EspenT

Hi

A while back I inherited a 03 Silverado 5.3 with 60k miles when my father died.
It turned out that 2nd gear was sliping. I used Efi live to up the line pressure and add some torque limiting when shifting to 2. Continued to use the truck for a while. Then it started slipping in 4th as well..
I did some research and came to the conclusion that the 2-4 band needed replacement. I removed the transmission and opened it.
As expected the band needed replacement. Also the drum was really burnt from the slipping band, so I replaced that as well. I installed a Sonnax super hold 2nd gear servo and a sonnax pinless accumulator 1-2 piston.
Replaced the seals and gaskets on the parts I had out. But did not take out parts I did not need to remove to change seals.

The transmission is now back in the truck. Reverse, 1st and 2nd gear works excellent. But transmission does not upshift to 3rd. I stays in 2nd all the way to the redline. Except for one try when it actually shifted to 3rd and stayed there until redline in 3rd. Stayed in 3rd accelerating and decelerating for a while while I was hoping for it to shift to 4th. But suddenly it shifted to 2nd or N.

Now I have no clue what to do next. I will probably have a look at the 2-4 servo. Donīt know why but I had a feeling when assembling those parts that there was something strange. But I was hoping for some advice for what to check.

This was the first time opening a transmission and Iīm an DigitalBroadcast engineer and not a mechanic. But I do understand the theory of how a transmission works.

GMCSIERRA5.3

Did you check the 3/4 clutch pack? The clutches have to be burnt for sure..when you had no 2nd you also didnt have 4th as its the same band..what was happening is the transmission was going from 1st to 3rd gear..did you install the sonnax servo apply pin aswell?

EspenT

Well.. When I got the car it shifted from 1st to 2nd which was like neutral. After I tuned it 2nd was ok when driving normal but slipped if I stepped to hard on the pedal. After I while the band started slipping going uphill in 4th. I then decided it was time to do something about it.

I donīt think the 3-4 clutches is the problem. There was no slippage on 3rd before the "rebuild" and it does not even try to shift. Itīs like it is in 2, not D

Yes, I used the sonnax servo apply pin. I had to grind away about 2mm≈0.075inch of it.

EspenT

Disconnected the cable that connects to the transmissions internal harness. If I understand correct that should give me 3rd when in drive? But it gives me 1st.

Talked a local builder and he suggested to remove the valve body and inspect for stuck valves or missing checkballs.

if the solenoid valve for 2-3 is stuck. Would manually selecting 3rd still work? There seems to be no difference between Manual 2 and 3.