How would I know? 4 speed with overdrive, all I know so far.
GM put out a
TSB on the harsh, clunky 2-3 shift and according to them, it's normal (lol)...It's actually not normal, per se and Transgo refers to it as a "2-3 bump-slide" and addresses it in their SK4L60E kit (IO believe Superior Tech does the same). Long story short, the 'clunk' is a product of a slight mis-time between 2-4 band release and 3-4 clutch pack apply. When the 700R4 and 4L60E shift from 2nd to 3rd gear, something like 80% of 3rd gear oil is used to push the servo assembly off of the band to release it from the reverse input drum. While this is happening, the remainder of the apply oil is sent to the 3rd clutch piston to compress the 3/4 clutch pack. This is a sequence that has to happen in perfect time, otherwise you'll get clunky, jerky up or down shifts OR flare shifts/tie ups if the sequence is really out of time.
What causes this?
It's usually the result of excessive 3/4 clutch pack clearance in combination with the load release springs GM started to install in all 700R4s in 88 and carried forward to all year 4L60Es...These springs keep the pressure and apply plate away from each other in 1st and 2nd gear to prevent centrifugal apply from happening. However, it was really a solution in search of a problem as the forward drum was redesigned in 85 to improve 'bleed off' of excess oil accumulating behind the 3rd gear apply piston which could potential cause the 3/4 pack to apply out of schedule at higher RPMs.
Well, 1>2 is not butter smooth either, it's just less jerky.
OK, so is it just crappy design and drive it as is until it poops or? When I had 99 Silverado, proverb about it was "It's a clunker, you can hear coming several blocks away, but it will be clunking like this for 300 000 miles".
If your 1-2 shift is also clunky (especially if it's also late), you either have a worn valve body (TCC regulator valve/P1870 among other causes) or broken 1-2 accumulator springs (though this is less likely in later 4L60e as GM delete one of the springs that was more prone to failure starting in either '06 or '07).
What to do about it?
You have a couple of options:
1) Live with it - honestly that would be my advice if it's only happening once in a while and you're not comfortable taking down the valve body and spacer plate to install a shift kit, assuming one hasn't already been installed (doubt it since you have this problem to begin with) and the transmission is behaving as it should in all other respects.
2) Diagnose and Install Shift Kit - Drop the pan, valve body, gaskets and spacer plate and remove the servo assembly...Check the feed hole sizes for your 2-3 shift and 3-2 exhaust in the plate to see if they're the same size (they should be to promote optimal timing between apply and release of the band). If they're not, drill them both to .093 and install the remainder of the shift kit following the instructions. Also repair the 1-2 check ball seating location if it's excessively worn otherwise the ball may get stuck in the plate causing 1-2 tie up issues.
that would be the 4l60e, I have broken a few of them.......in amazing ways lol, most commonly during the 1-2 shift.
why they ever put the 4l60 in a suv in beyond me, they can't take the weight
They can handle 1/2 ton SUVs w/stock power fine if properly set up (which is debatable based on how they come from the factory)....95% of these transmissions come in for overhaul because the 3-4 clutch pack has failed. The other two most common issues are fractured/broken sun shell (soft, weak metal) and the late harsh 1-2 shift (P1870) due to either TCC valve bore wear, converter or rear stator bushing excessively worn - I see this happening much more frequently on 95-2000 compared to other years.
ETA: heat, high rpm and lack of maintenance are the unholy trinity of factors that lead to transmission and engine failure in general. Keep trans temps to 200 or less; if towing, hauling or other intense applications Id add a big aftermarket trans cooler as I don’t think GM installed separate trans coolers in the 2WD trucks/SUVs but i could be wrong…
