2003 Chevy S-10 Rough Upshifting 1-2 and 2-3

  • 2003 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • 95,000 MILES
4L60-E trans has a really harsh 1-2 upshift. Sometimes it literally 'bangs' into gear, depending on vehicle speed. Similar symptoms are present when shifting from 2-3, although not nearly as pronounced. No problems shifting into O/D, or downshifting.

Recently had the trans fluid flushed and filled, the old fluid was not burnt. No leaks are evident, dipstick level is correct and consistent.

I've tried several variations of speed and throttle to smooth out the 1-2 shift. The only time I can achieve a smooth shift is when I wind out the engine to 3500+ RPM. Then, it shifts smoothly every time.

There is no slippage evident, and no unusual noises - other than some whirring when shifted from park into any gear (sounds like it's coming from the bellhousing). On the road, it behaves OK as long as you don't drop below second gear. On level surfaces, it holds speed without much effort w/cruise on.

A visual inspection of the tranny did not reveal many user adjustments. The wiring harnesses all seem to be in good shape, and all connectors have been removed and cleaned. The mounts are OK. Thus far no transmission or ABS codes have shown up, and the truck runs well otherwise.

The only mod I've done to this truck since purchase is to upsize the tires from the stock 205/75-15 to 225/70-15. The difference in tire height is minimal, though - only about +.15 inches over stock.

Looking for a starting point for troubleshooting. Over-revving the engine is no fix. Would appreciate any insight, or the sad news that a rebuild may be required.
Do you
have the same problem?
Monday, April 26th, 2010 AT 10:10 AM

1 Reply

There are no adjustments. It is possible that you have a valve body issue, warpage/leaking, or sediment causing binding is the most common. The fact that it smooths out with more demand may be result of increased line pressure. You can either remove and disassemble the valve body, checking that all valves slide freely in the bores, or replace it. I will include a chart that lists possibilities of a harsh 1-2 shift.
Slipping or Harsh 1-2 Shift

Valve Body Assembly (60)
" Mislocated valve body to spacer plate checkball or checkballs.

" 1-2 shift valve train stuck due to sediment

" Gaskets or spacer plate incorrect, mis-positioned or damaged

" 1-2 accumulator valve stuck or damaged

" Face not flat

" 4-3 sequence valve stuck or damaged

" #1 or #8 checkball missing or mis-located

" 1-2 accumulator valve bushing rotated 180

2-4 Servo Assembly (13-28)
" Apply pin too long or too short

" 2nd servo apply piston seal missing, cut or damaged

" Restricted or missing oil passages

" Servo bore in case damaged

2nd Accumulator (55-57, 104)
" Porosity in 1-2 accumulator cover or piston

" Piston seal or groove damaged

" Nicks or burrs in 1-2 accumulator housing

" Missing or restricted oil passage

" 1-2 accumulator piston spring not seated

" Rough finish in 1-2 accumulator bore in case

" A cracked 1-2 accumulator piston - allowing fluid to leak by

2-4 Band (602)
Worn or mispositioned

Oil Pump Assembly (4) or Case (103)
Faces not flat
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Tuesday, April 27th, 2010 AT 11:21 PM

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