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

[ShookieJay]

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

 

[Fless]

Nice low miles. I know you said you have had it serviced, but what does the tranny fluid look like now?

Also, what's the level look like on the tranny dipstick when it's warmed up and checked per the owner's manual procedure?

 

[rockola1971]

Yup check tranny fluid level first. If that is ok then I would suspect either 2-4 band servo is sticking, busted accumulator spring on valve body or sticking valve in valve body.

A 2003 with only 79k miles????

 

[ShookieJay]

@Fless @rockola1971
Thanks, I'll check that tomorrow. And yeah I got lucky. Got it from a dealership in Harrisburg, PA. One owner, elderly couple. Dealer got it from auction, not sure how or why it was there but the carfax and other records check out. Glove box was stuffed to the brim with every service record ever, like even for stupid stuff that I probably wouldn't keep receipts for. Rust free, looks like it was consistently under coated. Autoride was DOA when I got it so I replaced all 4 shocks and the compressor. The transfer case fell victim to pump rub about a month ago, so that was certainly unexpected and news to me. Other than that the only complaint I have is the headliners a little baggy. Really lucked out on this truck (so far)

 

[RAMurphy]

Wow crazy low miles. I laughed when you said owned by elderly couple. I had to add and it was only driven to church and back. How about some pictures.

 

[ShookieJay]

Update: got her nice and hot and checked the level following the procedure in the manual. It's right up to the full mark and it's nice and bright red, also doesn't smell burnt or anything.

@RAMurphy And yeah haha I was thinking the same thing, must've been the church mobile lol. I've been meaning to get some pictures up on my profile, I'll try to do that this weekend

 

[Mudsport96]

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.

My 06 Silverado does the same thing you are describing. Father in law owned if since 07 and the last transmission and the current one do the same thing. I am convinced the shift adapts in the transmission control part of the tune learned the way he drove "like an old man" and thats the way it shifts now. The daughter drives the same way he does with a soft foot so it just stays the same. Only when i drive it is the "slide-bump" noticed. Because under the little more throttle i give the truck it is shifting with a little more applied torque so it hasn't learned to apply mor pressure to the shift. If you know of a transmission shop around you, call and see if they are able to reset the transmission calibration or shift adapts. If not you may see if the local dealership has an updated version for your ride my Tahoe had one on the books so i had it done for like 65 bucks

 

[rockola1971]

A stuck 1-2 accumulator piston or broken spring will cause this exact problem. Its not at all uncommon for the spring to break in half. In fact its very common to find them broken in half when the tranny is opened up for the first time since the factory built it. Also not at all uncommon for the guide pin to wear the center hole of the piston.

Very common during a rebuild for the 1-2 accumulator to need a need a new piston, guide pin and spring. Most shops will replace it anyway if original so the tranny doesnt come back. The purpose of the 1-2 accumulator is to soften the apply of the clutch pack instead of it being harsh and fast. If any of the parts are worn or broken then it will cause the 1-2 shift to be very firm and fast. Doesnt hurt the tranny at all, just most people dont want to be snapped during the shift from 1-2.

 

[ShookieJay]

A stuck 1-2 accumulator piston or broken spring will cause this exact problem. Its not at all uncommon for the spring to break in half. In fact its very common to find them broken in half when the tranny is opened up for the first time since the factory built it. Also not at all uncommon for the guide pin to wear the center hole of the piston.
View attachment 385456
Very common during a rebuild for the 1-2 accumulator to need a need a new piston, guide pin and spring. Most shops will replace it anyway if original so the tranny doesnt come back. The purpose of the 1-2 accumulator is to soften the apply of the clutch pack instead of it being harsh and fast. If any of the parts are worn or broken then it will cause the 1-2 shift to be very firm and fast. Doesnt hurt the tranny at all, just most people dont want to be snapped during the shift from 1-2.

Well i suppose as long as it isn't doing any harm I'll leave it be. The transfer case already set me back over $2k. I appreciate you taking the time to explain this!

 

[Fless]

Yup check tranny fluid level first. If that is ok then I would suspect either 2-4 band servo is sticking, busted accumulator spring on valve body or sticking valve in valve body.

A 2003 with only 79k miles????

Beats my '04 with 111K on the clock. At least for age/mileage.

 

[afpj]

Sooo, from a transmission noob viewpoint, if I were to test drive one of these GMT 800s with 4l60e and it has snappy 1-2 shifts, how do I tell accumulator worn vs Corvette servo?

 

[rockola1971]

Sooo, from a transmission noob viewpoint, if I were to test drive one of these GMT 800s with 4l60e and it has snappy 1-2 shifts, how do I tell accumulator worn vs Corvette servo?

Corvette servo (2-4 servo) holds the 2-4 band. Does not cause snappy shifting. 1-2 Accumulator actuates the clutch pack which does cause snappy shifting.

 

[afpj]

Corvette servo (2-4 servo) holds the 2-4 band. Does not cause snappy shifting. 1-2 Accumulator actuates the clutch pack which does cause snappy shifting.

When they advertise a Corvette servo as creating firmer 1-2 shifts, that's a different feel than what worn accumulator parts? Or am I completely going psycho ( don't have to answer the latter). I had a Corvette servo installed when my trans was rebuilt about 25k miles ago, and the immediate difference is that the 1-2 shifts are faster (ie firmer, and to me, snappier) same with 2-3. It does stay in 2nd longer as well, not nearly as much gear hunting. Perhaps I'm using the wrong vocabulary. Appreciate the insight as always.

Perhaps the Corvette servo modifies how the 1-2 accumulator functions?

 

[rockola1971]

When they advertise a Corvette servo as creating firmer 1-2 shifts, that's a different feel than what worn accumulator parts? Or am I completely going psycho ( don't have to answer the latter). I had a Corvette servo installed when my trans was rebuilt about 25k miles ago, and the immediate difference is that the 1-2 shifts are faster (ie firmer, and to me, snappier) same with 2-3. It does stay in 2nd longer as well, not nearly as much gear hunting. Perhaps I'm using the wrong vocabulary. Appreciate the insight as always.

Perhaps the Corvette servo modifies how the 1-2 accumulator functions?

The corvette servo has around 50% more holding power against the 2-4 band vs the oem. The servo is located in the tranny case above the panline on passenger side under the big circle cover. All the servo does is hold the Sunshell stationary which is needed for Forward gear 2 and 4 to happen. The 1-2 accumulator is a separate assembly located on the valve body and is only used for 2nd gear and it applies hydraulic pressure in a metered fashion to the 2nd clutch pack. While the 2-4 servo and the 1-2 accumulator very much are needed for 2nd gear to happen, they do different things during the shift to 2nd gear.
I would have to guess that you are rolling around with a busted spring in your 1-2 accumulator also. I would bet that almost 50% of the 4L60E trannys on the road with over 100k since last rebuild have a busted spring. It really is that common. Doesnt hurt anything unless you dont like your neck snapped back during EVERY 1-2 shift.

 

[afpj]

As usual, awesome explanation. This is better than Google. I'm going to tell my wife i'm NOT too old to learn stuff.

 

[Mudsport96]

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

 

[ShookieJay]

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

I've never used tow haul, I'll give it a try next time I go out.

 

[ShookieJay]

I've never used tow haul, I'll give it a try next time I go out.

Also, on the subject of tow/haul, does it disable overdrive/lockup?

 

[afpj]

Negative ghost rider, toe/haul does not lock out "overdrive", at least on my 02 Yukon. It does tell pcm to hold in gear longer to reduce gear hunting under load, but definitely not fool proof. What has been recommended in several threads on this forum is to manually shift to 3rd for towing ( unless on a long easy flat or slightly downhill) to save wear in the 2-4 band.

 

[ShookieJay]

Negative ghost rider, toe/haul does not lock out "overdrive", at least on my 02 Yukon. It does tell pcm to hold in gear longer to reduce gear hunting under load, but definitely not fool proof. What has been recommended in several threads on this forum is to manually shift to 3rd for towing ( unless on a long easy flat or slightly downhill) to save wear in the 2-4 band.

Good to know, I don't plan on towing anything, but I live in an area with a lot of long winding hills, and I've found if I'm going about 40mph uphill, it likes to jump around between 3rd and 4th.