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

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?

afpj said:

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?

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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.

rockola1971 said:

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.

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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?

afpj said:

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?

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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.

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

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

Mudsport96 said:

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

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

ShookieJay said:

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

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

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.

afpj said:

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.

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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.