4L80e weird 1-2 shift

[CPay]

I have a 95 k2500, tbi 5.7 4l80e.

When I bought the truck, it shifted hard throughout all gears, but the shift points were about where I expected them, and all gears were there. It would intermittently go into limp mode or just not shift out of 1st, period. I changed the TPS sensor (old one was very old and felt crunchy when I turned the potentiometer) but now it wont shift out of 1st until 4k RPM. I can force it to shift by modulating my throttle but when I do that, the shift is very slow, if I put my foot into it where the trans would actually be under load, the shift is acceptable. 2-3 and 3-4 are firm and quick. Prior to swapping the TPS, 1-2 was very hard but it didn't flare or slip. Fluid is full and very clean - the trans looks relatively new. I'd rather not wreck this transmission so I'm not driving it currently. Any help is very appreciated.

 

[lxe4]

whats your speedo doing? I had this happening one time. The speedo would be reading zero until I was doing about 40km/h then it would go from zero to my speed instantly and shift from what felt like first into 3rd quite violently. new speed sensor on the transfercase fixed it.

 

[Sapperdaddy]

Anyone else have this issue? I had an obs Denali that did the exact same thing. Sold it to my father in law and he is trying to get it going as a daily.

 

[CPay]

whats your speedo doing? I had this happening one time. The speedo would be reading zero until I was doing about 40km/h then it would go from zero to my speed instantly and shift from what felt like first into 3rd quite violently. new speed sensor on the transfercase fixed it.

Anyone else have this issue? I had an obs Denali that did the exact same thing. Sold it to my father in law and he is trying to get it going as a daily.

NOT FIXED YET

Sorry for the late reply. Turns out it was shifting straight from 1st to 3rd, there is no 2nd gear. It doesn't even try to shift to 2nd, no flare or slip, just straight to 3rd. I ended up pulling the pan and replacing the filter and gasket (some jerk decided to gob rtv on the old paper gasket, that was fun). With the pan off, it didn't look particularly bad, but there was definitely a glittery presence, some shavings but something that I noticed was there was a good bit of small plastic chunks in the pan, pieces less than half the size of my pinky fingernail. At first I thought it was metal but it wouldn't stick to the magnet and if I took a piece, I could actually break it further.

I called my local trans shop that I trust, they rebuilt a 700r4 for me a few years back and did a fantastic job on it. They said that the weak link in those transmissions is a sprag clutch and if the transmission shifts hard or has too much line pressure, the sprag can fail. That would coincide with my hard shifts when I bought the truck.

Currently I'm going back and forth with whether I want to rebuild the trans or just offload the truck to someone else. It's not a bad truck, but definitely a workhorse in its day though. I bought it to be a tow pig/work horse truck anyway so that didn't bother me too much. I'm only in the truck $2000 but I'm sure the rebuild would be around that if not more. I'm just rambling at this point but if anyone else has any input to my dilemma I'd appreciate it lol