MattTheHam
Newbie
Good evening all. I am having some strange problems with the 4L80E in my 92 6.5L K2500, and I'm looking for some advice. The truck is new to me and has 180K on it, but the trans was rebuilt by a well known local trans shop at 152k. I've rebuilt blown manual transmissions before, but autos are new to me. Current codes are 68, 85, 87. Fluid was a nice red and smelled fine (as good as ATF can), small amounts of metallic grey stuff on the bottom of the pan. Gears 1-3 work great.
1st: Rev is flakey, it works great and will spin the tires in gravel when you first start the truck, but drive forwards for more than a minute and there is a 5% chance it will shift back into rev. If Rev is there, it is 'spin the tires' strong. If its not, it feels like neutral. No engagement or slipping, just nothing, you cant even tell it was shifted out of P/N. I do have compression braking and low at all times.
2nd: I have a snap-on brick and can see the TCU commanding 4th even when the PRNDL is in Drive (D). It is my understanding that it shouldn't command 4th unless the PRNDL is in OverDrive (OD). The gear ratio show 1.00ish so the trans is clearly still in 3rd. I have ohm-ed the harness from the TCU connector and couldn't find any shorts or out of spec solenoids. This one really has me stumped.
3rd: I have no OD or lockup (both 3rd and 4th lockup are missing) at any temp/speed/throttle level. This might be due to one of the above codes though, I defer to y'alls wisdom.
What has been done: All new speed sensors, AFL valve upgraded, TCC valve upgraded, new A-B solenoids, extended rev servo pin (set for 60-80 thou of travel, I think... I did that over the summer, can find the exact num if needed), new #7 rev/low check-ball seat, new separator plate check-balls.
Pressure Gauge @ idle (PSI):
Rev = 75 (will climb to 210 with light throttle)
N = 90
OD = 90
3rd = 90
2nd = 90
low = 110
1-2 and 2-3 shift time are under 0.4s
Im thinking it needs a full rebuild, but the weirdness of problem 2 makes me hesitant. I would hate to learn it was an electrical gremlin after I pull the trans and pay 1500 to get it rebuilt. Any ideas??
P.S. I'm a full time engineering student so I apologize for slow replies and bad grammar :')
1st: Rev is flakey, it works great and will spin the tires in gravel when you first start the truck, but drive forwards for more than a minute and there is a 5% chance it will shift back into rev. If Rev is there, it is 'spin the tires' strong. If its not, it feels like neutral. No engagement or slipping, just nothing, you cant even tell it was shifted out of P/N. I do have compression braking and low at all times.
2nd: I have a snap-on brick and can see the TCU commanding 4th even when the PRNDL is in Drive (D). It is my understanding that it shouldn't command 4th unless the PRNDL is in OverDrive (OD). The gear ratio show 1.00ish so the trans is clearly still in 3rd. I have ohm-ed the harness from the TCU connector and couldn't find any shorts or out of spec solenoids. This one really has me stumped.
3rd: I have no OD or lockup (both 3rd and 4th lockup are missing) at any temp/speed/throttle level. This might be due to one of the above codes though, I defer to y'alls wisdom.
What has been done: All new speed sensors, AFL valve upgraded, TCC valve upgraded, new A-B solenoids, extended rev servo pin (set for 60-80 thou of travel, I think... I did that over the summer, can find the exact num if needed), new #7 rev/low check-ball seat, new separator plate check-balls.
Pressure Gauge @ idle (PSI):
Rev = 75 (will climb to 210 with light throttle)
N = 90
OD = 90
3rd = 90
2nd = 90
low = 110
1-2 and 2-3 shift time are under 0.4s
Im thinking it needs a full rebuild, but the weirdness of problem 2 makes me hesitant. I would hate to learn it was an electrical gremlin after I pull the trans and pay 1500 to get it rebuilt. Any ideas??
P.S. I'm a full time engineering student so I apologize for slow replies and bad grammar :')
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