I rebuilt my 4l60e in a 2001 Silverado, and with help from mrvedit and others here it was a successful rebuild.
Fast forward 8 years and 65k miles I'm driving in slow traffic and as the truck goes to do the 2-3 shift it does a very harsh bang like it was stuck in two gears.
My 1st reaction was something in the drive train had catastrophically failed, but to my surprise everything seamed ok and was able to continue without issue.
It has done the same thing a few more times after that.
Friday driving home from work, slowed for traffic and then went to accelerate and engines just free revs.
Pulled to the side tried again and just free rev. pulled gear selector down into D3 and it engages and was able to get home.
Trans will be coming out, any ideas what has failed?
I have all gears except Drive and when in D3 it does seem to engage 1st and up shift into 2nd and 3rd.

 

To be clear, in (D), it free revs even pulling off from a complete stop? Or does it start from a complete stop in (D) and upshift 1-2, upshift again 2-3, then go neutral when it tries to upshift 3-4?

It sounds to me like something is broken in the OD (4th) clutch assembly. The lurching was probably free floating broken parts getting ground up. So there could be more damage from that as well.

I've been driving a 4L60E that slips in OD, so I just shift to D instead of (D) and it works just fine. It started slipping about 6 months ago. I've had lots of other priorities, and I haven't picked up a junkyard core to rebuild yet. In mine, it tries, but it just slips a lot. So I'm pretty sure mine is leaky seals and/or leaky solenoid valve(s) for OD and/or the TCC.

 

If I put the selector in (D) from a dead stop it will not move at all.
Put selector in (3) from a dead stop, pulls away fine shifts from 1-2 and 2-3 does not 3-4 because selector is in (3)?
Have not tried to shift to (D) while moving, was trying to minimize any more damage.
It does not make any strange noises idling in the drive way, and fluid has good color and no burnt smell.

 

That doesn't sound good. My next step would be to drop the pan and filter and inspect for damage. Maybe drop the valve body as well.

It's very weird that selecting "D" or "(D)" or whatever the normal overdrive range is marked results in no movement at all. It could be damage to the valve body or to the stuff on the selector shaft (the piece that rotates when you select gears) or in that area. The bang/lurch stuff definitely sounds like stuff breaking inside. It's just a question of what broke.

 

It sounds like the forward sprag is broken and when putting the shifter in D3 the overrun clutches are applied taking the place of the forward sprag.

 

this is what's happening.
trans needs to be pulled and fixed

 

Assuming he installed the 2-3 shift valve.

 

2-3 shift valve was installed.
Unit is coming out in the next few days.

 

Yup then I agree. Sprag has rolled over

 

DO NOT remove your tranny before you inspect your Forward Piston in the Valve body.
Ask me how i know.

 

I am assuming that you are referring to the Forward Accumulator Piston???

 

Yup. Sorry. The one that is in the VB under the cap with 3 bolts.

 

Its the sprag.

 

the forward accumulator sees oil in ALL forward ranges
so, even if it was COMPLETELY missing and puking all the oil out...it wouldn't make a difference in D4 or D3

If you have a different opinion, explain the logic behind that opinion and educate the rest of us

 

Okay Mr.

Once i installed a sonnax pinless forward acum piston and forgot to bang that pin hole with my 2 ba!!s that Sonnax provides because my wife called me and confused me by yelling at me how a bad of a person i am and how i ruined her life. So i assembled the valve body pan, filled fluid and this is what happened :

1. Drives good only in D1 and D2.
2. D3 once engages and once is neutral from dead stop. Once you raise that pressure up with RPM, the vehicle moves.
3. Once you shift from D2 to D3 while driving, it shifts pefectly.
4. D Doesnt work at all from dead stop.
5. D Works when you shift manually while driving fromD2 to D3 then to D.

You've learned a lot of theory and in practic, but even an old dog can learn new things.
This is a Verified experiment by mistake i had. And you can argue with these facts however you want.

6TDD 4L60e from a 2006 Trailblazer 4.2L.
There you go Mr.

 

Easy brother.......we're just doing tech talk here. Not bashing

 

Never bashing anyone. I love Maroon and this is the person i rely on any advice he gives.
Geez, whats wrong with me? Each time i write something, people think it's bashing or any kind of disrespect

Guys, i am from another part of the world, and maybe the way i speak sounds wierd. But please, accept me as i am and without any bad intentions in my words

 

NP

.....but the failure is the sprag on this one brother.

 

Maybe it is. Just recommended checking the easy part before removing the tranny.

A big leak on the fwd acum has the exacly same symptoms as a broken sprag has (I dont know if a broken sprag makes any noise so you can isolate the problem).
Leak on the acum piston = Sprag is inactive.
Broken sprag = Sprag is inactive.

So maybe some day someone will be lucky, and we'll save him a tranny drop.

 

how would a leak on the acum piston = inactive sprag

that is like saying "the power is out in my neighborhood...that means I my shoelaces won't stay tied"