I really need help here troubleshooting, I had started a crummy rebuild thread going but nobody's looking at it I only took some advice though I've been reading here for decades but I'm sure I missed something important and now I've got a problem that I'm struggling to figure out. I hope some experienced members can help me with a little troubleshooting list given what I have tried so far

The transmission takes off and finds second just fine in all ranges however it does not shift past second gear no matter what you do with it in 2/D/or OD it will ride 2nd all the way to red line. If the shifter is in D the overrun clutches will stay on if the shifter is in OD the overrun clutches stay off as they should.

I have property adjusted the shifter for the different transmission.

No codes are being thrown

I replaced all of the electronics yesterday anyways (careful to check the 2/3 solenoid) with another good set with no change and so today I also replaced the entire valve body with The non-original one that came with the transmission, This one is from an 02 and I know it is good it came off a transmission that would happily shift all four gears, I double checked the 2/3 valve train it moved smoothly this one even has a sonax HD 2-3 shift valve in it and the 3-2 stuff is blocked...

Still no change.

The transmission will however command and hold third and then shift to second when the harness is unplugged.

I checked the third accumulator check ball when I built it and it did not leak ATF though I forgot to tap it with a punch like I was told and I forgot again when I had the valve body off today, I probably should have.

Experience members please guide me where to look next, I've been all through this trial of figuring out how things come together with engines and it's been fun I try to help out in the engine section all the time so give me a hand with the transmissions now I'm eager to learn and figure out what I screwed up so I can be happy again and share what I've learned already 😂

 

Did you bench check your 3/4 clutch before installing into the case? Did you install the green o-ring at the bottom of fhe input drum? Did you air check the input shaft to drum press fit for leaks?

Seems to me you have a massive leak in your 3rd circuit which includes 3/4 clutch and 2/4 band

 

did you use a new internal harness?
your symptoms are that of a "B" solenoid that is stuck ON
bare wire in the harness somewhere could be grounding the solenoid keeping it on

the fact that you get 3rd gear when unplugged, and then still manual 2nd if you shift there, further implies the issue is related to the B solenoid being stuck ON for some reason

 

I did not bench check the 3-4 clutch nor did I air check the drum for leaks. Obviously I'm wishing I had done those things, I already moved a small air compressor over to my transmission working area in case I have to pull the transmission out again

I did change the green o-ring as well as the rest of the seals and the pistons throughout the transmission as well, I used the standard summit racing kit, The only changes I made to the transmission from stock was a transgo-boost valve Corvette servo and plastic check *****.

This transmission I rebuilt I didn't really find anything wrong with it inside other than a burned 3-4. The guy I got it from said it started slipping fourth gear and then lost third? The drum looked good and the orifice cup plug looked fine but it had a lot of miles probably?

I'll see If I can find anything electrically, (I'll check the harness today)I did replace the factory harness with a Rostra harness the one with the stuff wires when I rebuilt it so it could be that.

Otherwise I've got to tear down and air test all the circuits I should have done the first time

 

It sounds like you need to do more investigative work on why 3/4 failed in the first place. 3/4 clutch doesnt just wear out. Things cause it to wear out.

But also look into the electrical side as MaroonMonster suggested. A/B solenoids arent expensive and will interchange.

 

Guys this is really looking like an electrical problem. I just checked over the wiring harness from the PCM all the way to the transmission. This car is well taken care of and I didn't find any damage or rubbing to the harness at least nothing I could see or feel and I always take care to tuck it out of the way when changing transmissions.

I said before that I disconnected the transmission from the PCM and tested it. I did but I wasn't brave enough at that point to go out and drive it again while It was hot from driving it before as I still thought I had a serious mechanical problem. My car has 4.10 gears and 26-in tires so it is very obvious even at low speed as to what gear the car is in. I was able to shift 2-3 but I only tried it in the driveway because it was already hot and I didn't want to burn it up or make it worse and so I let it cool off gave up for the day.

This morning after checking over the wiring outside of the transmission and not seeming to find anything obviously wrong I disconnected it from the transmission and tried driving the car again.

It was very obvious to me that the transmission would start off in third gear with the shifter in OD or D and it will quickly snap to 2nd when you pull it down to 2 and it pops right back into third when you push the shifter back up into D or OD and the overrun clutches still work as they should when in D or OD.

I said the hell with it and I let my 6.0L have at it with trans in limp mode.

The car holds both 2 and 3 Just fine with no slipping felt in the transmission at all and the manual 2-3 shift is nice quick consistent and positive every time

This is my first rebuild and so I fully expected to run into some problems especially given the shortcuts I have taken as far as checking for leaks in the drum but it seems to me that this must be an electrical gremlin and not a hydraulic one because I would think and I could be wrong but any leak inside the transmission severe enough to not allow a 2-3 shift under normal conditions with all of the electronics intact and functioning properly would cause the transmission to slip and it does not slip at all and I have a 3,600 stall and a big cam and sticky tires and I really tried to make it slip this time and it would not. I guess I could just give up a little bit of my 60ft and drag race it like this in limp mode lol yeah right and If my next move doesn't work I don't know what I'm going to do with it

I mentioned before that I did replace the harness with a rostra I suppose next ill change out the internal harness for the ugly old one that I know worked fine and ill cross my fingers that there was something wrong with the rostra
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you get 3rd when harness is unplugged
which tells us the 2-3 shift valvetrain is not sticky/locked up

the B solenoid is just staying active.

find out why and correct it

 

Well I replaced the harness with the old one and put it all back together.

I was thrilled at first it seems to be working normally shifting all four gears as it should so I thought maybe the rostra harness was bad however after only a few minutes of driving around once it warmed up It started acting up again doing the same exact thing as before.

I looked at the plug on the harness the pins didn't look messed up or anything I suppose now I actually have to pull the whole harness out and look at it?

 

You think the solenoid might be physically stuck open, or have some kind of internal leak?

I've seen it happen on other automotive solenoids.

 

it would have to be physically CLOSED not open

it's possible...but OP said he's replaced them and tried another set to no avail

AND...when he unpluggs the harness, he can get 3rd gear...which implies the solenoid isn't stuck closed, and the valve isn't stuck in its bore. Because that valve needs to move in order to get 3rd gear.

I could be mistaken but all of the evidence currently presented is pointing towards the B solenoid electronically stuck ON whenever the harness is plugged in

 

I'm pretty confident at there's something wrong with the main external harness where it plugs in to the internal transmission harness. Thinking about this practically I have R/R The transmission in this car dozens (This is the first rebuild I did myself so hopefully it will last a while) of times having to unplug and plug in that plug so many times so I must have messed it up somehow.

At this point I've replaced all the electronics, the electronics internal harness, and the valve body. I think one of the positive signals from one of the other controls that is always on when the car is running is touching the positive lead on the two 2/3 shift (b) solenoid keeping it stuck on because I do get third when I unplug it.

It's raining here and I had left the car outside from playing around with it so I'm going to wait to mess with it hopefully this afternoon. I looked online and summit it sells the plug with a good length of all 13 wires on it to splice onto the original harness if I can't get mine fixed but it's on back order, so I'd probably just look too hack one off of another old harness somewhere If I can't get mine to look right, I'll let you guys know when I get another chance to look at it.

 

I haven't looked at a wiring schematic, but doesn't the PCM control the ground to turn the B solenoid on? If this is the case, all that is needed to check the harness is unplug the PCM harness from the PCM and check for continuity to ground on the control wire to the B solenoid.

 

Did you install the HD 3-2 Sonnax valve?

 

Update:

I left this problem alone all summer, I wasn't needing to use the car anyway as I've been concentrating on Auto X as I have another car that I use for that.

Gone through and checked all of wiring again, I have a new pigtail but I can't see replacing it as I could find no fault with the electrical system.

Thinking back when I first put the unit together and put it in the car filling it up and starting it for the first time, at first when I got the fluid full and tried to move it it would not move in reverse like it was stuck. Being the genius that I am I gassed it and I remember hearing a little pop and then boom the car popped in the reverse and shot backwards. I didn't think much of this until I remembered it later probably put it out of my head thinking there was an air bubble or something, denial is a wonderful thing.

I started driving it and got the 1-2-2-1 shift pattern right away.

I pulled the valve body off recently and I found that one of the bolts in the middle of the valve body, the end of the bolt was not right it looked broken off. So what did I do? Did I put too long of a bolt in the middle and did it get stuck on the reaction shell or something? I have no idea but I'm sure it screwed something up maybe it cracked the case where I can't see.

Anyways I'll pull it apart soon the rest of the way and see what I did wrong, If I did really ruin the case I have another one that I can clean up and use so we will see

 

Final update for the thread:

I was right I biffed the case putting a longer bolt in the valve body somewhere in the middle where it's stuck up far enough to reach the reaction shell. This didn't hurt the shell much but it did crack the Case a little bit around the bolt hole when it snap the end of it off.

I put together another transmission for my car with the good parts and another good case I had lying around, car drives and shifts Great now. I put a couple hundred miles on it and sold it and immediately turned around and bought an M6 car with the cash.

I still have another '02 Z28 with the original 4L60E in it 230,000 mi, hopefully I learned enough to keep that one going.

 

Thanks for the update.