find the reason for no Pressure Rise before pulling the unit. Installing new frictions will NOT fix anything.
Where did that Reverse Input drum come from? I always use a new AC-Delco RI drum when using a "wide" 2/4 Band, Drums from trans part suppliers are usually "Turned" OE drums & are undersize! You should not have 1/4" travel with that much "meat" on the band.
The Band looks fine, The 3-4 clutches will burn down first. You needed to find the reason for no Pressure Rise before pulling the unit. Installing new frictions will NOT fix anything.
That reverse Input drum was not replaced when I rebuilt it last year. The trans was rebuilt once before I ever opened it up so i can't say much about it. I believe the servo pin was the issue for extra end play. I will be replacing the force motor and pressure manifold switch for safety. Once I get the trans back together I plan on putting the gauge on it to check line pressure.
NJNETSFAN, how much are you planning to spend on the EPC and MPS? There's an AC Delco kit that has every single electric part, including the harness, and it may be cheaper than buying the EPC and MPS individually.
A new AC Delco reverse input drum is about $80-90. I paid $70 shipped a year ago but for some reason all 4l60e parts have dramatically jumped in prices since then, including solenoids and the MPS.
@coryforsenate I went with the AC Delco master kit for about $130 shipped. I also spoke with Dynamic and got the BorqWarner High Energy 34 clutch pack setup he suggested. Parts should start rolling in this week and hopefully this weekend I can get it back together.
Started putting things back together tonight. I replaced the 34 clutch pack and forward clutches. The 34 was toast but the forward clutches still looked new; Dynamic hooked me up with new frictions and steels so I replaced the forward clutches. One thing that is going in this build that was not in my first build are the 34 clutch load springs with brand new sonnax boost springs:
And here is a picture of all of where I stopped for the night:
In the morning I plan on testing the input drum seals and then assembling all of the clutches back into the case. Hopefully by tomorrow night the transmission will be mostly put back together and I can spend Sunday starting to put it back in the car.
I made a lot of progress today. I installed the drums into the trans, 24 band, and pump. I then dissasembled my old 24 servo and installed a new servo pin as well as the "corvette" servo. I cleaned all of the accumulators in the valve body and then installed the valve body. I also replaced all of the solenoids/EPM/and force motor. The trans is ready to go back in the car. The end play on the servo is somewhere right in spec between 1/16-1/8".
Looking good. I'm sure assembly seemed easier the 2nd (or n'th) time.
Did you check/estimate the end play on the input shaft?
The spec is .015 to .035.
I think you'll like the corvette servo. It gives just enough kick to be noticeable. It can be a little annoying in stop and go traffic, but otherwise it's great.
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