427TTA4

iTrader: (1)

First of all I'd like to thank the people who took the time to read my post ! Now to the main topic. It is a 2006 TBSS drove it home fine then after start up I went on a run to the store and notice that 1st revved to 4k then shifted. After the vehicle warms up it shifts around 3k or 20-25 mph but noticed that it hangs in 1st til 3-4k RPM then shifts straight to 3rd. I can manually select 2nd and it acts just as if I apply it to go in neutral it just revs up no slip what so ever. Trans shifted perfect before this happened. Trans has every gear besides 2nd. Reverse is great and 4th holds very strong under WOT top speed rolls from 65+. Talked to a few shops and TBSS owners and most say it's something with the 1-2 accumulator but never messed with Autos I've only owned t56 mounted cars.. Any help guys !? I will drop the pan and see if I can locate a cause for the issue within the next day or two. Thanks!

bbond105

Once you have the pan off you can remove the 1-2 accumulator housing and check the piston and springs. The plastic pistons break all the time. You can also check the band apply servo pin travel. This is on the right side of the trans, just behind the bell housing. Too much travel indicates the band is worn out. You can lengthen the pin or replace it with a longer one and get a few more miles out of it.

Check out this thread.
https://ls1tech.com/forums/automatic...cond-only.html

mrvedit

Drop the pan the remove the "dome" shaped 1-2 accumulator which only requires removing three bolts. A severely cracked piston could cause loss of 2nd gear.
A bad seal on the 2nd servo piston could also be the culprit.
From what you have said, it doesn't sound like an internal/major problem that would require removing the trans.

427TTA4

iTrader: (1)

Thanks for the quick reply guys! I'm actually going to pull it today in about a few hours from now. Will keep everyone updated on what happens later and what was the cause "If I can find it". Hopefully it will help someone else in the long run hate seeing all these treads without comming to a conclusion to the problem!

427TTA4

iTrader: (1)

I only have cell phone pics I'll upload them later but seems like the plastic piston is all the way down... Like pushed in all the way! I'll post pics later

427TTA4

iTrader: (1)

Why is the piston pushed all the way down upon removal? Is it suppose to be that way?

427TTA4

iTrader: (1)

Check ball seems fine??

mrvedit

Pull the piston out and show us what springs are underneath it. Stock, there are two springs that definitely would prevent the piston from staying pushed down like that.

427TTA4

iTrader: (1)

I'll take pics tomorrow of them but I'm 100% sure it just the small one for a fact from the pics I googled? Would the piston being all the way down stuck cause 2nd not to engage?

mrvedit

From my understanding (more theory than practice) a broken/missing spring results in very harsh 1-2 shifts, not a loss of 2nd gear.

You probably should follow bbond105's advice and measure (at least estimate) the end play of the servo by pressing on the cover to determine how much it moves.

GMCSIERRA5.3

07+ 4l60s only come with the small spring in the 1-2 accumalator

427TTA4

iTrader: (1)

I haven't had time to work on the truck due to it raining all day.. Will give you guys an update if installing a longer servo pin does the job!!

427TTA4

iTrader: (1)

installed a Sonnax servo pin #77787-02K and a corvette servo while I was in the process and now 2nd shifts fine !!! Goes all the way to redline with no problem but I will stay off of it. I know I am on borrowed time mean while I'll try to build my 4l70e or if I get convinced enough I'll swap a 4l80. Big thanks to all of your help ! I also installed a billet acumulator cover while I was inside but I doubt that was what fixed the issue!!!!

mrvedit

Sounds like the longer servo pin brought back 2nd gear, at least for a while.

Did you use it as-is or did you grind it down to reach the desired end play?

427TTA4

iTrader: (1)

I actually installed it and tried to see how much play it had and is was around an 1/8 so I left it as it is...I had around 1/4 or so of play before the pin swap.

mrvedit

Excellent!
And congrats on getting your trans working.
I'll bet you learned a lot and are much more comfortable with these beasts now.

427TTA4

iTrader: (1)

Thanks!! I actually did learn a lot since I only owned and worked on 6spds... If an auto started to act up for example slip or just not go in a gear I'd call it done ! And get a new one.. but not anymore !! Thanks again sir and the rest that helped !!!

bbond105

Good deal. You'll be rebuilding these things before you know it.