Strange transmission issue - no CEL thrown

[Awh1112]

2000 sierra 4x4 5.3L
truck requires you to start in 1st or 2nd from Park , manually shifting up to D or OD, however, once you do this, i can stop and take back off from OD or D and it doesn't seem to act/shift weird or anything when doing so. I have all my gears at that point, shift up and down automatically, smooth as glass, and i have reverse all the time. I know it seems the obvious answer is the forward sprag, but i just find it weird that it will take off from a stop in OD or D after i did the initial shift up from park to L1 or L2, with no problem. As long as i go from park to L1 or L2 first, i will a full gear spectrum afterward until i put it back in Park. Can this issue be something other than the Forward Sprag or is that still going to be the issue? If it is the forward sprag still, someone help me understand how i can take off in D or OD after doing my initial manual shifting 1 time.

thank you for any assistance with this puzzling issue for me.

 

[gmcman]

When you move the selector into 2nd, the trans will take off from a stop in 2nd gear, this is for slippery conditions.

When moving from PARK to 1st, you have to pass through the 2nd gear selection which could be helping you get started with the selector in 1st.

What is your maintenance history, condition of fluid?

Any type of shifting issues that aren't accompanied by a loud banging, grinding, or what sounds like something self-destructing inside the trans, could possibly be traced to a restricted filter, pressure plate switch, or the shift solenoids.

The shift solenoids are cheap, and easy to change with just the pan removed.

Without knowing your line pressure, it's almost worth a try to change the shift solenoids.

Hard to say what's going on, did you ever add any type of seal conditioner, or other additive to the trans other than fluid?

What happens if you put the trans in DRIVE and wait about 30 seconds? Just don't rev the engine with the trans not engaged, let it idle, or you could destroy the sunshell if it engages at a high RPM then it's game over.

 

[mrrsm]

Assuming that I understand you correctly... If you have to place the Trans Gear Shift into anything other than the Park or Neutral Shift Positions in order to get the Engine to Start... Have a close look at your Park Neutral Switch on the Driver's Side of the 4L60E Transmission.

Loosen the two outer Adjustment Ovals held by the 13mm bolts and then make some very slight incremental adjustments with the Black Plastic Body. When you find the Sweet Spot where the Engine Will Start when the Shifter is in either the Park and/or the Neutral Position... Gently tighten down those Two Bolts.

Don't forget to Chock your wheels Front and Back before you slide under there and make these adjustments with someone working the Shift Lever through the PRNDL123 positions... You Don't want the Truck to accidentally Roll Over You on any incline.

 

[Awh1112]

GMCman- I wish i knew the history. We purchased it from a government auction, so service history is unknown. I drove it 150 miles home with no issues at all. As said, once i shift manually to L1 or L2 from park, and manually shift up, it will allow me to drive in OD no issues, even coming to stop at stop signs and taking back off. it automatically shifts at that point.
I have not tried to put it in drive and let it sit for 30 seconds etc. I can try that tonight and see what happens.
Absolutely no shifting issues. it shifts smoothly and quietly in all gears. no jerking observed, no banging/grinding... this is what has me puzzled. Because if it was showing any other signs other than just won't take off initially from D or OD when coming from park position on shifter, i would believe it was a mechanical issue inside the trans. As far as the transmission fluid condition. I didn't check this yet. truck is at my dad's. He is supposed to let me know asap on that. If it looks burnt etc, i can make some good assumptions at that point that i need to pull pan to see how much metal is in my pan! haha

MRRSM- no it starts fine. it won't take off when you move from park to OD or D. It will only take off out of park when shift into L1 or L2. After that, as long as i don't put it back in park, it will drive in any gear and will shift to D or OD automatically down shift fine, i can even stop at stop sign and take off in OD just fine, after the initial manual shift.

 

[gmcman]

Sounds good, please post pics or update when you know the condition of the fluid.

One possible scanario is the trans received some high dosage of seal conditioner and the valve body could be lazy with swollen seals....but that's purely speculation and I wouldn't count that as a likely culprit as of yet.

I've heard horror stories of small doses of brake fluid to make a quick stop-leak so hopefully that wouldn't be the case.

The forward accumulator also comes to mind, but I believe you need to remove the valve body to access that piston which isn't terribly hard.

What's above my pay grade is what happens when the trans is placed in 2nd in regards to the forward accumulator. You would have to think that if someone starts the engine and only selects 2nd and not 1st, the forward accumulator must come on at that point.

I don't believe the shift solenoids come into circuit when going into 1st, but they do play a part if they are gunked up and could keep the trans in 1st.

The shift solenoids do come into play when selecting 2nd as the band would need to be engaged.

If that were mine, I would check the fluid, if it's anything other than a nice, pinkish color and have that lovely trans fluid smell, I would exchange what's in the pan for some Valvoline MaxLife.

With the pan off, I would replace both shift solenoids and the pressure plate since if the trans needed a rebuild, you could swap them over.

If you have to remove the valve body, get a new seperator plate from the dealer, that way all the circuits are drilled to the spec of that vehicle as it was when new.

Hopefully your issue can be resolved without pulling the trans.

Edit to add: @Awh1112 also check the shift linkage at the trans, that bushing wears out but generally if it fails you don't have the option to shift back into PARK. Mainly check for preventative maintenance.

 

[TJBaker57]

I am suspicious of the shift linkage myself. Just maybe when you come from Park the console end of the shifter goes to Drive but the business end is lagging behind from a poorly secured cable?

 

[Awh1112]

So, update: trans fluid is good red and smells good. Not burnt.
It has kick down when u get on the gas hard, I did notice that when I shifted from reverse to Drive, it would have a long delayed hard shift. Both times it did it, I had pushed gas down a lil to less than 1000rpm when it shifted hard into drive.

 

[gmcman]

These transmissions can easily go the distance, but only takes a few miles to eat a clutch pack or band if there's a big pressure loss.

I don't know what your pan looks like, but with good, fresh looking fluid, one thought that comes to mind is a standard pan with a deep pan filter, maybe a recent service.

I know I would at least remove the pan and check, especially if it shifts fine after you get going. Could be a restricted filter, missing seal, may not even be filter related. Comes down to labor to check against the possibility of a trans going bad.

What is the fluid level in the trans? Hot trans, engine idling, level surface.

 

[gmcman]

Any updates?