Hey guys. I posted a couple months ago about putting the kit together for building my 4l60e. I just got the trans back in the truck and picked it up last week. had a rear brake issue, parking brake was locked and dragging so i was parked until today when I had time to work on it and get it freed up. Truck sat a while.

Fast forward today and I got the brakes 100%. all tires spin freely, Got in to test drive it and it felt like it was still dragging. Pretty quickly realized the trans isnt shifting. I drove it home the night i picked it up and if shifted fine. (15 mile drive) it sat, and today was the second time I drove it. it doesnt even shift into second when I pull the stick into d2. Interestingly, I cant pull into d1. Im not sure why but its a hard stop at d2. D4 does appear to be actual overdrive however, and d3 on the stick does seem to be the real d3. but d2 does nothing and d1 is inaccesible. The truck feels like its starting in 3rd it gets to 60mph at roughly 3000rpm so I think its gonna be third. Even if I command manual 1 and manual 2 in HP Tuners, it doesnt actually go to 2. The "current gear" keeps changing in the scan tool like its shifting, but its definitely not shifting. I had it built buy a very experienced shop and i feel like the build is probably good. Im wondering if maybe its something in either the valve body I bought, or the Computer.

One main note, I do have a p0756 code. The truck is a 96 k1500. I replaced the 1 piece trans with a 2 peice (removable bell housing) trans out of a 99 tahoe (supposedly) I purchased a new tube and new dipstick for the 99 tahoe and that is whats installed. The truck is 411 swapped and has a 2002 express van tune in it, stock other then rear o2 sensor delete. Is it possible this trans is newer than 99 and needs a different dipstick? Fluid low can cause 756 correct? right on the hot line with it warmed up and in park engine running.


any thoughts on what I should check here? It seems odd to me the pcm is shifting through the gears on screen but not actually shifting. one other syptom. even if i get it up to highway speeds, 70mph, it doesnt shift to 4th unless i command it in the scanner. soon as i take the demand off it goes back to 3rd.

 

It sounds as if you have a mechanical shift linkage problem, either internal or external. If internal it could be confusing the PCM as to what gear the trans is actually in. I would short that out 1st and then go from there.

 

Agree I would sort the manual shift positions first then move on from there , But since you will probable have pan down anyway. I would change shift sol b and verify as best you can stroke of the 2-3 valve inboard, they have no spring so wont come back out, but if its causing the code would be because its stuck outboard. and that would cause a 4 gear start when 1st is commanded followed by 3rd then 4th again if it does not go to limp mod which it should , But sometimes they do not,
That code should cause limp mod ,
Another possibility is the valve IF USED IN THAT BODY behind the 3-2 valve is MISSING will cause massive AFL leak and no shifts. Alternately the clip could be missing from the PWM or 3-2 solenoid, PWM is a common miss on assembly so check all while you are there , should be able to do all without removing VB .

 

Frank its interesting you say that about 1st. I did verify that D4 is actually 4th gear when commanded, based on the speed vs rpm. So while there is a shift linkage issue for first, it does appear that d4 is d4, and it shows d4 in the PCM.

I might add, after the last test session the trans pan was HOT. significantly hotter than the engine.

However, what you just said that triggered me, is that I put the truck up on jack stands to determine if something in the 4wd was dragging. I noticed that when I commanded 1st gear on the jack stands, the rear wheels SPED UP, with no chagne in the engine RPM. I thought this was odd, but I chocked it up to maybe the TCC slipping or something with no load on the truck and just throttle held at 1000rpm. I thought to myself that maybe in first with it being a little easier to spin the tires, maybe it was just the TCC slipping less. I should have looked at the slip numbers but i didnt.


One last thing. since this truck is 411 swapped... should I, engine off, trans harness unplugged, start probing the pins for voltage while manually commanding shifts in the pcm?

 

I tend to think, Other than some linkage issue that you are indeed starting in 4th, 1st gear commanded without the 2-3 shift valve stroked is 4th and the wheels speeding up would pretty much verify that when you commanded 1st. Now this would only work in D4 if the same situation was created in D3 you would have 3rd gear and in manual second you would actually have 2nd. If you commanded 1st in this condition in manual low one you would still have second.
I would drop the pan since you are not getting electrical codes and check solenoid b and and the 2-3 shift valve myself . OH AND NEW solenoids can be bad, Seen it many times, Even seen them work at first then fail on the dyno more than once.
Another possibility and I have seen this a few times (cleanliness is godleness in a 4L60E ) something may have blocked the orice hole n plate that feeds SOL B , its super tiny and can easily happen with just a tiny grain of particle.
So me.
1- PULL PAN get shifter to move properly to all gear positions
2-PULL SOL B check its function or replace
3-MAKE SURE 2-3 SHIFT VALVE can stroke inward.

Put pan back up and try it (cross fingers) if not pull VB and check sol afl feed hole make sure not blocked.

 

will do and i hope thats it. Im hoping its not the pump gone and full of metal because the TC wasnt installed correctly. fingers crossed.