Hey Folks,

My first post, and I've spent weeks reading this forum and trying to soak as much knowledge as possible. I just recently swapped the engine out of my 2003 Silverado 1500 4x4 (swapped the 4.8L for a LQ9 6.0L), and while the engine was out, I thought it would be a good idea to rebuild/upgrade the transmission. I'm by no means a seasoned mechanic, but I love to learn/tinker and wanted to give this a try. I spent two weeks rebuilding the transmission (a little each day) and followed a set of instructions very carefully. I made the following replacements and upgrades during the rebuild:

Replacements:
Soft goods (gaskets, seals, orings, etc...), cooler line fittings, manifold pressure switch, filters, A&B solenoids, steels, fwd piston set, clutches, input sprag (one of the sprag elements fell out during rebuild), replaced torque converter with TMBX converter (recommended to me since swapping to 6.0l engine), band, neutral safety switch

Upgrades:
Sonnax heavy duty pickup build option A (line pressure booster kit, heavy duty reaction shell, 4th gear super hold servo, heavy duty 2-3 shift valve), corvette servo, Sonnax pinless accumulator pistons, added additional conical cushion spring parallel to OE cushion spring, Sonnax TCC valve and isolator sleeve kit (reamed out the hole using Sonnax reamer)

On the maiden voyage, the truck wouldn't shift automatically at all. I could manually shift into 1/2/3, but I reckoned I was in limp mode. Turns out the new VSS was bad (resistance reading was way off), so I replaced with the original one which fixed that. Now, the only thing I'm noticing is a bit of "flare"/hesitation between 2-3 gear when I'm in D. Sometimes it's there and sometimes not. The rpm's don't seem to change that much and it really feels more like a hesitation than anything else. Like the transmission is trying to shift into 3rd gear, pauses a sec, then shifts into 3rd. I pulled the upgraded servo parts, and put the OE part back in to see if that would make a difference. It didn't so I put the upgraded parts back in.

Here is what I was going to do next (in order): check the line pressure, check the resistances on the solenoids using a test harness, drain the pan and refill plus 1/2qt or so, ???

If y'all have any advice on how to diagnose this, I would really appreciate it. If you need additional info, please let me know. Thanks in advance.

Jim

 

What is your band clearance?

What was your 3-4 clutch clearance?

 

Thanks for the reply. I used the OE servo pin, and the travel was within the 0.075"-0.125" specified in the Sonnax 4th gear super hold servo kit instructions (measured with a dial indicator). I didn't write down exactly what it was, but it was around 0.085" if I remember right. The 3-4 clutch clearance was between 0.060"-0.085". I checked that during the rebuild.

 

Checked the line pressure today at idle. P-N-D-3-2-1 all around 75psi, R around 105psi.

 

how does it act when you manually shift it?

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I know this is a dumb question, but what do you mean when you say manually shift it? Start out in 1st and go through 3rd manually, or start out in 3rd and let it automatically shift?

 

He meant:

-Place the gear selector in the "1" position...
-Then shift to the "2" position at the appropriate time...
-Then shift to the "3" position at the appropriate time...
-Then shift to the "4" position at the appropriate time.

 

As 98Cayenne started you off perfectly with the correct questions... I will continue until he returns or someone else also chimes in.

Bigger Factors for 2-3 feel/ timing/ performance:

-Three-Four clutch pack: Friction Material (High Energy), clearance (0.030" to 0.055"). Your clearance of 0.060" to 0.085" is better than stock, but a bit too lose for a performance feel/ use on the 2-3 shift... High Energy Frictions should be used.
-Two-Four band: Friction Material (High Energy or a Carbon/ Graphite mix), Drum surface (New or 100% Flat), clearance (0.060" to 0.085") Your clearance of 0.075" to 0.125" is better than stock, but a bit too lose for a performance feel/ use on the 2-3 shift...
When using the GM "Corvette" calibration Intermediate Servo, you should tighten-up the clearance to what I typed above. Your drum surface must be perfect. The band should be High Energy or a Carbon/ Graphite mix.

-Addressing hydraulic leaks that involve the Three-Four Clutch pack applying in order to shift into Third gear...
There are many leaks through the valve-body; a quality shift-kit from Transgo will address some of them, and Sonnax sells small parts to also address these leaks.
If you are going to remove the valve-body, we can go into some detail.
Part of this process will involve disabling two of the valves in the valve-body, by blocking them in a fixed position (3-2 Control Valve and 3-2 Down-Shift Valve)

-The Separator Plate will also have some of the feed and exhaust passages enlarged for the proper 2-3 shift.

Note: If you installed a Sonnax "Servo Check-Valve" for the Third accumulator check-ball capsule; REMOVE IT!

If you would like to proceed with valve-body removal to try and improve things... then post your replay.
If the drum for the Two-Four band is good and your clearances are closer to the tighter end of the range... some improvement should be made.

 

vorteciroc, thanks for the information. I'm definitely down to remove the valve body and make modifications if y'all think that is a good place to start. Keep in mind that this is meant to be a DD, and I simply want a good shifting vehicle in the end.

Also, when I did the rebuild, I changed the band, but I kept the drum. I used a straight edge and light, and it looked good to me. I assume adjusting the 3-4 clutch pack would mean dropping the tranny again, and I really would like to avoid that for now if at all possible. I'm working by myself in the driveway, and I cant stomach having to do that right now after just putting everything back in. Seems like I'm right there...just need a little help fine tuning things. I could be wrong.

 

Yes, in most situations the valve-body alone can make significant improvements (as long as there are no major issues, or BIG circuit leaks).

Read through the Article in the Hyper-Link below to get some idea of just how many places can leak the circuits involving the 3-4 clutch:

4L60E 3-4 Clutch circuit leaks

 

I’ll read the article, thx. Is there a way to test for big leaks in that circuit with the transmission installed?

 

What does line pressure do when you're driving it, in particular during the 2-3 shift?

Both your band and your 3-4 clearance are on the pretty loose side, but with enough line pressure, it should not flare.

 

Stays pretty constant between shifts. Stays right around 75psi through all shifts. No clue whether that is normal or not. If a flare is a sharp rise in rpm, that isn’t what mine is doing. Feels like it’s about to shift, then hesitates for a sec and shifts. If anything, the rpm may even go down slightly.

 

If you are staying at 75 psi, then that is your problem. Your pressure is low, and you are getting no line pressure rise. You should be seeing anywhere from 130-190 psi under load, depending upon throttle setting...the greater the throttle setting, the higher the line pressure you should be seeing. With 75 psi as a base line pressure, I would look at the EPC solenoid. It may be plugged. You should be seeing 90-100 psi as a base pressure.

 

Any suggestions on troubleshooting low line pressure?? TIA.

 

Pull the main connector (the big round one) off of the transmission, start the engine, and watch the pressure gauge. It should read max line pressure for forward gears (appx. 180-190 psi). (Bear in mind, you will set a bunch of transmission codes, and it will be in 3rd gear, but with no current to the EPC solenoid, you should see max line pressure. Don't drive it this way, just check line pressure. You can clear the codes when done.)

 

Doing some research, could this have something to do with transmission adaptive pressure (TAP). I didn’t reset anything when I put the tranny back in.

Also, what will the pull plug test tell me about the tranny function? For example, if I see the ~200psi.

 

It will remove all power from the solenoids, and thus pulling the EPC solenoid wide open. It will tell you whether or not, if commanded to, the transmission is capable of making the pressure it needs. With the EPC solenoid wide open, there should be maximum boost pressure from the AFL valve at the boost valve (if the solenoid is working properly), and you should see max line pressure on your gauge.

 

Awesome. I'll do that test today and let you know what I find out. Assuming I get full pressure, what's the next step?

 

If you see full pressure with the connector unplugged, the next step is to find out why it's not commanding the correct pressure (ie. external electrical, tuning, etc.). If you don't see full pressure, you're looking at internal hydraulics (ie. the solenoid itself, AFL regulator, boost valve, pump, etc.). Given that you're only seeing 75 psi, which is low even for base line pressure, I'm guessing something in the valve body (solenoid, AFL regulator, etc.). That's just my guess based on what I've seen.