03 Tahoe - 4l60e "lurches" on 1-2 shift

[Fless]

Tow/haul doesn't lock out OD on my '04. I tow in 3rd.

 

[Jim b]

Not sure if this trans is similar to the ones used in 1997 but we have a 4L60E in our Astro Van. It started shifting just as you describe at about 30K miles. i changed to full synthetic ATF and it totally fixed it for years. The cooler line let go and dumped the ATF at about 90K. I repaired it and put in std ATF to get it home. The harsh shifts were back in spades before getting home. It threw a code that pointed me to a PWM pressure regulator in the valve body. The powertrain control was sensing a pressure issue and cranking line pressure up to prevent slipping. That caused the harsh 1-2 shift. The issue was caused by a worn bore in the pressure regulator. Sonax sells a kit with a stepped reamer and a sleeve/valve to repair the issue. I performed that repair and it has performed flawlessly since. Jim

 

[ShookieJay]

Does it also do this with tow/haul mode on or does it speed the shift up a bit?

Update: Just went for a drive with tow/haul on and it BANGS into 2nd hard as hell. So yes it certainly did speed up the shift by a lot lol

 

[Mudsport96]

Sounds like the accumulator is stuck or the spring is bad. Need to get that looked at asap or further damage could be done. It is also possible that there is a checkball stuck in the valvebody. Depending on your level of mechanical skill you could open up the transmission and take a look.

 

[ShookieJay]

Sounds like the accumulator is stuck or the spring is bad. Need to get that looked at asap or further damage could be done. It is also possible that there is a checkball stuck in the valvebody. Depending on your level of mechanical skill you could open up the transmission and take a look.

4L60E 1-2 Acuumulator Upgrade
Thoughts?

 

[29tomt]

Howdy y'all, I'm back at ya again with some noob questions lol

So I've recently noticed that when my transmission shifts from 1-2, there's sometimes a bit of a hiccup. It seems to be taking a while to fully engage, like a full second, and then when it does engage its very aggressive. Like it shifts into 2nd, continues to accelerate, and then suddenly it feels like it bites really hard, which causes the truck to lurch a bit. It happens mostly under light throttle, let's say 1/4 or less. Under acceleration at half or more throttle, it doesn't seem to do it.

FWIW, I had the transmission serviced less than 1k miles ago (fluid/filter) and the truck currently has 79k miles. Can't remember if it did it before the service. What could cause this? TIA

My 2003 Tahoe, which I purchased in 2014, has been doing that since I bought it with 128K miles on the odo and today it has 221K. It has been serviced with fluid and filter changes at least 3 times and it has had the Corvette servo installed as others have mentioned. It still does it but is much better now. The shop could not find anything as to what they could see when doing the fluid change. I finally figured out that if I applied a little more pressure to the gas pedal, it would not do it and if I hard accelerated, it did not do it at all. I guess over time I have become used to giving it enough pedal to minimize the hiccup in the shift but I really notice it when my wife drives and is slow on the acceleration. Still runs like a top, no major repairs and does not use any oil between changes.